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The nature and timing of deformational events and organic and inorganic metamorphism in the Northern… Moffat, Ian W. 1985

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Of  THE NATURE AND TIMING OF DEFORMATIONAL EVENTS AND ORGANIC AND INORGANIC METAMORPHISM IN THE NORTHERN GROUNDHOG COALFIELD; IMPLICATIONS FOR THE TECTONIC HISTORY OF THE BOWSER BASIN  by  IAN W. MOFFAT BSC, MSC A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS  FOR THE DEGREE OF  DOCTOR OF PHILOSOPHY  in THE FACULTY OF GRADUATE STUDIES Geological Sciences  We accept this thesis as conforming to the required standard  THE UNIVERSITY OF BRITISH COLUMBIA 1985 ®  Ian W. Moffat BSc, MSc,  1985  ? 8  In  presenting  degree  at  this  the  freely available copying  of  department publication  of  in  partial  fulfilment  of  University  of  British  Columbia,  I agree  for  this or  thesis  reference  thesis by  this  for  his thesis  and study. scholarly  or for  her  Department  of  The University of British 1956 Main Mall Vancouver, Canada V6T 1Y3  DE-6(3/81)  Columbia  purposes  gain  shall  requirements that  agree  may  representatives.  financial  permission.  I further  the  It not  be is  that  the  Library  permission  granted  by  understood be  for  allowed  an  advanced  shall for  the that  without  make  it  extensive  head  of  my  copying  or  my  written  A B S T R A C T The Basin  of  Groundhog  coalfield, located in the northeastern corner  north-central  sedimentary  British  rock, ranging  Cretaceous). Four the Jackson  in age  in the  in response  marine  Devils  gradients between of  of approximately  180° C-220° C. The  al these temperatures, odds  with  documents  studies  30°C/km  and  observed though  experimental  important  factors in inorganic  prior to deformation.  and  possibly three phases  of  deformation;  arenaceous  upper  variably-developed  is distributed  areally  observations  chemistry  phase.  35%.  as a  more  the above bulk  the first and  was  Deformational  solution  America.  buried  to  burial  a  paleo-temperature  interpreted to be other  stable  basins, is  at  leads to were  stratigraphic units  strain resulted from  style has  approximately  been  the  all  were  two  or  coaxial  and  strongly influenced  by  predominantly  rigidly whereas  conglomeratic  the underlying,  more  deformation.  cleavage,  of its dependence ii  area  Paleo-geothermal  from  third are  plastically during  function  source  history.  viscosity variations. The  pressure  northern  as well as permeability  The  outlined,  (Late  in vitrinite paleogeothermometry  stratigraphic levels behaved  argillaceous strata behaved A  with  early Tertiary times  lithologically controlled, apparent  unit  maximum  diagenetic/metamorphic  approximately  and  indicate a  (Early  been  cratonic North  Currier  of  to alluvial a  5.5 km  by  to the second  basal  thickness  overall regressive  through  the  structurally shortened  perpendicular  younger). An  indicate  compatable  m  stratigraphic units have  authigenic mineral assemblage  that pore fluid pressure  and  3700  Bowser  Jurassic) to Albian  terranes with  studies. Confidence  Albian  a  tectonic uplift of  40°C/km  conclusion  Between  (Middle  (Albian and  of allochthonous  Vitxinite reflectance depth  Bathonian  shales in the Jackson  Claw,  to convergence  approximately  Currier (Late Jurassic); McEvoy  Devils Claw  transitional from  maximum  from  (Bathonian-Oxfordian);  fanglomerates  contains  laterally continuous, informal  Jurassic-Cretaceous); and sequence,  Columbia,  of the  formed on  at low  temperature,  buckling grain  size  strains, and  intergranular stress. The  distribution and  geometry  of syntectonic veins which  fluid "sinks" implies that pore fluid overpressuring was  an  mechanism,  low.  The  and  that differential stresses were  timing of various deformational  orientations are compatible along  major  indicate  a  with  events and  the relative timing  strike-slip faults in north-central switch  from  northeasterly  north-northwest  in mid-Cretaceous  early  Superposition  and  generally  Cenozoic.  of  directed and  along  the northerly convergent  which  contains Bowser  Basin  principal  back  deformational  geometry  of  dextral offset  Offsetting  relationships  stresses in pre-Albian  time  to northeasterly in late Cretaceous  necessary  is considered consequence  strike-slip margins sediments.  iii  as  their predicted paleostress  British Columbia.  strain events  release of constrictional strain, a  and  important  acted  bounding  a  response of  to  contemporaneous  the allochthonous  to and/or  accumulation motion terrane  Table of Contents 1.  INTRODUCTION  1  1.1 LOCATION  AND  1.2  STUDIES  PREVIOUS  ACCESS  2 2  1 . 3 R E G I O N A L G E O L O G I C F R A M E W O R K 2.  STRATIGRAPHY 2.1  9  JACKSON  UNIT  2.2 CURRIER  UNIT  1  4  1  5  1  7  STRUCTURE  2  0  3.1 INTRODUCTION  2  0  2.3 McEVOY  UNIT  2.4 DEVILS 3.  9  CLAW  3.2 FIRST  PHASE  STRUCTURES  3.2.1 MACROSCOPIC  2 1  STRUCTURES  P H A S E  M E S O S C O P I C  S T R U C T U R E S  3  2  3 . 2 . 3F I R S T  P H A S E  M I C R O S C O P I C  E L E M E N T S  3  4  4  8  P H A S E  3 . 3 . 1 F  2  3 . 3 . 2F  2  S T R U C T U R E S  D E F O R M A T I O N O F F , M E S O S C O P I C S T R U C T U R E S  F O L D S  A N D  F A U L T S  3.4 DEFORMED  F  2  3 . 5 S I G N I F I C A N C E  :  S T R U C T U R A L  3 . 5 . 1T I M I N G  O F  3.5.2 STRAIN  DISTRIBUTION  3 . 5 . 3M E C H A N I S M S  S T R U C T U R A L  O F  8 6  ELEMENTS O F  4 5  3 . 3 . 3 F j C L E A V A G E  C O A L  1  3 . 2 . 2F I R S T  3 . 3 S E C O N D  4 .  2  R E L A T I O N S H I P S E V E N T S  4  6  4  6  7  7  0  7  6  8  4  D E F O R M A T I O N  P E T R O L O G Y  1  0  3  4.1 INTRODUCTION  1  0  3  4 . 2 R E F L E C T A N C E S T U D I E S O F  B O W S E R B A S I N C O A L S iv  : 1  0  4  8  4.2.1 VITRINITE 4 . 2 . 2T I M I N G  REFLECTIVITY O F  104 1 0 7  HISTORY  D I A G E N E S I S / M E T A M O R P H I S M SEDIMENTS 5 . 1 P R E V I O U S  ANTHRACITES  Q U A L I F I C A T I O N  4.2.3 COALIRCATION 5 .  IN  S T U D I E S  O F  115  O F  U P P E R  B O W S E R  M E T A M O R P H I S M  I N  L A K E  T H E  G R O U P  B O W S E R  BASIN 5 . 2 T H I S  130 S T U D Y ,  G E N E R A L  5.2.1 PETROLOGIC 5 . 2 . 2C L A Y  S T A T E M E N T  1 3 1  OBSERVATIONS  133  M I N E R A L O G Y  1 3 6  5.3 DISCUSSION  150  5 . 3 . 1I L L 1 T E C R Y S T A L L I N I T Y 5 . 3 . 2 M E T A M O R P H I C 5 . 3 . 3I N O R G A N I C  A N D  M I N E R A L  V E R S U S  C O A L  R A N K  1 5 0  A S S E M B L A G E S  O R G A N I C  5 . 3 . 4 P A L E O G E O T H E R M O M E T R Y  A N D  C O A L  R A N K  P A L E O G E O T H E R M O M E T R Y  O F  B O W S E R  L A K E  R E G I O N A L  6.1 DEPOSITIONAL  A N D  TECTONIC  6 . 1 . 1S E D I M E N T A R Y  I M P L I C A T I O N S  170 T E C T O N I C  G R A D I E N T S ;  6 . 2 . 2D R I V I N G  O F  S I G N I F I C A N C E  1 7 0 . . 1 7 3 1 7 5  E V E N T S  M E C H A N I S M S  I M P L I C A T I O N S  T E C T O N I C  D E F O R M A T I O N  6 . 2 . 1T I M I N G  1 6 8  SETTING  P R O V E N A N C E ;  6 . 1 . 2P A L E O G E O T H E R M A L  7.  1 5 6  1 6 2  C O R R E L A T I O N S  6 . 2 R E G I O N A L  . . 1 5 4  G R O U P  R O C K S 6 .  130  1 7 5 F O R  CONCLUSIONS  D E F O R M A T I O N  1 7 7 182  BIBLIOGRAPHY  188  v  F i g u r e 6 " D e t a i l e d s t r u c t u r a l geology map  ... " l i s t e d on L e a f  vi. "West h a l f " o n l y o f t h i s two-part map "East h a l f " i s not a v a i l a b l e .  va  was  handed i n by student  List of Figures  F i g u r e 1.  Regional  location  2.  Areal  3.  Structural  4.  Regional  5.  Composite  6.  Detailed  7.  Serial  8.  Generalized structure map (1:100,000)  9.  Interpretive structural cross sections (1:100,000)  location  ^ i • . CxIkcJh^ h  map  3  map  4  provinces  of  the  Canadian  Cordillera  8  stratigraphic correlation chart  10  stratigraphic section structural geology  structural  cross  11  map  sections  (1:50,000), west  half «ndreast-4trif  Tj?^  (1:50,000) %^ 3%  10. Photograph of large scale kink style folds developed in the Currier unit ..22 11.  Photograph  12.  Graph of axial planar of kink folds  13.  Photograph and line drawing of detached Devils Claw and McEvoy unite  14.  Photograph of Currier unit  tight asymmetric  megascopic  15.  Photograph  of  fold disharmony  and  16.  Photograph  of  a duplex  17.  Photograph  of  cleavage  18.  Contoured domains  equal  area  19.  Photographs  20.  Photograph  of  sigmoidal  21.  Photograph  of  syntectonic quartz/carbonate  22.  Photomicrograph Jackson unit  23.  Closure  -X-  W-e^f  of  of  hinge  collapse  saddle  thickness versus  fault zone  an  limb  formation  en  of pressure spacing  in a tight kink  folding developed kink  bands  between  developed  associated detachment in the  of poles  Devils  the  in  the  zone Claw  unit  unit  fractures  37 38 from  as illustrated in outcrop *ys hi^ C . k . < J e v 0 k  vii  31  all structural 35  vein  6  28  36  extension  depth  26  33  to fractures from  solution relationships in pebbles with  24  29  fracture sets echelon  fold 23  inclination, illustrating flattening  developed  stereoprojection  ^  reef  refraction in the Currier  of conjugate hkO  cleavage  and  the  39 41  24.  Increasing intensity of pressure thin section  solution  cleavage  with  depth  as illustrated in  25.  Photomicrograph  of strain shadows  26.  Photomicrographs collapse  illustratingbent  27.  Photomicrograph  illustrating syntectonic, synthetic vein relationships  46  28.  Photomicrograph  illustrating syntectonic, antithetic vein  47  29.  Contoured equal structural domains  area stereoprojection of poles to second 4 and 5  30.  Stereoprojections of second second phase cleavage and and 5  43 micas  resulting from  pore  framework  phase  cleavage  with  32.  Contoured equal area stereoprojection of second structural domains 4 and 5  fold axes  33.  The  34.  Photograph folding  35.  Contoured equal area stereoprojection of d o m a i n s3 , 4 a n d 5 ,  36.  Stereoprojection of folded first phase  37.  Stereoprojection of first and  38.  Photograph of "dome and basin" first and second phase folds  39.  Structure contour the Jackson unit  40.  hkO  fractures warped first phase  hkO  second  phase geometry  of second  phase  thrust fault zone  41.  Photograph  of high  42.  Photograph  of pencil fabrics developed  43.  Structure  44.  Structural map  45.  Effects of three superposed  by  illustratinggently warped strain events  vii'  54  second  fold axes  phase  from  on  interference the  55  structural 56  upper  between  contact  of  60 61 62  faults associated with  a  area  by  created by  3 constructed  on  53  59  Photograph  constructed  from  slickenside lineations  domain  map  52  57  from  dip-slip  phase  50  fractures  map  contour  phase  second  fold axial surfaces in the map  illustrating first phase  angle  from 49  phase and first phase cleavage intersections and bedding intersections, from structural domains 4  Stereoprojections illustrating the intersection of bedding fold axial surfaces in structural domains 4 and 5  phase  44  relationships  31.  trace of second  42  second  intersecting planar  phase  folds  elements  63 65  second  phase  fault surface  66  second  phase  cleavage  68  on  domainal first phase  fold  axes  69  46a. Stereoprojections and several folds  cartoons  illustrating cleavage/bedding  relationships  in  46b. Stereoprojections and several folds  cartoons  illustrating cleavage/bedding  relationships  in  and  bedding  orientations  72  47.  Stereoprojection illustrating first phase first phase fold  48.  Origin  49.  First phase  suprastructure throughout  50.  Photograph  of tight disharmonic  51.  Magnetic map (GSC Toodogone volcanics  52.  Deformation temperature,  53.  Photomicrograph Currier unit  from  the  54.  Line drawings of microscopic relationships of phyllosilicates in arenites the McEvoy and Currier units  from  55.  Photograph of core removed mineral filled breccia zone  56.  Mohr circle diagram illustrating the differential stresses required and bedding parallel fractures  57.  Diagrammatic representation of relationship between hkO bedding parallel veins and principal stress orientations  58.  Graphs  59.  Structural  60.  Theoretical distribution of isorank post-tectonic coalification  of cleavage  cleavage  71  in  fan  7787G)  the map  kink  area  78  folds developed  in Spatsizi  sediments  of well  sutured  detrital grains  from  the  Currier  from  62.  Orientation  of the reflective indicating surface  63.  Graphs  vitrinite reflectance versus depth  64.  Extrapolation level  65.  Burial  66.  Modelled relationship burial history  history of the lower between  of  93  illustrates a to form  90 91  .98 hkO 100  veins, cleavage,  102  area  106  coalification  vitrinite reflective indicating  fit  of 83  108 and 110  Experimental  least squares  unit which  lines following pre-tectonic  61.  of  in a sublitharenite  the study  cross section illustrating pre-tectonic  reorientation of  81  illustrating anomalies over surface exposures  vitrinite reflectance data  of  73 74  map of the pressure solution process, illustrating the effects stress, and grain size on strain rate  of  a  coalification  Currier  in folded  surface coal  112  seams  114 116  gradients  to a  zero  maturation  unit  reflectance  Vl(\  120  125 and  depth  assuming  a  specific  126  67.  Comparison  68.  Time-temperature  69.  P-T  70.  Photomicrograph detrital grains  71.  SEM  72.  Photomicrograph  illustrating growth  73.  Photomicrograph  illustrating stages of carbonate  74.  Photomicrograph  illustrating stages of ankeritization  75. X-ray  space  of modelled  and  calculated coalification gradients  history for the lower  for relevant low-grade  photograph  of clay minerals  Currier  metamorphic growing  128  unit  129  reactions  132  as strain shadows  or  "beards"  on 134  of quartz overgrowths  135  relationships of  diagenetic  albite  replacement  138 139  ....^..3..^.^?.  d i f f r a c t o g r a mt r a c e s f o r a r e p r e s e n t a t i v e s a m p l e s u i t e  76.  Graph illustrating the change heating  77.  X-ray  78.  Graph of Rubier reflectance  illite crystallinity index  79.  Graph of Weaver reflectance  illite crystallinity index  80.  Graph illustrating the relationship between illite crystallinity and reflectance from various sedimentary basins  81.  Graph of (002) and  82.  Graph  illustrating illite crystallinity index  83.  Graph  illustrating evolution  84.  The  85.  Stratigraphic correlation between  86.  Compilation map illustrating generalized structural trends in the map area a n d i n t h e n o r t h e a s tc o r n e r o f t h e B o w s e r B a s i n a n d w e s t e r n m a r g i n o f t h e 7 Sustut Basin . J ! g s g v" ~ > Displacement history along the major strike-slip faults in northcentral British Columbia 178  87. 88.  diffractogram  major  in illite peak  137  width  following  glycolation  traces for (006) reflections of muscovite  and  and  versus  versus  the  log  versus  the  log of vitrinite  the  ratio of  of vitrinite  following  of volatiles during  147  Tectonic boundary conditions active during deformational events  ix  and  intensity of  the second  the  153  167  Cordillera Bowser  and  151  164  coalification  southern  148  log  heating  tectonostratigraphic terranes of the Canadian northern  the  143  paragonite 144  r  illite crystallinity index (001) peaks  s>pecsa£i  third  169  Basin  phase  .171  180  sp-e-c^aS  List of  Table  Tables  Page  I.  d-spacings  for clay minerals  145  II.  d-spacings  of phyllosillicates  145  III. Identification of clay mineral IV.  X-ray  analysis of  phases  145  illite  149  x  AcltoQwledgments Special thanks The  is due  Dr.  R.M.  author benefited greatly from  Bustin  for his apt supervision and  discussions with Dr. J.V. Ross, Dr.  Dr. J.K. Russell concerning various aspects of the study. Gulf Limited  coal division personnel  in the petrologic  search  various  in the  colleagues  were  for the ever department  further  assistance of technicians Ed  draftsman Gord  Hodge  were  Energy,  Mines  with Gulf Research  from  Canada Council  post-graduate he  Resources grant  to put  Montgomery  and  Resources  Limited  and  A Natural  scholarship supported  Grant  P.B. Read  Sciences during Canada.  xi -  and  assisted with  thesis in its  proper  Bryon  Cranston  and  of the thesis. Funding a research  Sciences and Engineering  the period  and  debates  83-4081A,  Bustin's Natural  the author  the taxpayers of  No.  the and  invaluable to the completion  67-7337.  gratefully acknowledges  served  Barnes  Resources  elusive zeolite. "Hop-saturated"  perspective.The  obtained  W.C.  Canada  also helpful to this end. Dr.  patience.  was  contract  Engineering  Research  1982-1985,  Council for  which  1.  Over Western Bowser  the last decade  North Basin  America  the concept  has gained  in terms  INTRODUCTION  of accretionary terrane  increasing acceptance. Attempts  of a tectonic model  island arc terranes to the cratonic margin been  hampered  by  late Mesozoic  a,b) and  have  outlined  pre-Oxfordian  and  post-Albian  attempted  summer of  the Bowser  few  stratigraphic studies had  Basin. Structural studies were  northeastern delineation  comprehensive corner  of  utilized as the  strain and  the Bowser  framework  prepared. Macroscopic metamorphic  1971,  stratigraphic  of a mappable  allochthonous et al., 1982)  and  eastern  Richards,  been  and  for however,  in the northern  structural  for the  from  a geologic  which  study  was  Intitially this study  geometries revealed by  of  the  exposed map  mapping  at the mesoscopic  undertaken concerned  sediments. at the  and  the  itself with  This  scale of  together with  in  1:25,000  microscopic  of  organic and  and  deformation  of post-Bathonian  sediments.  accretionary  1  terrane  was  scales were  the relative timing  the  was  observations  to decipher  to evaluate  the  stratigraphy  and  is finally used  the  portion  to outline the styles of deformation  information  has  interval. Prior to  limited to casual observations  stratigraphy  inorganic metamorphism  the  1974a).  Basin.  phenomena  conducted  the  1976) of  biostratigraphy  to pre-Albian  have  margin  strata respectively. Little stratigraphic work,  fold trends (Eisbacher, A  the  to  the  structural studies in  along  (Tipper  of  Monger  lithostratigraphy and  in the intervening post-Oxfordian  of 1981  dominant  1981;  detailed stratigraphic and  a mappable  to explain  the accretion  (Eisbacher,  the southeastern margin  Basin  been  involving  succession. Stratigraphic studies conducted  (Eisbacher, 1974 Bowser  the paucity of  tectonics as applied  tectonic  of used  burial,  model.  This  2 1 . 1 L O C A T I O N  A N D  The  Coalfield, as defined  Groundhog  A C C E S S by  Buckham  northwesterly trending parallelogram enclosing an  and  Latour  (1950), is outlined by  area of approximately  in the northeasterncorner of the Bowser Basin (Figure 1) . The northernmost 129°  and  square  portion of the coalfield, approximately  latitudes 57°  km.  and  57° 50'; and  Physiographically  the area  the Nass, Skeena, Spatsizi and generally by  has an  forms  Klappan  a plateau  aircraft or helicopter from  Spatisizi wilderness  area  have  Columbia  right of way  river systems.  probably  entail motorized The  June  and  and  1983  traditionally gained  Future  field season  longitudes 128°  which  the  Smithers. access  on  Outfitters using horseback  via the  of anthracite resources the British Columbia  in the area  Railway  right of  and  will way.  August.  Late  also offers access in particularily long  summers.  During.  1982  characterized by  rain or snow  continually, effectively limiting access  on  most  days and  Coalfield  low  STUDIES  O'Dwyer  a possible railway The first published in the study area Dupont,  British  July and  The first investigation of geological relationships,in the Groundhog by  of  the  elevations.  conducted  700  headwaters  to higher  1.2 PREVIOUS  and  area generally encompasses  the field season was almost  study area is the  follows the valleys of the Little Klappan  development  in the study  early September  lying cloud  which  access along  from  km  rivers flow (Figure 2) . Access to the area is  wing  Skeena  by  2,400 square  areal extent of approximately  fixed  Railroad  bounded  a  1901. G.M.  and  extension  Dupont from  in 1898 and Hazelton  1899  to Dease  (Dupont, Lake  reference to coal in the Groundhog at the confluence Dawson  (1901)  significant anthracite reserves would  of Didene  Creek  in a summary be  found  in the  1901) while evaluating  (Buckham (a 10  and  report area.  was  and  foot seam  Spatisizi River) to the G.S.C.  Latour,  1950).  outcropping was suggested  by that  FIGURE 1: Regional map  illustrating approximate location of study area with respect  to various geographic features.  4  FIGURE 2: Areal location map illustrating approximate study area boundary (heavy line), 5000 foot topographic contour, major drainage systems, major peaks and permanent ice fields (IF).  5 The  period from 1903 -  in the Groundhog.  Although  primarily concerned  coalfield, several claims were (Buckham  and  in the area  Latour,  1913 was characterized by substantial coal exploration  staked in the northern  1950). These  (Malloch,  subdivisions, the Hazelton  drew  attention to the northwesterly major  reassessed many concerned  Group  valleys. During  predominantly  During was  of  was  (1970,  eastern margin  made  1971, 1972, 1973, Basin; an  subdivided  2.  Groundhog  Gunanoot  facies;  3.  Jenkins  Creek  Richards  and  Eisbacher  Western  and  Canada.  by  Group.  Hazelton  of Canada,  Latour  Malloch.  Lower  major  also  1957)  of (1950)  Although  the  a  reconnaissance  airphoto analysis from  fold axial traces were  the shown  1974,a,b,c, 1977) area  which  conducted  borders the  studies along  eastern edge  the  of  the  fades:  and  facies. Gilchrist (1979)  assemblage Mt.  and  rename  Survey  two  as well as the presence  quality, they did  the strata into several  facies;  Basin  fold systems  and  stratigraphy  to delineate the stratigraphy.  Slamgeesh  Bowser  trending  as Upper  Duti-River  through  River  Series. Malloch  the 1948 field season Buckham  1.  passes  the overlying Skeena  Basin. Numerous  of the Bowser  area. Eisbacher  the Gunanoot  the Klappan  the  the strata in the coalfield into  incorporated outcrop data and  the Bowser  attempt  Eisbacher  study  and  Stikine (Geological  constructed which  no  divided  with coal reserves and  Operation  northern margin although  near  of the coal bearing sections originally reported  stratigraphic divisions ol* Malloch  map  end  portion of  efforts resulted in the first outline of  1912, 1914). Malloch  main  faults in the  with the southern  and  Gunanoot,  (1981)  delineated  a  strata which  large northwesterly  they  referred  trending  syncline  as well as several fluviatile intervals within  summarized  emphasized  briefly studied  the  facies distribution in the  its significance in terms  the  eastern margin  to  as which  sequence. of  of the plate tectonic history  the of  6  Several  coal companies  the past decade. observations the  Details on  on  Ministry  analysis of previous stratigraphy and  Moffat,  age. The  1983). An  Basin Basin  Lower  1981). The  of paleogeothermal  Petroleum  is a  and  successor  underlying  Paleozoic  basin  Figure The  heat  A  has  been  to  reported  also been  of  comprehensive  their comparison  flux has  (Eisbacher,  1974  the previously their  recently  published  sedimentary  and  volcanic rocks  of plutonic, volcanic and  Atlin terrane and coincident with  to the  to the west  east by by  the Intermontane  a  Jurassic-Cretaceous  varied  the Omineca  which  Upper  volcaniclastic rocks  Triassic  (Eisbacher,  crystalline belt,  Plutonic complex.  belt of Wheeler  Basin  along  a  Bowser  the Sustut Group  and  to  The  Gabrielse  Basin  became  regional  uplift in the south  Skeena  orogenic  uplift north of and  and  at the surface  Group.  the east  Group  phyllites (Gabrielse a subsiding  is bounded To  succession, whereas  fault with Triassic Stuhini  Jurassic following Arch  and  the Coast  northeastern corner of the Bowser  greenstones, limestones and The  of  3).  are in fault contact with  are juxtaposed  c, 1976)  Stikinia or the Stikine terrane  andesitic to dacitic volcanics of the Jurassic Hazelton  older  Resources.  and  rocks are part of  Stikine terrane is bounded  terrane is almost  rocks  open file reports  F R A M E W O R K  Jurassic assemblage  north by  (1972;  and  in  general  analysis of regional coalification trends and  G E O L O G I C  consists of upper  the  and  area  1984).  Bowser  and  of Mines  structural style outlined in this study  1 . 3 R E G I O N A L The  active in the  coal measures  geological studies in the area  significance in terms (Bustin,  the strata surrounding  been  structure style are available in several unpublished  British Columbia  (Bustin and  (Gulf, Esso, Petrofina) have  Tipper,  1984).  depositional trough  during  along  and  the  Hazelton  to the  volcanics and  east-northeastly  by  north  Permian  the  and  Middle  trending  including the Atlin terrane. In  they  the  7 northern 1974b, from  half of the basin paleocurrents flowed 1981)  the  from  Skeena  uplift during basinward  the  uplifted Atlin terrane whereas  Arch  in a northerly  convergence  prograding  of Stikinia and  sediments  shed  from  uplifted Bowser  Formations  mid-Cretaceous  of the Sustut Group to Paleogene  strike slip fault systems strike-slip faults may and  Irving, 1980). The  rhyolite and Bowser  Basin  amount  Kluit, 1979). The  geology  trachyte flows of Pliocene (Gabrielse and  Cretaceous  Tipper,  as  there to Late  Tango  Creek  to recent age 1984).  Continued  time,  obscurred  by  and  Brothers  1985).  displacement  undeformed  in the northwestern  uplift  Basin  transported, northwards  cummulative  in  Cretaceous,  14 degrees of latitudinal shift  is somewhat  flowed  resulted  Cretaceous  (Eisbacher, 1974a, 1981; McKenzie.  to as much  bedrock  to have  rocks eastwards into the Sustut  time, the Stikine terrane was  (Templeman  (Eisbacher,  Jeletsky, 1975).  1981). In Early  accumlation. From  (Figure 3) resulting in deposition of the Upper Peak  and  Atlin terrane is thought  deltaic deposits (Eisbacher,  basin terminated sediment  southwesterly  to the south paleocurrents  direction (Richards  in the Bowser were  southerly and  From along, along  (Monger basalt,  part of  the  FIGURE 3: Structural provinces of the Canadian Cordillera (after Wheeler and Gabrielse, 1972); I=Insular belt, 11=Coast Plutonic complex, III=Intermontane belt, IV=Omineca terrane, V=Rocky Mountain Fold and Thrust belt, VI = Interior Plains, BB=Bowser Basin, AT=Atlin Terrane of Eisbacher (1981).  2 . STRATIGRAPHY In the study approximately  3700  area  the  m from  the  the top of the Toodoggone shale package  entire sequence,  part of the section, has  and  sucession  been  units. Correlation of these divisions with  above the  (Tipper  the Pliensbachian Late  through  Sustut  the package.  Use  in the  elsewhere  (Bustin  the study  area  and  and  Richards,  Figure  of marker  to  marine the  (Richards  into 4 informal  units  1976)  1983).  by  and  other authors  4 . In this study the  is applied  to all those  (Smith  term  sediments  et al., 1984)  5 illustrates a generalized  in  and  below  composite  section  horizons facilitated structural geometric  Descriptions  Moffat,  the thick  Assemblage  those made  Spatsizi sediments  Group.  area.  down  referred to as  divided  of  oldest to youngest, the Jackson, Currier, McEvoy  to Bajocian  Cretaceous  interpretations  been  surrounding area is illustrated in Figure  Group  thickness  of conglomerates excluding  subsequently  Devils Claw  Lake  1983), from  has  Moffat,  Bowser  a minimum  Latour, 1950) or the Gunanoot  (Bustin and  the coalfield and  has  stratigraphic exposure  volcanics. The  (Buckham  Gilchrist, 1979). The  statigraphic package  highest  in the lowermost  Hazelton Group and  Bowser  of these  units  on  A brief description  a regional of the  scale  is  given  units as  defined  for  1983)  is not  exposed  in  et al. (1984)  in the  follows.  2 . 1 JACKSON U N I T The  lower  the study  contact of the Jackson area. Based  Spatsizi sediments wavelength The  and  Jackson  on  work  unit (Bustin and conducted  approximately amplitude  Lake  Group  Bowser  Basin. The  exposed  conglomeratic  time  that: the  Tipper and  contact in the present  unit in order  study  area  Jackson  equivalent to the Ashman  as described by upper  Smith  east, of the  it is estimated  unit is roughly  Bowser  8 km  by  Moffat,  Richards study  has  and  average  is at least 2,000 Formation (1976) in the been  to facilitate structural mapping. 9  the  underlying  chosen  fold  m thick.  of the  upper  southern as a well  It is apparent  that  10  JURASSIC  Series Hazelton Qroup  Upper  Sustut-Slfton  Sustut-Slfton  Sustut  Suatut  Assemblage  Assemblage  Qroup  Qroup  Bowser Assemblage  Lower Part  Jenkins Creek Facies GunanootGroundhog Facies Dutl River Slamgeesh Facies  Assemblage  A isemblage  1979  NORTHERN QROUNOHOQ COALFIELD  Thla  Study  NORTHERN BOWSER BASIN Sustut Qroup 1  Qllchrlat. 1978  SOUTHERN BOWSER BASIN  T a k l a - H a z e l t o n Tat cla-Hazelton  -  Rlcharda A  Rlcharda.  NORTHERN BOWSER BASIN  Middle Lower  Tipper &  NORTHERN BRITISH COLUMBIA  Upper Part  1 • 74  Devils Claw Unit  Skeena Qroup Qunanoot  McEvoy Unit  Assemblage Bowaer Lake Qroup  Currier Unit  Hazelton Qroup  Spatalxl * Sada Jpottoggona ^^^volcanlca  J a c k a o n Unit  Takla Qroup  ???  Middle  (Smith e t a l . . 1 9 8 4 )  HGURE 1983.  Qroup—  Eiabacher. 1986  Lake  Skeena  a  —Bowser  Lower  Souther  Armatrono,  1  Upper  Upper  TRIASSIC  4 I960  QROUNOHOQ COALFIELD  Hazelton Qroup  CRETACEOUS  SOUTHERN GROUNDHOG COALFIELD  Latour.  Bowser Assemblage  Buckham Mtlloeh, 1914  4: regional stratigraphic correlation chart, revised from Bustin and Moffat,  LITHOLOGY  UNIT  U  conglomerate,  < —I O CO _J  sandstone, shale  M  > 111  Q  sandstone,  shale,  u  81II31 o n e, conglomerate,  111  ironstone  coal, shale, Ironstone,  shale,  \ L L /  *  o 2  sandstone slltstone  100m  * @ (*)  FIGURE  CURRIER  siltst-one,  JACKSON  sandstone,coal, ) conglomerate  I  >o >  Oxfordlan Albian  Ammonite  Palynomorph  5: C o m p o s i t e s t r a t i g r a p h i c s e c t i o n f o r t h e s t u d y a r e a .  12 detailed paleontologic regional  work  in this area  to further delineate the  exact  correlations. The  Jackson  characterized  by  unit in the study area consists of an  a thick succession  sandstone and  conglomerate  approximately  200  interbedded  with  interpretation consisted  m of  of  lenses in the lower  study  east of Conglomerate  upwards  contains  one  Over  the major  sandstone and  This  Creek,  is capped or  by two  cycle  capped  by'  of Didene  conglomerates  which  In order  been  Jackson  contain marine  inaequivalvis,  Comptonectes  was  and  coal  identified  which  grey-weathered, in the  conglomeratic  in thickness  and  Entolium,  comprises  light  grey-weathered  pelecypods  thin  area  west of the Spatsizi River.  portion of the study area the conglomeratic shale which  portion  identified only  and  range  siltstone with  to facilitate structural  a 2 m thick,  Creek  a laterally continuous  and  sequence  thin conglomerate  in the  particular unit has  north  coarsening  upper  sandstone,  limestone.  B i v a l v e s i d e n t i f i e d a s Otapeiria, Oxytoma  portion. The  grained  minor  upward  fissile shale  area, a local subdivision  conglomerate.  which  thinly bedded  fine to medium  a coarsening  sequence  of  shales, siltstone and  in the  chert pebble  The  is required  zone  from  zone  3 to 8 m.  is underlain  by  ammonites. Oslrea,  Corbula,  Plagiostoma,  Pleria,  subcompressa, ( C . S t e l c k , p e r s .  and Pleuromya  c o m m . ) t h e a m m o n i t e Amoeboceras ( P . S m i t h , p e r s . c o m m . ) a n d t h e e c h i n o i d Pentacrinus  (R. Thomson, pers. comm.) have been  located in the Jackson unit, the  l a t t e r t w o f r o m t h e u p p e r m o s t 2 0 m . E l s e w h e r e , Amoeboceras  has been identified in  the upper  Lake  Oxfordian  black shale facies of the Upper  Bowser  Group  in  the  s o u t h e r n B o w s e r B a s i n ( T i p p e r a n d R i c h a r d s , 1 9 7 6 ) . Pleuromya subcompressa, Oxytom and Oslrea h a v e b e e n i d e n t i f i e d i n s t r a t a v a r y i n g f r o m B a j o c i a n t o l o w e r O x f o r d i a n i n  a g e . A s w e l l Otapiria sp. i s k n o w n f r o m A l a s k a i n b e d s o f B a j o c i a n a g e . T h e a b s e n c e o f Buchia ( w h i c h i s g e n e r a l l y c o m m o n fossil sample suggests an  suite collected age  range  from  below  of pre-Oxfordian,  in Oxfordian 100  m from  and the  possibly Callovian  younger  marine strata) in a  top  the  of  Jackson  (C. Stelck, pers.  unit comm.).  13  Numerous conglomerates  thin sections were  of the Jackson  diagenetic/metamorphic fragments  by  cut from  unit in order  effects. Extensive  sericite and  carbonate  provenance. samples  Point counts on  could  are  percent  of  the total rock  altered grain boundaries (1981) suggested  the Cache  fragments renders  estimates of  the of  Atlin terrane chert and  group  mafic  volcanic rock  upwards the  zone  sequence.  zone  Trough  immediately  characterized by  with  In the  plant material. This  worm  conglomeratic zone  bivlaves and broken  shells were  shoaling might  ammonites.  in a be  barrier bar/beach  system.  Creek  40  invalid.  has  Eisbacher northern  and  and  marine  of the area  section has  the  by  preponderance area.  an  apparent  the  fining  fossils are absent  the conglomeratic  abundant  and  an  in  zone  upper  bivalves and  is zone  tube  shales containing abundant and  overall  strata in the Ml  feeding  in  Tahtsedle Creek  containing pebbles  coeval  representative of distributory channels  Jurassic onwards  and  thus likely represents an The  of  solution  out near the  the Middle  erosional base  is underlayen  zone  30 and  pressure  in the thesis study  In several localities beds  observed. This  in the majority  is consistent with  of Didene  an  upper  wackes  between  crop  sequences, tabular cross beds  rich in coal and casts. The  found  remainder  coarsening upwards  up  which  from  cross strata are common  below.  make  remaining  chert lithic  sections and  and  north of the thesis area) were derived  interpretation  the headwaters  is channel-like,  age  exposed  fragments  of rock  clast type the  depositional grain shape  30 km was  to the north. This  In the area between conglomeratic  which  concerning  extent to which  of Oxfordian  the nature  stress driven dissolution  observations from  fragments  present. The  the conglomerates  Creek  gained  the point-counted  tip of the basin (approximately15 from  be  chert litharenites and  the extensively altered sections, volcanic rock  and  of chert, quartz, feldspar and  unaltered sections and  (Pettijohn et al., 1973). In several of  clast type and  destruction of clasts by  which  indicate that the sandstones  to coarse grained sandstones  to determine  replacement  and  significantly limited the information  medium  imbricate upward  Klappan  the barrier system.  marine  area Eisbacher  14 (1974b;  1983) suggested that conglomerates  turbidity currents. Although  this origin is ruled  their close vertical association with within marine  within the Jackson  shales deeper  out  coal swamp  were  deposited  for the uppermost  by  conglomerates  deposits, thinner conglomerates  in the section may  have  been  deposited by  by  encased  turbidity  currents.  2 . 2 C U R R I E R The  lower  U N I T  contact of the Currier  occurrence  of Jackson  thickness  from  McEvoy.  The  350  unit in the study  conglomerate.  to. 400  m and  In the study has  sandstones which  in thickness  from  noted  assigned  Cladophlebis lindlegana,  by  Moffat  based  vaccensis, Coniopteris,  dissolution and  alteration. All samples  fragment  the  Jackson  weathering  (1983), a probable die presence  volume  waning  importance  and  transport may  of  of  suggest  a volcanic  either increasing though  the  unit  Jurassic  has  assemblage: Baiera pachynerve.  of  the  extensive  chert lithic  to the greater than  source,  this  sandstones  comprise  seams,  locally  Ctenophyllum  by  o  interbedded  are  Late  unit, hampered  fragments  lowermost  least 5 coal  digitata,  to coarse grained  volcanic rock  may  fragments  age  are chert litharenites or  in comparison  unit, which  and  in  weathered, finet  seams  Ginkgoites  uppermost  the  of the fossil plant  parvula,  fine  with  shales. At  unit. The  the  are characteristic of  as in the case of the Jackson  the total rock  or  in the  Nilssonia  contact  volcanic rock  lymenophylloids,  angustiloba,  (Pettijohn et al., 1973). In general  source  on  upper  by  unit ranges  orange-brown  nodules  of thin sections cut from  unit were,  underlying  and  is defined  the Currier  carbonaceous  occur  bands  and  to the Currier  Analysis Currier  Bustin  Sphenobaiera  and  1 to 5 m,  tectonically thickened. Ironstone  been  a. gradational  contain chert and  with fissile shales, siltstones, mudstones  As  area  Currier succession is characterized by  coarse grained  ranging  area  wackes  less than 30%  contribution  importance effects of  20%  of  in  a chert  selective  also contribute to differential clast distribution.  of  Where  15  unaltered grain boundaries are only of  moderately  can  be  sorted. The  detrital plagioclase  feldspar  observed, grains appear  grains  (20%)  and  volcanic  only  minor  reworking.  In the area west of the Little Klappan a thin  abundant  (1 m thick)  pelecypod  transport Thin  bivalves which  this unit. It is possible deposits  medium  coal seams  in a barrier  and  grained  and  are intact and  rock  Nass  ironstained  carbonaceous  that these  lagoonal  to sub-angular  angularity of the grains, together with  short distance of transport and  Creek  angular  fragments,  Rivers and  sandstone  appear  to have  environment  In one  are  abundance  suggests a  north of  Didene  which  contains  occurs  undergone  shales are present both  particular sediments  the  above  representative  locality marine  and  limited and  of  below  storm  foraminifera  {Ammodiscus, Trochamina; S . R o w e , p e r s . c o m m . ) w e r e l o c a t e d i n t h e l o w e r p o r t i o n o f  the Currier  unit. In contrast, the Currier  characterized by  sandstone  units which  ripple cross lamination. Here plant fragments and  and  Currier  upwards, much  As  lagoonal and  possibly interdistributary swamp  possibly  studies are required  in order  Mt  trough  Klappan  is  crossbedding  and  of the area in the uppermost which  represents  may  suggest  Currier,  non-marine  a transitional environment  shales and  deposits associated with distributory channel  sedimentologic  have  are common,  environments.  grained  the  fine  through  fossil tree stumps  such,  in the area surrounding  coals intermixed  sequences. More  with  with  coarser  detailed  to further establish these  relationships.  2 . 3 M C E V Q Y UNIT The  lower  (Bustin  and  contact of the McEvoy Moffat,  the  study  area  and  thinly bedded  characterized by sparse  1983)  between  the Currier  as well as locally. In general a unit which  sandstone thicker more  ironstone bands  unit with  and  an  contains  (Currier  unit) from  massive  sandstone  absence  unit is gradational regionally a division can  coal, shale, abundant the overlying and  of coal. The  be  made  ironstone  section which  in bands  is  siltstone, thicker shale interbeds, McEvoy  unit has  a  maximum  16  thickness  in the  approximately  study  600  divide between  area  m  of  the McEvoy  the Little Klappan  subunits of the McEvoy The  lower  weathered, which  have  subunit  medium  channel  River  been  and  4-6  conglomerate  coarse  grained  thick)  sandstone  increases upwards  and  The defined  by  a  weathered grained  though  The  13  m  thick,  chert pebble  McEvoy  and  greywackes.  Lenses  obtained  from  to Late  probably  Cretaceous  sandstone  interbedded  McEvoy.  lower  grey  and  two  weathered,  mappable,  Plant fossils and  sorted,  chert by  conglomerate and  carbonized  is generally  laterally  extensive,  300  ironstained,  thick) has poorly  layers  tree  are located south  m  of  Creek. a lower  contact  consolidated,  red-brown  thick interbeds of ironstained, coarse  thicker and  to thickly bedded, and  conglomeratic  the thickness of sandstone  (approximately  intervals are  friable  cemented,  subunit  has  massive  is locally replaced  quartz  which  greywacke  poorly  weathered,  variably  grey  conglomerate  uppermost  subunit  and  interbeds. Two  The  brownish  with  of Tahtsedle  of lime mudstone  McEvoy  drainage  thick) consists of  of the headwaters  conglomerate  date, neither palynomorphs  m  shale deposits. The  McEvoy  consist of massive  the  In the study area  500  to shale ratio and  south  sandstone. Sandstone  exposes  of  best exposures of the lower McEvoy  immediately McEvoy  west  Creek.  arenaceous  and  widespread  the sand  in the lower  upper  5 km  (approximately  coarse  thick, light grey  are common.  Ellis Creek  is a  or overbank  resistant. In general  fragments  about  Tahtsedle  to thickly bedded  which,  10 m  section which  with thin fine grained sandstone  m  pebble  A  mapped.  horizons are present in the lower  approximately  m.  to coarse grained, light grey  mudstone  (approximately  Early  800  is located  of the McEvoy  is generally massive  siltstone and  very  of approximately  closer spaced  grey-brown  than  weathered  in the  lower  arenites  calcareous siltstone are locally present  and To  o r p l a n t f o s s i l s w i t h a d i s t i n c t i v ea g e r a n g e h a v e . b e e n  rocks. Based age  range  latest Jurassic to Early  on  a  Late  Jurassic age  for the overlying Devils  Cretaceous  in  age.  for the Currier Claw  and  unit, the McEvoy  an is  17 McEvoy  sandstones are chert litharenites and  fragments comprise  less than  altered granitic rock  20%  fragments  of the total volume  contribute between  rock fragments. In sandstone  samples  which  to subangular  underlying  unit, grain angularity, general  much The  as  20%  detrital plagioclase  presence  perhaps  and  of granitic rock  the  Hotailuh  fragments  Large  sandstone  have  zones, fining upward  features typical of meandering unit immediately  origin (Bustin  and  overlying  McEvoy  becoming  more  2 . 4 D E V I L S The  by  calculated area  non-marine  the  the presence  short distance  of  of  as  transport  of a plutonic  source,  lower and  units. Such  trough  the  are thought  regressive  channels typically  crossstratification,  nodules  the transition from  a continual  affinities than  cross-cut friable siltstones and  deposits. Limestone  in aspect through  the Devil's Claw  approximately which  thickness  approximately  the Mount  in  recognized to be  with  the  of lacustrine  the Currier  cycle  in  unit to  the  the  deposits  time.  C L A W  an  conglomerate  and  sequences  1983). Thus  unit represents  of  of dissolution, the  importance  which  south of the study area  Moffat,  contact between  defined  channels  the upper  stream  highly  total volume  well sorted. As  unit has greater non-marine  features of both  McEvoy  to the  and  rock  north.  shales are common lower pebbly  10%  grains indicates a the  Volcanic  fragments  lack of sorting and  suggests  batholith to the  underlying Currier unit  5 and  are at best moderately  feldspar  ln general the McEvoy  of rock  exhibit lesser amounts  grains are angular Currier  chert lithic wackes.  Biernes  10  is massive  m  and  thick, dark  and  very  of approximately  600  200  m  more  800  red-brown  resistant The m  in the  section is exposed  synclinorium. The  thickness of approximately  underlying McEvoy  m.  Devil's Claw  In general the  unit is conformable  weathered, Devil's Claw  study in the  area. South  chert  pebble  unit has of  Devil's Claw  a  the  structurally lowest  unit thus has a  and  study part  of  minimum  exposed  is characterized  both  18 locally and  regionally  variably sorted and minor  by  abundant,  consist predominantly  quartzite pebbles. The  mudstones  which  channels  of limited  delineate  structural geometries  which  correspond  persistant conglomerates.  contain abundant  the  Though  Claw  unit was  precludes  non-marine from  nature of Devils Claw  obtained  either  southern  part of the Groundhog  plant  corresponding age  macrofossils  thinly  sandstone  shales. In order  to  subdivided  3 subunits  into  cycles floored by  better  thick, laterally  area, the  channel-fill  the use of these subdivisions for  more  sediments requires that ages  or palynomorphs.  A carbonaceous  be  shale  in  assemblage  Albian Aptian-Cenomanian  B a r r e m i a n -A l b i a n  Klukisporites foveslalus Cicatricosisporites cf. hallei  Berriasian-Cenomanian  Foveotriletes subtriangularis  Berriasian-late Albian  Lycopodiumsporites crassimacerius  m i d A l b i a n - C e n o m a n i a n  Cicatricosisporites sp.  C e n o m a n i a n ( D u n v e g a n )  range in ages together with the restricted occurrenceof  croosimurus i n A l b i a n s t r a t a e l s e w h e r e ( R o u s e , p e r s . c o m m . , range  of Early  Thin litharenite and  to Late Cretaceous  for the Devils Claw  section analysis suggests that sandstones chert  the  ranges:  Microreiiculatisporites uniformis  age  and  bedded  coalfield yielded the following palynomorph  Tricolpopolleniles croosimurus  The  are  locally contain  with  generally traceable in the study  probably  chert pebbles  plant fragments, coarse grained  rare carbonaceous  Devils  which  mapping. The  and  white  are interbedded  to gross fining upwards  origin of the conglomerates regional  of light green and  conglomerates  lateral extent and  roughly  to 15 m thick) conglomerates  stratigraphically highest conglomerates  cobbles as well as pebbles. The shales and  thick (up  lithic wacke  and  Tricolpopollenites  1985) suggests a probable unit.  conglomerates  (Pettijohn et al., 1973). Volcanic  rock  are  chert  fragments  19 generally comprise samples  15%  of the total volume  altered granitic rock fragments  total rock  fragment  the clasts and The stream  less than  volume.  are perhaps  Devil's  environment  Claw  Pebbles derived  occur and  of rock  fragments. In  contribute as much  several  as 10%  of white polycrystalline quartz comprise from  eroded  unit is considered  veins (Richards  to have  been  and  deposited  similar to that interpreted for the Cadomin  to  the  10%  of  Gilchrist, 1979). in a  Formation  braided in  the  R o c k y M o u n t a i n F o o t h i l l s ( B u s t i n a n d M o f f a t , 1 9 8 3 ) . T h e u p w a r d s i n c r e a s ei n thickness and  percentage of coarse conglomerates  overlying  Devil's  Claw  unit is thought  increased  uplift in the source  area.  from  the McEvoy  to reflect continued  regression  unit upwards  to  as a response  the to  3.  3.1  STRUCTURE  INTRODUCTION  Structural investigations comprised microscopic  levels. Field  observations at the mesoscopic,  studies involved  mapping  informal  stratigraphic units previously  bedding,  fractures, cleavage, intersection and  observations  pertinent to the  studies were  concerned  with  macroscopic  of large scale structures in  the nature  or  of cleavage  relative timing.  and  veining  respect to major  events. Bulk  and  cross  in the study sections  were  area  diagenetic/metamorphic  of individual strain events, and are  evaluated  constructed  at a  and  as other  Microscopic  in the area:  mineralogy  deformation  such  slickenside lineations, together with  orientation, distribution, relationship to the surrounding  strain partitioning, the timing  the  described, collection of orientation data  analysis of kinematics  structural and  and  their  timing,  with  strain, the nature  possible mechanisms  of  in light of the observations. Initially  scale  of  1:25,000  (illustrated  of  in Figures  maps 6  &  7 at a scaleof 1:50,000, back pocket). More interpretive maps and sections (Figures 8 &  9, back  pocket)  were  then  constructed  at a scale  of 1:100,000) using downplunge  projections and  surface observations. In general  the areal bulk  possibly three phases the  second  with  an  of deformation; axis at a  various scales related to each in the  following  high of the  strain can  to the  deformational  sections.  20  1:50,000  (illustrated  at a  subsurface interpretations based  the first and angle  of  be  described  third approximately other  two.  phases  Structural  by  two  scale on and  co-axial features  are described and  and at assessed  21 3 . 2 F I R S T  P H A S E  S T R U C T U R E S  3 . 2 . 1M A C R O S C O P I C  S T R U C T U R E S  Folds  The  dominant  northwesterly chevron  trend  and  vary geometrically  folds. In general, the majority of  (Faill, 1969) which  structures in the field area  distinguished by  long  are often characterized by  11). Folds dipping  are  lesser contribution than  a  kilometre  The  area  Faults  than  in magnitude  folds may  to asymmetric  open be  and  hinge  but  hinge  zones  of deformation  Lake  is Nass on  tight  10)  1974; with  seem  displacements  fault; Figure  kinks  (Figure  are locally overturned  (exception  Figure shallow  to have  a  usually  less  8, back  pocket).  structural style:  1.  Area  2.  Area east of Nass River west of Tahtsedle Creek and south of Klappan River.  3.  Area  south  4.  Area  west of  Kluayetz  Creek,  Didene  Creek  and  the Little Klappan  River.  5.  Area  east of  Kluayetz  Creek,  Didene  Creek  and  the Little Klappan  River.  Structural  Domain  Rocks  of Spatsizi River  which  wavelength  which  west of  Kluayetz  Creek.  crop out at surface in the area west of Nass  8). First phase  axial planes  and  River.  J  of shale, conglomerate (Figure  Klappan  general  collapse (Ramsay,  strain with  River and  a  described as megascopic  to the areal bulk  based  have  parallel folds to  sharp  to the first phase  is divisable into five domains west of Nass  folds which  broad  straight limbs  related  folding  from  saddle reefs and  generally upright  axial planes.  are  dip  and  thin sandstone  folds in the  area  are  and  lower  are  kink  style parallel folds  asymmetric  folds have  an  Currier  composed  of the Jackson  steeply to the west. Such  ratio of approximately  Lake  amplitude  1:1 (amplitudes of approximately  400  units with  to  to 600  m,  22  HGURE  10: View looking north near northeastern edge of study area illustrating large  scale kink Jackson  style folds. Dashed  (Jj) units.  line follows the contact between  the Currier (Jc)  and  FIGURE 11: Room problem solution in the core of a tight kink fold by hinge collapse (he) and saddle reef formation (sr). Mechanical pencil for scale.  24 wavelengths lower  of  600  Jackson  south-western  m)  and  are  shales  associated  corner  of  the  locally flattened (Figure with  map  a low  area  angle  (Figure  12). Parasitic folds in  shear  6 &  zone  occur  8, back  in  the  the  pocket).  Structural Domain 2  Between ranging from Jackson  Nass  Lake  the uppermost  unit are  exposed.  synclinorium  outlined by  Immediately  east of Nass  McEvoy  and  planes  which  (amplitudes Locally  and  Currier dip are  the core  Lake,  approximately  between  m  overturned  characterized  an  and  very  ratios of  Lake  beds  amplitude  wavelengths the west  broad  by  2,000 m). Towards  Creek  although  and  McEvoy  Nass  broad  of the Devil's Claw Devil's  unit  Claw,  style with  axial  are approximately  600  1:2 m).  with associated east dipping also dip  the  east  axial  towards  fold style is  folds predominant  approximately Lake  to the  400  detachment  m  with  and  zones  units are present locally (Figure  the fold style is identical to that axial planes  uppermost  ratio of  concentric open are  a  units  to wavelength  obliquely  1:5 (amplitudes  pocket)  including the  ln the central part of this domain  the Devil's Claw  directly east of Nass  to and  8, back  a distinctive mega-kink  towards  upright  of Tahtsedle  6 &  in the lowermost  crosscut fold limbs  wavelengths are approximately  thrust  units have  300  thrusts which  west  is, in general,  steeply to the east and  to wavelength  Immediately  unit down  folds developed  equivalent  significantly different with  developed  area  (Figure  relatively thick conglomeratic  of the synclinorium.  amplitude  Creek  Devil's Claw This  several folds are  planes. Small  Tahtsedle  13).  developed  in this area dip to the west  as  do  planes.  Structural Domain 3  O u t c r o p s i n t h e a r e a s o u t h o f t h e S p a t s i z i RiveT a n d w e s t o f K l u a y e t z C r e e k (Figure  6 &  8, back  pocket)  are  stratigraphically  equivalent  to the  uppermost  Currier,  25  FIGURE 12: Plot of T two beds at the hinge, T  versus a (after Ramsay, 1967) where To=thickness between = thickness between two beds parallel to the axial plane  and a=the angle of inclination of the layers. Data from several folds within domains 1, 4 and 5 (i.e., dl, d4, d5) illustrate IC folds' approaching a Class 2 geometry. Although a Class 2 geometry is nearly attained, the folds are not "similar'' in style but owe their geometry to flattening.  26  FIGURE McEvoy  13: Detached (KJmu).  detachment  folding in units of the lower Devils Claw  Shortening not accomodated  zone must  be accommodated  by  (Kdl)  and  folding in the units above  by thrusting.  the the  upper  27 McEvoy kink  and  lower  folds with  approximately kink and  400  to  McEvoy  amplitude m and  kink  in the  1:2 (amplitudes  Structural  dip towards  Creek  and  are generally asymmetric  The  amplitude  800-1,200 much  m,  amplitudes  although  usually  units are  the  Structural  Kluayetz  disharmony  limbs  Domaine  East  and  300  Currier  In both  open  to 600 m  and  lower  the  Devil's Claw  and  kink  in the area (Figure  more  equivalent units  zones  fold axial  planes  west  of  not  in excess  folds with  and  of 400  west  dipping  m and  and  Grizzly  short overturned  Creeks,  axial  wavelengths  planes.  of  limbs  have  style folds are common  shale intervals of the Currier on  Folds  approximately  folds with long upright chevron  Kluyatz  6 & 8, backpocket).  a small  are common  in  unit (Figure  scale in the  layer parallel detachments  cores  of  larger  as well  folds are locally overturned  14).  (Figure with  limbs.  5  of the valley which  Creek  in the  lower  out  River  locally tightly folded  valleys of Didene  long upright  units crop  of tightly spaced  Coal  15). In  and  locally certain overturned  siltstone, sandstone  structures. Fold  broad,  approximately  ratio of large scale folds are in general,  the interbedded shale  McEvoy  Little Klappan  larger wavelengths. Zones  and  to more  wall of a thrust fault whereas  to overturned  to wavelength  with  are  west  Jackson  the  here  1:2 to 1:3  m)  tight  4  the Currier and  Didene  600  wavelengths  7, section R-R').  the  are variable from  1:1.5 (amplitudes  tighter folds occur  hanging  of the thrust (Figure  Domain  Only Creek,  and  m respectively). The  thrust planes  ratio of  are approximately  folds are present in upper  footwall  in this domain  to wavelength  wavelengths  ratios of  1,200  units. Folds  units in the immediate  broad  and  an  folds with 600  Devil's Claw  (Figures  contains the Little Klappan  6 & 8, back  pocket),  sediments  River, Didene  exposed  are  limited  Creek to  and those  FIGURE  14: View  looking east near the headwaters of Didene  asymmetric  megascopic  within  Currier  the  kink  unit.  bands  developed  in thinly laminated  Creek.  Tight  shales and  siltstones  29  FIGURE  15: View  parallel detachment  l o o k i n g n o r t h w e s t i l l u s t r a t i n gf o l d d i s h a r m o n y of an  intrastratal peel  within the Currier  developed  unit,  by  layer  30 of the lower in domain  Currier  1 with  approximately from  600  and  kink  Jackson  units. Folding  folds present  1.5:2 and  whose  to 1,000 m.  whose  amplitudes  Axial planes and  overturned folds are quite common. folds with  Many  amplitude range  Near  from  400  to 600  the eastern edge axial surfaces  folds in the area  are  and  wavelengths  m  of the map  are present hanging  have  been  noted  ratios  generally dip to the  in shaly sections in the immediate  of the large scale kink  is similar to that  to wavelength  thrust planes  vertical to steeply east dipping  folds are common  in this area  west  area  and  several  Tight  parasitic  wall of thrust faults. flattened (Figure  12).  Faults In general, thrusts in the area either shallow dipping noted  dipping, near  'ramps' (Boyer previously such  a response  and  bedding  related to the first phase horizontal 'flats' or  Elliott, 1982)  which  thrusts generally have  to fold lock-up,  propagating  'Riedel' shears  (Nadai,  variable amounts  1950). Both  of quartz and  presumably both  east and  common  west  and  in thick, well of  flat lying  have  laminated  shear  although  also filled by  displacements on  shales  of  high  in this particular  duplex  zone  (Figure  area  16). Layer-parallel  sequences  also occur  small scale disharmonic  limbs.  are  thought  in shear  filled  zones. Faults  less than  in the  cores  of  a  few  folds. In  of shale  a conglomeratic  detachments  and  intrastratal peels  15; and  were  noted  Bustin and  mineral and  which  along  dip are bedding  domain  and  across  folds (Figure  or  with  metres  imbricated  and  be  sigmoidal  mineralization are common  4  to  strain accumulation  these faults generally vanish  in domain  As  the orientation of individual  generally  located  are  and  fractures are  thrusts are restricted to a thick package  faults  forming  zones  extension and  Displacements  Thrust  shale/sandstone  displacements  their origin to stick-slip behavior  in all domains.  planes zone  owe  small  are  shallow  zones are often characterized by  carbonate  fibres is different Brecciated zones  steep to relatively  cut across fold cores and  through  possibly along planes of weakness. Thrust  of deformation  2  a  siltstones. unit  into  a  to be  important  in  Moffat,  1983).  in  FIGURE  16:  View  looking  southwest  at a  conglomeratic horizon within the Devils Claw abundant  quartz and  carbonate  veining.  duplex unit  thrust zone Fault zones  developed  in  a  are characterized  by  32 3 . 2 . 2F I R S TP H A S E M E S O S C O P I C The cleavage  two  and  most  common  fractures. The  mesoscopic term  spaced  dissolution surfaces which  which  some  cohesion  has  across which  extension  or shear  occurred. has  across  refers to a surface of  occurred. In the field the  lost  difference  is  fracture surfaces are generally planar  (with  the exception  Jackson  a distinction becomes  unit where  particularily difficult in  fractures are closely spaced  and  and of  some  cleavage  is  penetrative. Cleavage  Cleavage  related to phase  is common  McEvoy  one  structures varies in intensity throughout  only in shales and  units whereas  units. Where  it is present  cleavage  is present  siltstones of the Devils Claw  in all lithologies in the  in folds, the cleavage  downwards  in anticlinal structures ("normal"  boundaries  between  (Figure  layers of varying  17). Shale  cleavage  which  horizons  in the  cleavage  lower  surfaces  Currier  fan  fan). Cleavage  transects the folded  layers and  refraction  is particularily well developed  adjacent  fault  surface.  in a zone  intense  grain  conglomerate  exposed  Fractures described  boundary  using  dissolution,  in the  core  in the area the  terminology  of shortening,  'b' is the  area the most  common  fold  well, a well  developed  otherwise spaced  of a tight overturned  related to the first phase as adopted axis  and  by  Stearns  by  immediately  characterized cleavage  of  by  a  is present  lack in a  anticline. of deformation (1968)  'c' is perpendicular  systematic fracture sets are b-c  common  parallel to the trace  location, cleavage As  across  locally  one  to a thrust  Jackson  convergently  characterized  is approximately  area.  upper and  lithology (i.e., viscosity contrast) is cores of tight folds are  the  and  the axial surface. At  of  closely  non-planar  surfaces). Such  lower  refers solely to  to be  Riedel  shales of the  are  surfaces tend  whereas  shear  in this study  "Fracture"  the nature of the surface. Cleavage  often anastamosing type  as used  divide the rocks into discrete microlithons  of shortening  by  structures present in the study area  cleavage  amount  recognized  locally  S T R U C T I J R K S  where  are  best  'a' is the  to 'a' and fractures which  direction  'b'. In the fan  study  FIGURE Currier  17: Cleavage unit  refraction  across a siltstone-sandstone  transition within  the  34 convergently "hkO",  downwards  where  h  in folds and  and  k  refer  infers parallism  with  the  outcrop  19)  the  than  (Figure  45°,  although  locally. Mineral  to the  c axis. As dihedral  rotated towards  there  is no  apex  (Figure  rocks (Figure  illustrated in a  angle  between  conjugate  the  en  20). In  echelon  surfaces  open  minerals. Layer as well and  21) suggesting  (Figure  synchronous  concomitant  following the cleavage  kinematically may on  bedding  60°  are  in less present  suggesting  their  As  related  to  are filled with  are generally filled  coaxially with  the  surrounding  In most  disruption, suggesting  cases  extension  event  related to the first phase  surfaces and  0  conjugate  with vein growth.  apparent  be  and  fracture surfaces locally are  parallel shear zones  and  are common  as  fractures in the area  rocks with no  Slickensides which  axes  18) and  offset their  are locally folded  deformation  growth  b  as a result of interlayer shear.  veins cut across cleaved vein  a and  relationship, thus b-c  termed  extensional fractures are, commonly  general most  carbonate carbonate  folded  set  fractures is generally  orientation often  hkO  deformation  with  bimodal  stereoplot  consistent chronological  of the  previously noted, sigmoidal  with quartz, and  intercepts  macrolithons present between  the  fibrous, quartz and  trending  systematic sets with dihedral angles as high  contemporaneity. The  zones  notational  filled fractures of hkO  counterparts, but  shear  a northeasterly  of  are perpendicular to local first phase  f o l d a x e s ( 1 , ) .S l i c k e n s i d e s a r e p r e s e n t o n h k O s u b p a r a l l e l f r a c t u r e s a s w e l l b u t t h e i r age  with respect to  3 . 2 . 3F I R S T  P H A S E  Cleavage organic cleavage  deformational  M I C R O S C O P I C  selvages  surfaces generally  individual grains (Figure  follow  to be  dark  irregular surfaces  other insolubles. In conglomeratic grain boundaries,  22). In medium  grain boundaries  known.  E L E M E N T S  in thin section appear  material, phyllosilicates and  occur along  events is not  grained  but are also common  although  in places  sandstones  cleavage  containing  samples  the  they  traverse  surfaces  within grains. Analysis of  usually thin  35  FIGURE 18: Contoured equal area stereoprojection of poles to fractures from all structural domains (contours describe percentage occurrence of poles in a 1% unit area). The bimodal distribution of steep a-c subparallel fractures indicate a low dihedral angle. Cartoon in lower left hand corner illustrates the geometric relationship.  FIGURE 19: Photographs illustrating conjugate fracture sets. In general, fractures have a dihedral angle less than 45° (LD) although locally sets are present with dihedral angles as high as 60° (HD). Hammer and 15 centimetre rule for scale.  37  —  V' i^' .<*..' £ >  0  ..^/^NFi" *• «8B^  ;  •^ r  -  •  FIGURE  20: Sigmoidal en  e c h e l o n e x t e n s i o n f r a c t u r e sw i t h i n a s h e a r z o n e . W i d t h  largest "extension gash" is approximately 3 cm..  of  nGURE 2 1 : L a y e r - p a r a l l e l s y n t e c t o n i c q u a r t z / c a r b o n a t e v e i n ( S V ) w h i c h h a s b e e n tightly folded  by  vein. Pen  scale.  for  later compression.  Cleavage  (cleav) is oriented  at a high  angle  to  the  39  RGURE grain  2 2 : P h o t o m i c r o g r a p h i l l u s t r a t i n g p r e s s u r e s o l u t i o n s e a m s t r a v e r s i n ga c h e r t from  boundary grain  (gi).  a (gb)  conglomerate but  in the Jackson  unit. Seams  in this particular case also appear  are  usually  present  at the  to traverse the interior of  grain the  40 sections cut from  medium  to fine grained  sandstones  stratigraphic section, illustrate that cleavage pervasive downwards organics  in rocks  through  of similar lithology  discontinuous  rocks tend  to be  (or  angular  and  grain  "rough"  as used  to sub-spherical  in shape.  contacts due  quartz, mica  Jackson  grown  "smooth"  (Figure  illustrate pervasive  at the ends kinked  with  insoluble  residue  (e.g., organics)  redistribution of No  definitive relationship between  feldspars were  most  appears  in other  thus in part be  present  in the specimen  factor.  appear  easily dissolved whereas noted  shape  diagenesis may  of  in cleavage unit can  also have  extensive  fibrous cleavage  selvages be  selvages; Powell,  of  classified as 1978).  Samples  in thin section do  apparent  pervasiveness of  prior to dissolution, and  degree  of solubility was  that volcanic rock  chert or quartz  environment  noted  fragments  quartz  (e.g., pH  the  collapse.  least soluble. on  not  of  related to the amount  to locally impinge  been  these section  and  solution related framework  on  and  part of the  in and However,  grain  grains. Thus  are also contributing factors to the  in the chemical  higher  grains in  oblate shape  quartz grains were  areas feldspar grains impinge  that grain curvature and  during  pressure  grain type and  qualitatively it would  solution process. Complexities chemistry)  occur  in the Jackson  may  in several sections, chert grains were boundaries,  micas  of  anastamosed  (Elliott, 1973)  in outcrop. This  these insolubles following  thin section although  an  dissolution surfaces at grain boundaries  in outcrop  24). At  of grains parallel to the  well developed  necessarily illustrate similar pervasiveness cleavage as recognized  &  In the lowest  grains have  26). Cleavage  (i.e., planar  23  1979). Individual  strain shadows  25). In several samples  unit sandstones  approaching which  to dissolution. Often  or chlorite have  direction (Figure  and  more  the zonal accumulation  size (Figures  in Powell,  composite  thicker and  selvages are variably spaced, very  cleavage selvages are generally pervasive sutured  of a  selvages generally become  the section as recognized by  stratigraphic levels visible cleavage generally  representative  it  pressure  variations, solution  a contributing, although  unevaluated  FIGURE 23: Closure of cleavage spacing with depth. A. spaced cleavage developed in a siltstone-claystone layer in the Currier unit B. closely spaced cleavage in silty shale from the uppermost Jackson unit C. very closely spaced cleavage in medium grained sublitharenite from lower in Jackson unit  '  4>V  HGURE 24: Photomicrographs illustrating increasing intensity of pressure solution with depth. A. subangular to subrounded grains in contact with fairly limited dissolution at grain boundaries (upper McEvoy unit). B. pressure solution seams developed at grain boundaries (Currier unit). C. extensive pressure solution in Jackson unit Note elongation of grains caused by dissolution and the thick dark pressure solution seams representing accumulation of less soluable organics.  43  FIGURE 25: Photomicrographs of strain shadows. A. clay beard (CL) growing at edges of pyrite grain (PY). B. clay beard (CB) growing parallel to cleavage plane in deformed litharenite (Jackson unit).  44  FIGURE framework  26: Photomicrographs due  to advancing  i l l u s t r a t i n gb e n t m i c a s ( m )  created by  pressure solution along cleavage seams  collapse of (cleav).  rock  45 The  majority of fractures in the area are filled with fibrous minerals.  mineralogy  of  the veins is almost  (calcite, dolomite, ankerite) present variable time of the  relationships; one  veins, however,  contact between  textural nature of  general  classificationof  In some  veins newer  and  the  "composite  lack  a  commonly  surface. fibres  Locally  generally  illustrate multiple deformational  (Figure  vein  vein,  indicative of rotational strain. In other  orientation is generally  at the expense Ramsay,  1980)  lithology with  abundant  inclusions of vein  veins  28). ln  varies from  associated  with  undergone  some  fibrous  vein  have  a  this particular vein sub-perpendicular  rotation, in a  breccias the carbonate  entirely of a highly  and  many  added  the  the composite  different  mineral  variable suggesting  Durney,  the  1973; Ramsay,  at the central median and  1980).  surface  Durney,  extensional  synthetic one  1973;  samples  the  or more  fault zone  quartz grains were  of  corresonds  are 5  mm)  discrete central in the  original have  "antithetic" veins (Ramsay of fragmented  within the  type, the orientation  fragments  microcracks  additions to the veins  surface composed  to perpendicular  walls  veins (greater than  different than  wall material  direction which  growths. Such and  wall-parallel  decidedly  medial  fault zones, large angular  mineral  and  their length. In  of the vein walls. Such  1973;  generally  show  the other, ln  but sharp  along  histories with  where  (Figure  non-linear  27). Wider  zones  Durney,  distinct species  "synthetic" veins (Ramsay  in the mineral  been  carbonate  coexisting in equilibrium;  composed  been  pervasive  obviously  to be  veins" (Ramsay  quartz and  have fibres oriented almost perpendicular to the vein  medial  minerai  both  later than  veins tends to be  vein material has  1980) commonly  often  generated  optically continuous  following extensional failure. Such Ramsay,  been  species appear  grains are  with  veins the two  individual fibrous species being  veins, adjacent  species. The  In some  having  the two  orientation of fibre axes being mineral  exclusively bimodal  The  fibrous  of mineral  to the vein  wall  mineral  walls. In  curved  breccias are common,  vein  fibres  vein wall material to the  and  veins  have nature  although  not fibrous but blocky with  of in  several  sutured  46  FIGURE example truncated  27: Photomicrograph an by  ankerite grain (A) an  extension  illustrating syntectonic, synthetic vein relationships. In oriented perpendicular to the vein wall (VW)  crack (arrow)  which  is in turn  Filled with  quartz  has (Q).  this been  FIGURE  28: Photomicrographs  filled vein relationships. Note during mineral  growth.  illustratingsyntectonic antithetic quartz (q)/carbonate that wall rock has  been  included  within vein  material  (c)  48  contacts, suggesting not  all of the  precipitation in an  veins  vein  space  exhibit thin twins in carbonate  section, deformation Such  open  lamellae  from  grains. As  characteristic of sub-basal  intragranular features suggest at least some  exotic fluids. Several, well, in one  glide in quartz  post-vein  3 . 3 S E C O N D  P H A S E  Second  (F2) structures in the study area are less dominant  phase  structures which of the two  noted.  strain.  S T R U C T U R E S  they  phases.  thin  were  emplacement  but  deform. The  Offset of F,  structures by F2  distribution of linear elements  than  first  phase  thrusts defines the  is consistent with  timing  this  relationship.  3 . 3 . 1 F , D E F O R M A T I O N O F F , M E S O S C O P I C S T R U C T U R E S The  geometric  relationship between  and  I, demonstrate  that F  and  thrusts. Figure  29  is a  contoured data  equal-area  cleavage  amalgamated  apparent  orientation of  S2  apparent  that although  the trend of F2  as  that the cleavage  than  of F2  dip  collected  dip  from cleavage  more  suggesting  a fanned  precludes  further evaluation of the origin of this geometry.  geometric  analysis, steeply dipping to  local S2/Sj S2/S0  paucity of outcrops exhibiting well-defined  F2  folds  this study.  cleavage Figure  (intersection of steeply dipping  (intersection of F  grouping  in  2  of  S2/S  0  2  in two  cleavage  and  F  2  bedding)  general areas on  F  second  poles  5 and  locally phase  cleavage,  2  folds  For  cleavage  however,  the purposes  of  30  the  cleavage from  illustrates  with F,  cleavage)  structural domains  F2  shallower  approximately  b  F2  the  is treated as being a &  to  trend of observed  variable and  The  F  and  S0  axial surfaces. It is  is similar to the  is considerably  axial planes, possibly  angle to Fi  4  the trace of F2  axial planes),  containing  domaines  geometry.  axial-planar  (F2  stereoprojection  in structural  determined  axial surfaces the  S2/S0), S2  folds are generally oriented at a high  2  from  12 (S2/S,;  orientation and  local  4 and  5.  either side of the stereonet origin  of  The  49  N  FIGURE 29: Equal area stereoprojection of F 2 axial planes (S2) as calculated from the mapped surficial trace and poles to F 2 cleavage (contours indicate percentage of poles contained in a 1% unit area). Though cleavage apparently has a fanned geometry, the trends are parallel to that of S2, suggesting cleavage may be treated as roughly axial planar.  N  1  FIGURE 30: Stereoprojections of lineations related to second phase folding. A. S2/S, lineation from domains 4 and 5. B. S2/S: lineation from domains 4 and 5.  51  corresponds bedding  roughly  planes (Figure 31) as would  pre-existing which  F,  plane  angle  which  fiexural-slip trending  to one  small  poles  The  33)  evidence  distorted  cleavage  F  bedding  little motion  rather than  superposition  of  with  result  (assuming  deformed  along (Figure  they  planes  and  component  be  some  of motion  is required may  a  the  a  in the  folding  12 along  model  bounded a  by  hkO  to form  2  about  displacement  of  h  progressed  via  a  northwesterly of  the bending  F,  (hkO) fractures.  hence  F  oriented  by  is oriented  occur  at  36). It is important  slickenside linears (Norris  The  high  along  indicate  F,  and  further substantiate  result of three dimensional  of 2 separate strain events.  are  superposition  fracture planes  (Figure  axial  generalized  a broad  girdle which  35) and  which  F2- folds  has  involving  on  belt  projection  of pre-existing  should  0  a broad  orientation of the F2  history. In addition, slickensides which  however,  hence  plot  axial plane  2  trending  and  to h  "macrolithons"  planes  area  comparison  Re-folding  consistent  34) of  fracture  planes, several  1968)  32). A  fall along  equal  generalized &  distribution of  northeast-southwest  Baron,  S2/Sj  contoured  S  folds are superimposed  2  for fold superposition is demonstrated  fold superposition  that very  F  folded  axial surfaces illustrates the two  angles  is thus  angles to the generalized proposed  29  (80°-90°).  at high  rotation (Figure  to the  A  circle locii on. the. stereonet  belt (Figure  rigid body  another  mechanism).  F2. Further  (Figures  axial planes with  geometries.  distorted trace of F]  is oriented  along  kink  the approximate  field  2  expected where  distribution of S2/S0.  matches  the  be  megascopic  in the  with  high  linears  by  the  as observed  axis  with  all 12 thus  axial plane  an  folds  encompasses  combines  at a  to the area of intersection of F  the  F] a to  note, and  constrictional strain  FIGURE 31: Contoured equal area stereoprojections of poles to bedding (S0) from domains 4 and 5. Contours represent percentage of lineations occuring in a 1% unit area. In lower centre of figure a stereoprojection illustrates the average limb orientation for kink folds as discerned from the contoured stereoprojections of S0, and the area of intersection of the limbs with the F 2 axial surfaces (S2). The shaded areas should thus be the locus of S2/S0.  53  FIGURE and  32: Contoured  5. Contours  represent  equal  area  percentage  stereoprojection of  of  all 12 in structural domains  lineations occuring  in a  1%  unit  area.  4  H G U R E 33: Contoured equal area projection of Fi cleavage/bedding intersection lineations (lj) from structural domains 3, 4 and 5. Contours represent percentage of lineations occuring in a 1% unit area.  FIGURE 34: Photographs illustrating folded F, hkO fractures. A. View looking southwest at Fj hkO fractures within the Jackson unit Macrolithons between fracture surfaces have been rotated by interlayer slip related to F 2 folding. Peak is approximately 250 m. above base of photo. B. Bent hkO fracture sets. Local 12 are oriented at a high angle to the photo plane. Stereonet analysis of these fractures appears in figure 35.  56  H G U R E 35: Equal area stereoprojection illustrating bending and rotation of F] a-c fracture planes by F 2 folding. Great circle fit from A is illustrated for comparison. Given the sub-parallel relationship of a-c fractures to F 2 axes, the scatter of data is consistent with fractures having been rotated by F 2 folding.  57  PREDICTED DISTRIBUTION  FIGURE 36: Equal area stereoprojection of slickensided orientations. In the upper centre of the figure the predicted distribution of superposed slip linears is illustrated. The lower centre of the figure illustrates an equal area stereoprojection compilation of all slickenside data (here plotted as pitches within planes, where the dot represents the pitch of the linear and the short line represents a portion of the great circle girdle which describes the plane of motion). A rose diagram of kinematic trends illustrates a bimodal distribution corresponding to F, and F 2 fold axes. Slickensides formed via bedding plane slip during Fi would be sub-parallel to the F 2 fold axis, whereas slickensides formed by the same process during F 2 would be sub-parallel to the Fj fold axis.  58 3 . 3 . 2F , F O L D S F abrupt  A N D  F A U L T S  folds are manifest  2  plunge  reversals of F  northeast-southwest,  in the field throughout folds. The  3  (Figure  37). In the northern  Currier  and  whereas  smaller scale parasitic folds have  Interference geometry map  between  and  exposed,  F2  which  was  of  low  an  traces  lithologies within a  box  kink  style  resulted in a  dome  and  38)  trend  fold axial  2  asymmetric  relief (Figure  constructed, on. the top  thrust faults, were  folds and/or  thrusts and  orientation (Figure in the northern covered  and  of. the folded Jackson  by  the  fold  geometry  geometry. basin  type  outcrop  in a structure unit upper,  contour  contact  faults tend  angle normal  area. The  between  (Figure  41, and  extention and between ambiguity  Fj  beneath  Tahtsedle  In  in Moffat  Creek  metres  many  areas  and  hkO  fractures and  these  the observation  and  Bustin, 1984) and  F2  high  F  bound  that, like Fj  them  2  angle  be  deformation.  fractures and  the  stage  those  most  with  the maps apex  of  (Figures F2  folds  related to outer  arc  The  orientation  similarity in  bending  demonstrated. faults, F2  klippen  but are  fault related fractures creates  be  F2  pocket). Late  are illustrated on  may  an  structures is  River;  with  F,  flat lying thrusts in  9, back  the Nass  of rotation or can  F2  the study area  faults coincide  in the field unless the presence  the fracture surfaces which  offset of  resulted in  southerly plunging  or more  inner arc contraction during  have  existence of other  reverse faults occur throughout  displacements of several hundred pocket).  flat lying and  interpreted in cross section, (Figure  and  in the area  8, back  to be  in the sub-surface  hence,  truncation and  their intimate relationship to parasitic folds with  40). Such  intervals and  abundant  identified in the field by  part of the map  anticipated and  from  area, where  F  rather  39). F2  6 &  define  reversals  large scale folds have  folds has  as illustrated in areas  (Figure  high  Fj  hence  part of the map  units are  of the area by  axis of these plunge  are laterally persistant and  Jackson  most  of macrolithons  Further  zones  some or  uncertainty arises  of cohesion  loss  are  N  28°30'  H G U R E 37: The trace of major F 2 axial surfaces and F 2 high angle faults in the study area. In the upper left hand corner a contoured equal area stereoprojection displays the orientation of 1, in domains 4 and 5 (see figure 32) >  60  •  FIGUPvE 3 8 : V i e w l o o k i n g n o r t h w e s t n e a r t h e n o r t h e r n m o s t e d g e o f t h e s t u d y a r e a . Beds  outlined by  thin lines are formed  into dome  and  basin geometry  by  the  i n t e r s e c t i o n o f f i r s t p h a s e f o l d a x i a lt r a c e s ( S i ) a n d s e c o n dp h a s e f o l d a x i a lt r a c e s ( S 2 ) .  61  STRUCTURE CONTOURS  FIGURE 39: Structure contours drawn on the top of the Jackson unit in the northern portion of the thesis area, the generalized map in the right hand corner illustrates the area overwhich the Jackson (Jj) and overlying Currier (Jc) crop out. The theoretical dome and basin interference pattern predicted from 2 phases of folding superposed at high angles to one another is consistent with the structural contour configuration.  62  FIGURE  40:  View  looking southwest  assymetric parasitic folds. Thrust veining. From  base  zone  at a second  phase  is characterized by  thrust with abundant  to top of cliff constitutes approximately  80  associated quartz/carbonate  metres.  63  HGURE fold (from  41: High Moffat  angle dip-slip faults associated with the apex and  Bustin, 1984).  of a second  phase  64 characterized by  3.3.3 F,  fibrous  and  non-fibrous  silicate and  carbonate filled veins.  CLEAVAGE Steeply dipping, northeast trending dissolutioncleavage is common  fold hinges  and  predominantly  Closely spaced and  Devil's  in the lower  fractures sub-parallel  Claw  2  bedding  angles  are common  and  Huber,  1985)  Jackson  stratigraphic units.  in strata within the to high  formed  by  2  angle  McEvoy  faults, ln  several  the intersection of spaced  F]  dissolution and/or fracturecleavage surfaces are present (Figure 42). Pencil  orientation and not  to S2  and  units especially in close proximity  areas pencil fabrics (Ramsay and F  Currier  only near r  length, is related to the relative spacing  parallel fractures are present  to bedding  sub-parallel  (where  bedding  to local li (where  In most  does  bedding  not  of Sj and  S  and  2  whether  cases pencils are oriented at  represent  a plane  is characterized  by  of  extension  late extension  or high  failure)  or  failure).  s h a p e a p p e a r s t o b e r e l a t e d t o t h e n a t u r e o f t h e i n t e r s e c t i n g s u r f a c e s .W h e r e  Pencil F  2  d i s s o l u t i o n c l e a v a g e i n t e r s e c t sw i t h F i d i s s o l u t i o n c l e a v a g e s u r f a c e s t h e p e n c i l s t e n d t o be irregular in shape. Intersection of F hand  results in smooth  shaped  relationships are common. or absence  of  The  3 . 4 D E F O R M E D There  pencils with straight edges. Combinations spacing of pencils is related primarily  thick dissolution seams  to the relative abundance  F ,  of organic  containing insolubles; and  of  evidence  that indicates the  more  complex  Possible  for a  later compressional  has  on  an  apparently  F  2  thrust surface  been  these  to the  presence  intimately related  material.  area is somewhat  drawn  hence  of  E L E M E N T S  is a modicum  evidence  and Fi closely spaced fractures on the other  2  folded  about  than  from an  is suggested  domain  event  deformational by  is provided  4 (Figure  axis which  two  history of  superposed by  43). This  the  strain events.  structure  contours  particular F  is subparallel to the  study  2  surface  generalized  65  FIGURE  42: Pencil fabric formed  F2  fracture cleavage.  A.  Well  defined pencils weathered  B. Pencil structure formed fractures.  by  by  the intersection of F,  out from  an  dissolution cleavage  and  outcrop.  the intersection of F,  cleavage  and  F2  closely  spaced  HGURE warping.  43: Structure contours drawn Contours  are  in units  of  100  on  F  2  k l i p p e n s u r f a c e s , i l l u s t r a t i n gl a t e r F  feet(e.g., 50  x  100 =  5000)  3  67 orientation of Fj event  in a  axial surfaces in this area, perhaps  northeast-southwest  decapitated by  F  planes of weakness  curvilinearnature to S  illustrated in Figure Inconclusive  2  29  evidence  Though  Group  rocks  the as  is consistent  with  F2  a  superimposed  northeast-southwest  effect on  li by  is summarized proposed  evidence  for a  above  as will be two  is tenuous  discussed  45. The  strain history suggests  further delineate the nature  3 . 5 S I G N I F I C A N C E Comparison  O F  of analysis has  permitted  strain events and  hence  achieved.  Late  superimposed  in the  2  the  suggest  low  Bowser  by rocks  7). The as  Lake  compressive  Sustut Group  (Chapter  in 1  by  anticipated  described  above  orientations required  detailed domainal  analysis  by to  strain.  S T R U C T U R A L  R E L A T I O N S H I P S experimental concerning  deductions to be the nature  is offered  is also suggested  in a manner  for further  made  compression.  northwest-southeast  event  later Chapter  , perhaps as  fracture which  Cretaceous  the need  made  and  theoretical structural studies  the origin of structures. This concerning the timing of  of the finite strain path, the nature  partioning in the stratigraphic package strain is  event  local variation  for inferences to be  directed  angle  are  general, gentle  at best, a northeast-southwest  in a  of superposed  b-c  2  high  wide  of field observations with  often allows  F  compressive  compressive  later strain events  in Figure  an  third phase  a northwest-southeast  1974a)  The  compression  later than  fold relationships present in the  (Eisbacher,  folds along  cleavage trends  2  northeast-southwest  slickensided linears on  described  later than  Fj  formed  entirely ruled out  local variation of F  northeast-southwest, directed motion  motion.  event  warping. The  for a post  presence of superimposed angle  is not  within  thrust planes  2  compressional  3  traces in certain locations is illustrated in Figure 44  2  post F  F  locally, rigid units  thrust planes, the possibility that F  2  previously folded (FO  suggesting some  direction. Though  suggesting an  and  the possible mechanisms  by  type  incremental  of which  strain such  the  68  FIGURE 44: Structural map near northeastern edge of study area illustrating the gentle warping of F 2 cleavage strikes (cleavage symbols) and hence the possibility of some post-F2 compression. Stippled area represents outcrop of Currier unit Scale = 1:50,000.  69  F I G U R E 45: Expected domainal structural relationships created by 3 phases of deformation the second perpendicular and the third parallel to the first (assuming  a  flexural-slip mechanism). Fi fold axes determined by the intersection o f Si cleavage and So bedding are fanned out along a small circle by a second compression oriented at 9 0 °  to the first compression. Later return to the original compressive  stress  direction results i n rotation of F j along small circles such that the area containing deformed F j linears related to all fold domains will be a broad trending belt  northwest-southeast  70 3 . 5 . 1T I M I N G  O F  S T R U C T U R A L  It is generally cleavage  assumed  of Engelder  formed  E V E N T S  that pressure  solution cleavage  (diffusional  et al., 1981), similar to that observed  in rocks  as cleavage planes perpendicular to the direction of maximum  (Dietrich, 1969; Siddans, 1972; Gieser, 1974;  GTOshong,  1975;  As  it appears  that one  such, from  the evidence  of importance formed divergent  discussed above  to the overall pattern of strain accumulation  relatively  over  early  in folding  fan configuration. Such  that offered by  history, an  Dietrich (1969)  strains have  already accumulated  compressive  stress throughout  involving early cleavage  fixed  bedding  should  point  however  show  bedding  the mechanism  of many  bisectrix is oriented cleavage  formation The  by  as a fixed  folded bedding  Figure an  directions on  described  directions on  layers of varying  48  plane  during  should  Nass  Lake  which  rotated  A  &  by  buckling  would  the  be  case  axis about  which  folds  and  do  consistent with 46  B; i.e.,  however,  early  that  cleavage (Figure  47).  buckling and  was  F]  cleavage  folded cleavage and  of  cleavage  later rotation of  rocks  cleavage  Figure  by  infers that the  buckling  Group  between  Dietrich (1969;  by  a  maximum  Lake  In  explained  to  favored  between  B).  during the early phases  to an  is  either fold limb. Several  also be  illustrates the planar coincidence of  anticline near  and  was  interpretation  the acute angle  viscosity followed  continued  correspond  which  orientation of the  46  1975).  earliest events  either limb). It is evident  might  interpretation that cleavage formed  rotated  plane  the bisectrix of the acute angle  distribution of this geometry in folded  the  in the study of Bowser  folds (Figure  formation  in opposing  Barnes,  is cleavage  to cleavage intersection angles which  for cleavage  of  is formed  to the changing  is favored  in opposite  strain  and  folded layers of varying viscosity. An  synfolding cleavage development  compressive  after significant  cleavage  bedding  limb  area,  where  and  either  study  formation  due  formation  the  interpretation for cleavage  to the consistent direction of the bisectrix of on  Ross  as a material  due  a  of  mass-transfer  axis is  bedding  requires either that cleavage formed  determined fanned. poles under  for  71  FIGURE 46a: Stereoprojections and cartoons illustrating cleavage/bedding relationships across folded surfaces from various structural domains.  72  FIGURE 46b: Stereoprojections and cartoons illustrating cleavage/bedding relationships across folded surfaces from various structural domains.  73  F I G U R E 47: Stereoplot of cleavage and bedding orientations across an anticline east of Nass Lake. Note that in general the two appear to be fanned (folded) about the same axis.  74  FIGURE 48: Origin of cleavage fans. The Figure illustrates that in folds where the bisector of the acute angle between bedding and cleavage faces the same direction across the fold then cleavage formed early at low buckling strains (i.e., cleavage to bedding a n g l e = 7 0 ° - 9 0 ° ) . Continued buckling results in a cleavage fan as shown in A 2 . B illustrates how cleavage might form due to varying viscosity in folded. layers (after Dietrich, 1969). The short lines are perpendicular to local  and hence parallel  to cleavage. If cleavage forms in a fold of low amplitude (d) is locked in and further fold shortening occurs, a cleavage fan C 2 develops. Both A 2 and C 2 fan types are present in the study area. The overall consistent high angle between cleavage and bedding suggests that, given the existence of A 2 , cleavage probably formed early at buckling strains of a few percent  75  conditions of low contrasts on progressive  buckling strain or that cleavage  pre-existing folds whose  in the  if permeability  is low  is commonly  thought  Ruby,  Gretener,  1959;  veining, cross-cut  cleavage  shear  stress.  dissolution (Ross  process  and  1972;  Barnes,  1979).  fold limbs  and  surfaces which  rotation  by  viscosity  during  have  the lack of tight folding of F folds, thrusts and compressive  by  a  as the previously  rise in pore  addressed,  locally been  2  increase in pore  sequences  pressure and  is responsible  to post-date  later). Thrusting into a plane  x  fluid  for  are associated with  appear  rotated  pressure  (e.g., Hubbert  a process  which  s t r u c t u r e s o n F  fluid  abundant  folding  is. further,  favored  of high  resolved  i s d e m o n s t r a t e d b y t h e o f f s e t o f F  thrusts, the folding of hkO fractures formed originally duringFj and  2  orientations at some  an  fold cores and  for this, interpretation.is  structures by F  characterized  1975). Such  in the thesis area  T h e s u p e r p o s i t i o n o f F  maximum  is a concomitant  It is likely that such  displacement  kink  (evidence  along  Fi  not undergone  to facilitate faulting in layered  thrusts of small  history  in fans created  strain.  Inherent  the  axes have  formed  p l a n a r s u r f a c e s ( e . g . ,f a u l t s ,c l e a v a g e ) . S u p e r p o s i t i o n o f  2  fabric elements by a later orthogonal strain infers that stress and time  the intermediate compressive  in the  deformational  dissolution event described Ft  which  cleavage. A  history. The  presumably  stress had second  formed  switched  phase  much  the  is locally  in the  same  way  possible return to a strain orientation  parallel to that of Fi has been suggestedby local foldingof F  2  thrustplanes coaxial  with undeformed Fj axes. The absence of intermediate orientations to principal strain axes the  infers that rotation of the area distribution  strain may  have  Evidence of  deformation  of finite strain and  in a that a  fixed  stress reference  shift in external  frame  forces  cannot  during  explain  progressive  occurred. for episodic high is provided  by  fluid pressures  the presence  throughout  all the  described  of syntectonic extension veins (both  phases parallel  76  to bedding  as well as in hkO  fibres that occur fibres in both  as  Fj  "beards"  and  F2  twinned  further  and  suggests  calcite and  a multistage F]  been  folded, syntectonic  traces and  the presence  history  cleavage  undeformed  syntectonic  is supported  by  masks  noted. The  has  presence  of  as well as strained quartz in  for vein fillings. The  replaces all grains indiscriminantly and  of  mineral  regeneration of veining events also  nature of vein offsets previously  untwinned  in part later than  have  parallel to cleavage  fault planes. The  resulted in the complicated both  orientations) which  fact that fluids are  the observation evidence  veins  generated  that calcite locally  of dissolution (Chapter  5,  Figure  been  and  74). Inasmuch  as all rocks in the  possibly three phases than  of deformation,  study area  have  the deformational  events must  deposition of the youngest unit of the Devils Claw  during  deposition of the overlying Sustut Group  Maestrictian, according deformational  to MacKenzie,  events and  setting appears  have  occurred  (post-Albian) and  1985). Further  later  presumably  (Eisbacher, 1981; Cenomanian analysis of the timing  their significance in terms  in Chapter  subjected to two  to of  of the regional tectonic history  and  6.  3 . 5 . 2 STRAIN DISTRIBUTION  An  understanding  of how finite strain is distributed throughout  at the large scale is best documented  from  an  analysis of the t  35%  of total shortening  shortening,  most  surface. Additional the contribution described area. The  of  which  shortening  (Dahlstrom,  results in an  is a consequence  of folding  attributed to stress driven  to the overall bulk  earlier, it is apparent  1969)  that  strain can  not  be  this strain is not  strata within the Devils Claw  and  uppermost  average  of  approximately exposed  dissolution is noted, estimated  McEvoy  cross  beanalyzed.  in the rocks  evenly  area  1:5,0000 structural  s e c t i o n s( F i g u r e 9 ) w h i c h a r e o r i e n t e d s u c h t h a t F s t r a i n sm a y Calculation  the study  at  although  in this instance.  distributed  across  are generally  As the  folded  77  into broad  open  wavelength  ratios, whereas  are  into megascopic  folded  flexures with  wavelength  ratios. This  which  observed  was  (Figure  fairly high  units within the lower kink  change  style folds with  that the  1969)  suggest  but  the  folding of  of  viscous unit would  the more have  relatively thin  wavelength  of  uppermost  McEvoy  and  relatively high  For  viscous  folds should  be  as a  zone  Lake  Group  two  models  viscous  of  detachment  in a package  to  the competent  Dietrich, control  As  that the  such, in the and  lower  conglomerate  ductile shales,  in the overlying Devils  units requires that strain accomodated  fold flattening within balanced by some and  Devils Claw  zones  within  the  lower  the well laminated  units. Abundant Devils  Claw  detachment  Jackson,  other shortening mechanism  Currier  The  and  fact that amplitude  lower  McEvoy  in the thick bedded  16) serve  to accomodate  and  to by  units  uppermost  listric thrusts of small displacement  unit (Figure  Claw,  coarse grained units are substantially  wavelength  in the  beds  the  and  higher  equal  thicker  thicker; thus resulting in fold disharmony ratios are  the  viscosity contrasts are  sandstone  of more  Gunanoot  unit will  unit is varied, it is predicted  competent  units  stratigraphic package.  more where  to  to  primarily  significantly smaller than  units where  amplitudes  in fold style is due  initial folds of larger wavelength.  well spaced  Jackson  of Mount  of rocks, the  stratigraphic units in the thesis area, where are  Currier and  differing viscosity (e.g., Biot, 1961;  package  of folds developed.  thickness  McEvoy,  amplitude  south  Bowser  layers of  that for a given  the wavelength  relatively low  locality immediately  contrast  contrasting rheologies within the upper concerning  and  in structural style is manifest  in the field in one  12). It is considered  Theories  wavelengths  is  McEvoy  duplex  at least a  thrust portion  of the strain. On McEvoy  a l a r g e s c a l e t h e uppeT c o n g l o m e r a t i c p a c k a g e o f D e v i l s C l a w a n d  units outline an  anticlinorium-synclinorium parasitic folds which  verge  overall suprastructure described composed pair. The towards  more  ductile units below  of  an  are telescoped  the core of the anticlinorium (here  upper  termed  into the  78 Nass  Lake  (Figure  anticlinorium)and  49). The  immediately  away  from  possibility that another  east of the study area  westerly limbs and headwaters  the core of the ML  anticlinorial suprastructural core  is supported  by  the presence  shallower easterly limbs approximately  of Conglomerate  Creek  (R. Thomson,  of deformation. The  northernmost  area  is characterized  scale parasitic folds and  flat lying thrusts of  package  by  high  angle  faults with  is suggested behave apex  as of  here blind  stacking  subsurface  at the  be  that the  and/or which  extension  in a manner frontal edge  that second within  would  are presumably  the  phase study  The study  area  disharmonic sandstone  here  is evident  due  the  1981)  1985). Such  leading  edge;  apparently  and  and  Moffat,  decreases  that competency  and  is absent  contrast plays in the  folding is evident at the outcrop thicker surrounding  to the large scale. The mass  in  units a  Shortening  high  angle  faults  observation direction  in the southern foreland  deformational  existence of thin  part  of  model.  style in  scale disharmony  of less competent  1982,  Currier  all merging  the  their  the  and  at depth. The  is further consistent with  at all scales. In addition  layers in a much  in  It  units  Belt (Jones,  by  by  fold above  of detachment  is accomodated  small  motion.  ductile  large  displacements  zone  of  in intensity in a southerly  Bustin, 1984) 1983)  more  Thrust  the zone  the detachment  folds,  uppermost  recognized  and  the  is. interrupted,  result in a  Fold  second  in  the  thrust sheets of the Jackson  represented by  listric towards  exposed  slip components  is commonly  of the Cordilleran  be  which  a the  large scale box  displace the  and  to what  the  by  dip  north of  associated with  monocline  to this large scale warping  area (Moffat  importance  similar  towards  folding  the coalfield (Bustin  1979,  foreland model,  stacked  due  plunging  present steep  orientation whereas  2  flat lying thrusts which  thrusts (Thompson,  gradually  roof thrust which  a southerly  F  left lateral, right lateral and  1985). In the prograding could  to be  is  of folds with  lower part of the stratigraphic package  sector of the study  is distinguished  10 km  verbal comm.,  suprastructure/infrarstructure relationship also appears phase  Biernes synclinorium  the  discussed, competent  shales  and  FIGURE 49: Fj superstructure throughout the study area based on the vergence of inferstructural folds.  80 coals requires that be area  characterized by  these thick shale units have  which  accomodate  disharmony  thrusting. Intrastratal peels this type of displacement to incompetent  fold disharmony  one  and  or a  with  transfer. The on  folds as compared  to lower units where  example,  near  characterized  litharenites and been  folded  surrounding  with  m  relationships noted  difference  1969)  folds. Based  on  allows  by  Smith  the Toodogone  volcanics. Reconnaissance  study area and  Cold  immediately  above  Lake  competent the  concentric  type  abundant  and  certain  zones For unit  fine to medium coal. These  is  grained  units  have  from  the  in fold style is presumably  (Figure  (129°  the Toodogone  1984) are folded into relatively low  6, back  to some  calculation of depth  related  depth  pocket)  to  in the  the volume  should  subsurface. method  to decollement  for the  surface  the lowest stratigraphic horizon  et al. (1984)  Basin suggests that this detachment  Fish  of  units, where  are common.  by  by  layers.  the estimated thickness from  in this study to that examined  of  is distinctly different  in surface exposures  for the  surfaces  part of the Jackson  of shale and  of the large scale (1:100,000) cross sections by  (Dahlstrom,  package  sandstones  anticline which  style folds. This  upper  however  the upper  thin laminae  lithology of the  shear  a consequence  into broad  of section dominated  concentric  are  The  are  study  to higher levels  layers are more  There  for extrapolation of characteristic geometries  Balancing  Bowser  geometry.  Grizzly Creek,  lithic wackes  the thickness and  allow  of 100  megakink  The  kink  approximately  into a broad  disharmony  incompetent  thick, closely spaced  the headwaters by  of  layers is large, deform  attain a flattened units where  zones  fold style is also apparent  to incompetent  within the lower  of bedding-parallel  effect that the relative percentage  ratio of competent  folds generally  1974). In the  possibly transfer displacement  associated  material has  number  (Ramsay,  would  near  lie approximately  in the area between 45', 57°  the  eastern edge near  low  wavelength  of  the  the top  37') indicates that the thick  and  of  the eastern margin  volcanics (Spatsizi sediments  amplitude  examined  of  the  shaly  Smith  disharmonic  of  et al., kink  81 folds (Figure 50) whereas 45', 57° 30') is broadly  the Toodogone  warped.  A  similar  anticline directly southwest of ML a  broad  asymmetric  sediments and  kink  (Thomson,  Lake  relationship  Will where  fold surrounded  in prep.). Such  the Spatsizi sediments  Bowser  volcanic section exposed  by  more  of  has crumpled.  detachment Simple  undergone  shortening, which  a  conclusion  of the basin of Spatsizi sediments the  stratigraphically higher  stratigraphic throw thrust at depth At basin  south  of Nass  near  1975  7787G)  show  Lake  the eastern edge core  of a  doubly  thrust fault coupled (figure  6  &  Toodogone the hanging  8, back  and a  Basin  volcanics. It is thus  suggested  wall of the thrust which 49).  maps  where  unit  the  upper  balance must  laws have  accomplished by  large  occurrence  and  near  the  edge  underlying Tipper,  implies  units  1984).  a large  of  A  detachment  for this portion of  from  which  reconnaissance  presence  immediate  of  Nass  a near  hanging  surface  units have River  in  area immediately  those  present  volcanics are exposed wall  unit strata immediately  that Toodogone  lies in the  River and  the  studies  include the study  this anamoly  Toodogone  in the  of Jackson the  which  in the valley of the Nass  anticline and  suggests  m)  information  similarity between  the prescence  pocket)  3,000  data, collected  large anomaly  plunging  (Gabrielse  Jackson  surface.  1978. Aeromagnetic  of the Bowser  anticlinorium (Figure  at the  available subsurface  (Figure 51). The  with  Formation  survey  been the  an  also  in thrust contact with  (greater than  evident  is restricted to aeromagnetic  map  Nass  is not  present the only  (GSC  Creek  above  shaly package  by  of  Spatsizi  physical mass  have  is supported  apparently  of this magnitude  which  the area between  the  Tango  may  (129°  volcanics are folded into  relationships indicate that the lower  the intensely kink-folded  scale thrust faulting. Such  Will  core  intensely deformed  indicate that the units below approximately 35%  in the  the Toodogone  act as a thick zone  stratigraphic package  is noted  at ML  of  been  valley and  a  to the  exposure  north  of  carried offsets  in  in the  FIGURE  50: View  Spatsizi sediments  looking southeast at tight disharmonic east of the study  area.  kink folds  developed  HGURE 51: Magnetic map (7787G). Magnetic contours are in gammas (nanoteslas). The anamoly in the valley of the Nass River (southern part of map) is distictly similar to anamolies which occur near the northeastern margin of the basin where Toodogone volcanics are exposed in the core of anticlines and in the immediate hanging wall of a thrust It is suggested that the Nass anamoly may represent a near surface exposure of Toodogone volcanics which have been carried in the hanging wall of the Nass thrust fault  83 x  84 The Thompson  structural model (1979;  British Columbia. and  River  here  is distinctly similar to that invoked  1981) and  Fitzgerald (1968) in the Rocky  Thompson  (1979, 1981) describes the situation where  clastic sequences  Besa  described  shales  are folded  which  into box  behaved  as a  like megakinks  zone  section is accommodated  competent  carbonates of Silurian, Ordovician and  quasi-blind apparent  are hence  displacement  shortening  taken  is much  up  the cross-sections which  is present  1974a)  may  by  Thrust  the surface  Belt (Jones  In summary study  area  are  unpublished response  open  1982;  simply file  of an  in the  reach  the  in  surface  but  at depth,  or  its  the  extra,  incorporated  laterally continuous  of the toe of a near  thick  thrusts never  of the Sustut Group  "triangle zone"  the  "blind thrusts"  thus been  large-scale  Formation  expression  probable a product  report)  O F  9. The  Peak  but  that the  blind  monocline  thrust at  the leading  into  (Eisbacher,  edge  of a very  structural complexities complicated  are predominantly  anisotropically layered  3 . 5 . 3M E C H A N I S M S  its actual displacement  Devonian  depth,  of  the  noted  in  Fold  1985).  it seems  not  the thrust fault does  in Figure  in the Brothers  similar to that recognized and  of  plate) has  carbonate  thrusts of  age. Such  theme  less than  northeastern  thin  Shortening  of stacked  Cambrian  of  the thick  "blind". The  folding in the upper  displayed  represent  the emplacement  termed  thrusts (those where  above  of de'collement  underlying  reach the surface and  by  Mountains  by  a  deformation  result of  stratigraphic package  to an  the  the  history  variable  imposed  (Esso,  strain  stress.  D E F O R M A T I O N  Folding The consistent slickensides whose  material properties of Fj with  a  flexural  in bedding  axis of  rotation  folds as described  slip origin. This  planes,  oriented  is parallel to the  is in part  in a plane b  direction  for the study  verified  by  perpendicular (Price, 1967)  the to Fj and  area  are  presence  of  fold axes the  common  and  85  occurrence of hinge collapse and reef vein  features is further predicted  (Stephansson, 1974) which  in less viscous layers and  within  buckle  folds. A  several of the kink Less  mega-kink sharp  nature  folds noted  in he  to folding of F  zones.  A  kink  is further  in keeping  flexural-slip buckle generally  by  the hinge  theoretical models  where  the maximum  flattening throughout fault planes plane of  and  hence  the  fold (simple  distribution of  and  shear)  are long- and folds, F2  products  of  at F2  fold  fold axes  and  increase  to the plane  stress is generally normal  by  Fj  angle  spacing  orientation to create buckle fractures towards  origin.  faults and  and zones  hence  the  such  zones  F2  of  fold  dip  of  to the  folds. The  fold hinge  of closely spaced  argues  angle  lock-up,  F2  rotated  (Figure  shear against  is important  to some  the possibility of  a  2  nature  34  fractures in the  F a-b  flexural slip origins. In contrast,  that layer perpendicular of  at a low  supported  folds past  the layers (Dietrich, 1969). In addition, the shallow  strains  in  is further  compressive  a  layer,  folds intragranular  concentration of cleavage  stress was  with  strain in natural, single  to the  of  straight are  the  folds.  classified as a type  1974). In such  perpendicular  layer parallel shear  wide  Spang,  in  in Fj  concentration of dissolution cleavage the  layers  folds where  that observed  that, like F,  to  Fillings is apparent  origin of F2  be  limbs  arc in viscous  buckle  stratigraphic units suggest although  vein  may  in that limbs  region. Such  in the proper  of high  reef  saddle  diffussion  from  of stress trajectories in multi-layered  bounded  suggests  prevalence  area.  suggests that the maximum  macrolithons  further  with  folds (Chappie  towards  study  implies  The  are parallel to bedding,  magnitude  saddle  1979)  geometry  buckle, flexural-slip mechanism. hinges  of  is significantly less than  Thompson,  stress induced  arc to the outer  folds implies that they  2  formation of  components  is available as to the mechanical  (Faill, 1969;  hinge  theories regarding  the inner  distribution  strain due  box-like  from  similar  information  accumulated  from  1974). The  predict the migration of mobile  hinges  The  saddle reefs (Ramsay,  &  35) the  upper extent, similar  86 Although  very  little is known  about  the stresses necessary  naturally occuring  folds, Fyfe  flexural-slip kink  folds with thickness to wavelength  MPa  and  where  the wavelength  area, in all domains much  et al. (1978)  less than  the  1/1,000  suggested  by  buckling is much four  times  the  ratio is 1/1,000  which  Fyfe  greater than  ratio was  tensile strength. With  frictional resistance to sliding would  on  1.0 MPa  that the  the compressive  buckling  ratios of  suggests that, based  et al. (1978)  less than  that the  and  hence  but  MPa.  It to  may  was create  be  it is anticipated  study  the  differential stress necessary  fluid pressures  decrease  100  and  100  1/100  reasoning,  but less than  in  In the  greater than  the above  in  is less than  1.0 MPa.  strength of the rock  high  buckling  resistance  1/100  it is less than  thickness to wavelength  differential stress required was further  suggest  to cause  less  that  than  the  facilitate folding.  Cleavage The  origin of cleavage in rocks at low  grades  of metamorphism  geologists since the 19th century (Sorby, 1853). Numerous  models  based  work  on  field and  modelling. pressure  thin section observations, experimental  Excellent summaries  literature (e.g., Williams, 1977; Group  McClay,  1977;  will be  concentrated by 1.  which  forms  of cleavage  Siddans,  1972;  Rutter, 1983). Cleavage  discussed  Cleavage  1972;  aligned  within planes  layer silicates become  rigid body  rotation  Wood,  interested  been  developed  theoretical  the evolution  of  are available elsewhere  in  1974;  Williams,  Groshong,  1976;  the  distribution in rocks of the Bowser  Lake  in light of this extensive literature.  is often characterized by  and  and  of the various theories regarding  solution as well as other  have  has  aligned  the presence  and  hence  of clay minerals  highlight a  which  foliation. The  are mechanisms  are:  of layer silicates into alignment  with  a plane  of  flattening  and/or 2.  growth  of  "metamorphic"  layer silicates within  the plane  of  flattening of  a  87 finite strain The  process  water-rich Siddans, of  ellipsoid.  of mechanical sediments  1977;  theoretically aid by  virtue of argued 1982;  and  Johnston,  compressive  dissolution process  domains  (e.g., Maxwell,  White  the principal  rotation may  (e.g., Durney,  "house  nucleation  for based  on  Woodlands,  mechanism  is the presence  flattening  of  process might  away  followed White  by and  Various have by  been Sorby  of  the  et al„ 1976; the  Gray,  orientation  Alignment  in a diagenetic/metamorphic  phyllosilicates  environment and  has  results (e.g., Tullis, 1976;  "pressure shadows"  (Elliott, 1973)  grain surfaces at points of low  which  and  fibrous  contact strain within  mechanisms;  in the ambient  Beach,  deBoer  have  of with  initially that of rotation into the clay-mineral of clay-minerals  by  alignment  closer approximation  of the two  into  been  Tullis, 1975;  as an  a  should  of phyllosilicates  for active grain growth  combination  grains by  1978)  less-soluble  1970;  the  the actual  the domains  strain field (Williams,  1977;  1978).  factors that might  emphasized  by  wide  temperature  range  other  factors in terms with  as a  1982; Mitra  (e.g., deBoer,  either catalyze or inhibit the pressure  a variety of authors  (1853). Temperature  intense cleavage  Spang  collapse mechanism.  some  being  empirical (e.g., Pique, observations  of  by  active destruction of surrounding  the finite strain ellipsoid. A  active growth Knipe,  direction controlled  evidence  from  in fact be  orientation process  in a  as well as experimental  1982). Compelling  plane  1981)  empirical observations (e.g., Honeywell  Nagtegaal,  growing  1978) or post-lithification (Clark,  rotation in concentrating  growth  1982)  minerals  Roy,  1972;  of cards" and  1962;  stresses. The  mechanical  a  progress either prior to lithification in  1977). however,  since the first observation  dependent and  The  variable has  Yonkee,  been  argued  1985) as well as  prevalence  of pressure  (Rutter, 1976). The  of  process  cleavage  for based  on  experimental  solution  suggested that temperature may  of the overall process  solution  be  fabrics over less important  close association  structural discontinuties in the field (e.g., Simon  a  and  Gray,  than of 1982)  88 or  with  the  areas of high  importance  of grain contact stresses in the pressure  Thermodynamically, which  the process may  be  lower  chemical  cleavage  more  1969;  elucidated  by  Gray,  authors  work  the presence  act as channelways  explain  some  analogous  1959;  process.  in fine grained  1978). The  lithologies has  the pressure  (e.g., Rutter, 1976). The solution process  a very  normal  lead  tendency  have for  several authors  to  solution process (e.g.,  nature of the grain size control has  of  by  relatively unstressed surfaces  Elliott, 1973; Robin,  been  further  fact that diffussion flow- is (Elliot, 1973)  thin film of water  along  has  led  grain  several boundaries  facilitating diffusion.  interplay between  the entire realm be  potential whereas  factor in the pressure  to emphasize  Evidently  might  1978). The  emphasizes  potential gradient; areas of high  that grain size has on  experimental  rate controlling  which  concentrated  the influence  Yoshida,  chemical  potential (Kamb,  to be  emphasize  high  solution  1983)  thought of as stress driven diffusion flow  diffusion occurs along paths of chemical  contact stress having  the  "stress" concentration in thin section (Nelson,  the various processes  of pressure solution. The  to diffusion flow  in metals  suggestion  is necessary  in order  that pressure  solution  led Elliott (1973)  to propose  to  the  f o l l o w i n g f l o wl a w : e  =UDefi/x r kT)0 2  2  where K = proportionality constant; De= lattice diffusion coefficient: Q, = the volume of 1 grain boundary defect divided by the number of slow moving vacancies in the defect; x— diameter of an equant grain; r— ratio of grains, longest to shortest dimension; K—Boltzmans constant; T—temperature: divided by the number of slow moving vacancies in the defect; o  = normal stress at grain  contacts.  Based solution  on  theoretical considerations Rutter  (1976) described  by: e=32  a a V C o Db (w/ R T p d ) 3  strain rate via  pressure  89  where a = applied stress; V—molar volume of the solid; Co=the concentration o a saturated solution in equilibrium with the unstressed solid; Db=the grain  boundary diffusivity; w=the effective grain boundary width; R=the gas constant; T—temperature ° C ; p = density of t h e solid: d = grain diameter.  From  these relationships it might  vary  inversely with  Rutter  grain size and  (1983, Figure  solution  on  expected  results and  proportionately  and  grain  mathematical  Rutter's. assumptions,- for, any strain rates for a given  an  given  grain  to pressure  solution. At  serves  as  in that effective grain hence  the strain rate due  phenomenon  influence  intensities in any  and  is consistent  grain  means  size to the  due  of subgrains  set of rocks  of Bowser with  of well sutured  combined  effects of rigid-body  to which  (Green,  occurs. Such  deformed  Lake  Group  at low rocks  contribution  solution  grains of  which  incorporate  of  larger  grain  the process  process.  higher  sizes.  As  strain  fasteT  in temperature  results  in  pressure can  proceed,  reprecipitation  1970). The  an  on  of stress, result in.  to dissolution and  of isolating less-soluble clays into domains  prevelance  pressure  results from  result in a variable  a combined  pressure  increase  effective shortening mechanism  solution should  given  In the study cleavage  an  development  pressure  increase  extent  to diffusion decreases  thus becomes  strains unless the may  diameters  values  in grain size which  limits the  stress.  to  stress,smaller grain sizes will have  a fixed stress an  would  52 illustrates that based  alternatively, dissolution  change  a factor which  of strain rate due  higher  solution  intergranular normal  size in a series of curves  temperature,  size or  increase in strain rate. The  solution  with  derivations. Figure  well, for any given temperature and rates due  that the rate of pressure  10) illustrated the dependence  stress, temperature  experimental  be  pressure  and solution  only for relatively small interplay of factors distribution of  temperatures  which  cleavage  (below  300° C).  it is evident that the distribution of temperature,  Evidence has  various composition  intergranular  for dissolution been  documented  (Figure  rotation of clay minerals and  of  grains  by  the  53). Arguments  active grain growth  of  stress as a  for can  the  90  FIGURE 52: From Rutter (1983), the relationship between pressure solution strain rate, grain size, temperature and intergranular stress. Solid curves represent 100 urn grainsize, dashed curves represent 8 um grainsize. The strain rate for various conditions is shown as a power of 10. See text for discussion.  FIGURE  53: Well  subhtharenite from  developed suturing of detrital grains in a the Currier  unit  very coarse grained  92 be made  based  on  petrographic observations. The  phyllosilicate flakes in open McEvoy  units which  have  ubiquitous occurrence which  54A  origin and bent  &  B)  owe  undergone  of  assuming  that  their alignment  rotation  within rocks from  within  oriented  the Devils Claw  and  limited pressure solution in contrast to  highly cleaved, implies an  element  at least a portion  selvages  (Figure  a differential  25)  clays  Jackson  present  framework.  is thought  units  The  with  process  are  detrital  presence  to further  stress field coupled  surrounding, detrital.grains.. The. common  the  of rotation to the  of the  to collapse of the pore  phyllosilicates in cleavage  evidence  spaces  of randomly  of aligned clays within rocks of the Currier and  are comparatively  (Figure  pore  predominance  of  provide  interference  occurrence, of clay beards  in  analagous  by to-  :  "pressure shadows" in well cleaved rocks (Figure 24), on the other hand, implies . preferential growth mechanism.  A  of phyllosilicates within  continuum  process  which  dissolution of adjacent grains and depths 1977)  and  growth  of  is advocated The  be  explained by  these  the observed  the combined  involves  suggested  folding  this relationship might  be  presumably above  decreases  gradually  is that at low  anticipated than accomodated  arguments  during by  (concerning  are  to  burial (Williams,  point  to a  buckling the  early in first phase  and  small  where value  strains more  Ramsay  the fold begins (fold  (1974)  stress on  where Spang,  angles  who decrease  to lock up  flattening).  grain to grain  and  may  intergranular strain. The  strain accelerating phase  effects of  later dissolution  sluggish, but as interlimb  layer parallel slip (Chappie the  levels of burial  geometrically analyzed by  the strain rate increases rapidly to some hence  due  at shallow  overprinting by  effects of temperature been  rate  minerals  framework  distributed cleavage formed  strain rate related to folding has  strain  orientation  observations.  lack of cleavage  that the initial rates of  as an  rotation of insoluble  phyllosilicates at deeper  interpretation that widely  folding history and  flattening plane  collapse of the porous  "metamorphic"  to explain  the  A  and  corollary  normal  of  strain  strain is 1974). From  dissolution rates) the strain  the  FIGURE 54: A. line drawing (microscopic view) illustrating random orientation of phyllosilicate grains in pore spaces (lower McEvoy unit). C=chert, CM = clay minerals. B. line drawing (microscopic view) inferring bending and rotation of phyllosilicates into the cleavage plane during dissolution. RF=rock fragment Q=quartz, CM= clay minerals.  94 accelerating  stage should  folding than cleavage  due  be  resulting  in a  result in increased  probably  fan  pore  the  higher  and  decelerating  in intergranular  phase,  approaches  buffering following  strain would  occur,  with  a concomitant  process of Griffith cracking and  a  in the  further value  decline  close  to  lock-up,  increases in pore it is possible  in a second  that  Coalfield, cleavage  of tight chevron  folds. One  uplift, progressively lower (Figure  52), at lower  maintain thought  to be  1974) thus  be  cleavage  areas  of high  immediate  higher  2  footwall  area  of a  areas  of stress concentration. The  shaly  units in comparison  on  transects  folds.  previously  Wright,  1984).  only  In  in the  Rutter's  cores  during  curves  unit, and  of folds are  stress concentration by  (Chappie  interbed slip. Fold A  pressure  folds, locally in the core Claw  increase  been  observed  Based  core zones  development.  of well-developed  Devils  pressure.  levels of intergranular stress are required  accomodated  for cleavage  however,  for this distribution is that,  encountered.  intergranular  not be  locations  of phase uncleaved  explanation are  confining  which  Boulter, 1979;  transects folds was  rate of pressure solution. The  for the presence  otherwise the  temperatures  a zone  favorable  possible temperatures  in that strain may  invoked hinge  the _same  which  1975;  also  a second  from  Barnes,  During  in  fluid  described  the Groundhog  continued  reprecipitation should  overprinting attributed to the flattening stage of folding has and  formed  thesis area.  Cleavage  other areas (Ross  flexural-slip  associated dilatancy hardening,  large  resulting  to  that are rotated during  to that observed  fluid pressure  by  strain rate due  that point, previously  dissolution coupled  fluid pressure  limits this influence  During  similar  progressive  stress as pore  pressure. The  a  act as fixed material planes cleavage  the accelerating phase  intergranular  by  to intergranular diffusion flow. At  planes should  folding  characterized  solution cleavage  of an  overturned  the intense development  Spang,  may  should be the  anticline within of such  locations having  restriction of cleavage  at higher  of well-developed  and  solely in  thrust fault, all such  to the presence  generally  core zones  similar argument  to  been  the  cleavage probable  stratigraphic levels  cleavage  in  irrespective  of  to  95 lithology at lower models.  As  stratigraphic levels can  previously  constant stress and grain size. As material lower  with  sedimentary  low  assuming  other  dominate  as an  factors remain  should  varies  undergoing  as  solution rate of  result in a function  the upper  have  of  (Bustin, 1983;  grain  Lake  Group  with  Based  on  a  temperature  Ruiter's  of approximately  curves  (Figure  52)  maximum  temperature  prior to deformation  regionally  exceed  MPa  type  at 300° C  and  other  the  general  ranges  to lO^'sec"1 competing  from  of  1  MPa),  and  the  of approximately phase  then  to 10"'"sec"1 for a fractions. The  of  suggested  (Price, 1973)  have  the  if stresses did  100  um  not  for this to  rock  pressure  fraction  and  interplay of pressure  solution  folding) further implies  faster, is on  average  of  that  this  "representative geological strain rate" of Heard  general range  10" "sec-1  and  the  C.  strain rate due  (i.e., interlayer slip during  well to the  would  brittle failure strength  incrementally  to  of coalification  to infer that, if  200° C  the  begins  of coalification  5500 m)  to 200°  it is possible  general  for finer grained  10")Ssec"' (Price, 1973). The  accelerating  100  overall strain rate, though comparing  value  a  10""sec-1  processes  magnitude, 10"'"sec"  (assuming  is approximately  solution probably 1010sec"'  100  given  cleavage  this study). Results  150° C  reached  cleavage  stratigraphy,  unit if the peak  and  to a  (1963)  estimated  strain rates for folding of  10"6sec"'  increase of  folding strain rates from  an initial  value  is further  of approximately  consistent  with  10"'"sec"'1 during  a model  to  at  reached, at approximately  m o d e l l i n g ( C h a p t e r 4 ) i n d i c a t et h i s d e p t h o f b u r i a l ( 4 6 0 0 corresponded  material  size in a  at which  been  contact of the Currier  prior to deformation  a  coarser  distribution of  constant, the temperature would  indicates that at  that for finer grained  a  theoretical  solution is inversely proportional  burial. In the Bowser  early strain response  of burial of reached  relationships  curves  the pressure  that approaches  strains which  package  of Rutter's  temperatures  to a value Such  analysis  rationalized in light of  the rate of pressure  well, at higher  is increased  associated  was  temperature  temperatures.  depth  indicated, an  also be  involving  the competing  to  96 incremental  strain processes  in the  accumulation  of bulk  strain.  Fracturing  broken  The  presence  by  extension  of antithetic syntectonic veins and fractures) in such  'crack-seal' mechanism Etheridge, pressure  (Durney  1983). Fluids and  overburden  hence  derived  cause  stresses. As  instantaneously but  and  veins has  Ramsay,  from  local zones  quickly begins  plane  cavity where Ramsay,  of  1973). The  being products  by  the  1981; Murphy,  supply  with  1984; Mullenox  and  transfer is important  dissolution, migration scale solution  of  1977;  fluids along  are required  fluids (Etheridge  1983)  well as larger  et al., study  pressure  Murphy, in the  area  it is thought  scale fluid transfer  of synthetic veins with  is necessary  associated zones  be  The  reinitiated.  in a  to  of  the  fluid  filled  1984)  1977). The  veins and  act as sinks  Barnes,  1975;  combination  small  vein  of  and  explain extensive "metamorphic"  mechanism  features.  crystals, in addition  has  Although  and  of crack-seal  to fully explain  "stetched"  veins  reprecipitation may gradient  fluids  Nelson,  fracture process.  geothermal  of  many for  to suggest that both  and  as  orientation  solution surfaces are in  hydraulic  high  and  previously suggested  to explain large scale advection  that a  the drops  perpendicular  been  Ross  grain boundaries as a  fluid  fluid pressure  1984). Textural evidence in many  transfer, factors such  sub-critical crack growth  1977;  to the vein wall (Durney  the veins have  Gray,  large scale solution  the  incrementally  (Phillips, 1974;  (e.g., Beach,  In  the pore  infinitesimal irrotational strain; the  dissolution process  a  approaches  to free crystal growth  extension fractures and  led several authors  small  fluid pressure  perpendicular  of  to increase pore  of the pressure solution process (e.g., Beach,  compatable  supplied  grow  opposed  is always  fluids which  fibrous-mineral-filled areas  are thought  if the  in terms  1980; Beach,  to rebuild until fracturing can  flattening as  crystal growth  interpreted  as the fracture is created  localized fluids, precipitate crystals which infinitesimal  been  1973; Ramsay,  failure in extension  soon  "stretched" crystals (i.e., fibres  to  as  Prescence brecciated  97 zones and  many  fractures where  filled fracture (Figure growth  points  is interpreted  crystallizationhas  55) in zones  studied  to have  only  initial buckling,  a  been  active  would  be  derived  pressure  either from  temperatures would folding  be  history. Additional  higher and  greater rate; Etheridge  metamorphic  1984), the release of  1967), and  the thermal  (Barker,  may  contributed  that such  of abnormal  is approximately  as compared  30°  criteria. Muehlberger conjugate  set to form,  that extensional explain  fractures  (1961)  conclusion that such during  of  pore  Gretener,  bimodal  occur. More  of synmetamorphic form  metamorphism  during crustal orogenesis were  less than 40  approach  of  utilized in the study  be  repeated and MPa  the Bowser  for several experimental sandstones (Mesa  a  of smectite  to  temperature  generally  to the  accumulation  for a low low  and  dihedral  dihedral  used  angle high  such  this theory  rocks. It was  hydrofracturing due  angle  failure  fluid pressure (1983)  extension  to  his  to high  pore  that this indicated differential stresses and  rocks  Verde,  at  hydrocarbon  set whose  veins in metamorphic  prograde  as  of revised Coulomb  recently Etheridge  from  advance  is the orientation of  systematic  that in order  continue  1979).  to the predicted 60° out  might  to increasing  importance  fluid pressure a  depths  fluid pressures, it is  the differential stress must  veins could  been  such  due  localized  therefore have  the conversion  water  rocks  veining  reactions would  during  vein  fluid to create  (i.e., at greater  processes  of marginal  1978;  form  pointed  failure could  the occurrence  fluid pressures  to high  to the discussion of pore hkO  other water  factors are probably  fractures. First phase  depths  expansion  fluid pressures (Magara,  Relevant  fluids must  dewatering  et al., 1983). Though  have  enough  thus pressure solution mechanisms  illite(Powers, 1972)  during  insufficient to supply  solution at greater  history and  (Meissner,  regionally  fluid  also spatially related to antithetic solution in the  deformational  considered  open,  as pressure  episodes throughout  generation  are  into an  to this dual source. Inasmuch  pressure solution source  throughout  which  obviously been  perhaps  as low  as 20 MPa.  is to take average  Kayenta,  Barns, Nugget  failure and  The  curves Cardium;  98  FIGURE Vien  5 5 : 4 i n c h d i a m e t e r c o r e o f t h e C u r r i e ru n i t ,i l l u s t r a t i n g a b r e c c i a t e d z o n e .  filling in this zone  precipitation in an  open  consists of blocky vein  environment  carbonate  and  quartz,  suggesting  99 Kirby  and  McGorrnick,  that could indicates  determine  exist to create extension that the  the maximum  possible differential stress  fractures as observed  differential stress which  conjugate set whose bedding  1984) and  could  dihedral angle is 30°  in the field. Figure  result in extension  is approximately  48  parallel extension veins this stress differential would Mohr  circle analysis (Secor, 1965;  see Figure  study  were  buried  m  due  area  rocks  to overburden  approximately overburden 76  MPa  108  would MPa  to a  be  of excess an  would  be  overpressure  pressure  will cause  of this magnitude with very low  (1979) argued  fluid pressure  importantly,  due  be  formation  reprecipitation are active processes then overpressures  due  to the concomitant  tortuoisity of  fluid paths. Thus  gradient and  attainment  of transient high  extension the amount  might  rapid burial could fluid pressures  fluid overpressuring  (i.e., sub-critical crack growth failure strength as predicted by  required  proceeds  that  o3  of  then  approximately  even  that  size and  solution  that depths  if dissolution  with  area. The  a  high  for  the  as sub-critical cracks fractures  Griffith failure criteria; Anderson  the  possibility  of the and  and  of significant  have, accounted  50%  of  pressuring.  increase in  coupled  to create hydraulic  at approximately  noted  significant  aquathermal  permeability,  in the study  a  burial to great  2 MPa,  simple  presumably  in  (1975)  expect development  fractures of the variety discussed propagated of  the  increase of temperature  by  in pore  pressure  that  the effective  generated,  as an  fairly low  decrease  extensive  be  loading, rapid  acquired  one  so  lower  Intuitively it is difficult to  approximately  of  the  much  deformation  permeabilities. Magara  that inasmuch  a  create  a pore fluid pressure  could  to pure  to increase by  for a given  geothermal  generated.  of  56). Assuming  during  MPa,  To  considered, to. be. 68, MPa-,  be  additions to existent overpressuring may More  100  be  must  to increase simply  is required. Gretener  5,500  MPa.  required to create failure. Because  fluid pressure  situation of perfect confinement for pore  of  approximately  stress at this depth, might  visualize how  1°C  depth  fracturing  necessarily be  as illustrated by  56  that  also  lowers  considerably  actual Grew,  tensile 1977).  100  FIGURE 56: Mohr circle analysis illustrating the failure curve averaged from the experimental data available for several sandstones (from Kirby and McCorrnick, 1984) and the stress differential required to result in extensional fractures (A) with dihedral angles of 3 0 ° . The effect of high pore fluid pressures (Pp) is to maintain the stress differential and move the Mohr circle to the left Layer-parallel extension fractures (B) form when the stress differential is even lower. The limiting condition of Secor (1965) is illustrated by heavy dashed lines.  101 As with  previously  stated the  relatively low  the lack of thrust faulting and  contrast to the Front fractures form  at a  Ranges higher  predominance  subprovince dihedral  where  angle  possibly in excess of 100 MPa  compatability  of a  of faulting is further predictable Syntectonic  veins  are commonly  1976;  (Jamison  viscous  Moffat, and  stresses and  fold theory  parallel or at a  very  3  "sinks"  history points to the possibilitythat a differential stress is consistent with interchange large  3  and  mutually  system.  Thus  2  be  subtle changes  situation of incremental  three dimensional  explain  distribution of finite strain  the  timing  and  were  achieved in the  2  during  superposed without boundary  constrictional strain may geometries.  The expense  to bedding,  as  plane (hkO). Figure  quite close. A  perpendicular  of principal stress orientations can  stresses to the  o  differential  at the  angle  and o  at different times  in  1961).  low  illustrates that these planes might open in extension if o  1972).  is  conjugate  and  folding  (Biot,  a-c  are active as  1980)  Spang,  well as in the conjugate orientation subparallel to the Fi  fact that either planes  consistent  thrusting is prevalent and  strain rate, low from  of differential stress is  of folding in the area. This  (Brown,  stresses were  relatively slow  value  57  are switched. The the  deformational  low value  of  strains in that  an  the application conditions be  and  sufficient to  of a  102  FIGURE 5 7 : The orientation of principal stresses required if both the hkO fracture planes and bedding planes are "sinks" for pressure solution cleavage. A reversal of o2 and a 3  is required which may infer a2  and a3  have similar magnitudes.  4 . COAL PETROLOGY 4.1  INTRODUCTION Coal  seams  in the Groundhog  Coalfield vary in rank  semi-anthracite  to meta-anthracite  (Bustin, 1984)  semi-anthracite  to anthracite. Coal  quality is highly  ranging from  0.4%  Comminution  of  to 5.0% and  coal  folding, ln many  areas  coal) is filled with seams,  bedding  Framboidal Seam  appear  to have An  order  has  and  in the study area  from  variable with  upwards  resulted locally from  closely spaced  quartz  5.0%  from  thicknesses  vary  variable  analysis of  to obtain  carbonate  less than  1 m up  vitrinite reflectance was  fractures  veins. As  well, in folded  carbonate are  common.  undertaken  the paleogeothermal  gradient;  3.  the maximum  depth  of burial of the sediments;  4.  the maximum  temperature  The  analytical methods  . min  study  area  to which  and  as part of this study  in  coalification;  by  rocks were  which  Polished  exposed  the above  (International Committee  and Ro  coal,  (Bustin,  and to.  information  for Coal  is obtained  Petrology, 1971) and  coal pellets were  prepared  are hence  according  to  well will only  , were recorded with the aid of a LeitzMPV2 rand  a photomultiplier  increase the precision and  is attached. The speed  system  of measurement. 103  is linked to an This  data was  be  methods  outlined by Stach et al. (1975) and Bustin et al. (1985). Measurements of Ro Ro  in  concerning:  2.  here.  Latour, 1950). flexural slip  to 5 m in the  the timing  briefly described  and  partings of pyrite are also prevelant  1.  documented  values  lateral continuity.  information of  massive from  (Buckham  "cleat" (systematic closely spaced  less commonly,  less commonly,  sulphur  cataclasis during  parallel, fibrous, syntectonic quartz and  and  1984).  seams  ash from  and  regionally  ,  max reflecting microscope IBM  combined  PC  XT with  to  104 measurements 1984) and  of Ro  recorded by  max  Gulf  Bustin (1984) in order to calculate paleogeothermal  paleotemperatures.  Oriented  well as several samples  samples  which  of coal blocks  contained  p o l i s h e d . M e a s u r e m e n t s o f R o max bedding the  (unpublished open file reports; 1982, 1983,  planes  and  collected from  a  major  , R o min  .  maximum anticline,  small scale folds in coal seams  were  as  also  a n d t h e i rr e s p e c t i v e o r i e n t a t i o n s r e l a t i v e t o  the axes of tectonic transport were  recorded  in order  to  determine  relative timing of coalification.  4 . 2 R E F L E C T A N C E  4 . 2 . 1V I T R I N 1 T E  S T U D I E S  layers) which 1982). The  O F  R E F L E C T I V I T Y  It is generally  agreed  become  B O W S E R  I N  B A S I N  C O A L S  A N T H R A C I T E S  that vitrinites consist of lamellar  progressively more  aligned  progressive devolatization and  concomitant  condensed  crystalline structure (graphite)  covalently bonded 'c' axis  of  carbon the  coal to graphite experimentally progressively graphite  atoms  which  crystal. Diessel  in meta-sediments  et al. (1978) of New  aligned  structure  parallel to the  was growth  not achieved.  direction  Caledonia.  Reflectivity  orientation of polarization of  the  of a substance principal planes  the incident beam  in plane  occurs  polarized  of  with  change  from  illustrated  a  true  to "rigid  body  crystallographic  axes  light is governed  and  along  became  stress (Levine  of vibration in the substance  together  volatiles, though  "c"  of  dimensional  et al. (1982)  that in addition  compressive  of light (Hevia  carbon  two  a progressive  structures in coal outgassing  of crystallites of graphite  oriented parallel to the direction of maximum  consisting of  Bonjoly  It is also possible  et al.,  structure consisting of sheets  documented  of  increases (Stach  electrostatically bonded  that distorted layers of polyaromatic  rotation", actual  1984).  organic  are weakly  (aromatic  increase in percentage  transition from  rings to a more  an  elements  as coal rank  content indicate the gradual  the  gradients and  with  Vigos, 1976). ln  and  by  Davis,  the  respect to  the  that reflectivity  105 is directly proportional in a coal sample theoretically be aromatic  to the  where  refractive index  aromatic  molecules  isotropic (Hower  molecules  and  and  hence  are randomly  Davis, 1981). The  into close packed  layers should  anisotropy. Traditionally,researchers have  density  (Forest  oriented  et al., 1984),  reflected light  progressive alignment  thus result in an  should  of  increasing  recorded the value of Ro  (maximum max  reflectance measured measurements  are  in oil) and  employed  easily obtained  them  in bituminous  indicatrix is generally uniaxial negative b e d d i n g s h o u l d c o n t a i nb o t h R o  and Ro  that in. anthracites which  Levine  and  and Ro  . min  Davis,  The  are  1984) that only one  1953)  and  Such  the  optical reflective  any  section normal  to  . v a l u e s .S t o n e a n d C o o k ( 1 9 7 9 ) n o t e , min  locally biaxial negative  gathered  in non-polarized  et al.,  1972;  analysis, which  surface will contain the true  measurement  of the random  reflectance which  light.  increasing anisotropy  anthracitic vitrinites from  by  unique  (eg: Cook  Ro max values. Hevia and Vigos (1976) suggested that all the reflectivities of the  indicating surface could be is obtained  coals where  (Williams,  max however,  in the study of coal rank.  the  is described  concomitant  study  area  with  advancing  coal rank  is illustrated in Figure  in detail later, also suggests  in  the  58. Oriented  that the  indicatrix is  sample slightly  biaxial; suggesting that problems may be encountered in obtaining accurate measures of Ro . Bustin (1984) however, suggested that for the coalfieldas a whole, the m a x varianceof Ro and Ro , b o t h i n c r e a s ew i t h i n c r e a s i n g g r a d e a n d t h a t R o is max rand max statistically 0.21% Ro greater than Ro . Figure 58 B & C illustrates this relationship rand for coals in the area although it is suggested that the increase in variance in the Ro m e a s u r e m e n t si s a t a g r e a t e rr a t e t h a n t h a t o f t h e R o ,. Ro , would thus max rand rand appear to be a combination of both Ro these measurements  precludes  max  and  Ro  . though the degree of error in min  the possibility of deriving any  empirical relationships.1  Thus at higher levels of coalification the divergence of 1 T i n g ( 1 9 7 8 ) i n d i c a t e s t h a t t h e o r e t i c a l l yr a R R o , should be = + R Q \ d min  1/3 (Ro m a x  +  Ro. i n t  106  nGURE  58: Reflectance plots for data measured during the thesis study.  A. bireflectance (Ro -Ro . ) versus random reflectance (Ro A This relationship max min rand illustrates the increasing difference between Ro and Ro . at higher ranks (ie. max mm increasing anisotropy at higher coal rank). B. reflectance (Ro and Ro _,) versus standard deviation of measurements. This max rand plot illustrates the greater variation associated with Ro values when compared with max Ro , as well as the greater divergence of Ro and Ro . at higher reflectances, rand max rand sugesting that Ro ^ should be a more precise measurement rand C. Ro versus other reflectance properties. This plot illustrates that Ro , and max rand Ro . are both less than Ro and that Ro , falls between Ro and Ro . . mm, max rand max mm  o CTN  107 R o  rand  , f r o m b o t h R o  encountered 1978)  and  when  a n d R o  max  . w i l li n c r e a s e , w h i c h s u g g e s t s t h e p r o b l e m s min  dealing with biaxial indicatrices are significant (Stone and  that for these anthracites R°ran(j  of the reflectance (Bustin, Inasmuch Resources  as the available reflectance data does  not always  of coals of similar grade traditionally been  from  more  accurate  representation  for the area (e.g., Gulf  deviation of Ro  necessary  rand into the study. Comparison  recorded. The m a x  =0.18%)  eliminates the possibility of using Ro  Canada  values, it was  with  other areas is also facilitated in that Ro  the only measurement  study (average standard  a  report Ro  values to integrate all data  m a x  be  1984).  Inc., 1981-1983)  utilize the Ro  might  Cook,  error that was  for detailed studies such  studies has  max  noted  is significant and  to  during  this  probably  as seam  correlations.  max For regional applications such are presented here, this error is thought to be insignificant. Based on this study it is recommended that future investigations should r e c o r dR o , a s w e l l a s R o a n d R o . f o r c o a l sa b o v e s e m i - a n t h r a c i t e g r a d e , rand max min  4 . 2 . 2T I M I N G  O F  C O A L I F I C A T I O N  Reflectance The deformed peak  Isorank  analysis of reflectance values in an may  allow  of organic  commonly  been  Kalkreuth  and  for a  determination  metamorphism employed McMechan,  isorank surfaces are theoretical  Configurations  1984;  Pearson  by  expected  as  coalification history. In the study together throw,  with renders  the  paucity  a similar  of  large  comparison  and  which  has  the chronological  the deformational  (Hacquebard  deformed  relationships  and  of  area  event  Donaldson, and  Grieve,  been tectonically  relationship between A  method  in press) is to determine  major  structures. Figure  a result  either  a pre-tectonic  area, the high amplitude  folds  variance or  difficult. Reflectance  has  1970; Teichmuller, 1982;  or cross-cut of  which  the  a  of  mean  fault with measurements  59 or  whether  illustrates the post-tectonic  reflectance  values  a significantly of  a  large  FIGURE 59: Theoretical distribution of isorank lines (IR) with respect to bedding in folds when coalification is pre-tectonic (A) and post-tectonic (B) (after Bustin et al., 1985).  109 coal-bearing  horizon were  anticlines in the area a post-tectonic and  obtained from  with  sufficient amplitude.  coalification and  compared  the crests and  to the observed  Hypothetical  a paleogeothermal values. The  troughs of the two reflectance values  gradient  of 40°C/km  results are listed  R o . m  Crest  4.02±.18  Trough  were  R m  2.811.59  3.35+ .234  .  0  2  3.95±.17  2.901.35  3.331.15 4  .  4  5  Crest  2.641.15  1.941.40  2.501.032  .  6  4  Trough  2.781.14  2.721.11  2.421.02 3  .  1  4  differences between  folds and one  field. Figure  lower  i  R o  n  the reflectances of samples  from  a  the crest and  o  x  trough  of  the  the calculated reflectance indicate that the coalification is pre-tectonic.  thrust fault which  wall and  calculated  calculated , rand  The  assuming  below:  measured R o max  major  60  offset coal seams  with  illustrates the relationships of the maximum  footwall of this fault which  rank. Both  lines of evidence  has  in this  was  thus suggest that the peak  recognized  in  the  reflectances in the  thrust coals of higher  pretectonic (see also Bustin, 1984). However, uncertainty  sufficient throw  Only  rank  over  hanging  coals  of  of coalification was  the scatter in the data  creates  some  analysis.  Orientation of Reflective Indicating Surface  Another gained  some  method  for chronological determination  favor involves the comparison  orientation to that of bedding  and/or  or empirical observations several authors  of maturation  that has  of the reflective indicating  structural geometries. Based (Cook  et al., 1972;  Hower  surface  solely on and  recently  theoretical  Davis,  1981;  110  FIGURE 60: Structural cross section from north central portion of map area near the headwaters of Didene Creek (Currier unit in stippled pattern), illustrating the thrust emplacement of coals • of higher rank (4.70 %Ro) on coals of lower rank (4.15% Ro), suggesting a pre-tectonic peak of coalification. The orientation of the apparent indicating surface in oriented samples from an overturned anticline- syncline pair illustrates that in each case the apparent  R o  m a x  is within the plane of bedding  (shaded area), further suggesting pre-tectonic coalification. The. tectonic axes a, b, and c are plotted on each sample (i.e., b=fold axis, a=direction of shortening). Values on ellipses are normalized lengths of the apparent maximum and minimum reflectances. The angle between bedding and Ro for each face is given. max  Ill  Levine  and  Davis,  coalification aromatic  1984; Ting,  in a hydrostatic  1984) have  suggested  stress field should  under  polymerization  conditions of  increasing  in a random  orientation  of  have  their peak  of  result  layers, decidedly anisotropic anthracites must  aromatization  that, because  reached  differential stress. It has  thus been  suggested  takes place preferentially in the direction of minimum  resulting in a plane of closest packing. Ro  that  compressive stress,  , which corresponds to the direction of max  closest packing,  would  system .(a,>a  = a3 )  a  2  triaxial stress system  Assuming  be  oriented  reached  (a1>o2>o3)  a  and/or  experimental  the importantance reflectance  major  direction  plane  of  flattening. In a  study  uniaxial  stress  authors  indicatrix  used  would  be  expected.  the orientation of the indicatrix with the peak  of coalification  deformation. still in progress  of strain and  temperature  in vitrinite. Several  triaxial cell at confining  biaxial  structures to infer whether  prior to or during  An  in the  the indicatrixwould theoreticallybe uniaxial negative whereas in  this relationship, the above  respect to bedding was  thus  pressures  of  (Bustin  has  in the re-orientation of the  cores 500  et. al, in review)  of  and  anthracitic  800  MPa,  coal and  were  indicated maximum  deformed  temperatures  of  in  a  350°  C  and 500° C. An original, nearly uniaxial indicatrix, which approximated an oblate ellipsoid with Ro oriented sub-parallel to the core axis in the plane of bedding max was  altered to an  perpendicular indicate the  and  then  to the core axis in the plane  to an of  the shape  of  the  the indicatrix, possibly by primary  electron bonding  bonding  within  hence some  sheets means  no  basal  max  of dislocation phenomenon  deform  during is  warranted,  without  an  the shape  (ie. the lack  the strength of the covalent  dislocation glide will progress  oriented  results  the principal stresses  increase in rank, might  sheets and  was  61). Such  also illustrated that stress applied  form  between  (Figure  Ro  vitrinite reflective indicatrix. Caution  in that the results obtained  increase in temperature, and  ellipsoid whose  bedding  validity of inferring the orientations of  coalification given however,  oblate spheroid  in graphite  of of  interatomic crystals at  112  FIGURE 61: Geometric relationship between Ro (long lines on crosses) and Ro . max mm (short lines) and deformed cores (bedding parallel to core axis) recognized in experimentally deformed samples. In sample GY-192 25% strain at 550° C resulted in reorientation of the indicating surface whereas GY-193 which was taken to 10% strain at 500° C resulted in incomplete reorientation (From Bustin, et al., in' review).  113 low  temperature;  Jenkins, 1973). Deformation  of  the indicatrix in this fashion  resultin an apparent "decoalification" as measured by Ro m a x indicatrix might  be  thought  In the study measured  of as an  area  analogue  to the finite strain ellipsoid.  from: oriented  2.  hand  samples  Four  oriented coal blocks were  samples  collected which  from  the  Little Klappan  the  shallow  the  overturned  River  dipping  oriented such  limb  a large  obtained  6 km  upright near  limb the  of  the  synclinal  that, within the margin  samples  A,  B, and  contain the apparent R° to bedding  regardless of  rotation due anomalous  south  (Figure. 60). Polished  m a x  C, which  faulted coal from  hinge,  asymmetric  1 and  ln  2  overturned of Butler Creek  were  3 and  all 4 samples  of error, Ro  4  collected were  the  from  collected  indicatrix  is contained  and  from  is  approximately  m a x i s a p p r o x i m a t e l yp e r p e n d i c u l a r t o b e d d i n g .  .  min  illustrate small and  faulting (Figure the  seams.  of the confluence  the location in the folded  in that although  an  samples  parallel to bedding  to brecciation and  and  anticline whereas  within the plane of bedding, whereas Ro Polished  fold;  exhibited folded and  anticline-syncline pair approximately  somewhat  . In either case the  the orientation of the indicating surface of vitrinite was  1.  body  might  long  limb  scale folds and the apparent surfaces or the 62  A&B).  R o  thrusts, also m  j  n  perpendicular  degree  Polished  of  rigid  sample  D  of a slightly asymmetric  was  fold  illustrated bedding parallel apparentRo , the short limb contained measurements m a x which indicated apparent Ro . at a high angle to bedding (Figure 62 D). The actual min values of Ro on either limb are statistically similar, which leaves 2 possible max explanations: 1.  coalification was  syn-tectonic  2.  coalification was  pre-tectonic followed by  of strain induced It is unlikely  followed  by  further rotation;  and  reorientation, possibly by  some  form  dislocation.  that coalification is syntectonic  in that to obtain  the  present  configuration  114  bedding in coal  FIGURE 62: Orientation of the apparent reflective indicating surface in vitrinite from several folded coal seams. See text for discussion.  115 of Ro the  from  max  layering  possible,  a post-folding  requires  such  orientation where  that a pre-existing  a phenomenon  Ro  anticline be  is unlikely.  Instead,  a  unfolded more  localized reorientation of the reflective indicatrix might strains, when 0, varied  throughout  localized high of the  the layer. Indeed,  samples  A,  large scale fold it seems reached  4 . 2 . 3C O A U F I C A T I O N  the  increasing Ro  as the  of a max  been  well  When  as samples  low  the  buckling  have  resulted  taken  in  reorientation  in context  1, 2, 3, and  that the peak  the  there  maximum  contact of the Jackson is utilized here  max coalification process at depth  4  with  from  of coalification  should  1956).  In general  be reasonably eliminated. Data headwaters  a  the  was  reasonable  Ro  63  on  a  is a log  max of the assumed first order  there is considerable  the  be  reflectance. Figure  unit versus  in view  (Karweil,  although  flattened anticline near  there  is a  which  of Didene  was Creek  scale. reaction  trend  dispersion of the  plot  towards  data,  obtained  from  has  anomalously  an  the  . Because the seam here consists of extremelysheared coal,samples may oxidized with no  possibility is that high flattening  for  area.  stratigraphic level and  Several data points may  have  as  to conclude  in this  the upper  max  explanation  H I S T O R Y  log scale for Ro  low Ro  C  coalification is pre-tectonic,  kinetics of  Though  that during  et al., in review).  Inasmuch  above  be  across  its hinge.  localized strain induced  relationships  of height  core  concomitant  Reflectance-Depth  between  The  B, and  reasonable  prior to deformation  correlation  reasonable  anisotropics in the layer may  strain concentrations and  from  about  parallel  w a s o r i e n t e da p p r o x i m a t e l y l a y e r p a r a l l e l , t h e m a g n i t u d e o f s t r a i n s  vitrinite reflecting indicatrices (Bustin evidence  is everywhere  max  stage  possibly lowering  of  stresses, normal  folding Ro  recognizable oxidation rims (Bustin, 1984).  might  have  to the resulted  axial plane, in a  incurred  strained  (Bustin et al., in review). Data  during  reflectance  obtained  Another  from  the indicatrix,  the  west  side  116  R max 0  FIGURE 63: Plots of reflectance versus height above Jackson stratigraphic unit Least squares regressions are expressions of the coalification gradient. Plots of all data (A) and those with anamolous data removed (B) and (C) illustrate that even with all erroneous data removed the function does not explain the stratigraphically highest samples. Two log linear functions are thus suggested to better explain all the data, suggesting that the uppermost units experienced a lower coalification gradient than the lowermost units.  117  of Nass  Lake  from  the lowermost  Currier unit are also anomalously  unlikely in this area as the measurements errors. Samples suggesting  were, however,  the  this area  possibility of  are  restored  strata for which been  separated  have  been  geothermal  collected from  a tectonic  folds which  apparent  were  have  low  gradients were  at least 20  km.  extensively flattened,  "decoalification".  If the  sediments  calculated it is possible that they  Over  laterally variable, the more gradient than the more  such  a  westerly  of  having  have  flow  may  a  lower  experienced  easterly sediments, resulting in lower  in Currier  may  distance the basinal heat sediments  is  standard  to their palinspastic position relative to the position  higher by  are reproducible and  low. Oxidation  Ro  for max  similar burial depth.  This  in the  recognized  and  basal Currier  by  the apparent  immediately magnitude more not  west  of  exclude  general  low  is further supported by  Bustin  by  the high  (1984)  in the eastern margin  reflectance values (<2.5%  the study  area  Ro)  measured  (Esso, oral comm.,  the possibility of  reflectance values of  by  the  conclusions as to coalification gradients and  as seam depth  coalfield  this  correlation,  of  Ro)  Esso geologists  1985) Variations of  detailed analysis such  (5.0%  burial are  although probably  invalidated. Determination  of Coalification  It is theoretically calculated Bustin  possible  coalification gradient  et al. (1985)  Gradients  to reconstruct Assuming  indicated  that the  a paleogeothermal  a constant slope  geothermal  gradient gradient  of a plot of log Ro  from with  a depth,  versus  depth  was  m a x proportional  to the geothermal  a regressed  coalification  can From  be  gradient  these  plots  it is obvious  not surprising  flow  that rank  from:  the subsidence  all the  data  (C), data with any a  log  linear  (i.e., Devils  in that the geothermal  related to heat  and  for (A),  logically eliminated, and  especially for coals of lower  be  gradient  (B), data anomalously  function  Claw  history. Figure  and  gradient and, hence  does McEvoy  57 illustrates  excluding low not  that  values yield  which  eliminated.  a perfect  unit coals). This  the coalification gradient,  fit, is can  118  Q  =  K.G  where Q=heat flow, K= thermal conductivity, G = thermal gradient.  As  illustrated in an  earlier Chapter,  dominantly  of shales and  percentage  of sandstone  siltstones whereas and  and  a K for sandstone  calculate  the  value  conductivity  can  be  K given  approximated  Sshale 100 90 80 70 60 50 40 30 20 10 0  a uniformly  (30 C/km  the  units would  Currier  and  D illustrates  and  in the geothermal expected  to have  a possible  log-linear fit of  two  W . . . . . . . . . . .  by  Bustin  (1983,  to arrive  gradient  Thus  a geothermal  1984)  is utilized where  to  assuming  that  a bulk  components:  geothermal  gradients  the data  the Devils Claw  gradient somewhat in terms  functions rather than regressed  at a paleogeothermal  it is possible  / m ° Q 6 8 0 2 4 6 8 0 2 4 6  average  curves  gradient  a specific  lower  to the data.  data  which  McEvoy  and  for this data  burial  and than  of this relationship  one  to the  explains the distribution of reflectance values in the upper units. In order  two,  1.6  shale in the bulk lithologycan result in  units. Re-evaluating  or more  global  higher of  of rock  K ( 1 1 2 2 2 2 2 3 3 3 3  an increase of 20%  Jackson  suggests fitting two 63  flow  1981),  the  a linear combination  distributed heat  be  of  a much  composed  a K. for shale  (Gretener,  combinations  0  10° C/km  section has  material. Assuming  0 0 0 0 0 0 0 0 0 0  - 45 C/km),  increase of  McEvoy  by  of the stratigraphy is  upper  3.6 W/m°C  various  feandsi 0 1 2 3 4 5 6 7 8 9 1  Assuming  an  of  portion  the  conglomeratic  W/m°C  of  the lower  history  the  Figure  better Devils  Claw  approach  is modelled  for  used  119  various  geothermal  comparison  with  gradients  and  a theoretical  actual measured  coalification  gradient  is obtained  for  gradients.  Calculation of Maximum Depth of Burial  Bustin  (1984)  estimated  Currier unit, based and  an  on  3,500  published  m to be  the  depth  of burial for  thicknesses for the Sustut Group  estimate of the thickness of the eroded  method  maximum  Devils Claw  (Eisbacher,  units. An  is to project the regressed coalification curve(s) to an  Ro  the  1974)  alternate value of  0.20  m a x which  is the  Figure  64  1.  a single  coalification  2.  a lower  coalification gradient  m  an  starting reflectance  A & B illustrates  the For  assumed  underlying  2);  suggesting  includes  explained  elsewhere  0.2%  Ro  the  is based  1978: Ro  heat  be  (Middleton,  s q u a r e s , fit t o  McEvoy  in burial additional  and  Devils  the Tango Bustin,  zero  all data;  Claw  2,600  Creek  4600  1972).  and  units than  m (case  to 3,500  for  has  been  Formation  level is represented  (1972). Bustin (1984) and  entire range  be  time  attained  5,500 above  removed.  This  for reasons  that  are  1984)  maturity  additional  1) to  m of section  Ro  700 of  m of  based  on  1984). In these areas  a reflectance (1984)  the  both  an  Ro  et al., 1977:  with  Fig. 3; Bostick  the coalification gradient  i max  n  exponential  the coalification process. In basins equilibrium  of  reflectance  of 0.15%  burial, assuming  is short, thermal (Bustin  by  England  max material. Utilizing a zero level value  residence not  is from  unit which  level reflectance of 0.15%  and  flux may  of  Middleton  for the  Fig. 6; England, may  the  results in an  is rapid  range  6 and  woody  coalification gradient  derived  on  in immature  deposition  is a least  for the  an  a portion  that  maturity  study  which  0.2 the  (Chapter  m a x  Bowser  of  all or  assumption  observed  gradient  burial  assuming:  strata of the Devils Claw  The  utilize a zero  at shallow  extrapolation  approximately  the present uppermost thickness  an  a coal  units.  initial reflectance  (case  such  of  below  where  basement et al., 0.35%  linear rather than exponential (England, 1985). The final increments  of  120  60001 data from Devil's Claw, upper McEvoy  5500^ £ "». 'c 3  j»  500045004000 3500-  m=4J)5 x 10  3000 o a ~  m/cycte  R : .867  2500 2000  ® 1500  75  ' o.'e ' o ! 8  I  i  5—niTTOo  data from Jackson, Currier, lower McEvoy  fli=4£8x1(r  m/cycte  4  5  Rgmax  F I G U R E 64: 0.2% R o  max  Extrapolation  6  7 8 910  of coalification gradients to an assumed initial reflectance of  . The intersection  units assuming a pre-tectonic  corresponds to the maximum  depth of burial of the  peak of coalification, and using a log linear function  (B)  which is a best fit for all data and a log linear function (A) which is a best fit for the upper 800 m of exposed section,  to fit the data. m=slope of function  expressed by metres/magnitude change i n reflectance.  See  text for further  as discussion.  121 burial may  be  contemporaneous  foreland molasse attained  basin) which  for a portion  estimated  of  burial depth  equilibrium was extrapolated  the  would  with  depths  of  (as would  suggests that thermal Late  Cretaceous  thus  be  not reached. For  burial  deposition  a consequence  mand  expected  equilibrium may  sedimentary  the purposes  5,500  be  history.  of assuming  of  in a  prograding  not have  been  A decrease that  thermal  this study zero maturity  4,600  m are  thought  in  to be  level  reasonable  averages. Determination of Paleogeothermal Gradient and Paleotemperatures  It is generally on  agreed  the time- temperature  (Teichmuller  and  reaction can  be  that the level of  history which  Teichmuller, described  by  the  organic  organic  maturation  is directly  material has passed  1982). Karweil  (1956)  demonstrated  the first order  reaction kinetics of the  dependent  through  that the coalification Arrhenius  equation: K  = A exp  (-E/RT)  where E— activation energy, T— absolute temperature, A —frequencyfactor, K—reaction constant, R = universal gas constant.  From  this relationship Karweil  energy  of 8.4 kcals/mole  assume  temperature  relationship is still utilized, most an  a nomogram  for the entire range  duration of burial, maximum Karweils  constructed  of  that the level of organic  time-temperature  history of the strata (eg:  1982; Gretener,1981).The  by  the  maturation Lopatin,  is an 1971;  activation the Although  prefer methods  which  integration of the Waples,  1980;  in entire  Middleton,  Lopatin method (see Waples, 1980) assumes that. and  considers  duration  10° C  assumed  various processes involved  coalification increases exponentially with temperature each  an  graphical interpolation.  petrologists now  integral of the activation energies of  coalification and  on  the coalification process. Given  is derived coal  based  increment  of  calculate interval maturations. The  heating  and  the  total maturation  (TTI)  linearly with time. The of each  is the sum  increment of the  method to  interval  122 maturations: _ T T I  n m a x . A nmin  v  =  Z  n . T n ( r )  where nmin and nmax are the lowest and highest temperature intervals, number of temperature intervals, maturation  Bustin  illustrated that the  is given  Ro  from  logTTI  method  (modified  organic  metamorphism  an  exponential  and  the  +  Curtis (1982)  process  slow  and  time  presented  (1983)  a r e a fit a m o d e l  noted  where  function of temperature  that time by  temperature  the  been  subjected  75° C/km.  and  Price (1983)  and  Barker  that within of  (1983)  locally in excess the depth  value of  of  5 km  on  area  should  quoted have  from  a geothermal  as a global placed  rocks  solely  amongst  reasoning, the  coalificauon curves  would  of  Also, the  of  have  gradient  exposed  gradient  at  again  a strict correlation  been  within  is  are lost  a geothermal  average.  well, time  metamorphism  analysis of the  thus have  of  a relatively  rocks of the Currier  350° C and  As  rate and  kinectics described  on  Oleum  the rate  similar empirical  A cursory  would  in  that in the  the effects of time  approximately  400° C with  out  collected  indicate, based  the study  generally  pointed  level of organic  effect  a regional basis the Currier  is twice a burial  j'  to temperatures  On  temperatures which  observable  r a n c  data  rather than first order  no  important, factor  at a very rapid  that  whereas  has  to R°  vitrinite  is relatively unimportant.  reaction proceeds  Barker  that multiple order and  and  temperatures (<50°C)  the various sources of error. Price (1983), based suggested  TTI  0.5011  that the most  at very low  is extremely  is relatively unimportant.  logTTP  relationships  Gretener  (>130°C)  geothermal  relationship between  0.20647  Lopatin approach)  temperatures  young  +  the above  coalification is temperature.  high  of heating.  by:  = -0.10528  It is obvious  if the assumption is made that the  doubles for every 10° C increment  et al. (1985)  reflectance  and r=2,  n=the  of  to  80°  C/km.,  such  temperatures  Greenschist  facies  if  123 not the Albite Epidote  Hornfels  fades  of metamorphism  (Turner, 1981). In this  (Chapter 5) the stratigraphically deepest rocks examined (Jackson unit) are sub-greenschist completely Lopatin  grade.  and,  It is suggested  that the  until further experimental  (1971, Waples,  1980), Middleton  effect of time  work  proves  (1982) and  cannot  be  study of  disregarded  otherwise, that the approach  Gretener  and  Curtis (1982)  of  is  presently the more satisfactory. In this study, Lopatin's TTI  was  calculated and  the conversion of Ro  to max  TTI  (Bustin et al., 1985)  from  the field and  was  utilized. The  burial-uplift history utilized was  laboratory observations which  study. Briefly, the coal bearing Currier sequence ago  (Oxfordian)  Claw  and  was  progressively buried  unit approximately 100 Ma  have was  been  outlined elsewhere  deposited approximately  to the end rocks were  then uplifted; based  angular unconformable  relationship between  the Bowser  Lake  overlying Tango  Formation  occurred until approximately Brothers Peak  Formation  ago, the probable  (Campanian  the prograding  foreland basin. From  study  considered  area  day  to have  level of exposure. Due  most  of the temperature  organic not  are  matter.  necessary  the peak  As  the Maestrichtian onwards been  deal  timing  at a  constant  Based  on  of uplift has  of accuracy  to yield useful  of organic maturation and  to the initial deformation.  uplifted  hence  results. It has  the  rocks and  the  further burial  time  the  1985) as molasse  the rocks within rate to their method  constraints  already  been  the greatest temperature  was  the calculated relationship of Ro  rank of  in  the  present  to time  little effect on  in the  Ma  Devils  on  and  this  160.  of deposition for  to the insensitivity of the Lopatin  a great  for the model  time  to Maestrichtian; MacKenzie,  range, the  such,  Group  (Eisbacher, 1974a, 1981). Deposition  70 Ma  in  of deposition of the  ago. The  Creek  formulated  over of  the  uplift  illustrated reached  is that  prior  to depth,  it  max is suggested is between burial  that the depth 4,600-5,500  of the  Currier  m.  to which The  the Currier  burial model  unit to approximately  was  buried  incorporated 3,600  m  prior  here  in this part of the arbitrarily assumes  to the  minor  uplift  basin initial event  124 Assuming  an  Formation  in the  with  uplift of 500 study  its maximum  (Eisbacher,  area  65  from The  1 (burial  models  hence  Ro  the models  and  (Bustin, 1984;  and  presented  either 1,500  m or 2,500  eastern margin  of  m,  the basin  which of  Creek  is  consistent  1,500 m  m)  attempted  was  case  2 (burial to 5,500  varied the time  the amount  is considered  500  the curve  slopes for the  m.  The  defined by  absolute  temperature.  gradients of  (see Waples,  to represent the modelled  et al., 1985). The  as  influence of  the Lopatin method of  m)  which  n o t s i g n i f i c a n t l yd i f f e r e n t °  during burial for geothermal  straight line portion  unit  intervals of burial  of initial uplift by  reached was, however,  as predicted by  My  and  for the Currier  here, suggesting the overwhelming  66. The  Bustin  possible burial models  in coal rank  50°C/km  uplift event at 90  Case  the  were  which  max  illustrated in Figure  gradients  be  to 4,600  which  exponential change  40°C/km  near  represents two  factors as large as 20 Ma and  would  thickness  to case  above. Other  TTI  the resultant estimated thickness of the Tango  1974).  Figure correspond  m,  various  following  30°/km,  1980) are the  minor  coalification gradient assumed  geothermal  are:  1  slope  Case  2  slope  30°/km  8,260 m/cycle  30°/km  5,440 m/cycle  40°/km  4,680 m/cycle  40°/km  4,480 m/cycle  50°/km  4,400 m/cycle  50°/km  4,390 m/cycle  Where cycle refers to an order of magnitude increase in reflectance.  For  case  for case  1 the observed 2 a slope  data  of 4,950  suggest m/log  a slope cycle  was  of approximately obtained,  ln  4,580  either case  m/cycle the  whereas 50°C/km  125  Time  170 160  1  150 140 '  1  130 120 110 L  '  "  100 1  90  (My)  80  1 - — - i  70 1  60 i_  50 i  40 I  30 1  20 I  10  0  L  •  -500 •1000 -1500 dep^  -2000  3" -2500 -3000 -3500 -4000 -4500 burial to 4 6 0 0 m burial to 5 5 0 0 m  -5000 _.  -5500 •6000  HGTJRE 65: Burial history for the lowest Currier unit, assuming burial to 4600 metres (solid line) and 5500 metres (dotted line). See text for discussion.  0.4  0.6 0.8 1  S 6 7 8 9 ' '' T 0 -500 -1000 -1500 -2000  O CD  -2500 -3000  £  -3500 -4000 -4500 -5000 •5500 R max (%)  -6000  0  0.2  B  0.4 _i  0.6 0.8 1 1—i—i—i i i  R max (%) 0  FIGURE 66: Plot of reflectance versus depth of burial for modelled burial histories involving A: burial to 4600 metres and B: burial to 5500 metres, the straight line portion of the curves following minor uplift are represetative of the coalification gradients. Note that following final uplift there is very" little change in Ro max suggesting the overwhelming importance of temperature in the coalification process.  127 geothermal model  gradient model  may  is significantiy higher  relevant  modelled  be  ruled out in that the maximum  than  measured  coalification gradients  paleo-geothermal  gradient of 30°C/km  from  Lake  the Bowser  Group  in this study. Figure  with  the  calculated  to 40°C/km  values  Ro  attained in  67 compares and  illustrates that  these gradients to  the maximum  rocks were  exposed  and  that the rocks spent in any  temperature  range  (Figure  rocks of the lowermost approximately  180-230°  for a period  of  As  subtraction of result in an  process  that  15  noted  uppermost  and  these 80  the assumption Ro  several hundred  metres  from  variation  As  no  well, the change  It is obvious,  is necessary  of  however,  to yield more  to which  units were  remained  the  given temperature  exposed  at temperatures  to  is  above  150°  C  Ma.  below  estimated  Jackson  rocks  disequilibrium  burial temperature. negligible.  and  between  previously  level or thermal  C  temperature  analysis suggests that the maximum  Currier and  a  be  representative, it is thus possible to determine  68). Such  the  is consistent with coal reflectances  stratigraphy. Assuming  the duration of time  the  that  of either a 0.15% =  max  0.35%  zero  variations  in the  maximum  10° C  understanding  accurate estimates of  or  burial depth. These predicted  in calculated paleogeothermal a better  maturation  max results in the addition  the estimated  greater than  Ro  of  the  gradient  is  coalification  paleotemperatures.  128  % Romax  FIGURE 67: Reflectance (Ro ) versus depth (metres) relationships for calculated max coalification gradients (solid lines) from the lower part of the stratigraphy (B arrow) and the upper part of the stratigraphy (A arrow) and modelled coalification gradients for burial to 4600 metres depth (dashed line) and 5500 metres depth (dashed and dotted lines) for geothermal gradients of 30° C/km and 40° C/km. It is apparent that the paleo-geothermal gradient in the area ranged between 30° C/km and 40° C/km.  129  170  160 150 140 130 120 110 100 9 0 —i i i 1 1 i i  i  80  i  70 l  60 i  50 i  40 1  30 •  20 •  10 •  0  250  burial to 4 6 0 0 m Time 170  160 -|  150 140 130 120 110 100 9 0 I I I I l l l  •300  (Ma) 80 l  70 I  60 I  50 I  40 l  30 '  20 1  10 •  0 \Q  300 Time  (Ma>  FIGURE 68: Time-temperature history for the lower Currier unit assuming the determined paleo-geothermal gradient range of 30° C/km  to 40° C/km  for burial to  4600 metres and 5500 metres. Stippled area represents the range in temperatures experienced by the lower Currier unit during burial and uplift.  5 . D I A G E N E S I S /  M E T A M O R P H I S M  O F  U P P E R  B O W S E R  I . A K F ,  G R O U P  SEDIMENTS An of  analysis of diagenesis and  the Groundhog  Coalfield by  low  means  stratigraphically representative set of evaluate  the  boundary  results with area  conditions  the conclusions  as well  as from  other  of petrologic and samples  active  drawn  grade metamorphism  was  during  from  in the northern  x-ray  analysis of  carried out in order  burial  and  uplift, A  for a comparison  of  a  to  further  comparison  coalification studies (Chapter  basins, allows  portion  of  4) in the  organic  and  these study  inorganic  paleogeoth ermometry.  5 . 1 P R E V I O U S  S T U D I E S  O F  Prior to this study the degree has  been  poorly  documented.  M E T A M O R P H I S M  I N  of metamorphism Malloch  and  connected  with  area  is not  Canadian (Monger  (1914, p. 191) reported  penetrative cleavage, the A  regional  term  compilation  Cordillera indicates rocks exposed Hutchison,  the Intermontane  statement, though post-Bathonian metamorphic rocks from  Lake  perhaps sediments  1971) Tipper  these "schists" are  metamorphic  Richards  exposed  premature,  is an  conducted  t h e s t r a t i g r a p h i c a l l yh i g h e r T a n g o  130  Creek  are  the  (Borradaille,  facies present  Basin  grade  in  the  unmetamorphosed  metamorphism.  rocks This  accurate generalization for  in the study area. The  alteration in the region was  in  (1976) state that Mesozoic  Belt all display sub-greenschist somewhat  rocks  "schistose" as generally used of  rocks  (Hazelton study) have been stones have in some cases them a slightly schistose  in the Bowser  and  Group  that:  (1950) suggest that the areas characterized by  applicable.  and  Bowser  B A S I N  lines of thrust faults that traverse the region. Although  often have  1982)  within  Latour  B O W S E R  of Upper  In places the black shales of this foimation Formation-equivalent to Jackson unit in this metamorphosed into schist and even the sand developed enough micaceous material to give look. Buckham  T H E  by and  only Read  the  detailed examination and  Eisbacher  Brothers Peak  (1974)  Formations  of on of  131 the Sustut Basin  immediately  east of the study  zeolitization, albitization and A  recent  compilation  Cordillera has an  index  The by  of regional  attempted  of metamorphic  5 . 2 T H I S  S T U D Y .  clay mineral  area. These  metamorphic  fades  grade (P.B. Read,  distributions in the  oral comm.,  (1961) where  a concomitant  undergone  of mica-defined  equilibrium  approach  towards  important  factor in determining  PIT „ = H 2 0  P  in rocks  published  reaction curves (e.g., Zen  grade  , it is possible t o t a l  to predict  of zeolite fades, and  1969; Perry and  and  Hower,  1976;  function  of  Eberl,  burial depth  dehydration. non-expandable  In general  1974) and area  as  T T  _  <  assemblages  Hower,  1978)  the  1970) and clay mineral  (i.e., pressure this predicted  layers at the expense  and  of  smectites.  unit)  rocks should  be  T T  _  =  69 should  present  the coalification  model  reactions  are  are anticipated. Muffler  data (e.g., Eberl  expected  in response  as  P„ ., < P fluid total  higher grade  are  of on  4). Figure  1967; Burst, 1969;  assemblages  variation favors the  based  (Jackson  limited experimental  temperature)  scenario  calculated  of dehydration  Hower,  an most  a simple  the  without  is  a s s e m b l a g e 6s  P_ ., or P fluid H20  of even  and  defined  is the  (Chapter  units studied  unit, assuming  empirical observations (e.g.. Maxwell  White,  that there  taking  stable  of time, the temperatures  considerably (Liou, 1971) and  and  by  that zeolite grade  p r o p o s e d i s c o r r e c tI f e i t h e r c o n d i t i o n s P H20  on  and  in the study  the deepest  as  degree of metamorphism  anticipated  in the stratigraphic pile as the McEvoy  Based  some  Thompson,  ideal conditions  existed for protracted periods  "burial metamorphism"  1974)  the  and  illustrates that under  lowered  Basin  1985).  schistosity. Assuming  (Fyfe,  history of sediments  high  Canadian  the Bowser  of this grade, that temperature  temperature-pressure  display assemblages  sediments.  S T A T E M E N T  rocks have  development  extensive  tuffaceous  to incorporate coal reflectance data from  G E N E R A L  describe  authigenesis in tuffs and  rocks studied fit well the general category of Coombs  authors  to  to vary progressive  stability of clays  with  as  a  132  100  2 0 0  3 0 0  4 0 0  5 0 0  6 0 0  T E M P E R A T U R E ° C  H G U R E 69: P-T space for low-grade metamorphism with relevant reactions plotted (after Zen and Thompson, 1974). Note that the assumed burial history for Bowser Basin sediments places them within the laumontite stability field at at slightly higher grade if pHjCXp  .  pH 0=Tp^^ 2  and  133 5 . 2 . 1P E T R O L O G I C In thin  O B S E R V A T I O N S  section  identifiable authigenic  minerals  include:  albite,  calcite-dolomite- ankerite, chlorite, mica, unclassified clay minerals, and assemblage +  calcite (or  water  is considered  assemblage Ghent,  in a C0  1979).  Coombs  Albite  a common  temperatures common  as  a metasomatic  minerals  spaces  are  it has  predated  stage  and  been  representative  been  by  means  a calcic  zeolitic  1961;  Ghent  and  1972)  burial and  quartz  Miller,  calcic plagioclase  is also  high  grade  1974;  (e.g., thought  diagenetic  described, is apparently  subjected to low  in thin section occur  quite  metamorphic  rocks, chlorite and  chert grains (Figure  and  Relationships syn-tectonic  3). Examination  noted  section  ed for a-n Michel L Assuming Ab100 for  had  commonly  occur  as overgrowths  aid  oral comm.,  ormal determ evy technique that the com a multimodal  of  the  that is  rare  the and was  of plagioclase grains the  as  mica  as a cement  71). Although  occurs  with  open  been  as a vein filler however,  of refractive oils (P. B. Read  atedgrains which allow The application of the from +14° to +20°. of Ab^o and Ab96 -  which  in  in thin section suggest  (Figure  cement  oriented  70). In thin section  of a number  stratigraphic  micas  in origin. Quartz  that quartz  as randomly  solution effects and  directions in rocks  clay pore fillers. Quartz  of a  for  to deep  identified in several samples.  of  assemblage  relatively free of pressure  indeterminate. pre-  +  1969).  quartz and  later (Chapter  Where loc yielded Ab100 which ranged a compostion 2  on  is both  precipitation  sections 2  are  mineral)  feldspars (Middleton,  recognized  is indefinite it appears  presumably thin  White,  micas  which  generally  precipitation  paragenesis  and  clay  total assemblage  rocks have  The  other  (Zen,  subjected  solution. In cleaved  phyllosilicate beards  although  and  system  as crystallites parallel to cleavage  subject to pressure  polytypes  stable  potash  in sediments  in other areas where  (or  alteration of more  or perthite and  mineral  crystallites in rocks  kaolinite  equivalent  (Blatt. et. al, 1980); The  Clay  clay  the  +  rich, fluid dominated  conditions (e.g., Muffler  pore  carbonate)  to be  2  it al, 1959)  to be  other  quartz.  from  25  universal  1985) determined  that  ination techniques always yielded extinction angles positon is unimodal yields composition.  FIGURE  70: Clay  detrital chert grain.  grains.  minerals growing C=chert,  as strain shadows  pss=pressure  solution  or seam,  "beards" (tip of  arrows)  A = ankeritized  dolomite  HGURE grained  71: SEM  photograph  litharenite from  of euhedral quartz overgrowths (Q)  the Currier  unit.  in a  medium  136 c o m p o s i t i o n s r a n g e f r o m a p p r o x i m a t e l y Abioo t o n o l e s s t h a n A b investigated  albite occurs  original compostion has  grown  from  characterized  as a replacement  (Figure  by  euhedral  investigated. Carbonate  (with  the exception  extent from  only  replacement  of  by  cleavage  specimen  carbonate  suggesting  (Figure  and  CCy"~  The  between  most  on the  is common  73  A,  B  &  x-ray  C).  and  to increase  ankerite with  less  carbonate  rich  fluids entered  towards  formed  cement  was  of other authigenic minerals  as  a  has  73  C). In  a carbonate-filled  the rock  minerals  complete identified:  existing grains (Figure  appears  in  phases  analysis indicate that ankerite  74). In several samples  feature  It varies  Carbonate  dolomite  a  in all  late replacement  one  vein  via fracture systems. It is  multi-stage, syn-  of cross-cutting relationships of other minerals  reliable identification of clay minerals (Weaver,  the number  1958). In that the  was  with  pre-  of tetrahedral and  for 3 layers  peak  corresponds  (2:1  clays), and  14A  is by  "thickness"  to  to cleavage  syn-tectonic.  the use  of  d-spacings  for 4  layers  of  the clay  octahedral layers and  layers) results in characteristic x-ray  clays), 10A which  as a  and  M I N E R A L O G Y  diffraction methods (dependent  carbonate  which  is  lamellae  of existing feldspar grains to almost  that precipitation of carbonate  selvages suggests that growth  unknown  and  vein-filling carbonate).  analysis are dominantly  replacement  post-tectonic. Absence  5 . 2 . 2C L A Y  described  carbonates  albite twin  exclusively  selvages as well as replaced  that Ca"  suggested  developed  almost  (Figure  section and  of dolomite  overgrown  present  x-ray  calcite. Thin  replacement  occurs  slight replacement  all grains  and  of albite grains by  of the previously  thin section and  abundant  thus  replacement  of  as interstitialmaterial. Albite  greywackes  crystal outlines, well  . In the rocks  of relict plagioclase  less commonly,  solution is present in both  lack of inclusions. Later samples  72) and,  product  9 4  (2:1:1  to the true layer thickness, is generally  minerals  the  of 7A  x-ray  material  for 2 layers clays). The  used  (1:1  (001)  for identification  137  FIGURE and  72:  as a pore  Jackson  unit  Albite  (A)  as a replacement  filler in a arenaceous (2).  of  skeletal  detrital plagioclase lime  rudstone  from  (1) in a the  litharenite uppermost  138  FIGURE 73: Various stages of carbonate replacement A. feldspar grain with minor replacement by carbonate (c) along crystal cleavage surfaces. B. extensive replacement of plagioclase feldspar (P) grains by dolomite (D). C. ubiquitous replacement of grains and masking of pressure solution surfaces by late carbonate precipitation. Q=quartz, RF=rock fragment, C=chert  138  139  FIGURE  74: PhotomiCTOgraph illustrating replacementof detrital plagioclase feldspar by  unidentified low  relief carbonate  (c; calcite or  dolomite)  and  ankeritization of pre-existing  carbonate  grains is indicated  Various  stages of  change  in relief and  darkening  of  the  mineral.  high  relief ankerite by  (a). a  140 purposes  (Weaver,  ibid). Other  further information Srodon,  peaks, are however,  concerning clay crystallography (Dunoyer  de  in order  Segonazac,  to  obtain  1970;  1984). Progressive  diagenesis and  metamorphism  of authigenic  illite, in that continual  rearrangement  of  regularity of  Kubler  (1964)  (001) peak  height  at 10A  layer clays are  a measurement  the  of crystallites and by  which  (1961) sharpness  ratio is defined  as the ratio of  metamorphism  as  this  ratio and  flank at 10.5A. The  progressive  transformed  of  structural  applied methods  to the intensity of the peak  theoretically increase with  of mixed requires  commonly  sharpness  and  dimension  quantified are the Weaver  crystallinity index. The  this ratio should amounts  be  increase in "crystallinity"  K'-fixation  increase in the  the layers (Kisch, 1983). Two  of crystallinity can  results in an  dehydration,  ions results in an  degree  index  often compared  the  the  value  of  increasing  to discrete illite. Kubler's crystallinity  half peak  height  width  of  the  (001) illite  r e f l e c t i o n , o r i g i n a l l y m e a s u r e d a n d r e p o r t e d i n m i l l i m e t r e s a n d m o r e r e c e n t Kubler  (1968) noted  that measurements  of the sharpness  w i t h i nt h e d i a g e n e t i c z o n e ( c r y s t a l l i n i t y i n d e x > whereas  the crystallinity index A  (002)  comparison  illite peak  illite octahedral I(002)/I(001)  of the  was  preferable  intensity of  is considered  the  to reflect the  layer (Esquevin,  Al  an  + + +  Esquevin's  on  contention, based  is illite crystallinity a valid  cluster of points  on  de  to the  Segonzac,  of metamorphic  a plot of illite crystallinity versus  intensity of  to (Fe++  +  Mg+")  in the  ratio  occurs  during  1970;  Kisch,  empirical observations, that only indicator  accurate  ; sharpness ratio< 2.3)  increase  reflects the increasing fixation of Al"1"""which to illite (Dunoyer  most  grades.  illite peak  ratio of  1969). Presumably,  alteration of montmorillonite  0.25  0.4 A2 6  al higher (001)  ratio were  when  the  the  in  the  of progressive  1983). It  I(002)/I(001)  grade.  Comparison  I(002)/I(001)  with  of the  was >  the predicted  . I t i s n o w a g r e e dt h a tb y r e p o r t i n g i l l i t e c r y s t a l l i n i t y i n t e r m so f A 2 9 r o c k s f r o m different areas can be compared without the errors which occur due to different analytic conditions (Ogunyomi et al., 1981; Islam et al., 1982; Kisch, 1983; Srodon, 1984). 3  141 clustering for illites subjected de  Segonzac,  1970;  of metamorphic  p  318)  to varying  degrees  is commonly  used  of post-depostional  as  a  analytic  alteration  tool in the  (Dunoyer  determination  grade.  X-ray  identification of Clay  Species  Methods Clay  mineral  Phillips X-ray (generally  assemblages  generator.  mudstones)  A  were  were  representative crushed  and  time (based on StokesLaw) the <2 mounts were made. The contamination some  by  <2  larger  contamination of peak  detrital micas  metamorphism  due  widths to mica  with  a 0.5 M  KG  (centrifuge technique a  desiccator  heated and 1.  at 550° C 7A  CuK  settled in distilled water. Mm  (Kisch <2  1980,  ym  a  lithology  After  1983). Although  8 hours  settling  to achieve  in Jackson,  of  2.5 hours  it is likely  size fraction (Srodon,  area. Observations  solution  for a period  utilizing  fraction was removed from which oriented  were  analytical conditions applied  on  the grade  of controlled  ion  were  clays. Samples  to discriminate  in this study  for  untreated clays, clays  clays which  layered  that  of this size fraction  made  1956), and  in order  1984),  late diagenesis/low  conditions  identification of expandable  chlorite. The  of similar  recrystallization validates the use  as outlined  to allow  diffractometry  samples  of all size fractions during  qualitative analysis in the study treated  suite of  x-ray  fraction is commonly utilized to avoid the  um  still exists at the  convergence  identified by  saturation glycolated  were between  in  then kaolinite  were:  radiation,Ni filter a  2.  Time constant =  3.  Chart  4.  S c a n s p e e d= 2 °  5.  Range  6 . The  speed  =  =  2xl0  2  cm/minute  26 2  1 - 2s e c o n d s  -  /minute 2xl0  3  S c a nr a n g e = 3 ° - 3 0 ° 2 6 analysis reported here involved qualitative identification of mineral  phases  present  142 in each the  sample  and  measurement  of illitization of expandable  clays  in  samples.  Results  of  Analyses  Table  I lists the primary  their alterations under the  of the degree  basal  conditions  and mixed  following chlorite and layers, or  12A  - 20A  treated with  t o 2 0 ° 2 6  a n d I I i n t h e r a n g e3 °  the assemblage  75)  using  Figure  glycolated sample  76  expandable  which  exhibit enhanced  peak  kaolinite, illite, chlorite, and  of  illustrated by  (back  from  no  various  separation  Tables  the change  mixed  appearance  layer clays throughout  demonstrates  versus the Ro  pocket)  I  a r e g i v e ni n T a b l e I I I .  of phases.  presence  illite  case of illitic  75  the relationships  the stratigraphic section with  The  pure  ions (Kisch, 1980) in the interlayers.  4  clays is stable throughout 4  In  will  than  layers. Figure  KC1  samples.  in the  and  II illustrates  of smectite in them  layers collapse either to 10A  Figure  layer clays  heating. Table  to 550° C all clays other  due to fixationof K  identified (i.e., see  In general  proportions  in the case of chloritic mixed of the samples  mixed  phyllosilicates in oriented  layer clays with heating  the various  glycolation and  non-swelling  illite/chlorite mixed  in the range 10A clay phases  reflections of  ethylene  glycolation. Upon  illustratesthat many  The  of  reflections for various  general, smectites or mixed expand  basal  or  layered disappearance  the succession is  in 20  upon  further  heating a  of associated coaly material (shown  to be  roughly  illustrate the greatest change  contain  m a x equivalent  to depth  in Chapter  the greatest proportion  of  4); samples  expandable  which  layer clays. Analysis  of x-ray  scans  in  the  i n t e r v a l 2 0 ° - 3 0 ° 2 6  d e m o n s t r a t e s t h a t w h i t e m i c a ( p a r a g o n i t e a n d / o r m  occurs  (exception  in almost  in LRS1,  LRS2,  all samples LRS3,  CRS14  reflection of the white mica  and  CRS1)  1228  component(s)  and  a mixed  layer  (Figure 77). Although  paragonite/muscovite  analysis of the  suggested the non-muscovite  member  samples 1228, 1231 and 1232 are from the Devils Claw unit,samples CRS14, CRS10, 1235 and 1237 are from the McEvoy unit, samples 1239, CRS6, LRS1, and LRS3 are from the Currier unit, sample CRS1 if from the Jackson unit  (006) was  4  LRS2  143  H G U R E 76: Change in peak width upon glycolation of a KC1 saturated specimen. The two samples with a large increase in peak width upon glycolation are also samples with paragonite/muscovite mixed layers as well as mixed layers.  paragomte/Na-mondnorillinite  144  28 28 24 2S i—i—i—i—i—i—i—l  30  CRS 1 4  CRS10  1235  1239  CRS6  LRS2  LRS 1  1  I  30  FIGURE paragonite  77:  x-ray  (PA).  The  paragonite/muscovite  I  28  Ws I—1—I—1  26  24  CRS 1 1  «~  *  e  d i f f r a c t o g r a m t r a c e s f o r ( 0 0 6 ) r e f l e c t i o n so f m u s c o v i t e ( M U ) broad  spread  mixed  layers.  between  3.35  A and  3.21  A  represents  and  145  T a b l e I  D-SPACINGS  Mineral 14A M M-V M-C V CH-V CH M-V M-CH 12A M 1-M 1-V 1-CH 1-12A M  D-SPACINGS  mineral  kaolinite pyrophyllite muscovite , paragonite margarite chlorite  Table  III  Sample  1228: 1231: 1232: CRS14: CRS10: 1235: 1237: 1239: CRS6: LRS1: LRS2: LRS3: CRS1:  Glycolated 18 15.8 16 14 14 14 15.8 16 18 13.8 12 12 13.8 10  Normal 14 14 14 14 14 14 14 12.5 12.5 12 12 12 11 10  1  Table II  FOR CLAY MINERALS ( a f t e r Milliot,1964)  OF  PHYLLOSILICATES XDD2)  IQCLD  7.15-7.2 9.2 10 9.65 9.65  14.1-14.3  K , I ,C H , M , I - M , C - V K , 1 , C H , I - M , C - V K , C H , J.-M(?)  I, CH, I ,C H , I ,C H , I ,C H , I ,C H , I, CH, I ,C H , I ( ? ) ,  K,  1, I-M,  I-M M, 1-M(?) M, I-M I-M(?) 1-M I-M M ( ? ) , I-V C H , I-V, 1 - M  I , C H , I-V(?)  M-C  4.68-4.72  (0010)  1.84 2.01 1.93 1.91  2.82-2.86  C L A Y M I N E R A L  Clay M i n e r a l Assemblage  K, K, K, K, K, K, K, K ,  2.38 3.07 3.35 3.21 3.20  7.06-7.10  I D E N T I F I C A T I O N O F  (after Frey, 1978) {006}  3.57 4.6 5.03 4.82 4.82  Heated 10 10 12 10 12 14 10 12 10 10 10 12 10 10  %Ro  2.10 2.33 2.35 2.60 2.78 2.97 3.32 3.52 3.96 4.02 4.13 4.14 4.60  Where K= kaolinite, 1= illite, CH— chlorite, M' = montmorillonite•, J-M — illite/montmorillonite mixed layer, 1-V— illile/vermiculite mixed layer, C-V= chlorite/vermiculite mixed layer, M-C= montmorillonite/'chlorite mixed  layer.  146 paragonite  and  not  separate the two random  mounts  margarite, except  being  measured  and  (1978)  indicated  that it is often impossible  orders of reflection (0010). Diffractograms  suite generally resulted in very weak  identifiable as a  weak  x-ray  peak  high  to for  order  at 1.93A  in only  one  ratio  were  (LRS1). In this study  (Table  at higher  of the sample  reflections; paragonite sample  Frey  and IV).  both  recorded  Figure  the  illite (001)  for normal,  78  A  glycolated samples  &  B  KC1  crystallinity index saturated, and  illustrates  to Ro  the  of  nearby  &  crystallinity  samples  index  units. Although  max b e a g e n e r a l d e c r e a s e i n A 2 6 w i t h i n c r e a s i n g .R o relationship is not clear. Figure 79 A in KC1 and glycolatedsamples to Ro  sharpness  glycolated, oriented  relationship  of coal from  and  of  there appears  what in the 1983)  in the should  be  Kubler has  evaluation  max illustrates a similar plot of sharpness ratio . In the glycolatedsamples there appears to B  max  (1927)  index.  with  a pattern  is developed  increasing depth  It is possible  the assignment grade  purposes,  (1964; of  expected  sample  and  which  indeed  that a combination limited data  of  is the reverse  1967)  rocks  errors  (Kubler,  available makes  any  of various arbitrary diagenelic/metamorphic  is often  futile (Kisch,  to classify shales from suggested  "anchimetamorphism"  crystallinity index. These  areas:  of  the reverse of that  1983),  it is instructive,  the study area  based  on  to describe  limits have  or disappearance  one  the revival of the term first applied by this zone.  Arbitrarily  Kubler  lower and upper limit to the anchimetamorphic zone of 0.25 A2 9  appearance  0.7)  noted  1968;  Kisch,  further  impossible.  pre-greenschist  Kubler  treated  resulted in this pattern. The  Though  comparison  KC1  to  (i.e.,increasing depth) the. exact  be no significant pattern developed (values ranging from approximately1.7 whereas  KC1  varied from  of mineral  assemblages  author  to author  present  divisions to for such  scheme.  Harrassowitz assigned  a  and 0.4 A28 illite based  on  in their respective  the study  147  2  1-5  x: S i  1.3-  £  1.1  I  co CO  » 0.9  CD  H  0.7 0.5  0.3  B  m  :'Kcl & etelene.glycol' saturated  0.1 %Ro max  -I 3  1  1  1  4  5  6  FIGURE 78: Plot of illite crystallinity index (Kubler index) versus the log of vitrinite reflectance. Stippled band indicates the anchimetamorphic zone as defined originally by Kubler (1964) and refined by Ogunyomi et al. (1980). See text for discussion.  148  F I G U R E 79: Plot of illite crystallinity index (Weaver index) versus the log of vitrinite reflectance. See text for discussion.  149 Table  IV  X - R A Y  S P # 1228 1231 1235 1237 1239 L R S 3 L R S 2 LRS1 CRS 14 C R S 1 0 C R S 6 C R S 1  A N A L Y S I S  O F  C I N 0.75  2/1N 0.57  0.60 0.45 0.30 0.70 1.35 1.45 0.80 0.30  0.90 0.90 0.60 0.60 0.69 0.75 1.00 1.00  0.70  0.71  C I K 1.00 0.90 0.65 0.60 0.70 0.70 0.90 0.90 0.80 0.60 0.65 0.60  ILLITE 2/1K 0.03 0.38 0.30 0.30 0.50 0.23 0.15 0.15 0.25  C I G 0.85 0.60 0.60 0.65 0.60 0.60 1.50 1.40 0.75  2 / 1 G 0.36 0.30 0.60 0.36 0.55 0.42 0.40 0.50 0.40  0.28 0.40  0.45 0.75  0.54 0.25  R o % 2.10 .2.33 2.97 3.32 3.52 4.13 4.14 4.02 2.60 2.78 3.96 4.60  where SP#=sample number; CIN = Kubler Index for untreated sample; 2/1N = 1002/1001 for untreated sample; CIK = Kubler Index for KC1 treated sample; 2/1K = 1002/1001 for KC1 treated sample; CIG = Kubler Index for glycolated sample; 2/1G = 1002/1001 for glycolated sample; and Ro%=maximum reflectance of associated vitrinite.  Author  ranee  Kubler  (1967)  Frey  (1970)  Frey  et al.  Dunoyer  0.30 - 0.56  et al.  Sagon  &  D.de  Kisch  (1978,  Islam  0.56 - 0.30  Segonzac  Chennaux  Ogunyomi  (1969)  Segonzac  0 . 4 •- 0 . 6 4 (1972)  0.21 - 0.38 (1980)  0.23 - 0.42  (1982) large  0.24 - 0.43  the  at length  later, utilization of a  al (1980)  0.27 - 0.32  1980)  Although  et  0.41 - 0 . 6 4  (1970)  et al.  et al.  index  0.25 -0.4  (1980)  de  in Kubler  and  "anchimetamorphic"  variability in these  Mam and  in crystallinityvalues and  boundary  et. al (1982) "anchizone" do  values  is quite  important  similar to that of  Kubler  is useful for comparative as will be  not imply  used  and  (1967),  purposes. The  in this study  specific metamorphic  will be  thus  boundary  define  discussed Ogunyomi terms a  conditions.  range As  150 can  be  seen  from  Figure  anchimetamorphism al. (1980) and  5.3  and  80  all samples  from  the study area  occur  in a range  categorized  by  fall above  Kubler  Islam et al. (1982) as late diagenetic (0.42 -  the zone  of  (1967), Ogunyomi  0.72 A20  et  ).  DISCUSSION  The  increasing attention that has  and/or  early metamorphism  metamorphic to define and  indicators with facies or  Kubler  focused  led many  on  rocks subjected to late diagenesis  authors to attempt  illite crystallinity indices and  subdivisions  the attainment  1979;  has  been  for the zone  which  of greenschist metamorphic  et al., 1979). Coombs  (1961, p. 214)  mineral  spans  grade  to correlate organic assemblages  in  the interval between  (e.g., Kisch,  1974;  order burial  Herroux  et al.,  states:  Certainly any model of the metamorphic process must make provision for all changes accompanying rise of temperature and pressure following burial, as well as subsequent events which have left their impact on the mineralogy of the rock. A  comparison  of  vitrinite reflectance  paragenesis measured from  in the Groundhog  other areas should  thus be  area during metamorphism  (1971)  Coalfield samples  defined  and  the  mineral  with similar  comparisons  useful in delineating conditions in the  of the sedimentary  5 . 3 . 1 I L L I T E C R Y S T A L L I N I T Y Kisch  data, crystallinity index  A N D  the lower  sequence.  C O A L and  Groundhog  upper  R A N K boundaries  corresponding  to  Kubler's  anchizone as being >2.5% Ro , and <5.0% Ro , respectively. Frey et al. (1980) rand rand based on the definition that the beginning of the anchizone corresponds with the wet gas deadline, incorporated values of 4.0% of  this zone.  Ogunyomi  b o u n d a r i e s o f 2 . 8 %Table shales  used  IV  et al. (1980)  Ro  and  3 . 8 %a n d 2 . 7 %-  and  Ro  max Islam et al. (1982) 5 . 0 %R o max  illustrates that for coal samples  for illite crystallinity index  5.0%  from  determinations,  to define the limits  max arbitrarily  placed  , r e s p e c t i v e l y , o n t h e a n c h i z o n e . the study that almost  area  adjacent  all samples  to fall well  151  %Rorhax  FIGURE 80: Correspondence between illite crystallinity index (Kubler index) versus reflectance of the indicated authors and that noted in this study. Stippled band indicates the anchimetamorphic zone as defined originally by Kubler (1964) and refined by Ounyomi et al. (1980). See text for further discussion. Star represents the crystallinity of a synthetic muscovite measured on the. diffractometer used in this study.  152 within  the anchizonal  that noted  limits as defined  for crystallinity index  above.  where  few  Figure  a plot of reflectance  crystallinity index  1980;  Ogunyomi  selected data  not  Groundhog  from  index  et al., 1981;  Lake  value than  review were  in any  with  is also  Figure  81  illustrates an  Kubler  illite crystallinity index)  associated  Esquevin  plot with  suggests  that, based  aluminum  fixation  undergone  strong  inclusion the were (1983)  for a  Frey  with  Esquevin  Kisch  (1983)  et al., 1980;  carbonaceous whereas  on  the crystallinity index  in the octahedral  on  A2 0  ). Assuming  on  they  are  value  the  literature  as forming  crystallinity (Zingg  de  a  perhaps  coals  related to the  illite (002)/(001) Comparison  Segonzac  trend towards  layer, the rocks may  be  classified as  1976). versus  of  (1970, p.  the  "late  from  et al.,  values and  ( >  0.56  temperatures  between  200° C these  coalification temperatures  homogenization  that in general A2 0  the  318) increasing having  270° C  temperatures (Chapter  below  obtained  from  200° C  characterized  less than  temperatures  (0.30-0.56 A2#  generally and  temperatures  temperatures  ) whereas  characteristic of the anchizone  ) and  the  diagenetic recrystallization.  zone  A2 0  from  units, anthracite grade  glycolated samples.  the predicted trends of Dunoyer  studies, indicated  indicated  and  Kisch,  lack of correlation is  plot (i.e., intensity of  for KC1  samples  states that, based  illites of anchizonal (1969)  succintly via  vitrinite reflectance  studies cited. This  American  more  the glycolated given  classified as  to a significantly lower crystallinity  in certain areas  et al. (1980), based  diagenetic  be  in others. In certain areas graphite, documented  anthracite,  Frey  that  elsewhere.  "anchizone"  could  from  and  correspond  of the other  Australian and  related to the  for data  et al., 1982  rocks  relationships  of European,  diagenetic" zone  Group  samples  illustrates these comparisons  suite. It is apparent  Bowser  at odds  Islam  relationship contrasts significantly to  if any  falling within the anchizone. versus  80  This  between  ). Similarily, Islam and  200° C  for  the  diagenetic  for the anchimetamorphic  are representative  4), the Currier  200° C  then, based  unit should  have  zone on been  zone  fluid  and  270°  C  Hesse ( >  (0.24 -  0.43 0.43  the analysis exposed  of to  153  1.6-,  16 .-1 1.4<D  w 1.2-1 .e  i 1.0H 0.8-  '5  0.6-  2. 0.4-5 0.2-  ethelene glycol saturated i  i  .2  i  I  .4  i  l  I  .8 illite ( 002/001 ) : Al  I  I  1  1.0 /Fe & Mg  1—  12  - I  1.6  FIGURE 81: Plot of illite crystallinity index (Kubler index) versus the ratio of intensity of the illite (002) and (001) peaks based on a technique originated by Esquevin (1967) to illustrate the ratio of A l + " to Fe^and Mg~ in the octahedral site. See text for further discussion.  154 temperatures  consistent with  should  have  thus  a lower  actually observed  that defined Kubler  if equilibrium  for the  index was  value  energy  for  this transformation  their study, a 20%  a high  attained. Experimental  sample  expandable  Comparison  of  100%  in a short  expandable  time  at low  a. kinetic standpoint, coal  low  percentage  whereas  rank  coals with relatively low  for the Groundhog  data  Hower  expandable  1978)  on  the  layers could  be  reduced  fairly low  layers and  hence  data  should  higher  supports activation  collected  in  to less for 78  described  than days).  (Chapter  be  4)  associated  illite crystallinity;  crystallinityindex have other  an  (e.g., 150° C  rank  kinectics  further  (ibid) quote  previously  was  of the  Based  temperatures  of  as well as in many  been  areas (e.g., Zingg  documented  et al., 1976;  Frey  1980).  5 . 3 . 2 M E T A M O R P H I C Many  often the  M I N E R A L  A S S E M B L A G E S  A N D  discrepencies exist in the literature on  metamorphic  at  Hower,  3.5 kcal/mole.  with clays of  et al.,  and  crystallinity) than evaluation  and  the kinetics of the coalification model  indicates that, from  high  (Eberl  Eberl  19.6 ±  containing  layers  with  [KVNa+],  Illite crystallinity values  (i.e., higher  related to the smectite to illite transformation this prediction. Assuming  anchizone.  mineral case  pangenesis.  that comparison  Although with  C O A L  R A N K  correlation of coal rank  locally such  with  correlations are predictable  correlations developed  for other  areas is  it is  tenuous  best Several  which  authors  correspond  have  suggested  to the attainment  that kaolinite is destroyed of an  Ro  >  1.5%  at burial  (e.g., Foscolos  conditions et al.,  1977;  max Heroux  et al., 1979;  persistence of from  kaolinite to high  Westphalia, analcime  is present  Kubler. et al., 1979). Kisch  West +  in a large  Germany.  quartz range  rank  (1983)  anthracite grade  Kisch  (1974)  on  the  in Upper  other  hand  Carboniferous  notes  the  rocks  indicates that the transition:  albite of coals, from  flame  coal (0.7%  Ro  ) in the  Lena  Coal  155 Basin of northern Yakutia South  Wales.  Helvetic and  to gas coal (1.2% Ro  Kubler  et al. (1979)  based  Pennine  areas, documented  on  a  in the Tamworth  max regional  study  the disappearance  of  Trough  the  Jura,  of analcime  of  New  Pre-Alp,  at >  0.6%  H°max' Kisch (1983) describes the presenceof heulandite -  clinoptilolite and analcime  in coals ranging from  . He  laumontite  <  is associated  medium  1.1% Ro with  coals  max of high  max A  volatile bituminous  further notes that  (1.1%  Ro  )  to  max Australia and  ) rank in parts of Russia, New max Zealand, whereas it is associatedwith coals of low volatilebituminous (1.75% - 1.9% Ro ) grade in the Helvetic zone of the Alps. The occurrence of prehnite and max pumpellyite and absence of laumontite was correlatedwith a zone of 3.3% - 4.0% range  volatile bituminous  to coals of 1.3% Ro  in Ro  in central and  max  of Brianpon, prehnite and 3.72 Ro  max  5.5% K°  r a n (  and  max  =  j- Heroux  2.5% -  meta-anthracite  greenschist grade (1979)  eastern Switzerland  pumpellyite  and  in the  zone  houillere  are associated with reflectances which  Glass  south  range  from  (1958) describe the occurrence  (>  suggest the appearance  of anthracitic  5.0% Ro  max Basin  of epidote  as 2.0% Ro  ) with  rocks of the biotite-chlorite subfacies.  of Rhode  Island U.S.A..  Heroux  (indicative of greenschist grade,  (semi-anthracite) whereas  et al.  Winkler,  Stalder (1979)  1980)  suggests  max the appearance  of epidote  attainment of 99% although  fixed  does carbon  greenschist assemblages  Pennsylvania that in south and graphite (Ro > 10.0%). max  northern  not occur  in the Taveyannaz  (meta-anthracite are associated western  grade). Kisch with  high  coals of anthracite rank  (which  Groundhog  Coalfield; Bustin, 1984;  Chapter  assemblages  ranging  rank  sandstone (1974)  until  from  low  have  been  the  indicates that  anthracites  Australia greenschist assemblages  ln summary,  rocks with mineral  an  5.0%) in rocks of muscovite-chloritesubfacies of greenshist  in the Narrangansett  at reflectances as low  whereas  et al. (1979) correlatethe appearance of prehnite with  as low as 1.5%. Quinn  coals (Ro grade  (1.3% Ro  documented  in contain in  the  4) are regionally associated  temperature  zeolite grade  up  with to  156 greenschist 350° C  grade,  (assuming that P  associated (Kisch, and  corresponding  with  a  range  1980;  Ogunyomi  this study;  see  diagenetic" to The  -  P  80)  control in one  up  to greater  corresponding  to a  than  0.45 A2 0  range  of the processes  suggests  to  been 0.2  (Frey  A2# et al.,  from  Dunoyer  Segonzac,  de  between  that  or factors such  as pore  permeability are more  "late  organic  either pressure  1980  1970).  and is a  more  fluid pressure  important  in one  and  process  other.  The  V E R S U S  view  1983)  in attempts  O R G A N I C  P A L E O G E O T H R R M O M E T R Y  beween  Illite Crystallinity and  of many  authors (e.g., Kubler,  that the illitization process to match  phase  Temperature 1967;  is strongly  complete  alternatively  at temperatures as  high  Broadlands  as  1968; Perry  temperature  as low  200° C  as  (Salton  area of New  115° C Sea,  layers has, however, (Dunoyer  Muffler  and  Zealand, Eslinger and  de  Segonzac,  White,  of  expandable  temperature  and  layers in a  interlayer water,  single outcrop  i l l i t i z a t i o nu n d e r  In addition  to simple  from  100%  expandable  is dramatic  evidence  certain conditions (Nadeau  collapse of the expandable  the illitizationprocess  has  resulted  The  conversion  been  noted  or  230°  also involves the  and  area.  factors.  the  expulsion  of cations  New  The than  independence  Reynolds,  lattice by uptake  C  layers to less of  to  or  Savin, 1973; Wairakei  existence  in clay composition  1973;  1970)  1969)  Steiner, 1968); thus indicating the strong influence of other range  Hower,  controlled  Zealand,  a  and  transitions with characteristic temperatures.  of montrnorillonite to illite/montrnorillonite mixed  50%  100° C  in conditions  correspondence  indicators  rock chemistry and  Relationship  (Ohaki  approximately  (i.e., true metamorphism;  temperature  5 . 3 . 3I N O R G A N I C  be  of  illite crystallinity indices of less than  lack of a one-to-one  dominant  range  , ) . I n a d d i t i o n , a n t h r a c i t i cc o a l s h a v e total  Kubler  "epimetamorphic"  chemistry, bulk  temperature  et al., 1980)  metamorphic  Kisch,  ^  Figure  apparent  the  H20 of  inorganic  than  T T  to a  1981). of from  of  157 solution, and  their loss to interstitial solutions (ie: K+,  interlayer space  and  their transference to the octahedral  1970). Experimental and  [KVMg  1978;  + +  ]  increase  activation  activity of K et al. (1976) a given poor  to explain  temperature  permeability  de  (and  layer (Dunoyer  1981)  slower  de  [KVCa"]  of an  Such  low  potassium  is metasomatic Segonzac  (1970) be  very  for development  K+  and  Kubler  important  of more  may  than  and  low  Eberl,  Hower  predicted  in sediments  rich feldspars (Srodon permeability  A  (1970) and  illite crystallinity lower  activity is expected  Hower,  two-fold  rates; Pytte, 1982). Kongukhov  the  Segonzac,  [KVNa+],  resulting in a  reaction  the presence  variations might  species; allowing  hence  Lahann,  Teodorovich and  and  the illitizationprocess  and  suggested by  range.  in detrital micas  (1967), Dunoyer  Robersome  energy  has been  +  their fixation in  inhibit the transformation of smectite to illite(Eberl and  et al., 1978;  of  Na*),  evidence suggests that the presence of low  may  Eberl  Ca",  thai  for are  1984). In  control reaction rates.  et al., (1971) suggested  Kubler  that local  in controlling the distribution of  crystalline illites in sandstones  that  than  clay in  shales. An white  important  mica  (paragonite and/or  of, or concomitant The  side effect of  pathway  by  with which  low  margarite)  the similar  mica/muscovite.  document peak  an  width  results from  caused the  by  by  Kubler  (1969),  typical assemblage  from  lead  + +  ]  is the tendency  montmorillonites  montmorillonite  (1967), Frey  montmorillonite and/or (1970;  1978)  and  at the  to illite to  the presence of paragonite and/or  general appearance Frey  (1970)  to classify paragonite  indicative of anchizonal  conditions.  et al. at 10A  micas  expense  muscovite. layers  (1980) half  height  an  increase  (9.65A)  within the anchizone and  for  layers containing  margarite. Such  of white  of paragonite  mixed  Frey  increase in illite crystallinityas measured  slight difference in (001) d-spacing  (muscovite, 10A). The  [KVCa  this process occurs involves the formation of mixed  Kubler  apparent  or  to form  transition of  containing paragonite (or margarite) and white  [KVNa+]  and illite as  paragonite/muscovite  defined as  a  158 The  importance  less well known. Gugenheim,  of other chemical  Certain experimental  1984)  suggests  controls on  the illitization process are  evidence (Eberl and  that high  P  during  Hower,  hydrothermal  1978;  much  Koster  and  alteration may  inhibit  H 2 0 dewatering thought  and  collapse of smectites. Low  to favor the  in the system  hydrogen  transition of montmorillonite  in fact explain  the  documented  occurence  Mineral  The  which  wide  temperature  grade  range  over  for example,  whereas  (125-210° C;  has  been  noted  and  as occuring  during carboxylation  might measures  Temperature  of the late diagenetic to  mineral  (Muffler and  paragenesis  to be  by  high  activity of Na+  (Dickinson  el al., 1969;  Ogunyomi  et. al, 1981). As  calcite and/or factors such  dolomite  and  Mg"  less than  120° C  (e.g., Merino,  temperatures  and  potassium  albitization of  of  consideration (Boles,  or release Fe"  and  calcic plagioclase  rich feldspars (Middleton, over  which  feldspars occurs should  permeability, Mg"  (150° C-180°  stability field, ln the case  range  the presence  or Na"  strongly  of other  C,  1978), feldspars 1972;  ankeritization be  has  1975;  an  important  such, the temperature  as detrital mineralogy,  might consume  mineral  is an  and  Ijima,  to be  favors the albilization of more  Boles, 1982)  and  temperatures  Miller, 1974). In either process, cation activity is considered  4  temperature  White, 1969; Matsumoto  as well as at higher  factor controlling the size of the  other factors.  stable in the  higher  early  albilization of detrital feldspar grains  at temperatures  Boles, 1982)  ankerite, the activity of Fe+ whereas  minerals  in certain areas  Boles, 1978). Similarily, complete  et al., 1981;  important  which  muscovite  illite crystallinity in coal  in other areas ankerite persists to much  documented  Ogunyomi  by  also  feldspar,  Paragenesis and  are stable suggests controls on  range of approximately 80°C-120°C  Ghent  potassium  subdued  Relationship between Metamorphic  Ankerite,  been  is  kaolinite to illite and  decrease of pH of  pH)  1967).  metamorphic  1981)  or  kaolinite-montmorillonite-pyrophyillite,  m u s c o v i t e - i l l i t e - g i b b s i t e( S r o d o n , 1 9 8 4 ) . T h e  (Kubler,  activity (i.e.,high  of  governed  reactions  as well as temperature.  159 The  steep  P  H 2 0  -  T  curves associated with dehydration reactions in  zeolites implies  a  strong  dependence  in many  predictable  mineral  +  areas,  quartz,  and  1974; Ghent  laumontite and  importance  1.  2.  P  phase,  parageneses  such  overlap  extensively  quartz  has been  Ghent,  as: analcime  Coombs,  in zeolite paragenesis. The  1974;  +  quartz,  (e.g., Read  1975). As  was  1979),  and  well documented  heulandite  Eisbacher,  noted  than temperature  role that pore  however  for illitization,  must  fluid pressure  (e.g..Greenwood,  be  of  plays  in  1961).  Two  exist:  P_ ., in which the H,0 chemical activity is lowered due to the H20 fluid presence of various solutes; and PT, ^5sP„ ., < P , in which permeabilityis high and the fluid pressure no K H 2 0 f l u i d t o t a l T T  _  <  longer The  (Zen,  albitization processes, factors other  progressive metamorphism possibilities  temperature  Miller, 1974; Boles and  ankeritization, and some  +  on  the  "supports"  effect of  1 and  the weight  2 above  is to reduce  resulting in dehydration  such  zeolite by  reaction:  the  laumontite  as C02  +  the  =  P  at lower  , (Liou, 1971). The total  favors the  C02  rock.  stability field of  reactions proceeding  for the ideal condition PT, _ H20 reactive phases  of the overlying  calcite  the  kaolinite  + (Zen,  hydrous  temperatures  than  dilutionof H20  stability of clay at the  +  more  quartz  expense  +  with  of a  1961) 2  0.0075  (Thompson,  during  progressive  Ghent,  this "clay carbonate grade  calcium The  1974).  facies" may  If a  high  remain  P  calcium  H20  Stable coexistence of carbonate with laumontite requires that XC0 1971;  predicted  is maintained  stable at the expense  of zeolites and  burial higher  silicates (e.g., prehnite). apparent  control on  reactions  by  the  fluid phase  further  points  to a  direct  variation with permeability. Juxtaposition of permeable and impermeable units results in a gradient in P_ .,; favoring zeolitization of "higher grade" in the more permeable fluid  160 zone  (Kisch,  1983). The  maintenance  fluids is slow, suggesting whereas  zones  fades"  if C02  Ghent  and  dominant  proceeds  volatile phase  rapidly  under  conditions of shallow  is subject  temperature  being  generated  and  carbon  generation  (Barnes  burial, are  of organic matter. The  "clay-carbonate  with  a decrease  of aliphatic and  of gases, such  With  alterations  Page,  as a result  and  oxygen  alicyclic chains (Barnes  as H70,  Increased  C0  and  2  temperatures  1974;  CH4,  and/or  cell-wall  consequence  structure  and  a gradual  of increased molecular  increase  packing  The  understanding  increased evolve  direct consequence  of  and  gradual of  in  the  results in bonds  diagenetic  loss of  incident  at  visible  light as  a  density.  ankerite, the albitization process  controls that affect the stabilities of  the coalification process is dependent 4, almost  organic  breakage of C-C  in reflectance  clay minerals,  in Chapter  of  vitrinite coal macerals,  with  noted  fulvic  decrease  In comparison  assemblages,  the numerous  and  results in a gradual  the increased compaction  optically by  humic  Accompanying  changes  noted  diagenetic  types progressively  as a  and  microorganisms  duration of heating  Within  early  et al, ibid).  of methane.  are  begins  increased burial,  this stage kerogen  in hydrogen  matter  organics from  this stage results in generation  was  formation  and  largely biochemical;  increased crystallineordering of aromatic compounds.  as  (Stewart  of  Temperature  component.  to geochemical  duration of heating. At  volatile component.  various  zeolite  et al., 1984). Organic  remaining  part of the kerogen  primarily  and  breakage  plant  favor  favor stability of the  Metamorphism  surficial conditions  acids eventually form  the  might  contrast to inorganic diagenesis, diagenesis of organic  metabolizing much  towards  requires that mixing  Miller, 1974).  effects, under  matter  zones  permeability may  Relationship between Organic ln  [C02/H20]  that highly permeable  of relatively low is a  of a high  solely on  of the coalification processes have  the  and  solely on former.  the zeolite temperature Though  not as yet been  a  the  mineral and thorough  achieved,  time  and,  161 experimentally  it appears  that the only  contribute to the process  is high  coalification process at higher  factor other  confining pressure  values (Huck  independence  than  and  temperature  which  might  hinder  Patteisky, 1964;  However,  pressure  in the coalification process  extent by  the occurrence of coals of low rank (1.1% Ro-1.5%  which  may  the  Bustin pers.  comm.).  is substantiated to Ro  some  associated with max  high appear  pressure  metamorphic  that a  much  assemblages  better approximation  vitrinile reflectance and information  concerning  precautions  (Bustin  adhered  process might  serve to make  1974)  although  concerning  relationships and assessment  experimental  is present  vary  between  of  zero maturation  fluid composition  well documented  200° C  in excess  350° C  techniques thus prove  of  experimentally. Based  in metamorphic useful.  allow  for sediments for Neogene  from  modelling  can  be  to suggest  more  for the  presendy  sediments.  petrology  at grades  The  Ma  obtained allow  assemblage  generally lower  1975;  Bostick  coupled  with  from  coal than  vein  for qualitative present  of temperatures  of  (dispersed  has  coalification models,  (Carboniferous)  application  the  actual  Meriaux,  accepted  determination  as old as 300  of  accurate. In  modelling  metamorphic  normal  utilized (Bostick,  that the  time-temperature  on  that  phytoclasl material  sediments,  grade  detailed  accurately  level projected coal gradients may  vitrinite reflectance studies could approximately  to define more  effective confining pressure  if the low  that  from  measurement  lithologies (Blanquart and  derived from  lithostatic and  and  thus  obtained  requires only  of reflectance from in most  be  from field data and  work  inconclusive evidence  Foster, 1975). Temperatures  information  been  may  obtained  temperatures obtained  there is some  reflectance obtained and  to. Further  matter), which  This  can  in the collection of samples  of coals, the measurement  solid organic  modelling.  the burial history be  et. al., 1985)  (Bostick, 1974). It would  of paleotemperatures  time-temperature  reflectance be  the absence  in California  and  up  to  presumably  petrologic greenschist  should  162 5 . 3 . 4 P A L E O G E O T H E R M O M E T R Y The  assumption  O F  B O W S E R  that time-temperature  L A K E  modelling  studies yields the best estimate of paleotemperatures evaluation of the Bowser empirically and  Lake  experimentally  Group  G R O U P  based  temperatures  vitrinite reflectance  at sub-greenschist  mineral assemblage  derived  on  R O C K S  by  grade  permits  direct comparison  with  for similar stable assemblages.  The  occurrence of ankerite in the study area over the temperature range of 100° C 220° C  is comparable  to empirically  other authors (e.g.,80° C and  -  derived  temperature  ranges  quoted  of albite within  this temperature  range  odds with previousestimates from other areas (e.g.,<120°C Miller, 1974;  Merino,  assumption  is valid  high  P  analog  albite would  be  1975; that  Ogunyomi  albite  formed  to laumontite, approximately  for albite to be  stable  then 180° C  at depths  presence  comparison  of mixed  Sea  geothermal  to many  during  of  although  with  in syntectonic  veins  of illite from  montmorillonite Lake  <  Group  carbonate  and  150° C  at  and the  assemblage  as  formation  of  Miller, 1974). In  it is apparent  a  order  that one  or  P_ ., must have prevailed, fluid slightly in excess  of  200°  not at odds  with studies from  certain  and  1969), is anomalous  in  White,  Texas, Perry and  experimentally  derived  Hower,  1970; Gulf  temperatures  acidic conditions created by with  low  1984). The  of high pore  to reduce  C  areas  Coast, reaction  generation  2  inhibit  of carbonate  theoretically favor  presence  rocks (experimentally shown  C0  and  permeability could  equilibrium assemblage  suggests alkaline conditions, which (Srodon,  well, not  1 8 0 °C , G h e n t  limit for the  (Ghent  less than  of coalifled material coupled of an  a clay  temperature MPa  is, as  by  Matsumoto  1982). If, however,  clays to temperatures  1978). Although  i l l i t i z a t i o np r o c e s s , t h e p r e s e n c e  in the Bowser  at 100  Boles,  with  lower  areas (e.g., Galveston  Hower,  maturation  a  lield, Muffler  Burst, 1969). It is also at odds rates (Eberl and  associated  , or P„ _ H20 layer  in excess of 5,000 m,  (e.g., Salton  et al., 1981;  at temperatures  bothconditions P_ ., < P fluid total The  previously  210° C, Muffler and White, 1969; Boles, 1978;  Ijima, 1981). Formation  -  and the  quartz formation  fluid  the rate  the  of  pressures  163 expandable  layer  collapse  during  heating)  is also  a possible  explanation  for  the  apparent  inhibition of the illlitization process, although  limited experimental  regarding  pore  as yet available. A  fluid pressure  factor which  might  relativelylow  hinder  effects on  the  the transformation  values of [KVNa+],  [KVCa  + +  sodium  colbaltinitriteillustrated the absence  Group  rocks. In addition, there appears  fragments  or  might  plagioclase and  Na  have might  +  been have  been  montmorillonites or brines. The collapse and have  concomitant  contributed  to a  indirectly lower  mica Figure  82  which  An  the average  A2 0  anchizone  as  by  has  hour  period  The by  sections stained with  of  K*  value  Kubler  of Na  is 0.4 which  white  half  corresponds  framework  in  The  illite peak  height  rich  +  peak  may  lower  mica  at  to the  effect  white  is illustrated in widths  versus  identical, as would to the lower  (1969). It is anticipated that heating  end  be of  should  the  collapse  ) a n d h e n c e r e s u l ti n i n d i c e st h a t d e m o n s t r a t e  synthesized at analytic  identification of a Na+  the characteristic peaks:  of  the  calcic  cation activity is  of illlite (muscovite).  broadening  on  carbonates also  resulted  effect of high  indices are almost  crystallinity if equilibrium  of 0.20 A2 0  hence  rock  ions. Ca"  dissolution,  formation  Lake  foliated metamorphic  the breakdown  cations and  illite (001)  the Kubler  (i.e., a muscovite  crystallinity index  of  on  a l l e x p a n d a b l el a y e r s t o 1 0 A ( 8 . 8 ° 2 6 of  Thin  the dissolution or albitization of  available from  likely  rich feldspars in Bowser  absence  illite crystallinity by  maigarite)  expected,  degree  ].  limited availability of  additional  is a plot of heated  defined  a  with, the formation  vitrinite reflectivity.Although  a high  of potassium  from  mobility  expected.  of, or concomitant and/or  + +  p r e c i p i t a t i o n o f p h y l l o s i l l i c a t e s ,q u a r t z a n d  the apparent  (paragonite  [KVMg  an  more  layers to discrete illite is  reduction of permeability by  decreased  crystallinity indices than  expense  and  to be  derived  are  of mixed  ]  large detrital micas, suggesting  the other hand  process  information  was  attained  at 600° C conditions  rich smectite  and  during 200  MPa  heating yielded  identical to those  in three samples  for  the  2  a  described  (1228, LRS2,  here). LRS1)  164  FIGURE 82: Half height peak width of illite following heating. The expected collapse of all expandable layers to 10 A following heating and the lower than expected degree of crystallinity (star represents the crystallinity of a synthetic muscovite measured on the same diffractometer) obtained indicates the prescence of a non-expandable mica or clay with a d-spacing similar to illite.  165  dry  3 . 5 °2 6  normal  K  4 . 0 ° 2 6  saturated  glycolated  3 . 2 °2 6  heated  9 . 0 °2 6  (Kisch,  1983)  suggests that paragonite 3 Na  may  montmorillonite  have +  formed 2  via the reaction:  albite  3 paragonite  +  8  (Chatterjee, The  presence of paragonite, paragonite/Na-montmorillonite  vitrinite reflectances ranging noted on  in several other  areas  2.2%  Ro  (e.g., Frey  at 200  MPa  synthesis 1971;  determined  at 2 MPa  Chatterjee, 1974;  conditions: PH20 <  F  2  in the  1976). This  deformation  is consistent with  max  less (Chapter  3). The  fluid phase  (e.g., C02,  by  pressure  of  Chatterjee  greater  formed  (1973)  of  temperature than  330°  C  for  300° C  (Velde, of  v  via crack-seal  of ubiquitous low  mechanisms  during  dihedral systematic  i n s t a n t a n e o u s l ye q u a l t o P  and  F,  shear  probably never  total  are expected  (1979, p.163)  based  , during metamorphism. The  presence of phases which CH4)  that  associated temperatures  relationship further suggests the occurrence  the presence  might  lower the activity of  in lithologies similar to those  illustrates the importance  the coalification process at temperatures  theoretical burial-time-temperature Welte,  derived  P „ . , a n d / o rP _ . , < P fluid fluid total  and  with  200° C, however, does not agree with the  confining  of antithetic veins which  in the study area. Hunt during  -  temperature  fracture sets suggests that P„ ., was fluid much  max  Ro  pargonite/muscovite  confining pressure or the experimentally determined  of margarite  predominance  synthesis  to 4.0%  1973)  and  et al., 1980). The  time-temperature modelling of 150° C  experimentally  and  from  quartz  modelling  1978, p. 219) indicate that during  in excess of  Juntgen  and  of volatile  100° C.  Klein  Based  (1975;  the coalification process N2,  present  generation on  in Tissot CO,  H20  C02,  and H20  166 and some  CH4  are generated  increasing amounts  point during the process however, CH  volatile phase with  in ever  being  Jiintgen and  becomes  4  generated. Correlation of Kleins  mode!  reflectance of approximately  (Figure  1.35%  83)  Ro  until a plateau  the  proportionately the  Lopatin  (1971)  illustrates that CH4 and  a  is reached.  temperature  of  dominant  coalification becomes  At  5  model  dominant  approximately  at  a  150° C.  max Thus, material  during with  metamorphism fairly low  of a sedimentary permeabilities,  reachedthe condition PTI _ H20 would  proceed  at lower  <  as  package  temperatures  containing  abundant  slightiy in excess  coaly of  100° C  are  P_ ., would be attained and dehydration reactions fluid  temperatures. C0  2  generated  further explain  the stability of carbonate, kaolinite and  zeolites and/or  the calcium  silicates prehnite  and  from  degasification of coal  quartz  pumpellyite  at the expense if low  of  permeabilities  would calcic are  maintained.  The model involves gradual burial to 3,000 m in 20 Ma and retention of coals at 3,000 m for an additional 20 Ma under the influence of a 40°C/km geothermal gradient  167  2.0  Time (MY)  FIGURE 83: Evolution of volatiles during coalification, based on Juntgen and Kleins (in Tissot and Welte, 1978; p. 219) model. Included is the curve depicting Ro max increase with coalification (Lopatin method) as modelled for the burial history specified by Juntgen and Klein. See text for burial model and further discussion.  6 . R E G I O N A L The  Western  C O R R E L A T I O N S  Cordillera has  been  A N D  I M P L I C A T I O N S  described as  a:  ...collage of terranes of varied origins that became attached continent at different times... (Monger and Irving, 1980). Price  et al. (1981)  assemblages  and  which  (Figure  84). The  formed  Bowser  and  carbonates  and  Eastern  superterrane elastics from Middle  the  prior to accretion to the  and  which  are  with  Monger  to Late the  1981;  Cordillera Monger  Alexandria,  further  Cretaceous  "stable"  links another  to the composite  extensive  systems.  Paleomagnetic been  restoration based displacements  northward  been  craton  as to Jurassic  suggested  North  American  that  to 900  168  Basin of  (Tipper,  pulse  throughout II, Price  of much  of  and  1984). terranes  a series of  strike-slip  dextral  that these  kilometres northwards.  whereas  the  et al.,  various Cordilleran  suggest  in  this  smaller terranes, Wrangellia  features (Gabrielse km  reworked  widespread times  Cache termed  of  Bowser  (superterrane  described  along  several thousand  in the order of 750  craton. A  terrane  suggest that the  various offset geologic  shedding  into the  Early Oxfordian  composite  displacement  terrane  postdates the amalgamation  data (Irving et al., 1980) shifted by  on  American  Triassic to Middle  the composite  sediments  terrane previously  lines of evidence  undergone  terranes have  overlain by  et al, 1982) consisting of the two  Several  composite  volcaniclastic rocks, basic  et al.. 1982). The  shale deposition in Bathonian, Callovian and the  North  major  the terrane described  Permian  uplifted cratonic miogeoclinal  terrane  on  terranes, thus forming  et al., 1981;  Jurassic through  composite  into two  and  Jurassic stratigraphy ties Stikinia to the Quesnelia,  assemblage  I (Price  tectonostratigraphic  volcaniclastics (Price et al., 1981). It has  late Triassic to Middle  Creek  10  further grouped  Basin lies unconformably  acidic volcanic rocks and  the  outboard,  been  consists of Mississippian  andesitic volcanics  recognize  the  contrasts in stratigraphy, metamorphism  10 terranes have  were  "Stikinia" which  et al. (1982)  are identified by  structural style. These terranes which  Monger  to  1985)  have fault  allochthonous Palinspastic indicates  the offset of Late  Pleinsbachian  169  E A S T E R N A S S E M B L A G E  •  Q U E S N E L L I A  1  C A C H E  C R E E K  STIKINIA  BRIDGE  RIVER  C A S C A D I A  GRA  VINA  N U T Z O T I N A L E X A N D R I A  W R A N Q E L L I A ^ P A C I F I C  RIM  C H U Q A C H  S00 km  FIGURE and  84: The  Monger  amalgamated  major  *9°  tectonostratigraphic terranes as illustrated in Price et al.  et al. (1982). I and  II represent  prior to accretion (BB=Bowser  composite Basin  or superterranes  for reference).  u)  which  (1981) were  170 faunas,  which  of 500  km  have  a  distinct geographic  (Tipper, 1982). An  which  shaped  the terrane  6 . 1 O P P O S I T I O N A L  A Basin  similarites and model. of a of  the  episode  this thick shaly  northeastern  edge  part of the basin Tipper (mid-Oxfordian abruptly and  in age  overlain by  conglomerate. sedimentary in the  and and  grained  Formation)  (Tipper,  1985)  with  receiving coarse Richards  hence  sandstone non-marine  material. The  south  (Tipper  and  and  of the  Richards,  Basin  various  and  1976)  terrane  the thick  Richards,  1976)  near  Creek  indicates  a  the  period very  the  southern  overlies  (Figure  abundant  and  85),  both as  diverse shelly  with interbeds of siltstone, coal and assemblage  consist of  with the  lower  pebble  volcanic, granitic to Trout  Jackson  Jackson/Currier  transition (this study)  of marine  shales to lithic  litharenites and  coals is striking and  presumably  represents  of  assemblage  unit), which  Formation  section  accumulation  to represent  detritus at this time, ln  lithoiogic similarity of the Ashman Richards,  Bowser  1976) illustrates  with  limited areas  conglomerate, with an  Creek  the  clastic deposition. The  describe the Trout  sandstones  of  the accreted  is thought only  part  in the north  equivalent to Jackson  and  Clasts in the Trout  northern  (Tipper  gradationally the shales of the Ashman  consisting of marine fauna,  fine  (Ashman  of the basin  timing  are consistent with  in the south  of predominantly  relative tectonic quiescence  in the  unit (this study)  sediments  sequence  order  I M P L I C A T I O N S  part (Tipper  of which  of the Jackson  to Oxfordian  wide  T E C T O N I C  strata in the southern  Equivalence  the  S E T T I N G  lithoiogic variation  differences both  Bathonian basin  of  on  "collage".  P R O V E N A N C E :  comparison  with coeval  the tectonic setting and  T E C T O N I C  6 . 1 . 1S E D I M E N T A R Y  displacements  analysis of the geology of the northern Bowser  yields further constraints concerning events  zonation, suggests  to  Creek  and  transition  upper  conglomerates,  a period  of  increasing  uplift  171  K I M M E R ID G IA N T R O U T  C U R R I E R  C R E E K  A S S E M B L A G E O X F O R D I A N  UNIT  IH  D  A S H M A N  C A L L O V I A N  J A C K S O N  F O R M A T I O N  UNIT  B A T H O N I A N  G  c B A J O C I A N  S M I T H E R S  S P A T S I Z I  F O R M A T I O N  S E D I M E N T S  B  ^  T O A R C I A N N I L K I T W A F O R M A T I O N  ^  / T O O D O G O N E /  P L I E N 3 B A C H I A N  V O L C A N I C S  A SINEMURIAN  FIGURE 85: Stratigraphic correlation chart for the southern Bowser Basin and the northern Bowser Basin. A. Fine grained greywacke, tuff, shale siltstone,limestone B. Greywacke, sandstone, argillite, tuff C. Greywacke, shale tuff D. Sandstone, conglomerate, siltstone, minor coal E  volcanic breccias, tuffs and flows  F. Shale, siltstone, tuffaceous sandstone, tuff, sandstone, minor conglomerate G. Shale, siltstone, minor sandstone H. Conglomerate, sandstone, shale, siltstone, coal  172 along  the basin margins  sandstone  composition  paleocurrents which  from  Oxfordian  are attributed to the flowed northwards  the  Pinchi belt in the  and  southerly to southwesterly  the northern Eisbacher,  part of  southern  in the south  the study area upwards  the  Cretaceous which  there are  composed  no  suggests  a  the persistent white (Tipper  difference  and  in source in the  area) may  apparent  granitic rock  fragments  area  in the  Group  and  and  may of  mid  is absent  in the  (i.e., an  area  and  in turn  to  In  Late Lower  thickness ago  to  be  Devils  Claw  1983).  southern unit  to the  of phyllitic and  their relative scarcity in the  The  pre-Albian  unconformity between  the Skeena  lake Group  recognized  in the southern  to  unit, although  Moffat,  in the  abundance  a response  terranes.  Group  distribution.  identified in the Groundhog  100 Ma  the Devils Claw  restricted detrital mica  not been  Oxfordian  possibly signals increasing rates  the  has  explain  convergence  defines the Skeena  1976),  source  Late  of  in the north.  distinct lithologies (Bustin and  terrane material  southern  the presense  increase in cummulative  ago  in  counterparts  source  sedimentation  continued  mica, which Richards,  1976)  Gilchrist, 1979;  tuffs of  between 160 Ma to 80 Ma  the Skeena  partially coeval, have  coeval  p. 36,  crystalline belt  and  by  from  of Jurassic plutonics (Hotailuh Batholith?) and  100 Ma  during  previously noted  apparently  material  area  Richards,  is further illustrated by  northern  in this interval. Increased  uplift in the source As  from  southwesterly  Omineca  of quartzite and  approximately 80 mm/y  sedimentation  and  a,b; Richards  apparent  quartzites (Eisbacher, 1981). The  approximately 120 mm/y  Basin  area  terranes, as indicated  arch and  andesitic volcanics, breccias and  stratigraphy  was  of sediment from  of  the Skeena  the Atiin terrane and  the increasing importance  through  Cambrian  from  contrast in source  for which  slight differences in  variation in source  the basin (Eisbacher, 1974  1981). The  The  part of the basin (Tipper from  isolated piles of basaltic and age  time onwards.  series and  part of the basin (Tipper Coalfield (Bustin and  Indeed Bowser north.  schistose northern  the Upper  and Moffat,  A  Richards, 1983).  source  Bowser 1976)  173 Although uppermost  the contrast in deformational  McEvoy  misinterpreted shortening  units and  as an  existence  or  unconformity,  larger folds and  of  thus thought within  the Currier and  in all units is similar and  relationships with The  angular  a  zone  to be  more  the strata are  of  to the  not ruled  in the  in order  Maestrichtian).  need  4,600  to  m  Inasmuch  zero  5,500  as  obtained  part of  of  paleogeothermal For  of  m  coals  level  max  to  the  unit would  required.  the  study  in the Currier  more  burial  area -  been  40° C/km  unit in the southern  suggests  regional  (Oxfordian  this study  Projection  of  more  exposed  that  high  through of  die  heat  flow  to coalification  calculated  coalification  which 3,500  to high less  demonstrated  as levels  4) suggests  of  lower,  coalification  (Chapter  of burial  thickness  been  be  yield clues  abnormally  detailed analysis  a  relationships  must  strata might  of the  time  depth,  it has  that they  is  relationships.  Basin  a depth  units.  unconformity  unconformable  that an  of  parasitic  S I G N I F I C A N C E  study  estimated  have  is  p a l e o g e o t h e r m a l g r a d i e n to f 3 0 ° of Ro  a  yielded  a greater  within  period  from  with  gradient  a  this interpretation.  in contrast  time  on  the coalfield during  maturation  the Currier  period  the Bowser  of  uppermost  significant  crustal type  (1984) proposed  for a protracted  for a re-evaluation to a  flow and  amount  in the  it is suggested  T E C T O N I C  heat  coalfield, Bustin  northern  gradients  longer  G R A D I E N T S :  Information  levels in the  a  to satisfy the structural  tectonic setting. Based  coalfield  than  and  be  units have  developed  rather  out, although  gradients calculated from  in the Groundhog existed  decollement  Claw  easily  that the  that folds in the lower  close association between  depositional  units might  it is emphasized  the suprastructure  fold  6 . 1 . 2P A L E O G E O T H E R M A L  paleogeothermal  Jackson  the Devils  consistent with observations. Minor  less paraconformable  The  style between  ranged m  from  (Bustin,  temperatures  the  1984). for  a  unusual  in Chapter  4 that  a  appears to explain the data. High values part of the coalfield (Ro  max  as  high  174 as 5.8%;  Bustin,  45° C  50°C/km  -  45°C/km value  ibid) suggest  proposed  by  Bustin  gradients of 30°C/km Geothermal  need  (Figure 67, Chapter  to 75°C/km  incorporated  the  up  of  by  for a paleogeothermal 4). This  2.00 W/m°C  to 50°C/km  (4.8 x 10  Heat  cal/cm.sec)  1  4 0 ° C / k m  8 0  m W / m  J  5 0 ° C / k m  1 0 0  thermal  m W / m  conductivity for various  W/m°C  sandstone  3.6  W/m°C  limestone  2.4  W/m°C  coal  0.5  W/m°C  dolomite  3.2  W/m°C  diabase  2.4  W/m°C  (Clark, 1966; a contribution  section is necessary Bowser  Lake  of approximately  to result in thermal  Group  50%;  2.40 W/m°C.  calculated heat  employed flow. When  by  The  resulting in an  Bustin, 1983) can compared  80%  Gretener,  shale  conductivities as low  strata the contribution by  generally less than  range  in a  1981) dominantly  as 2.00 W/m°C.  shale to the post-Oxfordian  estimated  thermal  clastic ln section  conductivity of no  less  flow values using a conductivity of 2.0 W/m°C  thus be  of  lithologies of:  1.6  that  a  2  shale  it is apparent  and  Flow m W / m  average  of  results in heat flows of:  Gradient  an  between  Bustin. Utilizing the average thermal conductivity  6 0  on  of  is in contrast to a gradient range  3 0 ° C / k m  Based  gradient  thought  of as minimal  estimates of the  with the average global heat flow value of 65  mW/m  2  the is than (as heat  175 (Gretener, required  1981)  to explain  Groundhog  flows of a similar magnitude  documented  for various  Watanabe, Complex  back-arc  heat  beneath  the  rifts) are  British Columbia. uncertain  average  heat  in the southern  for  100  6 . 2 R E G I O N A L  flows  are  part of  the  have  though  O F  years  subduction  associated high  heat  Mesozoic  the  Coast  Basin  a  unreasonable active  geology  fluid flow  high  depo-centre.  flows (e.g., ocean regional  tectonically  of  is consistent with  the position of the Bowser  in a  been  ridges,  in  north-central  to the  heat  to expect  a  flow  stable  is  fluid  area.  E V E N T S  history oudined  unit (Chapter  3). Eisbacher  relationship between underlying Bowser  Lake  Tango  in the field area  progressed (1971)  the Tango  suggested  Sustut rocks. The  indicated the presence  Creek  assemblage  had  it is evident  that  Formation  of an  of the Sustut Group  near the southeastern edge  that deformation  occurred  angular  prior to and  Formation,  however,  uplift been  great enough  unconformable and  Creek  in the Bowser  during  deposition of  (Tatlatui Basin  the  Groundhog  Claw  indicates that not until the Tango  Claw  of the  coincidence of paleocurrent directions in the Devils Creek  the  after deposition of at least the Devils  coincident with deposition of the uppermost Campanian?)  involves  superterranes  the  have  in the "Western Pacific (Schlater,  intuitively it seems  million  deformational  the lower  amalgamated  structural relationships  Coalfield and  which  mW/m2  D E F O R M A T I O N  6 . 2 . 1T 1 M T N G From  model  basins  84  possible contribution of subsurface  at this time,  pattern  A  not. consistent with  The  (approximately  (back-arc)  flux, coincident with  tectonic settings which  continental  flow  marginal  et al., 1977).  Plutonic  Other  the coalification gradients recognized  than  Coalfield (Bustin, 1984).  Heat  1972;  the calculated values suggest that higher  unit  time  the  and  period  member;  to switch  paleocurrents  176 from  a south  Deposition  southwesterly  of Brothers  direction  Peak  of the thrust belt which indicates deformation The Basins  is poorly  northernmost Gabrielse  and  westernmost indicate noted  progressed  A  compilation  of the Bowser  Tipper, 1984) and edge  beyond  Lake  (Eisbacher,  prograding  Group  Maestrichtian  and  of  general  fold trends  the northeastern edge  (Figure  corner  86, back  of  from  suggested  strata  and  Sustut  the  of the Bowser  1957; Basin  and  and  Tipper,  Eisbacher  the 1984)  (1976;  p.116)  Basin:  The northeasterly trending folds are clearly overprinted by northwesterly trending northeastward verging folds. further  Creek  of Canada,  pocket).  the Bowser  basin  time.  Basin (Geological Survey  fold trends  that in the northwestern  it was  foredeep  Tango  of the Sustut basin (Eisbacher, 1974a; Gabrielse  2 predominant  1981).  of the incremental shortening events in the Bowser  constrained.  margin  direction  coarse elastics in the eastward  contains uplifted Bowser  which  absolute age  to a northeasterly  younger  that:  Because the northeast trending folds are essentially confined to the channel fades they may have formed in response to gravitational movements down the basin slope contemporaneous with clastic deposition. In reference  to the  Sustut Basin, Eisbacher  north-northeasterly  to north-northwesterly  northwesterly trending folds and tip of the Groundhog  (1974a) overturned  thrusts near  Coalfield). Again,  indicates an  Mosque  evidence  overprinting  folds and  thrusts by  Mountain  of  early  later  (adjacent the  southern  for this interpretation was  not  offered. Evaluation the two  of the various  predominant  fold trends present along  subparallel to the first phase the  study  area  southeasterly  and  and  second  it is clear that the  trending  directed component "brittle"  structural trends  lack  folds (FJ of motion  of  a  and  northeasterly  folds as defined trending  structures. As  deformational  in Figure  86  the edges of the Bowser  that thrusts with  offset F,  "plastic"  phase  displayed  style  illustrates that Basin  in the thesis area.  folds (F2)  have  a predominantly  deformed southeasterly  well, the preponderance rules  out  a  are  syndepositional  of  a  In  177  deformational  event.  It is thus  relative timing of fold events  suggested discerned  basin. If the timing  of fold superpostion  correct, then  be  it can  suggested  southeasterly trending Sustut Group and  as noted  however  which  third phase the timing  with  Basin  of superposition near  clearly delineate  these  6 . 2 . 2D R I V I N G  M E C H A N I S M S  Assuming approximately  accomplish  a comparison would  on  dextral strike-slip  prior to deposition  can  Creek)  Tango  be  whereas  of  strata is  to a  of the Sustut Basin  trending  amount  Creek  attributed  in  the  southeasterly The  is  resulted of  possible  detailed structural studies  edge  concerning  are needed  to  D E F O R M A T I O N  back  associated axes  with the  of stress, then  deformational  some  shift from  and  it is possible  events in the  mechanism  an  individual fold events  is required  western by  which  orientation of northeast-southwest  to northeast-southwest  are  to relate  Cordillera.  the To  the principal  axis  to  in the interval between  incremental palinspastic restorations of the displacements faults in the Cordillera,  for the north marked change pre-Albian tim north-northeast 87  Eisbacher which  (Tango  the  Albian  and  times.  Based  Figure  western  strain axes  strains to other  Paleocene  the  by  of deformation  structures in the  rocks. Further  F O R  three superposed  north west-southeast  rocks  probably pre-Paleocene.  strain which  parallel to the principal  of compression  and  the  relationships.  that bulk  such  for Sustut  occurred  is that  is consistent throughout  to pre-Santonian  trending  the minimal  in the Bowser  interpretation  resulted in northeasterly and  northwesterly  inconsistent  area  that the first phase  folds respectively,occurred post-Santonian with  reasonable  in the study  hence post-Albian  third phases  strain associated  more  folds in the thesis area  rocks and  the second  a  summarizes  Gabrielse  central Cordillera, at least, in general orientations of e to north-northwest in th in late Cretaceous and/or the displacement  (1985)  there princi e mid early  history along  along  various  suggested:  appears to have been a pal stress from northeast in Cretaceous to Cenozoic times.  the major  strike-slip faults in  the  178  mid JURASSIC-mld CRETACEOUS  mid CRETACEOUS-Late CRETACEOUS  Late CRETACEOUS-EOCENE  FIGURE 87: Displacement history along the major strike-slip faults in northcentral British Columbia in relative chronological order of A, B, C, D (after Gabrielse, 1985). Arrows indicate approximate orientation of principal compressive stresses assuming some cohesion along the fault zones. HF=Hotailluh fault; KF=Kutcho fault; TkF=Thudaka fault; PF=Pinchi fault; VF=Vitali fault; SF=Swannell fault; TbF=Thibert fault; NF=Nahlin fault; KSF=King Salmon fault; KtF=Klinkit fault; PfF=Pittman fault  179 northern Cordillera and  the concomitant  shortening  have  which  might  orientation might  vary  incidence  against  resulted  displacement  along  Salmon  and  the  Nahlin  Kutcho  fault hanging  the King  Salmon  and  associated  local steeply plunging  Nahlin  the  pre-Late Kutcho  segment  for a  Salmon-Nahlin  system, if coupled  Strait faults, might the predominant  timing II  strike-slip  (lOOMa)  from  which  longer  Quesnellia  suggest  the Thibert  period was Salmon  with coeval movement  strike-slip motion  zone  of  along  the  dextral Salmon  fault is  of constrained  that displacement  of time. The  occurred  assumption  transported northwards and  Nahlin  faults  along and  of the  along the Denali  fault system  King  and  constrictional strain (Figure the Denali  of  have  a component  the northerly trending segments  result in a  fault  time  King  are steeply dipping and  along  of the King  along  possibly  relationship between  ibid) it is possible  somewhat  with  convergence  trending  dating of micas  of  the northwesterly striking segments  fold axes  displacement  west-northwesterly trending segment  Though  northwesterly  the of  and  the angle of  southerly directed thrusting of  (Gabrielse,  strike-slip motion  trend. The  occurring during mid-Cretaceous  faults, fault planes  the superterrane containing Stikinia and  Chatham  of  initiated.K-Ar  minor  of  angle  et al., 1982)  terranes. As  wall rocks. Along  transported by  fairly high  faults is consistent with contemporaneous  Although  Cretaceous  this  accretion of superterrane  1 (Monger  a system  fault and  Nahlin  transcurrent displacement.  at a  points out that the geometrical  fault and  along  Cretaceous  was  that  Initially, telescoping  a northwest-southeast  Early  Pinchi, Thibert) was  displacement along  being  craton  of telescoping of the combined  strike-slip  King  fault zones.  American with  to note  of  the coefficient of sliding "friction" or  terranes of superterrane  (Gabrielse, 1985). Gabrielse  as  North  rocks suggest that dextral motion  Kutcho,  on  the various  post-dates  inboard  faults (Kutcho, zone  "stable"  event  the amalgamated  decreased,  within  in early structures  this compressional  yields the age  the  orientation of direction  responsible. It is important  considerably, dependent  effective viscosity operative superterrane  been  approximate  88). is  that the  FIGURE 88: Tectonic boundary conditions active during second phase and third phase deformational events in the study area. F2=northward advance of te Stikine terrane between the boundaries imposed by the Kutcho-King Salmon fault zone to the east and the Denali fault system to the west results in a zone of constriction and concomitant strain (arrows indicate major compression) manifest as folds and thrusts of second phase orientation in the study area. F3=continued build-up of strain energy might be relieved by displacement along the Ingenika-Findlay fault system which is approximately parallel to the plane of no finite longitudinal strain (NFLS) for the infinitesimal strain ellipse corresponding to F 2 . Rocks in the study area thus are under compression in a NE-SW direction, resulting in F 3 fold orientations. See figure 79 for key to fault name abbreviations.  181 post-Mesozoic the Hines and  (Lanphere,  Creek  Craddock,  segment  pre-Late  (Wahrhaftig  the Shakwak  and  with  northwards  of  constriction need  of intermediate/minimum  displacement  and  not  be  northeasterly  direction;  accumulation  of strain energy  displacement  along  Ingenika and  a direction  Takla  A  area is compatible  if allowances  anisotropics  for variations  etc. are ignores  the  exact  the individual deformation  motion  along  through the  to Paleogene Kutcho-Pinchi  Such  complexities  the Pinchi, Kutcho,  Findlay events  is to some system  also  area.  Continued from  (Gabrielse  expected and  of  if some Thudaka  discerned  extent at odds  (Gabrielse, 1985).  in the  no  to  second  contribute  Findlay,  and  to  in the  the Pitman  a pattern  primary  Findlay,  compression  the Thudaka,  Lake  a  to the plane of  could  along  reversal  in  transference  in sliding friction, minor  considered.  along  post-Albian  along  the  a  trend  the Thudaka,  orientation of third phase  contemporaneous of  motion  a  requisite  study  a  of  that  finite strain ellipse corresponding  as well as sinistral displacements  simplistic and  timing  along  existence  to cause  which  in the  relieved by  sub-parallel faults east of Dease  1985),  S2  probably  3) suggests  orientation corresponds  with dextral displacements  faults stystem  admittedly  been  in relative plate  reorientation of paleostresses. The  reorientations,  have  whose  slight change  I. The  folds  (Brailey  active  in order  itself as  to that of  strain of a generalized  structures.  several smaller  manifest  fault to displacement  fault system  been  as  two  Saleeby, 1985) has  high  the  paleostress orientations.The  similar  might  the Kutcho  finite longitudinal  Gabrielse,  and  such  segment  between  history (Chapter  exceptionally  maximum  strain would, presumeably  Takla  various segments  of superterrane  deformational  constrictional  phase  and  Wallace, 1985; Gehrels  differential stress throughout  magnitude  et al., 1975)  Cretaceous, suggesting that this boundary  contemporaneously low  along  1985), in addition to transpressive convergence  superterranes (Engebretson began  1978), strike-slip displacements  the study  Ingenika fault  and  and  Tipper,  1984;  stress  deformation motion  is is  faults. Indeed, field area  with pre-Late  the of  Cretaceous  7. A  reconnaissance  organic-inorganic  study  the  stratigraphic,  diagenetic/metamorphic  Bowser  Basin  has  1.  The  approximately  can  be  revealed the  divided  3700  m.), and  sedimentologic,  structural  relationships in the northeastern  m.  2.  The  been  laterally continuous  the Jackson  Devils Claw  (1100-2000 (>  800  further divided into two  succession represents an  Bathonian been The  (lowest Jackson)  deposited  units which  m.). In order  granitic rock  and  younger  northern are  suggested  Bowser 3.  and  fragments  upward  Richards, 1976) and  data  from  stratigraphic succession the base  of  Lower  have  prograding abundance  of  relative  close  suggests  of  of  Cambrian  in source  deltas.  quartzite  mid-Mesozoic quartzites in  terrane rock  for differences in clast lithology in the  of a least squares  suggests  by  from  to  increase in the percentage  areas. Differences  projection  max  is thought  fragments  northeastern source  The  Ro  rock  batholith) and  the  and  in age  detrital clasts and  plutonics (Hotailuh  Basin (Tipper and  McEvoy(  a n d D e v i l s C l a w .u n i t s  suggests the increasing importance  explanation  from  m.),  ranging  setting characterized  volcanic  area  to better delineate  Claw)  of angular to subrounded  as an  the  three subunits respectively.  (Devils  marine  to the source area. An  and  and  to Albian  detrital plagioclase feldspars and proximity  of  are,  m.), Currier (350-400  overall regressive sequence  in a marginal  predominance  corner  thick stratigraphic succession within the study  structural complexities within the study area the McEvoy have  and  following:  into 4 mappable  oldest to youngest: 800  of  CONCLUSIONS  fit linear  the northern Bowser  regression  of  to a pre-coalification  the Currier  was  buried  to a  vitrinite value depth  type southern  Basin. reflectance  of of  0.2% 4600-5500  m. 4.  The  parallism  of the  of isorank lines with  vitrinite indicating surface  folds and  suggest 182  thrusts as well as the  that coalification was  orientation  pretectonic.  183 Time-temperature  modelling  based  on  the method  history constraints indicated by field mapping supplied 1973,  by  previous  1974  1981), suggest  northern part of the Groundhog 30° C/km-40°  C/km.  As  minimum  estimate  uplift were  in the range  40°/km  gradients respectively.When  source  reflectances  of high  is thought  heat  to be  coupled  flow  material  is required.  compatable  with  base  C.  basin  of  2.00  for 30° C/km  2  and  with the necessarily higher  part of the  of coaly  180° C-220°  mW/m  the  of  for strata in the  y i e l d s c a l c u l a t e dp a l e o - h e a t f l o w s o f 6 0 - 8 0  relatively high  in  temperatures attained at the  conductivity  in the southern  1972,  gradients  in the range  W/m°C  gradients present  information  (Eisbacher, 1971,  that paleo-geothermal  such, the maximum  of thermal  this study and  Sustut Basin  Coalfield were  of the Currier prior to major A  during  studies in the nearby  a, b, c, 1976,  of Lopatin, utilizing burial  basin (Bustin, 1984) and in Sustut  Deposition  the estimated  Group  the  rocks, a  in a marginal  sustained  (back-arc)  paleo-heat  flows  and  5 km.  circulation  basin  the  sedimentology. Burial  of  the  strata to depths  of approximately  and  metasomatic fluids has resulted in diagenetic/metamorphic authigenic  assemblage  ankerite) and <2  Mm  alterations. An  consisting of albite, quartz, carbonate  clay minerals  was  identified in thin section. X-ray  illite/montmorillonite, illite/vermiculite,  relative abundances  throughout  plagioclase feldspars, growth  (often The  analysis of  the  chlorite/montmorillonite,  white mica (paragonite?), white mica/montmorillonite -  appear  (calcite, dolomite,  clay fraction illustrated the presence of kaolinite, illite, chlorite,  montmorillonite,  varying  of  to be as a  pre-  and  assumption  the section. Albilization of detrital  of clay minerals  syn-tectonic, whereas  late replacement)  is pre-,  that time-temperature  white mica/muscovite in  syn-  and  the precipitation of  the precpitation of and  modelling  quartz  carbonate  post-tectonic. of vitrinite reflectance yields  184 reliable paleo-temperatures  indicates that the persistence of expandable  clays, the subdued  illite crystallinity and  Bowser  Lake  Kubler  Group  for the respective stability fields. The  time-temperature organic  modelling  matter, and  matter and  [H 0]  condition that  PH 0 2  of the volatiles generated  increased  contribution  assemblage  species in. the  of C02  at the expense  to such of calcium  three phases  of deformation;  phase  the other  two. The first phase  increment  of total bulk strain and  amplitude  cross-cut  folds initiating by  are however,  to be  a  a  late feature  synchronous  decollement The  folds have  saddle  two  being  NW-SE  geometry plane  and  coaxial  perpendicular  vary  folds  in  a box-like  have kink  folded first phase geometry.  and  zones  faults  strain than  suggests  do  folds  fold lock-up.  Layer-parallel  accommodate  shortening in zones  structures. Locally, second  Relatively  flat-lying  the  which  second phase of deformation produced broad open  folds which  and  wavelength  slickenside geometries  Thrust  to  greatest  trending  and  less to the bulk  with folding and  The  possibly  roughly  resulted in the  mechanism.  following  to CH4. carbonate  reef features in kink core  buckle  fold limbs contribute much  thought  trending  collapse and  has  is manifest by  the area. Bedding  gradually  3  calcium silicates.  third phases  kink  organic  H 0  stabilizes a clay  of deformation  of  abundant  respect  is oriented approximately  a megascopic  throughout  of hinge  fiexural-slip  have  with  is characterized by  the first and  the intervening second  thrust faults. Folds  volatile phase  zeolites and  of the stratigraphic package  presence  maturation  characterized by  a system  Deformation  whereas  during  on  low permeability at temperatures in excess of 100° C,  a less abundant  are  empirically  is predictable based  2  suggests that in sediments  becomes  and  in  P„ ., is sought as an explanation for the stability of these minerals at fluid  lower than predicted temperatures. Low  9.  of phengites  rocks are inconsistent with experimentally and  derived temperatures <  the presence  lattice  thrusts which  and  faults  NE-SW phase have  of  185 resulted in klippen  and  have  northern part of the map cleavage  further  area. The  absence  indicates relative timing.  the gentle warping slickensides. The apparently  offset first phase  of second third phase  phase  of tight folding of F  Tenuous  compression  was  viscous  member,  phase  outlines  and  have  been  to have  developed  a  more  relatively high relationship  with  thrusts in the monoclinal  and  suprastructural  high  with  disharmonic  folding  a second  short  appearance combined  phase  northeast-southwest the second less than  phase  one  and  wavelength  which stacking  the shortening  angle  extension.  The  is indeterminate one  and  but  folds  2  flat  a  by  the  thick shales  which are  localized  deceptively  complicated  attributed  as measured  to be  three events. The  to  in  Shortening  appears  of  lying  listric at depth)  shortening  35%.  Jackson  parasitic  accomplished  give  bulk  by  phase  there is abundant  three compressions  that calculated for phase  a  Wherever  which  thought  Currier and  of  faults (presumably  first  plunging  are  and/or  have  and  more  southerly  faults which  arc compression  cross sections is approximately compression  but  large-scale  infrastructure characterized  layer detachments  phase  plane  as a  a  phase  angle  folds. Imbricate  to the overall geometries.  by  the lower McEvoy,  relatively thin sandstones and  is  by  units behaved  characterize the overlying suprastructural package. interbedded  phase  the first phase  characterized  by  comprises  infrastructure balances  flexure cut by  McEvoy  to outer  ducu'le first phase  amplitude  fault  strongly controlled  late stage high  as a response  less viscous strata which  units forms  Upper  pair and  flexure interupted by  faults or  2  thick section of conglomerates  a suprastructure  anticlinorium-synclinorium  monoclinal  The  and  superposed  the  strains.  within the area  in the Devils Claw  in  for a third  coaxial with  lithologically controlled viscosity contrasts. The sandstones  evidence  structures and  contributed only minimal  Structural geometries  structures, are present  attributed  to  substantially  contribution  of  186 phase 11.  three  Spaced  folding to the  pressure  deformations.  solution cleavage  Cleavage  distribution in the area  law  normal  grain size as factors which  stress and  (Rutter, 1976;  was  mechanisms  accelerated  developed of an  behaved  cleavage  overturned  cleavage  and  importance forming  in the immediate of high  process  well-developed and  McEvoy  cleavage  high  slip and  only  and  in second  otherwise  on  in all lithologies  characterized  by  well  a  the  lack  hinge of  thrusts demonstrates  the  cleavage  occurrence  of  the Devils  Claw  or less ubiquitous occurrence  solution distribution at lower  range  of  in  of  influence  temperatures. to have  become  approximately  C.  widespread  occurrence  associated pore  of  units, indicates the significant  a temperature  by folds  folds, near  lithologies within  to the more  within  grain  cleavage  localized strain to the  in fine grained  pressure  of the  phase  is relatively low. The  Jackson  of  other  occurrence  footwall of first phase  temperature  cleavage  size has  150° C-200°  nature  when  interbed  coalification studies, pressure solution cleavage appears  important  The  by  intergranular stress and  in the Currier  on  zones  area  units in comparison  initial grain Based  hinge  anticline in an  considerations  history of many  buckling resulted in fanning  near  phase  influence diffusion flow rates.  as fixed reference planes. The  only  by  second  incorporates temperature,  relatively early in the buckling  folds strain accomodation  surfaces, which  both first and  folds suggest that strain accomodation  the area. In these during  minimal.  is explained  1983), which  fans related to first phase  intergranular flow  to be  is associated with  the relevant flow  Cleavage  12.  total strain is thought  with  all phases  fluid pressures  predominance  of conjugate  coupled  the notion  with  of syntectonic veins of both  have  of deformation played  suggests  the  in the deformational  systematic fracture sets with of  antithetic and  "crack seal" vein  formation  low  synthetic  important  role  process.  The  dihedral  angles  that  suggests that differential  187 stresses were  generally low  for the Rocky Spang,  Mountain  (<  fold and  hkO  plane  suggests that the minimum times during magnitude.  low  plane  and  intermediate stresses were hence  conditions during  progressive  Based  on  the relative age  of northeast and  Sustut  Basin,  The  superposed  it is suggested  proposed  through  and  although  model  time  the  and/or  intervening folds and energy in a  and  in which  along  plate would  and  via slight changes  with  third phases  occurred  paleo-stresses  and  then  later shift to former  orientation of third phase  to  north-northeast  strike-slip faults in the Northern  Cordillera  of  times based  of strain events  displacements  along  the  in  the  is contradictory. to have  Kutcho-Pinchi  fault system. Northward  and  motion was  of  A  occurred Thibert the  manifest  as  orientation. Relief of constictional strain  slight change  paleostress warping.  from  palinspastic  displacements  a  the  occurred  result in constrictional strain which  coupled  folds in  deformation  shift in stresses is proposed  phase  in  on  for age  the  axes  time.  Early Cenozoic  the Denali  thrusts of second  perhaps  similar  trending  of  the superposition  evidence  as a result of simultaneous fault systems  northwest  to north-northwest  is consistent with  is suggested  of  various  deformation.  the second  restoration of units across numerous  thesis area  switched at  strains is attained  to early Tertiary  Late Cretaceous  1985)  and  orientations  probably  shift in general orientations of maximum  (Gabrielse,  Jamison  sub-parallel  were  that the first phase  pre-Santonian  northeast in pre-Albian again in the  documented  differential stresses the interchange of principal stress  boundary  post-Santonian 14.  a bedding  to create the three  and  100 MPa;  and  required  post-Albian  to those  of antithetic syntectonic vein fillings in  deformational history and With  in comparison  thrust belt (>  1971). 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