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Lithiotis bioherms in the Pliensbachian (Lower Jurassic) of North America Nauss, Anne L. 1986

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LITHIOTIS  BIOHERMS  IN  THE  PLIENSBACHI A N  (LOWER  JURASSIC)  OF  AMERICA  by ANNE  A  THESIS THE  SUBMITTED  L.  NAUSS  IN  PARTIAL  REQUIREMENTS MASTER  FOR OF  THE  FULFILMENT DEGREE  OF  OF  SCIENCE  in THE  FACULTY  OF  GRADUATE  STUDIES  (GEOLOGY)  We  accept to  THE  this  the  thesis  required  UNIVERSITY  OF  JULY  ©  ANNE  L.  as  conforming  standard  BRITISH  COLUMBIA  1986  NAUSS,  1986  m  NORTH  In p r e s e n t i n g  t h i s t h e s i s i n p a r t i a l f u l f i l m e n t of  requirements f o r an advanced degree a t the  the  University  o f B r i t i s h Columbia, I agree that the L i b r a r y s h a l l make it  f r e e l y a v a i l a b l e f o r reference  and  study.  I further  agree t h a t p e r m i s s i o n f o r e x t e n s i v e copying of t h i s t h e s i s f o r s c h o l a r l y purposes may department or by h i s or her  be granted by the head of representatives.  my  It i s  understood t h a t copying or p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l gain  s h a l l not be  allowed without my  permission.  Department of The U n i v e r s i t y of B r i t i s h Columbia 1 9 5 6 Main Mall Vancouver, Canada V 6 T 1Y3 Date  DE-6  (3/81)  written  ABSTRACT In  North  Pliensbachian bivalve  strata  formed  marine  massive,  Oregon.  three  Life  and  debris,  Assemblage  is made  free  and  is an elongate,  as  the  Lower  Konbostrea. formed  occurs  Jurassic  A l l three  Tethys  Ocean.  Pliensbachian Ocean,  East  which  Corridor.  endemic  center  robust  articulates  and  are found  water,  marginal  distribution  Pacific,  East  During  to the  marine  Pacific that  o f North  Pliensbachian  East  attached with  face  valve  is  a n d the Life  over  and  of  and  the  fragile  valve  by a  t h e attached  valve.  Upper  in l o w  30 c m in  a thin,  in a similar  paleoenvironment Cretaceous  diversity  oyster,  bioherms  that  environment. is widespread.  region  the bivalves America  and  the  America  Tethys  through t h e  migrated and  Eastern  during t h e  Western  occurred  Lithiotis  Lithiotis  in the  existed  and  migration  o f South  ii  brachiopods  t h e attached  Toarcian  Pacific  and  Assemblage  reaches  o f Lithiotis  of  the Lower  terebratulid  that  Circum-Mediterranean center  comprise  Lithiotis.  occurs  bivalves  o f east  is characterized b y  t o bedding  bivalve  Cochlearites  indicates  Hispanic  stick-like  bivalve,  A n endemic  in the  vertical  situ  marginal  Assemblage  T h e Death  parallel  o n t h e cardinal  paleogeographic  i n the  lying  in morphology  in a shallow The  valve  structure  is similar  the bioherms.  up o f a thick,  T h e free  ridge-and-groove Lithiotis  u p o f in  is made  valve.  of  and  water  Formation  Assemblage  Upper sessile  Formation  (2) a Death  Nerinea  in  epifaunal,  Robertson  the Robertson  Flank  gastropod  The  in shallow  i n the  Assemblage;  Reef  occurs  Lithiotis  Nevada.  bioherms  of  bivalves  Lithiotis  Lithiotis height  The  and  extensive  Flank  t h e perimeter of  diversity  bioherms  the  pelecypod  California  most  Assemblage.  marks  comprised  are  (1) a Reef  shelly  Lithiotis  low  Lithiotis  biofacies; a  t h e aberrant  in Oregon,  facies, which  central  (3)  America  from the  t o the  Eastern  Tethys  Ocean.  likely  due to  marginal water  The  absence  collection  facies. Offshore  marginal  marine  o f Lithiotis failure  exploration facies  or  i n the lack  could  in Wrangellia  area.  iii  of well  Canadian  suspect  appropriate reveal  in the  shallow  Lithiotis Queen  terranes i s water  in a shallow  Charlotte  Islands  Table  o f Contents  ABSTRACT  ii  LIST  OFFIGURES  vi  LIST  OFPLATES  viii  ACKNOWLEDGEMENTS I.  II.  III.  IV.  ix  INTRODUCTION  1  A.  INTRODUCTORY  STATEMENT  1  B.  PREVIOUS  C.  LOCATION  4  D.  METHODS  6  WORK  3  STRUCTURE  7  A.  STRUCTURE  O FTHE  JOHN  DAY  INLIER  B.  STRUCTURE  O F THE  SUPLEE-IZEE  7  AREA  8  STRATIGRAPHY  12  A.  STRATIGRAPHY  A T Lithiotis  B.  STRATIGRAPHY  O FTHE  C.  STRATIGRAPHY  A T Lithiotis  LOCALITIES  IN N E V A D A  27  D.  STRATIGRAPHY  A T Lithiotis  LOCALITIES  IN C A L I F O R N I A  28  E.  STRATIGRAPHY EUROPE  REEF  STRUCTURE  A T  AND  LOCALITIES  SUPLEE-IZEE  Lithiotis  IN O R E G O N  12  AREA  14  LOCALITIES  IN  SOUTHERN  PALEOECOLOGY  29 31  A.  GEOLOGIC  SETTING  31  B.  BIOHERMS  AND  34  BIOSTROMES  1.  Lithiotis BIOSTROME IN THE ROBERTSON FORMATION  2.  Lithiotis BIOHERM COW CREEK  C.  ENVIRONMENTAL  D.  CONCLUSIONS  IN THE  TYPE  SECTION  ROBERTSON  OF THE  FORMATION  A T 35  CONTROLS  ABOUT  35  THE  46 Lithiotis  iv  REEF  ENVIRONMENT  50  V.  VI.  PALEOBIOGEOGRAPHY A.  GLOBAL  B.  MIGRATION  C.  TECTONIC  D.  CONCLUSIONS  B. VII.  DISTRIBUTION  55  O F Lithiotis  59  IN N O R T H  AMERICA  TAXONOMIC  AFFINITIES  DESCRIPTION  1.  SHELL  2.  THE  ATTACHED  3.  THE  FREE  4.  BODY  5.  THE  6.  SUMMARY  O F Lithiotis  OUTLINE VALVE  65  .70 73 PLATE  O F Lithiotis AFFINITY  74 MORPHOLOGY  O F Lithiotis  78 78  O F Lithiotis  SYSTEMATIC  65  66  VALVE  FURROWED  O F Lithiotis  66  CHAMBER  TAXONOMIC  60 62  AND  MORPHOLOGIC  TAXONOMY A.  ROUTES  O F Lithiotis  IMPLICATIONS  MORPHOLOGY A.  55  91  DESCRIPTION  „  91  CONCLUSIONS  94  BIBLIOGRAPHY  97  v  LIST  1  Fig.  1-1;  2  Fig.  1-2:  Location  map  Location  O F FIGURES  o f the  Suplee-lzee  o f stratigraphic  area  units  America  in eastern  containing  Fig. 2 - 1 :  Major  4  Fig. 3 - 1 :  Terranes  5  Fig. 3 - 2 ;  Stratigraphic  6  Fig. 3 - 3 ;  Measured  7  Fig.  3-4:  Robertson  structural  John  sections  Bioherms  o f the  Day  relations  o f the  o f the  o f the  Suplee-lzee  area  <f / 3  Mowich  Robertson in  Group  ;  9  Fig. 3 - 6 :  Sandstone  10  Fig. 3 - 7 :  Cross-section  11  Fig.  and  Bioherm  lime  mudstone  from  from  Formation  northern  in the  from  the  X t o Y o n map,  t h e Robertson  it-  exposures  Suplee-lzee Robertson  of  Nerinea  13  Fig. 4 - 3 :  Death  14  Fig. 4 - 4 ;  Life  15  Fig.  5-1: the  gastropods,  Assemblage Assemblage  Paleogeographic  from i n the  i n the  Formation,  Zonation  allochthonous  terranes  o f the  Fig. 6 - 1 :  Morphology  18  Fig. 6 - 2 :  Cross-sectional  19  Fig. 6 - 3 :  Thin  20  Fig.  section  Flank  Creek Creek  Formation  northeast  of  Cow  — —  Assemblage  ¥Z.  bioherm.  o f Lithiotis  and  migration  routes ^t>  within  the  Pliensbachian  Cordillera  63 (of  o f Lithiotis.  (o%  o f Lithiotis  Cross-sectional  view  3 ? 39  o f Lithiotis view  2JL Z.b  bioherm  displacement  Western  — ZO  —  latitudinal  17  6-4:  Cow  _ and  Reef  Cow  distribution  bivalve.—.  5-2:  the  •  area  .  Fig. 4 - 2 ;  the  Fig. 3 - 5  Creek 12  15  Formation  —•  Robertson  5  ;  Formation.—-— Map  Fig.  in North  Inlier.  a n d biostromes  Fig. 3 - 5 :  4-1:  divisions  o f the  8  16  Lithiotis  2.  . .  3  of  Oregon  o f Lithiotis  vi  70 illustrating  the  position of  the 21  Fig. body  free 6-5:  valve  l-Z.  Cross-sectional  chamber..  _  view  o f Lithiotis  illustrating  .  22  Fig. 6 - 6 :  Internal  structure  23  Fig. 6 - 7 ;  Ridge-and-groove  the  shape —  o f Lithiotis structure  vii  o f furrowed  plate  o f the —:  ^5  LIST  OF PLATES  1  Plate  1: H o r i z o n t a l  cross-sections  o f Lithiotis  #3  2  Plate  2 : Horizontal  cross-sections  o f Lithiotis  %f  3  Plate  3 : Horizontal  cross-sections  o f Lithiotis  25  4  Plate  4 : Strongly  5  Plate  5 : Lithiotis  float  specimens  6  Plate  6 : Lithiotis  float  specimens.  7  Plate  7 : Lithiotis  morphology  8  Plate  8 : Lithiotis  morphology.  ribbed  and  smooth and  shells  Lithiotis juvenile  bivalves.,  ;  2 6 fff  _ ;  . 29 90  viii  ' I Smith, this  would for  like  his  project.  committee,  I  help,  Dr.  Melanie  Montgomery  W.  C.  like  Barnes many  and  Dr.  thanks  photography  his  numerous freely to  Gord  terrific.  shared my  his  husband  Hodge  his  for  members  of  field  the  their  to  Taylor  make a  from  and  P.  L.  work  my  advice  and  and Jung;  to  deal  Ed  rather of  Portland area.  on  graduate  some  great  Suplee-lzee support  Dr.  assistant, Art  drafting;  provided  D. of  for  superb  continuing  ix  during  managed  Dr.  advisor,  patience  Danner  excellent  Douma  and  graduate  other R.  he  knowledge for  the  an  -  my  endless  W.  to  Yvonne  thin-sections  to  and  thank  for  look  thanks  to  and  making  indebted  my  Sullivan  fossils  am  also  I owe  dubious  University  express  encouragement  would  encouragement. to  to  ACKNOWLEDGEMENTS  help State  Finally,  encouragement.  I  I.  A.  INTRODUCTORY  STATEMENT  GUMBEL  Lithiotis  INTRODUCTION  (1871)  is an epifaunal,  massive  bioherms  in  bioherms  are found  in C a l i f o r n i a  Suplee-lzee square  area  are  bivalves  forming  majority unusual.  of  bivalves  In (1930) a  North  as  junior  1977;  and  California  Africa  far east  The 1.  of  tightly  over  (Figure  in  the  several  1-1).  The  packed  Lithiotis  contrast  with the  heights  of  thickness  is  also  30 c m or  of 3 c m . The  and secreted  tremendously  size.  w a s first  described  b y Lupher  has since  PI i catosty I us (Loriga  Lithiotis  America. The  the bivalves  reaching  formed  extensive  that  of  that  extend  5.5 m  communities  body  North  than  producers  t o their  gregarius.  and Neri,  been  a n d Packard recognized as  1976; Benini  and Loriga,  1980). distribution  and Nevada  (Hillebrandt, throughout  as Timor  purpose  greater  they  The morphology  Lithiotis  1965; Taylor,  America  Northern as  of  geographic  Vigrass,  South  America  Wiedenmayer,  Oregon,  where  exclusively  carbonate  bivalve  but are most  and stick-like,  in proportion  synonym  in  o f 4 to 6 c m and an average  PI icatostylus  The  reefs.  prodigious  skeletons  of  l o w diversity  is elongate  a width  Oregon  almost  extremely  strata  and Nevada,  thicknesses  Phanerozoic  were  Pliensbachian  central  composed  Lithiotis  with  large  east  k m a n d reach  bioherms  more,  of  lower  sessile  in  o f Lithiotis in  North  1977; Hallam, 1981a).  is  America  Lithiotis  and s c o p e  t h e d e s c r i p t i o n , structure  (Loriga  of this and  is  1  found region;  and  thesis  ecology  (Lupher,  it i s f o u n d  of  Neri,  lies  a n d Peru  in southern  1976; Geyer,  a Lithiotis  areas: bioherm;  in  Europe and  in the M i d d l e  in three  in  1941; Dickinson  1983) a n d in Chile  the Mediterranean Indonesia  widespread;  East and 1977).  2  Figure  1-1  :  Location  map  of  the  Suplee  Izee  area  in  eastern  Ore  gon.  3  2.  the  3.  the  morphology  and  taxonomic  paleobiogeographic  affinities  implications  of  of  and  Lithiotis  the  geographic  distribution  of  Lithiotis. The  Oregon  because or  B.  the  bioherms  are  far  were more  selected  for  extensive  in  the  focus  these  areas  many  papers  of  the  than  in  study Nevada  California.  PREVIOUS  WORK has  Lithiotis described the  localities  Lithiotis  (Gumbel,  bivalve  Ostreidae  Ostrea,  which  Ostreidae.  He  Spondylidae  Italian  authors  a  a  be In  Packard, studies 1941;  of  Lithiotis  In  was new  Loriga the  subject  family,  1972;  Loriga  bivalve,  gregarius  of of  1903  has  and  Neri,  morphological  from  The  Oregon,  and  REIS. and  a  paper  on  not  the  major  near  In  of  Benini  taxonomic  review  suggested  papers  Bosellini  review that  family 1903.  deal  1977  This  the  since  papers  (Cavicchi,  to the  series  Italian  1976).  Lithiotis  Spondylidae,  a  was  with  unchanged of  it  included  Lithiotidae,  first  bivalve  Cochlearites  the  remained  the  be  published  the  since  comparing  should  to  Lithiotis. the  papers  Reis  related  published  comprehensive  PI i catosty I us might  a  paleoecology  similar  that  classification  and  Bosellini,  several  1906).  believed  this  on  and  published and  he  and  in  wrote  suggested  1892  and  Bosellini  1971;  and  mentioned  Boehm  proposed  1971,  taxonomy  briefly  1871).  (Boehm,  Lithiotis  been  by the  and  Loriga,  and  Loriga  of  also the  with  In  Lithiotis discussed  two  bivalves  synonomous. North  America  1930)  and  Oregon,  Silberling,  PIicatostylus  several Nevada  1959;  authors and  has have  California  Dickinson  and  been  briefly  included (Muller  Vigrass,  and  1965;  described  the  bivalve  Ferguson, Stanley,  (Lupher in .1939;  1971).  and  regional Lupher, Lithiotis  4  bioherms  in  North  America  paleoecological  point  have  not been  closely  this  thesis, along  with  distribution  C.  studied  and the taxonomic  examined.  These  subjects  the paleobiogeographic  in  a n y detail  affinities are of  of  a  the bivalve  major  implications  from  interest  in  of the geographic  LOCATION Suplee-lzee  Mesozoic central  marine  Oregon.  extensive Inlier  part  over  an  Creek  within  Oregon  of  area  area,  U.S.  is easily highway  roads  and  accessible Two  which  the Blue  to  D a y Inlier,  cover  Group  area.  exposures  in  o f the  of  also  occur  of  the Suplee-lzee Prineville  (Figure  criss-cross  the  area,  along C o w 1-2). Several  are most  o f the  prominent  C o w Creek. The  via Paulina;  and John  is  crops out  Suplee  along  covers  throughout the  Formation  to the west, Burns  which  t o the northeast  area  inthe  Formation  is exposed  Suplee  east  The John Day  province,  of  mostly  k m in break  The Robertson  which  of  and from  Day.Numerous making  most  ranch places  dry weather.  c o l l e c t i n g trips  alongside  Oregon.  15 k m n o r t h e a s t  3 9 5 t o the east, between  by vehicle  of  of Seneca. The bioherms  accessible from  roads  an important  The Robertson  Formation  region  650 square  geologic  Idaho.  15 k m s o u t h e a s t  7 k m north  logging  much  Mountains  from  of Robertson  fossiliferous  approximately  Mowich  extends  M a y 1 9 8 5 . T h e area  desert,  highly  of the John  Jurassic  that  the northern  area  covers  the Suplee-lzee  exposures  Suplee-lzee  a  and westernmost  in t h e north,  small  that  volcanics  o f the lower hills  is  It i s p a r t  is located  rolling  area  strata  Tertiary  northeastern  and  view  not been  of the bivalve.  The  in  of  have  were is  Ochoco  made in  to  the  and  the  Suplee-lzee  northwestern  Malheur  national  area,  corner  of  forests.  in  July 1984  the  Oregon  5  /  SUPLEE-IZHE»  /  # S E N E C A  Robertson Fm.  IDAHO  OREGON CALIFORNIA  NEVADA  PLUMAS COUNTY •  #  • S H O S H O N E MTS. Sunrise and Ounlap Fm.  Thompson Limestone 100km.  *GABBS V A L L E Y RANGE\ Sunrise and Ounlap Fm.  i  Figure  1-2: Location  C L A N A L P I N E MTS. Sunrise Fm.  of  stratigraphic  units  containing  Lithiotis,  in N o r t h  America.  6  D.  METHODS The  Lithiotis  bioherms  the  Suplee-lzee  area.  The  Oregon-Grant  County  map  throughout  N4400-W11930/7.5 Seven  sections  metre  stick  to  cm  with  a  thin  over  the  the  in  recrystallized  if  traces  a  of  attempted  for  analysis  thin-sectioned rock  units  microfossil  of  organic was  on  the  Al-lssam). and  their  and  content.  several  off  but  were  details. The structure  as  were to  lost.  The  Lithiotis  processed  could  be  University  the with  specimens  bioherms  were  Samples were  Quaternary-0  a  were as  the  were to  isotope of  recrystallized  examined.  for  see  highlighted,  the  extensively to  Hydrate)  sent  float  laid  slabs  oxygen  too  were  considerably  and  be  sprayed  successful  Carbon to  into  photographs  are  shell  and  the rock  cut  negatives  (Triketohydrindene the  reef  thick,  fossils  is  map.  using  later  acid  as  SEM  not  base  of  and  mm  used  bivalves.  within  subjacent  were  slabs  in  0.3  and  a  Formation,  Four  sheets,  the  proved  morphology and  Robertson  Quadrangle,  as  etched  staining.  Numerous  used  were  "Ninhydrin"  fossils  was  Formation  Butte  slabs  shell  fossils, which  Funny  collected  of  by  Robertson  were  peeled  template  the  (1962).  Acetate  the  in  m  bivalves,  revealed  the  0.3  morphologic  stain,  superjacent  thin-sectioned  The  the  detail  but  communication  lab.  dried,  of  protein  nothing  was  by  acetone.  were  the  Compton  m  displaying  the  in  photographs  and  with  however  and  details  peels  stained  the of  enlarged  of  acetate  in  coating  slabs  of  taken  slices  0.7  mapped  through  outlined  approximately  6  series  measured  technique  measuring 3  were  were  to  work Ottawa  (written collected, from  the  collected, check  for  II.  A.  STRUCTURE In  the  Devonian  to  OF  THE  JOHN  DAY  John  Day  inlier  the  Triassic  components  of  of  materials  oceanic  elastics but  are  thick  of  the  the  upper  relations,  Triassic  rocks  actively that  associated  upper  with  arc-continent Early  Jurassic.  representing Regional a the  Largely  relations  continental  arc  strata  the  the  it.  Dickinson  on  the  downward  The  same  to  style  to of  suggests related  that to  the  rest  margin.  7  in  deformation  downward  to  are  mainly  (1979)  as  relations  was the  basins  perhaps  during into  Jurassic all  upper basins  trench-like  on  both  the  persisted  and that  suggest  Regional  mid-upper  sequence  terrane  wedge-shaped  northwest,  to  Triassic  volcaniclastics report  the  complex  Baker  elastics  north."  occurred the  the  southeast  local  and  Upper  changes  unconformably  Jurassic  subduction  the of  west  on  is  Ophiolitic  subduction  Thayer  facies  volcaniclastic mid-lower environments,  a  melange, and  and  sedimentation  terrane.  Triassic  uplifted  succession  margins  assemblage  consumption.  upper  dispersal a  is  unconformably  trends  sediment  rock  Baker  melange plate  The  eroded  in  of  rest  sediments.  subduction  forearc  continental  of  Triassic  collision.  lowest  locally  accumulated deforming  structurally  that  paleocurrent  and  INLIER  during  against  Triassic  transport  suggest  terrane  comprised  tectonic  with  imply  deformed  faulted  turbidites  "Structural  melange  terrane  Izee  largely  reworked  STRUCTURE  older  associated southeast  the  strata, units. with along  8  B.  STRUCTURE The  (Figure  1.  The  of  2.  strata  northeast The  Jurassic  strata.  4. strata of  the  terrane  Creek  lying  east  be  divided  Upland  that  is  crops  out  Downwarp  is  of  southeast  most  an  the  Paleozoic  Pine  and  upwarp,  along  can  into  four  major  structural  a  belt  along  of  up-faulted  Paleozoic  the  western  edge  of  the  area.  The  3.  area  AREA  2-1)  Baker  Suplee-lzee  the  SUPLEE-IZEE  Western  the  Jurassic  THE  Suplee-lzee  divisions:  rock  OF  lying  the  the  upper  upper  Upland Triassic  of  the  Triassic  upwarp  of  of  downfolded  and  flanked  on  rock.  area  rocks  is and  folded  the  Mowich  flanked  Triassic  rock  by lies  area.  Syncline of  of  feature  companion  of  Lonesome  by  synclinorium  Paleozoic  exposures  cored  edge  southeast  Western  structural  unnamed  northwest The  by  dominant  anticlinorium An  the  a  is  a  Mowich  deep  structural  Upwarp  along  trough  the  of  Jurassic  southeastern  edge  area. The  which  Suplee-lzee  are  divided  Jurassic-Cretaceous The Paleozoic  basal rock  sedimentation Permo-Triassic  area  can  by  the  divided  into  three  Permo-Triassic  major  structural  unconformity  units  and  the  Orogeny.  unit  is  a  substrate  representing and  be  a  little  volcanism.  The  unconformity  of  indurated  known end  when  period  of  this  orogeny  and  and of  mildly upper  period  metamorphosed Paleozoic  is  igneous  marked  marine by  intrusion  the  halted  sedimentation. The sequence upper  middle  structural  representing  Triassic  strata  a is  unit  period an  of  is  an  marine  accumulation  upper  Triassic  sedimentation of  clastic  to  upper  Jurassic  and  volcanism.  detritus  eroded  The from  9  Western  Figure 2 - 1 : M a j o r structural V i g r a s s , 1965, p.12.  divisions  upland  of  the  mainly  Suplee  Paleozoic  Izee  area.  From  Dickinson  and  10  tectonic  highlands  and  contemporaneous Jurassic,  volcanism  sedimentation  resulted had  in  major  terminated  rests  Suplee-lzee  area  upon  the  tight  upright  as  before  Triassic or  as  Suplee-lzee  Mowich  90  the  Mowich  Group  the  Ochoco  Orogeny  that  it  to  much  northeast  with  local  or  erosion  part  of  Group  the  The  east.  rise  to  the The  earlier  of  the  raised age  onset  of of  Robertson  Formation  Formation  in  the  strata  in  folds,  and  open  the  was  Jurassic  Pine  deformation Ochoco  as is  Orogeny  in  place  the  between that  the  west  set  of  or  north  orogeny.  until  mild  debris  late  early  warping  and  of  the  western  removal  of  the  Mowich  Downwarp.  distinct not  of  is  Upwarping  by  Creek  strata  volcaniclastic  middle  accompanied  platform  of  took  the  the  parallel  sources  unconformities.  was  part  deposition  some  suggests  in  the  into  In  part  This  during  the  thrown  trends.  longer  crudely  activated  other In  A  of  discordance  slight.  which  discordance  were  eastern  the  is  Orogeny  underlying  the  continued  west.  rapid  angular  bioherms  western  and  the  time.  of  strata  the  which  part  angular  northerly  Triassic  from  Suplee  with  early  Group  western  which  and  in  axis  this  Formations,  the  The  Mowich  marked  Group  faults  area  the  Limited  Orogeny,  strata.  Jurassic  Mowich  Orogeny  Suplee-lzee  northwest  established  reverse  Triassic  with  During  Ochoco  In  folds  earlier  Jurassic  gave  rests  underlying  contributions  middle  lower  basins.  detritus.  the  the  Group  intense  Ochoco  subordinate  Jurassic  the  the  the  more  of  strata.  into  started  trending  After  The  by  the  tectonic  clastic  older  the  pushed  and  the  Brisbois  between  was  of  overturned  degrees.  area  was  and  slightly  discordance  much  all  Begg  to  faulting  deposition  the  adjacent  interrupted  and  on  in  added  was  folding  unconformably  places  deposited  from  the  necessarily the  to  the  west,  and  of  the  Suplee-lzee  west,  upwarping  Izee  basin  middle  of  suggest  to  Jurassic.  restriction  thinning area  The  of  the that  the Hyde the  11  Suplee  platform The  upper  sequence intense  existed  by  the  deposition  of  folds  gentle  deformation. downward  into  thousands  of  during  the  east the  from  position  where  position  where  Following  interrupted  and by  or  trending  feet  of  structural  Orogeny  horizontal the  the  In  original  relief.  folds  refolded with  were were  Cenozoic. intermittent  period  warping,  strata  as  a  upper  result  the  northerly and  in to open  of  was  downfold  Triassic  prior area  sequence a  clastic  resulted  platform  developed  isoclinal,  the  arched  with  many  strata  folded  statistical  fold  strike  a  vertical  nearly  random  to  to  a  axis  open.  continental  This  Suplee  and  a  Jurassic-Cretaceous and  Jurassic  Syncline,  The  Jurassic  orogeny  Jurassic  Lonesome  were  folds  trends  the  This  of  the  thick  position  original  the  alteration  the  east  from  Orogeny.  strata.  basin  Jurassic.  divided  southeasterly  Izee  sedimentation  Cretaceous  diagenetic  the  a  is  Cretaceous  Cretaceous  Ochoco  changed  marine  and  middle  unit  Jurassic  upper  In  the  structural  deformation  with  before  Orogeny volcanism  of  faulting,  a  occurred  sedimentation uplift  and  period  and  of  shallow  through  the  volcanism  was  erosion.  III.  A.  STRATIGRAPHY  east-central  Mowich is  Group  made  up  distinguished al.,  1984)  terrane"  Izee  the  the  the  Jurassic  late  is  Izee is  by  Inlier.  representing  divided  part  made of  Mountains The  a  to  It  is  crust  and  variety crops  was  Mowich  area"  The  age,  in  by  assemblage  as  rock the  Group  out  deep well types  the  Devonian  12  in  the  marine as  corner  "Melange and  age.  the  to  the  (termed  the  lower  Vester sequence base  of  "Central  part  of  disrupted  the upper  strata  admixed  of  blocks  et  al.,  1984).  The  of  the  John  Day  of  the  terrane  Thayer  clastic  Jurassic  at  tectonically  et  and  sedimentary  (Silberling  and  rocks  units;  of  Inlier  (Silberling  northern  belt  the  bounded  middle  terrane  of  "Mesozoic  situated  area  The  sedimentary  is  melange  Dickinson of  the  lithologic  southwest  as  Inlier.  fault  through  Baker  a  Day  unit  Jurassic Volcaniclastic  crops  of  characterized  Grindstone-Twelvemile disrupted  out  the  basal  stratigraphy  clastic  main  Group,  associated  of  of  Suplee-lzee  the  are  (termed  Triassic  four  up  mid-Triassic  wide  terrane  made  which  up  the  John  distinctive  late  (1979))  in is  the  terrane  into  Dickinson  of  their  volcaniclastic sequence.  Paleozoic  tectonically  The  OREGON  Formation  terranes  by  Formation.  oceanic  It  as  another  (1979))  Aldrich  terrane"  Grindstone  out  IN  Formation  Robertson  distinct  3-1).  Lonesome  Day  Inlier.  one  terrane  Paleozoic  Robertson  volcaniclastic rocks  and  John  crops  Dickinson  Formation,  melange  the The  three  (Figure  subordinate The  which  from  by  in  Oregon.  of  LOCALITIES  LITHIOTIS  occurs  Lithiotis of  AT  STRATIGRAPHY  (1978)  Triassic  and rocks.  is  a  13  Suplee-lzee area  Eastern Oregon  0  50  100km.  Izee terrane Baker terrane Grindstone terrane Figure  3 - 1 : Terranes  of the John  D a y Inlier.  (adapted  from  S i l b e r l i n g , et a l . ,  1984)  14  B.  STRATIGRAPHY The  OF  Mowich  Paleozoic  to  reflected  THE  Group  Triassic  locally  in  the  rolling  uplands  folded  upper  Triassic  and  underlie  The  Triassic  and  Brisbois  1965).  In  faulted  (Smith,  a  Members  of  northeast  fossiliferous  The  up  1981),  angular  period  the  unit  tentatively  which  surface  of  erosional  surface  in  The  Mowich  Nicely  and  Hyde  (Figure  3-2).  It  distance  flank  of  axis  of  of  the  km  of  Pine by  Formation.  The  western  out  the  of  in  a  the  between area  lower  the  and  two  on  into  east  was to  into  Dickinson  continuous  It  Mowich  units  is  an  conformable  in  the  this  area.  angular  1965) for  southeast along  northwest  Jurassic  east.  Suplee,  and  was  an this  exposures  patches  Group  middle  and  of  absent  is  over  Vigrass,  nose  discontinuous  marks  created  Robertson, and  Group.  rocks  which  belt  plunging  Mowich  in  are  Pliensbachian  deposited  the  Vigrass,  sporadically  older  west  Begg  Members  exposed,  and  area.  the  and  Brisbois  Orogeny,  Group  Paleozoic  Suplee-lzee  (Dickinson  Group  2-2).  The  Tightly  the  southwesterly  Downwarp.  2-2).  by  1941,  (Figure  (Figure  overlain  from  in  in  lower  Mowich  and  out  to  (Lupher  the  crop  divided  and  Ochoco  nearly  rocks  Triassic  divided  thin,  are  older is  the  poorly  been  transgressive  contact  part  has  upwarp  Creek  the  The  Upwarp  the  a  Mowich  transgressing  along  Mowich  overlapped  the  sea  Formations  40  flank  relief.  Group  crops  the  northwest  a  the  of  Begg  upper  diastrophism,  low  the  unconformably  between  km  the  lithology  unconformity  and  Shale, as  Suplee  Formation  area  dated  also  widespread  erosional  a  is  thick  Vester  Creek  of  on  whose  Paleozoic  square  m  the  Inlier  angular  100  400  of  Keller  unconformity  of  with  the  part  Day  southwest  lie  to  John  unconformity  Formation.  and  rocks  angular  the  Robertson  are  against  of  west  AREA  with  approximately  rocks  the  rests  rocks  gently  rocks  SUPLEE-IZEE  of  the the  progressively Snowshoe  unconformity  in  15  F i g u r e 3-2: Stratigraphic (adapted f r o m D i c k i n s o n  relations of and V i g r a s s ,  the M o w i c h 1965)  Group  in  the  Suplee  Izee  area  16  a.  Stratigraphy  o f the Mowich  The  Group  units  in  Suplee,  b.  Mowich  Robertson  the South  absent  100  part Fork  rapidly  measured  sections three  reaches  at  in the Pine are indicated  volcanic  John  types;  older  Mesozoic  the  Robertson,  into  sandstone  and Pine  located  Swamp  Creek  area  in Figure  of  unit  Formation  of  of Suplee and Formation of  in  the  green  on  northern of  Formation  conglomerate,  were  Suplee  3-3).The locations  3 - 4 . The Robertson  is  approximately  13 k m s o u t h e a s t and  Point  the group. T h e  northeast  Ranch;  Group  Pyramid  of  the Robertson  (Figure  polymictic  a n d grey  East  thickness  Creek  of  of the Mowich  the Robertson  maximum  Section,  basal  area.  is the basal  Sections  Creek  unit  D a y River  a  Creek  t o the east.  rock  divided  is the basal  Formation  Swamp  Ridge;  exposures  overlies  (Figure 3 - 2 )  the Suplee-lzee  o f the  at t h e T y p e  Robertson  has been  Formations.  of  Formation  m between  thins  area  Formation  and the Suplee  Robertson  unconformably  FORMATION  the western  and  c.  and Hyde  ROBERTSON The  in  which  the Suplee-lzee  Nicely  Group  these  includes  and  brown  limestone.  CONGLOMERATE A  basal  Robertson  Formation  formation. which  The  have  Formation. grained  conglomerate where  Begg  been  conglomerate  is  Member  contains  absent.  of  the  underlies The  southern  Begg  exposures  Member  chert-pebble  incorporated  and  exposures  Member  i n the  the Triassic  reworked  In n o r t h e r n  Brisbois  is found  Robertson  the  Robertson  into  underlies  the  conglomerates the  Formation  formation  of the  and  conglomerate  Robertson the finer the  basal  can  be  Jms  Jswb  Jsws  Jsws  Jsws  Jsws  Jsws  III VI V  TRbr  mm  Section 5 Cow Creek  TRbg Section 1 Type Area  TRbr  •mudcracks  Section 6 Cow Creek  TRbr Section 2 Swamp Creek  10 - 5  - Life A s s e m b l a g e  - 0 metres  TRbr Section 4 Spring Creek  - Death Assemblage  1  - Reef Flank Assemblage - lime m u d s t o n e -  TRbr Section 3  silty/sandy lime m u d s t o n e  13  TRbr  Triassic Brisbois Member  TRbg  Triassic Begg Member  TRbr  Pine Creek  Section 7 Cow Creek  Jms  volcanic sandstone conglomerate  Jswb  trough c r o s s b e d d i n g ripple c r o s s b e d d i n g  Jurassic Mowich Group Suplee Formation Jurassic Snowshoe Weburg Member  Formation  Jurassic Snowshoe Warm Springs  Formation  shell debris  Figure  3 - 3 ; Measured  sections  of  the  Robertson  Formation,  locations  on  Fig. 3 - 4 .  18  V PRIMARY STUDY AREA Mean Current Direction  s e c o n d a r y highway unimproved r o a d creek Lithiotis bioherms —  Lithiotis biostromes A  3,4,5,6,7  (b)  Figure  3-4,  Formation the  primary  Life Assemblages l o c a t i o n of m e a s u r e d sections  ( a ) a n d ( b ) : Lithiotis from study  Wilson area  Creek  bioherms to  and biostromes  C o w Creek.  Current  in t h e  data  Robertson  collected  at C o w C r e e k .  t  from  19  distinguished by  the  from  angular  rounded  and  The  conglomerate cobbles  rare  in  the  is  in  the  d.  it  area,  two  a  35%  exposures  bedding  the  in  and  for  and  contains  (Figure  Swamp  more  Robertson  sandy  approximately  central  the  the  resistant  bedding  in  Conglomerate  formations  massive,  accounts  Member  pebble  layers 40%  Creek  of  of  the  area  and  3-5).  SANDSTONE The  dominant  sandstone  which  sandstones arenites. grains  of  detrital range  are  They  hyalopilitic  are  is  Begg  internal  shows  boulders;  northern  the  defined  locally  type  Triassic  dividing  conglomerate  formation absent  better  which  and  underlying  unconformity  clasts  Formation.  the  are  or  are  fine  show  thin  of  sand  grey  cross-laminated,  well  are  of  glassy and  granule  and  and  cement  the  calcite,  green  65%  dominantly  (Figure  The by  weather green.  to  (A)).  are  the  1965).  brown.  subrounded  5%  of  of the  The  sandstones  common  sandstones  and  In  celadonite  the  result  Silty  Those  The  volcanic  fragments than  chert.  most  volcanic  sorted  Less  chlorite  3-6  sandstones Vigrass,  and  a  formation.  subangular  augite.  felsite sand.  is  volcanic . rock  minor  cemented  cross-bedding  spotted  to  Formation of  originally  grained,  Robertson  45%  locally  to  (Dickinson  phyllosilicate  for  quartz,  medium  commonly  the  pilotaxitic texture  commonly  alteration  of  composed  plagioclase,  from  beds  accounts massive,  grains  green,  lithology  northern of  areas  diagenetic  calcarenites with  and  are  iron-bearing  zo  Paleozoic rocks TRbg  T r i a s s i c B e g g M.  TRbr  T r i a s s i c B r i s b o i s M. 'PCB  Lower Jurassic Robertson Fm.  Lower and Middle J u r a s s i c  •  Upper C r e t a c e o u s  (4)  L o c a t i o n s of m e a s u r e d sections  Tertiary Picture Gorge Basalt  - —  paved  Figure 3 - 5 : L o c a t i o n of Lithiotis bioherms and Formation in the Suplee Izee area. Detail of C r o s s - s e c t i o n (X to Y ) in F i g . 3 - 7 .  Lithiotis b i o s t r o m e s and bioherms  highway  gravel road  b i o s t r o m e s w i t h i n the box (upper right) in  Robertson Fig. 3 - 4 .  21  e.  LIMESTONE Lenses  Robertson of  grey  Formation  theformation  from  hard  highly  light  above  rudstone  o n eanother.  northern  The  Lithiotis  Death  Assemblage  found  within  represent Cardinia,  the  and  o f three and  inter-reef Chlamys,  Pinna,  Pleuromya,  Trigonia  these  inter-reef  limestones  have  also  1965; been  Ostrea,  Hallam, found  Gervillia,  Parallelodon, and  1965). in the  and  between  Weyla  (Batten  mudstones  bioherms  Flank  Assemblage,  1976;  Camptonectes,  cf.  Lima,  decemcostata, found  within  Dickinson a n d  recrystallized (Figure  lenses  Isocyprina,  been  a  bioherms  Lithiotis  P.  have  in S e c t i o n  mudstone  the  in  environment.  in detail  Astarte,  and West,  Smooth-shelled, lime  stratigraphically  between  Pholadomya,. unca  vary  the sandstones and  Grammatodon,  cf.  beds  biostromes and  Calcareous  The pelecypods  Coelastarte,  Modiolus,  Vigrass,  a Reef  as 40%  to massive  depositional  assemblages:  areas.  Lucina,  shallow  Assemblage.  lenses  repeated  discussed  sandstone  limestone  within  found  5 % ofthe  a s much  Lithiotis  bioherms,  a Life  volcanic  been  a very  and  The  are often  have  indicating  biostromes  arecomposed  units  than  mudstone  are interbedded  Mudcracks  areas,  lime  and bafflestone  limestones  less  exposures  exposures.  unfossiliferous  and biohermal  the  constitute  in t h e southern  grey  The  biostromal  limestone  in t h e northern  indurated  bioherms.  4,  of  ostracodes  3 - 6 (B)).  Figure  (A)  3-6:  Green, medium grained, volcanic  sandstone.  (B) L i m e m u d s t o n e c o n t a i n i n g s m o o t h R o b e r t s o n F o r m a t i o n at C o w C r e e k .  shelled  ostracod.  23  f.  AGE  OF  THE  The Formation eastern  Suplee in  of  the  the  basal  of  green  far  The  formations  Suplee Keller  Suplee  Shale  (Smith,  ammonites  from  the  likely  Upper  to  Pliensbachian  SUPLEE  angular the  for  Suplee' in  Suplee in  the  Robertson  shallow  water  to  a  East  nearshore  of  Creek  Izee  the  Shale.  The  from  the  contains  zone  Formation  bivalve  in  very  Formation  age.  is  1965).  Carlottense  is  Robertson  which  Mowich  Vigrass,  ammonites  the  age,  the  and  Suplee  The  Suplee  Formation  Keller  Robertson  the  Group.  the  of  west  Formation,  in  the  Formation western  unconformity  area.  The  fossiliferous are  the  Toarcian  age  the  in  Mowich  edge  Pliensbachian  but  within  east.  the  Robertson  (Smith,  in  part  a  Formation  is  is  Lithiotis  supports  upper  an  Upper  Formation.  FORMATION  The Formation  the  Pliensbachian  Pliensbachian  g.  of  on  the  Pliensbachian  As  the  occur  the  in  and  area  from  in  environment  1981)  Izee  Robertson  change  basal  the  (Dickinson  environment  upper  communication).  equivalent  the  on  of  central  that  unconformably  zone  facies  eastern  facies  contains  Suplee unit  Formation  a  depositional rests  the  sandstone  indicates  Pinnaforme  personal  the  restrictive  Formation Creek  as  represent a  water  the  is  Robertson  which  to  in  area  east  3-5),  equivalent  shallow  conformably of  part  deposition  rests part  as  (Fig.  Formation southwestern  Intercalations  Upwarp  FORMATION  the  part  Formation  ROBERTSON  abundant;  on  Suplee  grey the  part older  of  conformably  the  pecten  rocks  consists  sandstone  on  Suplee-lzee  Mesozoic  Formation  calcareous large  rests  and  Wey/a  is  in of  the  area the  found  but  lies  eastern  up  sandy  Robertson  to  23  limestone. in  nearly  with  part  of  m  of  Fossils every  24  exposure as  well  the  and the pelecypods as rhynchonellid  formation  Gervillia, locality  Gryphea  (Dickinson bivalves  is s o numerous  Imlay  Pliensbachian. which  Paral lelodon.  and Vigrass,  by  1965).  T h e fauna  (1982)  Modiolus,  w h o assigned of  large,  Assemblage  B,  pelecypods  They  the assemblage  thick-shelled from  a  In o n e  limestone  in c o m p a r i s o n  Formation  in  Meleagrinel la,  coquinite  o f t h e unit.  the Suplee  ornate,  a  a r e rare  part  Trigonia  a n d Homomya.  it f o r m s  Ammonites  Other Pinna,  Goniomya  that  in the upper  (1968)  are relatively  Taylors'  are c o m m o n .  Coelastarte, Lucina,  but d o occur  studied  brachiopods  include  Ostrea,  Astarte, Camptonectes, Pleuromya,  have  to been  t o the Upper  contains  bivalves  a n d characteristic o f  shallow  water  nearshore  the Suplee  Formation.  environment.  h.  NICELY  FORMATION  The It  Nicely  consists  Formation  dominantly  intercalations  of  thickness  Spheroidal  concretions  exposures.  Upper  Lupherella  boechiformis  the  Camptonectes, 1965).  grain  C, which  in  (HYATT)  the eastern  size  occur  of  part  in of  of  the  a r e abundant  beds  are found,  the strata  is characteristic  and reaches  common  in s a n d y  a n d Pinna  Formation  subordinate  and the monotid  are the most  pelecypods  Modiolus  with  and sandstone  ammonites  brachiopods  Oxytoma,  depth.  m  a n d shale  up t o 30 c m in diameter  put the Nicely  Assemblage moderate  91  and occasional  T h e fine  ammonites  of  overlies  mudstone  siltstone  Pliensbachian  Rhynchonellid  formation  o f black  calcareous  maximum  1968).  conformably  and good Taylor's  (Imlay,  Entolium,  and Vigrass, collection  (1982)  an offshore  pelecypod  the base o f  including  (Dickinson  area.  in s o m e  fossils  near  a  of  Composite  environment  of  25  i.  HYDE  FORMATION  The rests  Hyde  unconformably  overlain  by  reaches thick  a  the  of  sparsely  fragments  locations.  of  The  pyroclastic  Hyde  of  Toarcian  erupted  The m,  marine  Formation  debris  365  reaches  a  the  Mowich  and  is  Hyde  is  tuff  thickness  Bicostate  rynchonellid  represents the  a  sea  flood and  of  which  dominantly and  been  It  conformably  maximum  have  Group.  Formation,  composed  andesitic  ammonites  into  of  Formation  fossiliferous.  late  unit  Formation.  grey  which  upper  Nicely  thickness  beds  is  the  the  Snowshoe  greywacke  Formation  is  on  maximum  massive  volcanic  and  Formation  of  of  tuffaceous 365  m.  brachiopods  found  in  slightly  distributed  The  some  reworked  by  bottom  currents.  j.  THE  MOWICH A  small  northeast north  side  made  up  square is  of of of  km.  gastropods  three A  60  the  areas  of  terebratulid  exposures miles  of  exposures of  black  much  shale.  of  Formation is  it  north  located  of  by  totaling  Seneca Lupher  limestone. present.  is Black  on  the  in  shale  one  Nerinea  some  located  is  limestone  bivalves,  unf o s s i l i f e r o u s .  fauna  the  (1941),  Formation  found  to  approximately  Lithiotis  are is  Suplee  also  is  Robertson  brachiopods  shale  AREA  locality, described  containing  Nicely  four  sequence  m  although  Group  area,  This  thick 18  SENECA  Mowich  small  Robertson to  THE  Valley.  sandstone  the  correlated  of  m  above and  IN  Suplee-lzee  Bear  limestone  calcareous above  area  the  present  the  GROUP  parts A  of  brown  apparently tentatively  26 k.  CONCLUSIONS  bioherms  Lithiotis Creek  underlies  Mowich  Begg in  Member  related  underlies The  t o the basal  reworked  from  basal  barrier  except  occurrence  conglomerates  environment,  Swamp  Creek  the Robertson  and  Member the small  is present. area  JURASSIC  created  is probably Member  derived a result  exposed  Creek, the appears may be  Formation  which is  It i s p o s s i b l e  a  formed more  a slight protected  area  from  of  the  t h e nearby  o f current  action  (Figure 3 - 7 ) .  Northern  Area  that  o f Lithiotis, A t  o n a small  conglomerate  and along  bioherms  Formation  rests  Brisbois  area  Swamp  f o r the proliferation  Formation  This  and  Member.  which  o f Pine  a n d Lithiotis  o f the Robertson  ideal  of Brisbois  Swamp Creek  Formation  in the Begg  a basal  near  o f biostromes  Upwarp,  water  and  area  side  the Triassic  In t h e t y p e  o f theRobertson  shallow  Begg  Formation.  conglomerate  FORMATION  o n the north  where  f o r a small  conglomerates  Member  area,  the Robertson  on the Mowich  Brisbois  OFTHE ROBERTSON  extensive  Creek  the Robertson  Upwarp,  biostromes.  the  are most  a n d in t h e S w a m p  Member the  ON STRATIGRAPHY  bioherms  ROBERTSON  FORMATION Ochoco Orogeny TRIASSIC  X  / 5 ;  ».o''jo-  ~t  BEGG  VESTER  BRISBOIS  MEMBER:  MEMBER  FORMATION  Figure  The  3 - 7 ; Diagrammatic  bioherms  here  Lithiotis  biostrome  Lithiotis  bioherm  cross-section from  are not a s w e l l  developed  X to Y o n map, Fig. 3 - 5 .  a s in the northern  areas,  Y  27  possibly  indicative  of  type  the  ideal  in  in  Springs  This  the  west  central  a.  Both  member  of  the  and  were  biostromes  are  possibly  established  Sunrise  east  and  southeast  in  less  Robertson on  of  the  Formation,  the  Mowich and  Formation.  Upwarp  upwarp,  east  Weburg  Robertson  Mowich  the  initially  and  that  the  shallower.  IN  NEVADA  Formation of  and  Dunlap  Formation  in  Formation  in  Reno.  FORMATION reefs  are  developed  Mountains  have  been  the  which  are  Sunrise  consists  in in  are  the  of 366  the to  to  in  1959)  the  et  Realm  732  of  interpreted  as  rare  Member, al.,  situ  the  1983).  (Taylor  marine  shallow  ex  Lithiotis  Mountains  Pliensbachian  Tethyan m  Sunrise  Alpine  Peak  (Taylor late  the  and  Clan  Mina  Formation  Hettangian  of  locally  (Silberling, found  occurrences  characteristic  mudstones  side  the  the of  LOCALITIES  the  which  formation  Snowshoe overlie  the  exposure  western  sides  significantly  overlies  isolated  transgressing  in  contains  are  a r e a , the  eastern  LITHIOTIS  Formation  1971).  The  Upwarp  becoming  the  sea  Shoshone  specimens  Along  that  Nevada,  1981).  Mowich  an  unconformably  occurs  SUNRISE  in  Members  AT  Lithiotis the  environment.  conformably  and  Upwarp.  northern  areas  STRATIGRAPHY Lithiotis  area  southern  northeastern  C.  type  the  suggests  covered  the  communities  Formation  Mowich  and  Warm  along  pioneering  the  the  Upwarp  and  Suplee  Formation of  of  "semi-protected"  conditions.  The  side  a  area  representative than  of  The  Sunrise faunas  a l . , 1983).  carbonate  shelf  uppermost  ammonite et  (Smith,  deposits  rocks  The and  (Stanley,  28  b.  DUNLAP In  the  Formation been the  FORMATION Gabbs  conformably  found  in  Gabbs  1939).  The  presence  of  Dunlap  than  1,219  conglomerates  Formation  alluvial  fan  and  prior  a  (Smith  D.  Jura,  a  fossiliferous.  basis  a  of  general  made are  and  flow  Dunlap are  sequence.  District  marine  (Stanley,  1971).  bioherms Formation  contains  a  benthonic  was  of  in  derived  1971).  Range  shallowing  established  fauna  Clan which  into  The  accumulated  a  the  maintained  pure  Valley  of  were  rocks  carbonates,  of  Gabbs  example  Sunrise  environment  mixture  (Stanley,  the  (Smith,  sedimentary  unit  in  specimen,  position  terrestrial  of  Pliensbachian  sediments  volcanics  classic  Lithiotis  A  intertidal  volcaniclastic  Formations a  clastic  and  sandstones  The  of  has  Ferguson,  ammonite  heterogeneous  Triassic  and  stratigraphic  up a  single  Dunlap  southwest  (Muller  sparsely  the Lithiotis  Formation  Hills  marine  and  Mountains  shallow  Garfield  Mountains  Formation.  Dunlap  predominantly  and  Westgate  the  just  Alpine suggests Toarcian.  1981)  California  Plumas  brachiopods.  is  regression.  STRATIGRAPHY In  Jurassic  regressive  Mountains,  which  sandstones,  Sunrise  to  is  Sunrise  the  its  shallow  debris  Shoshone  upwards  that  and  the  and  thick  and  lower  of  is  Shoshone  the  the  Formation m  Dunlap  The  on  Lithiotis  The  local  in  suggested  sandstone,  from  part  Formation  the  quartz  lower  Dunlap  been  and  overlies  Range  has  more  the  Range  Valley  age  1981).  Valley  AT  Lithiotis  County, The  LITHIOTIS  along  Thompson  LOCALITIES  occurs with  in  IN  the  Thompson  Nerinea  Limestone  CALIFORNIA  is  Limestone  gastropods dated  as  and lower  at  Mount  terebratulid Jurassic  29  (Pliensbachian?) from  the  from  lower  the  1978).  top  the  E.  the  of  Calcari  Venetian  (Bosellini  and  regressive  current  facies:  molluscs,  to  lower  Limestone  to  a  grigi  Mormon  the  of  a  hiatus  Bajocian  Sandstone  possibility  LOCALITIES  study  on  Verona to  and  lower  IN  occurs  (Batten  regression  SOUTHERN is  Lithiotis Belluno  Toarcian  occurrences  are  Yugoslavia,  is  a  Liassic and  1971). which is  in  and at  the  strata  Albania  EUROPE  the  where  found  composed are  of  (Domerian)  lower  northern  of  the  Italian  occurs  Lithiotis  in  Calcari  Greece  in  grigi  southeastern  and  of  lithologies  with in  member and  oolitic to  named which  Spain,  (Loriga  Lithiotis  and  Lithiotis  lowest  Toarcian  is  crops  into  composed  laminated  algal  calcarenites, represent  and  a  grouped  into  micritic  and  bivalves  are  strata.  of  cyclic  limestones. with island  Rotzo,  is  five  main  limestones  with  micritic  coquinas  the  members  barrier  can be  (3)  in  commonly  of  (2)  out  three  Member  algae;  coal.  which  the  calcarenites; and  unit,  subdivided  oolitic  formally  foraminifera  to  been  considered  bioclastic  limestones rich  has  The  member,  and  carbonate  include  which  variety  sometimes  Pliensbachian  of  Trento,  brachiopods, (4)  suggests  Pre-Alps  oolitic  the  the  depositional  1977).  upper  of  limestones; marls,  Toarcian  Apennines,  member  (1)  the  Loriga,  The  composed  through  area  structures,  complex.  A  LITHIOTIS  sequences  middle  fossils.  Equivalent  1976; Geyer,  western  Lithiotis  (Domerian)  central  The  the  Limestone.  Viceriza,  Limestone). south  of  hiatus  AT  Pliensbachian  Neri,  a  classical  provinces  The  Such  Thompson  The  (Grey  basis  Jurassic  STRATIGRAPHY  the  the  Thompson  Taylor, of  on  and  (5)  grey  found  pelletoidal or in  black upper  30  The a  oolitic  lagoon. and  lagoon.  A  restrictive  the  traces  foraminiferal below  are  bioherms  Lithiotis  lagoon  disappears  limestones  the  conditions  of  of  interpreted  are  found  coal  an  occurs  bioherms,  extremely  a  along  represent  microfauna  Lithiotis  as  a  barrier the  the  marine  region  that or  the  edge  of  of  the  beyond  the  deposits  and  edges  lagoonal  suggesting  shallow  at  shoaling  swampy  within  bar  they  estuarine  represent nature.  IV. The bioherms Tethyan and a  2.  shells  settings. These lack  stress The  and  STRUCTURE  and biostromes  apparent  high  1.  massive  REEF  of  A N D PALEOECOLOGY  the elongate  in r e s t r i c t e d  bioherms  marginal  are unique  of bioerosion, which  bivalves  Lithiotis marine  in their  suggests  environments  extremely  that  form  thick within  l o w diversity  the bivalves  thrived in  environment.  purposes  T o describe  o f this  chapter  the geologic  are fourfold:  setting  o f t h e Lithiotis  reefs  in North  America  Europe. T o describe  Formation  in detail  o f east  central  3.  T o assess  4.  T o propose  a model  A.  GEOLOGIC  SETTING  a.  and bioherms  in the Robertson  Oregon.  and consider  NORTH  biostromes  Lithiotis  the environmental  of the  reef  Lithiotis  controls  o n the reefs.  environment.  AMERICA  OREGON In  east-central  Robertson a  transgressing  Formation the  Formation  Oregon which  lowermost  w a s deposited  s e a (Dickinson  represents  a  reefs  Lithiotis  portion  of  the  occurs  in  the  o n the Suplee  and Vigrass,  marginal  marine  are found  1965).  shoaling  transgressive  in t h e Shelf  The Robertson environment  Mowich  in  in  Group.  NEVADA Lithiotis • western  Nevada.  Sunrise  Formation  Lithiotis in  the  Sunrise  reefs  are  Shoshone 31  and  Dunlap  developed Mountains  Formations locally  in  in t h e  (Silberling, 1959)  32  and  rare  ex  Formation  in  these  the  of  also  Gabbs 1939)  the  Valley (Fig.  Gabbs  a  formations  Hills  the  al.,  Formation  a  seen  the  Sunrise Both  1983).  (Muller  of  uppermost Lithiotis  southwest  of  and  Shoshone  overlain  unit.  The  the  Ferguson,  Mountains  by  the  Sunrise  upwards  the  Dunlap  and  regressive  shallow  water are  Dunlap sequence  of  a  been Above  Formation  Formation  well  into  regressive  the  deposited this  trend  is  equivalent  in a to  can  be the  embedded  water  less  than  in  situ  present  day  bed a  middle  Above  vertically  is  (Taylor  the  sediments.  containing  pelecypods,  Ostrea  (Smith,  nature  1981).  Jurassic  although  have  Sunrise  continued  beds  to  the  unnamed  formation,  (Smith,  bank  an  this  interpreted  and  the  Mountains  deposition  occurrence  Gryphaea  shallowing  by  Marine  deep  terrestrial  overlain  within  ammonites  and  conformably  Alpine  Jurassic  m  et  the  1981).  Member,  (Taylor  Garfield  Range  Clan  1983).  Lithiotis  (Smith,  Peak  Dunlap  in  1983).  the.  conformably  oyster  is .  dominantly  al.,  In  10  Valley  comprise  et  in  the the  found  1-2).  Formation,  al.,  Mina  Formation  in  been  Mountains  the  in  Formation  (Taylor  in  Range  the  Sunrise  are  found  have  Alpine  Sunrise  been  In  et  Clan  occurrences  member has  specimens  situ  of  1981).  CALIFORNIA Lithiotis County  in  northern  Thompson Sandstone,  occurs  Limestone a  shallow  in  the  California  Thompson (Batten  conf ormably(?) water  unit  Limestone and  Taylor,  overlies  containing  an  the  abundant  of  Plumas  1977).  The  Hardgrave pelecypod  33  fauna  including  (Di I l e r ,  Gryphaea  unconformably  b.  SOUTHERN  Morocco  sequence m  facies  are  Limestone  (Hallam,  Sandstone  (Imlay,  facies  Lithiotis uncertain The  1980).  have  area  circum-Mediterranean  region  o f detailed  5),  tentative  Toarcian.  very  shallow  recorded  in  many  of the  including been  Recent  Perna,  mistaken f o r  authors  identification  use  a n d in  the this  are specified. of  study  on  is in t h eSouthern  work  but  commonly 1971).  a thick  circum-Meditteranean  bivalves  and Loriga,  identifications  to  h a s been this  Spain  c a n exceed 1000  t o the lower  Lithiotis  Several  southern  and Greece,  supratidal  throughout  t o indicate  classic  of  Section  suspect.  from  The sequence  1975).  strata  Bosellini  region  theTriassic  a n d Cochlearites  (Cavicchi,  deal  Mormon  the Apennines  evidence  and Toarcian  Gervi I leioperna  great  from  provide  identifications  report  Alps,  (see Paleobiogeography,  Lithiotis  Trigonia a n d  Pecten,  Bajocian  is developed.  and ranges  environments  region  The  the Thompson  t o the Southern  Pliensbachian  term  overlies  Entolium,  the circum-Mediterranean  in thickness  subtidal  1908).  o f limestones  Individual  Gervillia,  EUROPE  Throughout and  Pinna,  has been  in  Lithiotis  the  Alps  i n Italy  where  a  Alps  Lithiotis  is found  done.  ITALY the Rotzo  In within  the lower  underlain the  region  b y Triassic  Dolomia  members.  Jurassic cyclic  Principale.  The lower  o f the V e n e t i a n  The  member  Calcari  Grigi  lagoonal  and  Calcari  Grigi  is composed  Formation tidal are of  which  is  flat  deposits  of  divided  into  cyclic  three  sequences o f  34  dominantly The  middle  current  limestones  member  structures  island the  oolitic  complex  Member  bioclastic  which  Rotzo  organisms; (5)  B.  The or  in  carbonate  black  micritic  with  marls  The  facies:  (1)  (3)  bioherms  Rotzo  is  protected  from  of  middle  member  and  coal  open  Oolitic  and  molluscs, and  presence  of  biostromes;  (Bosellini  interpreted  the  barrier  micritic  Lithiotis  in  with  member,  with  subordinate  rich  a  upper  with  lagoon the  represent  1971).  algae;  character.  calcarenites  limestones  locally  of  to  main  and  Member  oolitic  in  sea  as by  (Bosellini  and  always  found  and  a  deposit  the  barrier  Loriga,  1971).  BIOSTROMES  shells  which  are  a  five  limestones  The  complex  AND  biostromes,  or  of  Loriga,  comprises  limestones  grey  formed  thick  Biostromes  (4)  1971).  BIOHERMS  and  (2)  regressive  considered  foraminifera  Loriga,  island  are  calcarenites;  micritic-pelletoidal  are  composed  (Bosellini  of  brachiopods,  and  is  which  flat  buildups  of  are  bivalves  Lithiotis bedded  bedded  structures  whereas  composed  are built  bioherms  of  mostly  the  Robertson  in  up are  situ  by  in  sedentary  lens  or  skeletal  bioherms organisms.  mound  shaped  remains  (James  1983). occurrences  Lithiotis area of the  are the  biostromal area.  In  formation's  limestone  the  in  the  southern  southern  thickness  constitutes  in  up  to  part  exposures  in 50%  contrast of  the  and  Formation biohermal  limestone to  the  formation.  of in  the the  constitutes northern  Suplee-lzee northern about  exposures  part  7%  of  where  35  1.  B10STR0ME  LITHIOTIS  IN  THE  TYPE  SECTION  OF  THE  ROBERTSON  FORMATION Approximately Robertson  Formation  mudstone. thickness grading of by to  3  m  m  is  of  to  thick. At  typical  fine  the  limestone  of  extends and  sandstone  the  biostromal  and  calcarenite  medium  m  of  biostrome,  of  green  2  A  into  10  half  the  minor  the  with  and  occasional  calcarenite  matrix.  Lithiotis  shelly  into  Lithiotis  bivalves  matrix The  is  of  2.  lie  biostrome  sandy the  biostrome,  c a l c a r e n i t e and  LITHIOTIS  the  most are  on  Creek  km  west  weathering the  north  and side  the  form of  the  calcarenite  of  Izee  (Figure  prominent Suplee  of  buff  Izee  some  mudstone  rapidly  into  Pine  Creek The  coloured  from  ridges  which  sandy abundant  numerous  is  The  evident.  contacts  between  sharp.  the  At  top  sandstone.  COW in  Wilson  limestones  the  Nerinea  AT  bioherms  0.5  abundant  andesitic  FORMATION  Lithiotis  3-5).  are  of  plane.  calci lutite  m  overlain  a  more  bedding  The  16  mudstone  in  a  before  by  biostrome  the  brachiopods.  m  concentrations  containing  of  road.  to  the  has  and  brachiopods  into  although  30  calcareous  large  parallel  or  Ridge  sandstone  the  ROBERTSON  side  are  of  calcareous  underlain  up  exposures  north  of  is  further  calci lutite  THE  It  gradually  terebratulid  extensive  Formation 15  IN  Robertson  becomes  calcarenite grades  BIOHERM  grey  debris  to  grey  is  volcanic  lenses  arranged,  laterally  rest  section  approximately  terebratulid  calcarenite  occasional  biostrome  The  sandy  thins  and  and  chaotically  dominantly  gastropods the  the  type  beds.  biostrome  Nerinea  the  on  for  andesitic  gastropod  upward  area,  calcilutite  interbedded of  the  laterally  grained  base  and  in  CREEK  the Creek  Robertson to  Cow  are  resistant  to  can  be  on  seen  36  The  largest  northeast more m.  side  than  and most  of  coarse  particularily  is  of  offset  t h e reef  along  the offsets.  continues  above  The flanking composed  of  Assemblage Death by  a.  REEF  calcareous  marks Flank the  unfossiliferous  than  to of  below  1 m in  places  down  is abrubtly  sandstone  fine  60 m  In s e v e r a l  small  dry creeks truncated at  o n the western  calcareous  mudstone  lenses  of the bioherm. a  lens  shaped  reef  derived  from  the  (1)  Reef  Flank  a  up the core  o f t h e reef  which  4-1).  marks  core  reef.  surrounded  The  bioherm  Assemblage, The Life  mound  (2)  by is  Death  Assemblage and  a n d are surrounded  the perimeter  o f t h e reef.  ASSEMBLAGE of  mudstone  the bioherm to  floatstone  gastropods  the perimeter Assemblage. mudstone  o u t into  o f 5.5  cross-bedded,  less  has occurred  the for  lenses  Approximately  sandstone.  (Figure  the base  Nerinea  height  massive,  limestone  Assemblage  Assemblage  FLANK  At  debris,  make  Flank  lenses  biofacies;  a n d (3) L i f e  the Reef  reef  of  on  extends  is locally  of the bioherm  up o f  partially  three  Assemblage  side  side  is made  sediments  of  bioherm  interbedded  o f the reef.  b y 2 t o 12 m . E r o s i o n  interbedded  100 m  with  the volcanic  the western  bioherm  than  is located  a maximum  The sandstone  portion  The bioherm  with  more  part  The eastern  dry wash.  Sandstone  into  3 - 4 (b)). T h i s  sandstones  a  bioherm  and reaches  mudstone.  the bioherm  is embedded  steep  by  the western  faults  side.  underlain  calcareous  exposed  (Figure  the hillside  volcanic  below  centre  diameter  a  along  grained  unfossiliferous  the  C o w Creek  190 m  The bioherm  completely  is  The  of  andesitic  sandstone contains  which  and terebratulid  the contact  gradational.  reef  and  between The  base  is  is overlain  characteristic  the underlying of  the  shelly  Lithiotis  brachiopods.  This of  by  fauna  the  Reef  sandstone and  mudstone  contains  Lithiotis Bivalves  Fossil  Abundance densely packed  Reef flank mudstone to f l o a t s t o n e Death assemblage rudstone  V|V|  L i f e  a s s e m b | a  Robertson  occasional  Figure 4-1: Lithiotis bioherm from the Robertson C r e e k , i n t h e p r i m a r y s t u d y a r e a ( m a p 3 - 5 ) . A , B, 4-3 and 4 - 4 .  Formation, northeast of C and D refer to Figures  Cow 4-2,  o  e  sandstone  38  occasional  fragments  calci lutite  matrix.  of  It  grades  shelly  debris,  brachiopods  often  found  in  calcilutite abundant out  into  the  reef  near  in  the  is  the  on  eastern  edge  the  edge  the  of  the  The but  truncated  and  are  most  Assemblage  bioherm.  is  are  calcarenite  bioherm,  bioherm  Lithiotis  brachiopods  the  or  gastropods  the  Flank  of  with  Nerinea  both  Reef  calcarenite  packed  The  in  The  center  before  sandy  terebratulid  western  near  a  floatstone  The  matrix.  the  in  gastropods.  4-2).  calcilutite  covered  a  concentrations  (Figure  sandstone  into  and  large  matrixes  shells  Lithiotis  lenses base  of  crops at  out  a  steep  wash.  b.  DEATH  ASSEMBLAGE  Above which  the  makes  biofacies  up  is  parallel  to  bivalves  Reef more  than  the  which  bedding have  are  commonly  50  the  shells  virtually  cm  parallel  is  are  small,  specimen.  calcite  attached  valve  wholly  or  only  few  is  and  always  the  body  that  the  partially remnant  the  Death  separated  The  consists either  wide  and  shell  shells  15  free  Assemblage  the  intact.  off  cm  thick  long is  valve free  top  of  of  the  is  in  a  infilled  solid  or  bivalves  and  unequal  the  Lithiotis  chamber  cavity  are  lying  arranged  base  body  extremely  broken  of  stick-like  the  to  the  remain  and  the  The 10  bivalves  chaotically  cm  about  Assemblage  solely  shelled  off.  Assemblage  Death  Lithiotis  thick  two  or  Death  The  bivalve  solid  bioherm.  are  chamber  of  and  pieces  and  the  packed  broken  shaped  robust  Within  8  is  fauna  and  another.  consists  Lithiotis  comparison.  a  means  The  over  long  cone  the  tightly  plane.  one  cm  Below  which  carbonate.  to  of  by  fallen  lying  Assemblage  50%  characterized  are  bivalve  Flank  50 with  tubes  valves, paper  valve  attached  the  thin  is valve  of  in  either and  Figure 4-2: Assemblage.  The gastropod Nerinea, c o m m o n l y ( L o c a l i t y A o n Figure 4 - 1 . )  found  within  the  Reef  Flank  40  In  the Death  tendency  to  bedding. and  curve  that  upwards  The bivalves  are either  parallel  Assemblage  t o o n e another.  they  were  but  have  chaotically  biofacies  fallen  for  along  a  composed  limestone  (Figure  4 - 3 (A)). T h e tightly  along  the  are exposed  bivalves  individual  bivalves  exposures  existed  bivalve front  lying face  of were  localities  along  and  along  the  to  clearly  of cracks  exposed.  plane  to compensate  bivalves  their  of  a n d the length  of  T h e trend where  of good  surrounding  measured  only  were  the bivalves  and the orientations  is  indurated  w a s counted  Measurements  T h e trend  suggests  in  specimens  were  lying  are exposed  length  bivalve  position  piles  highly  a to  Assemblage  and fractures.  of  life  large  massive,  along  Trends  in  the bioherm  the measured  the bioherm.  vertical  T h e Death  packed  number  the bioherm.  the bedding  stereonet  face  w a s measured  parallel  bivalves  within  the front  of  show  lie parallel  of the bivalves  action.  exposed  cross-section  their  alignment  t o current  bluff  from  fossils  part  or are found  T h e parallel  subjected  the most  over  arranged  occasional  were  the  o n the  where  taken  the  at  13  w a s measured corrected  f o r the d i p o f the b e d (Pettijohn  on a  and Potter,  1977). The line  of  orientation  movement,  Robertson  is  basin  along fossils  were it  w a s towards  east-west  with  the edge alignment.  of  the stick-like  not a direction  Formation  Suplee-lzee movement  of  a  is  of  formed logical  vector  the basin  mean is  movement.  on  the  (Fig. of  specifies  A s the reefs  shoaling  assume  to  the shoreline  bivalves  Lithiotis  that  edges  the  in t h e o f the  direction  3 - 4 (b)). T h e g e n e r a l  267  Longshore  as  cause  the  of trend  degrees.  hypothesized  a  drift  of the  41  The 4-3  tightly  (A))  make  indurated.  Death  buff  sandy  The  to  are  Reef  LIFE  Life  assemblage  in  to  most  areas  The a  Flank  and  and  biofacies  is  thick  the  form  highly  occasionally  Assemblage  strong  (Figure  and  and  large  offers  erosion  unbedded  Flank  distinct.  Reef  Assemblage  thick,  Reef  matrix  the  resistant  for  (Figure  less has  (B)).  individual  vertical  growth  current  or  until  bivalves under  bivalves of  areas  the of  to  they would  the  and  the  fossils  and  contrast  Death  bluffs  The  to  the  Assemblage  that  m  be  extend  over  seen  bivalves  able  to  that  that  sedimentation. that  growth,  body  have  fallen  back  is  at  consisting  a a  The the  bioherm  of  the  bioherm  towards  knocked growth  if  were  of in  well  vertical  were  not  Lithiotis uppermost  adapted  of  horizontal  over  curving  the  the  base  a  Presumably  they  length only  Life  of  position.  the  to to  bioherm.  been  growth  bivalves  over  the  continue  great  However  twisting  to  chamber  these  of  upwards  growth  The  bioherm  base  have  resume  bivalves.  the  the  must  only  the  fauna  edge  bending  able  of  brachiopods.  above  been  the  western  vertical  indicates  bivalves  the  their  other  outcrop  diversity,  resumed be  centre  terebratulid  1.5  and  the  entire  low  from  can  action  fact  valves  continue  m  in  the  rare  bivalves  position.  rapid  Assemblage  150  wave  of  extremely and  numerous  and  30%  Approximately  several  buried  an  appears  4-3  upwards  than  bivalves  Lithiotis  Assemblage  able  of  Assemblage  The  part  calcilutite  is  the  and  Death  ASSEMBLAGE  accounts  the  calci lutite  abrupt  the  which  between  matrix  more  and  by  is  of  Flank.  The  of  is  contact  grey  bivalves  rudstone  matrix  calcarenite  fossils  c.  a  Assemblage  light  the  up  The  calcarenite.  packed  the  Life  position  position,  to  are  which  Figure 4 - 3 : (A) T i g h t l y p a c k e d b i v a l v e s of the D e a t h A s s e m b l a g e , e x p o s e d bluff of m a s s i v e , highly indurated l i m e s t o n e . ( L o c a l i t y B on Figure 4-1) (B) occurs  in  the  Transition  center  of  the  from  the  Death  photograph.  Assemblage  (Locality  C  on  to Figure  the  Life  4-1)  along  a  Assemblage  1 0  43  indicates  that  individuals  before  stratigraphic occurs All  Clusters  of  radiate  from  bivalves  have  contrast  to  parallel  the  Cretaceous  away  adult  confirmed rudist  by  interlock  as  grow  in  with  upright  fan-like  some  growth  direction  of  from  in  another  and  Although  views  also  mutual (Bein,  of of  similar  1976).  In  some  clusters, morphologically  the  the  resembling  1971),  an  upper in  both shells  to  grow  parallel  of  the  Lithiotis  this  was  not  Radiolitid  morphology  neighbouring  areas  of  attempting  Elongate in  In  planes  juvenile  alignment  of  grow.  Lithiotis  upward  Lithiotis  cementation  they  Konbostrea,  bivalves.  to  The  though  surfaces  the  4-4).  (Lawrence,  as  which  parallel  and  their  resembles  eroded  impression  are  flow  turn  bases  (Figure as  are  supporting.  their  current  then  bivalves  mutually  align  in  the  The  which  clusters  The  hammer).  twisting  closely  position.  above  near  sunlight  these  bivalves  situ.  other  bury  positioned  continues  each  of  grows  (B),  extent  for  oysters  to  vertical  another  capacity  cross-sectional  habitat,  in  amount  the  which  growing  as  1986).  give  bivalves,  they  one  4-3  other  that  a  (Figure  to  Japan  enough  vertically  one  away  habitat,  from  can  are  to  on  the  from  (Chinzei,  bioherms  to  to  lean  maximum  and  cm  fossil  radiate  oyster  morphology radiate  and  rapid  back  are  tremendous  bivalves  gain  grow  each  recent  commissure  as  a  30  and  bivalves  not  horizontal  above  together  the  away  Lithiotis  from  bivalves  packed  was  grew  approximately  the  closely  they  transition  within  of  to  sedimentation  individuals  Radiolitid coral  and  rudists  heads  (Bein,  1976). The bafflestone grades  into  vertical (Figure sandy  bivalves  Lithiotis 4-4).  The  calcarenite  matrix in  some  in  the is  areas  Life  Assemblage  calcareous of  the  mudstone reef.  form  a  which  F i g u r e 4 - 4 : ( A ) a n d ( B ) V e r t i c a l g r o w t h of Lithiotis s e e n in the c o r e is c h a r a c t e r i s t i c o f the L i f e A s s e m b l a g e . ( L o c a l i t y D on Figure 4 - 1 )  of  the  reef  45  In  most  mudstone  and  bivalves little  are  areas the  detail.  In  remove  exposing  0.5  cross  bivalves  than  the  the  m  are  the  long  and  the the  and  during  diagenesis.  chambers  up  varying  show  indicates that  that  at  bivalves  although  the  bases  sediment  the  majority  sediment  was  deposited  essentially  drowned  The biofacies, or  the  have from  d.  Life is  the  out  of of  outcrop.  COMMUNITY  different  bivalves valve  the of  the  erosion  and  many  forms large  ends  SUCCESSION  at  IN  the  THE  possible  to  of  reef  into  slabs  the  darker  valves  from  infilled  body  reef  which  of  levels.  well  is  of  This  means  anchored  of  the  in  matrix  established  and  reef.  biofacies, to  in  which  Most  were  reef  chambers  possibly  not.  bivalves  body  section  were  was  cut  sections  at  sections  Outcrop  cross  is  the  is  The  There  pieces  of  growing  after  and  parts  the  it  matrix  each  each  sandstone  faulted  calcarenite  buff.  were  The  in  the  more .resistant  bivalves.  In  indurated.  Several across  calcareous  study  calcarenite  cm  is  to  to  levels  Assemblage  andesitic been  were  grey  difficult  protected  recrystallization  highly  is  rock. 30  matrix  and  sandy  to  through  shells  is  reef  up  with  it  is  the  the  matrix  and  matrix  infilled  carbonate  massive  and  of  sections  Assemblage  is  two  the  sections  approximately  the  where  large  Life  carbonate  between  areas  the  limestone  grey  contrast  of  like  than  the  the  Reef  prominent pieces top  have  of  Death  the  ROBERTSON  Assemblage  Flank  bluffs.  Assemblage These  tumbled Life  bluffs  downslope  Assemblage.  FORMATION  Lithiotis  REEFS  Lithiotis Flank  biostromes  Assemblages  Assemblages.  The  and  in Death  biostromes  the  Robertson  Assemblages represent  Formation but  pioneering  do  consist not  Lithiotis  of  Reef  include  Life  communities  46 which  are  analogous  succession diversity  described is  Death  of  the  bioherms  are  Assemblages  which  beds  substrate sites  the  than  the  found  of  the  in  by are  only  sand  flats  more  above  of  and  to is  Reef the  transgressive  the  Assemblages  and  Life  Assemblage  and of  a  stage  bafflestone  and  more  far  Death  readily  cements  Lithiotis  Life  Lithiotis.  Assemblages settle  of  more  to  on the  attachment  biostromes. are  sites  reef  stabilizing  colonization  provide  the  the  clusters  bivalves As  and  of  low  Flank  would  attachment  still  Species  abundant  The  the  community  (1975).  Flank  in situ  growth  to  effect  Reef  Assemblage.  reef  important  regressive  diversity  of  is  Assemblages.  surrounding  on  the  growing  Death  debris  analogous  that  stage  Alberstadt  of  Life  Assemblages  terms  are  has  consist  suggests  controls  controlled  in  skeletal  vertically  Death  the  The  controls  low,  shells  overlain  Assemblages  shell  and  bioherms  from  stabilization  Walker  succession. Species  constructed  the  by  Lithiotis  Assemblages  community is  of  Lithiotis  biofacies  the  characteristically  accumulation substrate.  to  intrinsic for  growth,  the  or  bivalves.  particularily  sequences  biologically Extrinsic  water  common  to  depth Lithiotis  reefs.  C.  ENVIRONMENTAL  Lithiotis that  bivalves  enabled  CONTROLS  lived  in  an  them  to  environment  that  excluded  sponges  gastropods.  and  secrete  optimum massive, common  environment thick  for  shells.  bioeroders  carbonate  They  such  production  flourished as  boring  in  an  algae,  47  a.  PALEOLATITUDE is  Lithiotis and In  its  continental  North  which  and  Oregon  otherwise  Mowich the  of  Group  Sunrise  through The  Tethyan  the is  about itself.  rare  boreal  ammonites  is  carbonate  equatorial  al., purely  paled-latitudes are  and of  in the  analogous  same  seaway  the  (Taylor  have  present  of  of  day  low  been"  faunas  al.,  concentrated  Jurassic  portals  the  fauna  of  1984).  in  tropical  warm  ocean  Tethyan low  found in  ammonite  et  early  Realm  comparatively  the  areas  region.  Tethyan  ammonite  some  to  the  beyond  Nevada  Tethyan is  to  (Liparoceras)  In  deposition  belt  assigned  Tethyan  1984).  Tethys  circum-Mediterranean  the  Tethys  et  Jurassic  circum-globally  characteristically  Realm  early  the  Formation  the  low  at  (Taylor  Modern  the  Lithiotis  extended  seaway  paleo-latitudes  with  it  of  throughout  America  that  Tethys  In  margins  South  means  the  characteristic  waters currents.  s e a w a y - and  latitude  tropical  environments.  b.  PALEOTEMPERATURE Temperature  maximum  size  pelecypods  such  rudists  found  are  is  pelecypod  as  Tridacna  in  tropical  seas  any  process  such  Lithiotis Realm  suggest  are  the  tropical  increase to  of  a  warm  and  large  saturated temperature  of  with  the  1975). Tethys  paleo-temperature  all  influencing  extremely of  1964).  regard  to  The  and  CO  from  carbonate  ions,  thick  seaway  similar  and  Present  CaCO  removes to  large  Inoceramus  (Nicol,  which  bicarbonate  (Wilson,  factors  species  environments  change  paleo-latitude  important  attain and  gigas  precipitation  low  most  will  essentially  tending  lime  and  warm,  as  seawater  encourages  of  a  day  normal  one  to  shells and  of  Tethyan  present  day  48  tropical  seas.  Paleotemperatures carbon  isotopes  isotopes (Dodd only  during  in  calcium  be done  1981).  on well  concentrations.  University  for  of  Isotope  was  reliable  Ottawa).  Isotope  and  also  indicate  of  alters  bivalves  but  the  from  fossils  high  of zooxanthellae  the  are t o o Al-aasm,  potentially  extremely  can  isotopic  communication, could  of  dependent  paleotemperature  Lithiotis  indicate  fractionation  as diagenesis  analysis  oxygen, or  is temperature  (written  the presence  as  of  give  an  or l o w salinity algae.  PALEOBATHYMETRY  by  Lithiotis  bioherms  formed  desiccation  cracks  between  Formation. directly  The development  below  subaerial  Formation above both  overlying  ex situ  indicate  sandstone  the  Lithiotis  Lithiotis  second  and extending  lithology.  The  mudcracks  composed  of calcareous  order  that  surface  cracks  rather  biostromes  in  Formation, laterally between  mudstone.  deposits  the Clan  the  the  in  Carbonate  laminae  caused by of  the Dunlap bank  Alpine  found  Mountains  conditions. in  the  t h e Lithiotis reefs  Lithiotis  Robertson  a s a result  and the oyster  between from  were  than  interbedded  lenses  the  and algal  nearshore  water  as is indicated  in  the mudcracks  occurrence  mudstone  water,  bioherms  the terrestrial  in s h a l l o w  o f the Robertson  shallow  Lithiotis  indicates  Nevada  deposition  carbonate  bioherms  of  in very  of the sediment  In w e s t e r n  the  The  the cracks  exposure  synaeresis.  and  of  results  of paleotemperature,  c.  fossils  attempted  estimation could  skeletons  analysis  analysis  Formation  by analysis  of carbonate  preserved  Isotope  recrystallized  carbonate  the precipitation  and Stanton,  Robertson  c a n be determined  andesitic  biostromes  are all similar  bioherms  are  m u d c a n be produced  in  also in  49  several  ways.  skeletons, and  T h e physical  weakening  mastication  processes lightly  produces  lime  In  below  indicate  that  of  Although  part  bioherms  deposits  o f calcareous  the  grigi  Dasyclad  alga  (Bossellini  a n dLoriga,  in lower  interpreted  environment  a lagoonal  deposit.  1975). A  produced  by  calcareous  mudstone  i n the  breakdown of  and  abrasion  bioeroders, the  o f algal  o f the  deposition in  mudstone  Venetian  bioherms  near  t o b e representative  (Conrad,  which  marine  is derived  (Pia)  found  Geneva,  Calcari  similar  algal  grigi flora  in Italy,  is found  i n rare  Thaumatoporel la  between  the bioherms  a n d rare  dasyclads are  Switzerland  o f a protected  The  Pre-Alps  and  Thaumatoporel la  strata  mats  marginal  o f the  is commonly  Cretaceous  bioherms  water  mediterraneus  Lithiotis  1971).  layers  algae.  Formation  (Raineri)  are  evidence bulk  sandstone  b y algal  the absence  the  also  1967).  mats  physical  the  Paleodasycladus  below era  of  and  that  and  breakdown o f  t h e Lithiotis  o f shallow  the  because  breakdown  parvovesiculif  as  from  it i s p r o b a b l e  Calcari  Algal  dominant  post-mortem  i n the  deposited  calcarenite  is derived  Shinn,  between  was  characteristic  o f the  occurrences  are  found  mud  o f the  and  are  The  disintegrate  laminations  exposed.  skeletons,  nature  the  found  are  1977).  In the  and  mudcracks  from  Formation  1966).  carbonate  micro-organisms  benthos  (Mathews, that  of  b y boring  vagrant  Ginsburg  the mudcracks  carbonate  the  by  algae  (Stockman,  (Wray,  shallow  red  subaerially  cyanobacteria  Lithiotis  and  the carbonate  later  waters  green  a n d abrasion  particles  production  Robertson  directly  were  mud  mud  the  o f skeletal  a n d ingestion  o f lime  calcified  breakdown  middle  Formation might  where  have  they  infralittoral  is  interpreted  been  present  50  in  the  d.  Robertson  TURBIDITY Turbidity  restricts  caused  carbonate  photosynthesis, by  restricting  feeding  the  that  coarse  The  grained  the  of  a  certain  of  by  andesitic  amount  of  in  inhibiting algae,  sandstone  water  water  interfering  by  sandstone  in  thus  calcareous  Lithiotis  deposition  particles  light, of  the  andesitic  indicates  silt  invertebrates  in  alignment  Robertson  which  growth  bedding  and  and  reducing  benthonic  Cross  was  clay  with  of  current  the  action  movement  is  and  in  well  sorted  wave-agitated  waters.  the and  LIGHT The  elongate  it's  body  the  bivalves  to  are  regions  of  light.  Lithiotis  warm  building carbonate  in  be  a  areas  are  skeletons  This  adapated  adaptation  sedimentation,  cemented  to  suggests  to  is  that  competition algae,  the  raising  would  enable  however  lower  the  would  the be  juvenile  and  elongate  between  light  for  median form  of  bivalves  for  an  extremely  parameter.  LITHIOTIS  precipitate more  restricted and  rapid  symbiotic  THE  invertebrates  of  This  response  bivalve  substrate.  found  harbored  ABOUT  Lithiotis  the  bivalves.  waters.. Many  corals  of  environmental  CONCLUSIONS Modern  live  mature  could  important  off  commonly  Lithiotis If  stick-like  chamber  bivalves  clear,  discouraging  growth  there  environment.  suspended by  Formation  indicates  e.  and  by  production  mechanisms.  Robertson  D.  Formation.  to  REEF  thicker  calcareous such  calcareous  ENVIRONMENT calcite  algae  and  thrive  aragonite  there  shells  and  many The  environments  (Wilson,  1975).  mudstones,  probably  the  result  in  reef thick of  51  calcareous bivalve  algae,  also One  secrete  lived of  extremely  and in  the  large  a  size  may  symbiosis energy  fractionation attributed  large  host.  of  coral  surrounding  seawater.  each  during  other  current  suggests  harboured  was  Lithiotis other Judea reefs  fauna.  that  were  fact  rather  low  able  to  of  thrive  similar and  were  deposited  and  regression  and  bivalves  to  (1975)  the  their  of  is  the  body  releasing  of  that  algae  aligning  their  as  it  of  carbon  algal be  isotopic than  radiate  the  away  commissures be  of  could  rather  would  Algal  deal  shells  bivalves  Lithiotis  great  to  Algal  shells.  a  thick  able  size.  characteristic  showed  that  were  Lithiotis  large,  important,  other  setting  a  in  puzzling  high  exists  in  from  with  the  if  the  bivalves  with  the  absence  of  these  rudist  the  in  shelf,  events,  in  bivalves, reef  is  of  rudists in  Israel  elongate achieved  basin  The  chondrodont are the  the  rudists upright  the  These  nerinid Lithiotis  environments  vertically through  in  1976).  quantity to  that  inhibited  reefs  with  similar  water.  that  (Bein,  together  is  and  shallow  indicates  rudist  significant  reefs  slope  It  environment  Cretaceous  Formation  solely  along  features.  stress  present  of  reefs,  Lithiotis  fossils  Lithiotis  stability  of  Yafe  almost  reefs.  interlock  in  Talme  The  to  The  by  the  most  situation  gastropods.  fashion  only  their  The  similar  was  the  bioherms  Lithiotis  anomalies  than  diversity  pelecypods.  transgression  hosts  al.  that  that  algae.  constructed  They  et  the  size  resembles  sunlight  one  Limestone  in  Lithiotis,  Land  of  proportion  isotopic  tissue  is  A  large  in  The  extremely  bioeroders,  for  growth  symbiotic  The  in  found  symbiosis.  composition  skeletons the  indicate  Lithiotis  bivalves.  Lithiotis  If  of  environment.  features  calcification  were  to  tropical  the  account  the  restrictions  striking  of  promotes to  warm,  most  tremendously  symbiosis  of  geographic  during  grew  in  a  individuals  crowding  of  the  52  interlocking difference to  other  Other  fossils in  their  reefs,  Texas,  from  the  than  growth  neighbouring  rudist  central  rather  pattern  rudists. such  contain  shoreline.  No  as  offshore,  shoreline  in  environment  of  substrate. rudists  is  seen  Cretaceous the  lagoonal  reefs  are  well  biostromes analogous  in  locally reefs.  Rose  reef  environment,  of  in  away  within  the  along  the  developed  that  major  Lithiotis  developed  are  to  The  cement  Glen  to  oyster is  firm  this  Comanche  that  a  individual  evidence  rudist  and  to  that  restricted  Caprinid  facies  is  the  rudists  lagoonal  an  attachment  (Perkins,  Lithiotis  1974). The Japan  elongate  also  oyster  grows  in  environment  (Chinzei,  than  grow  1  m,  thick.  No  stratigraphically the  surface  interpreted  1986).  well  grew  desiccation  cracks  zonation  nearshore  been  of  studied  in  for  shelly  marine  environment  related  composite  co-occurrences the  Robertson  Western  to  offshore  Cordillera  primarily  relative  Formation  area  are  by  on  the  were  Composite  of  of  taxa.  Composite  Assemblages.  of  height  the  on The  marine of  beds  boring  (Chinzei, as  more 2  in  sponges  on  have  been  1986).  indicated  by  the  Formation.  who  Jurassic  Depth  shallow  basis  Composite  Four of  A  in  a  water depth unique  bioherms  Lithiotis  Assemblage  has  proposed  Formation. the  m  or  paleocommunities  (1982),  Snowshoe  defined  abundances part  in  northern  approximately  Robertson  Taylor  zonation  a  communities  faunal  in  marginal  oyster  water,  invertebrate  depth  assemblages  These  the  a  banks  communities  in  strata  reach  traces  shallow  bioherms  in  the  for  individuals.  Suplee-lzee  based  in  within  except  extremely  invertebrate  and  found  brackish water  between  the  model  or  Cretaceous  which  together  sediments  in  oysters  crowded are  in  communities  Individual  preserved  intertidal  Lithiotis  diversity  fossils  adjacent  of as  low  densely  other  found  Konbostrea  of  Taylors'  Assemblage  A  53  includes  faunas  environments. numerically the  most  from  Species  barrier  Pre-Alps island  Atlas by  in  Mountains  a  Nevada, water  bordering Calcari  on  which  grigi  lagoon  Loriga,  in  and  Italy  high  Epifaunal  energy taxa  terebratulids  a  Formation protected  1971).  reef  DuDresnay,  are  in  1965).  the  from  are often  sea  common  Evidence to  by to  Moroccan  from  Lithiotis  western  the  the  protected  limits  in  Bivalves  complex  lagoon  conclusively  basin  the  also  a  the  a the  High  open  sea  from  Oregon,  very  shallow  the grown  and  has  that  a  the  of  most  (Bossellini benthic  appears  more  with  grigi  with  the  and  part  Broglio  and  marginal  in  a  Loriga,  bioherms  marine  and  of  fauna  Perna  Italy  lagoon,  1971). of  The  species families.  is  areas.  brachiopods  Lithiotis  Alps  Ammodiscidae  Lithiotis  terebratulid large  Venetian  f oraminif eral  the  stressful  the  internal  Ataxophragmidae  Aeol isaccus,  occur  in  swamps  Lituolidae,  tolerate  Calcari  Glomospira  Smooth  and  thin  Nerineidae  bivalves  (Bossellini  1971). Cretaceous  which  are  in  have  ostracods,  The  opens  oyster onto  intercalated  conglomerate water  and  a  Dahar  bioherms  Formation  can  Loriga,  beds  in and  bou  (Agard  foraminifera  gastropods  a  Jbel  marshes  to  only  walled  and  low.  particularity  Calcari  grew  (Bosellini  the  to  grigi  belonging  spp.  the  Italy  bioherms  interpreted  The  sublittoral  environment.  Lithiotis are  of  reef  Morocco  shallow  characteristically  brachiopods,  in  formed  barrier  is  very  organisms.  complex  facies  Lithiotis  and  bioherms  Lithiotis  to  diversity  dominant abundant  Venetian  intertidal  deposits  lenses  in  which  (Chinzei,  Konbostrea  the  Pacific,  sandstone are  1986).  is in  limited the  beds  considered  Kiji  to  the  area  containing to  be  of  innermost  part  Japan. The coaly  non-marine  oyster  matter or  of  and  brackish  54  In edges  the  of  bivalves. basin. of  Robertson  the  Mowich  The  current  shallow  pelecypod (1971)  sea.  green  is  to  marine of  Formation  might  beds  would  algae  the  formation  which  Algal  account  of  Japan  marginal  marine  are  longshore  marginal  A  model  growing  on  a  sand  sheltered  suggests have the  another  environment.  of of that  back  the  the  example  a of  of  action  from  sandflats by flat  reef  or  the  reefs  bioeroders. bivalves  aligned  the  the  Smith  lagoonal  in  and  The  in  The  living  the  grigi  Robertson environment  Konbostrea within  which  extremely  Calcari  restrictive  Roy  amongst  habitat,  the  edge  interspersed  interspersed  bivalves  similarily  the  Suplee-lzee  with  Chave,  along  along  Formation.  Lithiotis  in  absence  on  Lithiotis  areas  conditions  Robertson  the  grown  current  marine  areas.  a  shoaling  drift  some  in  in  areas  grew  in  for  some  communities  environment  also  In  in  environment  Italy  grew  Lithiotis  possibly  grew  molluscs  calcareous  marginal  was  communities  shows  similar  Upwarp.  bioherms  Lithiotis  the  Formation  a  oyster  restricted  V. The in  the  global  study  of  displacement  distribution plate  and  supports  (Smith,  1983)  the  of the  of  Cordillera  to  tectonic  using  of  A.  The the  Europe,  a.  the  along  terrane,  of  Africa,  routes  Atlantic  The  of  Hispanic"  North  in  the  and  Smith  the  Corridor preceding  and have  and  Stikinia  of  The  estimated  The  presence  in  the  constraints  on  Lithiotis  places  on  1986).  been  data.  absence  American  constraints  Tipper,  paleomagnetic  and  North  place  terranes  Sonomia  the  the  used  1984;  Wrangellia  tectonic  Jurassic.  been  with  demonstrate  migration  the  component  reconstructions.  seaway,  early  al,  important  can  displacement  terranes.  LITHIOTIS  margins  of  Lithiotis  of  North  Middle  North  America  Lithiotis  (Lupher,  1941;  EAST  an  of  along  has  the  (Fig.  is  tectonic  rifted and  et  distribution  continental  on  allochthonous  Quesnellia,  geographic  is  widespread  and  East  and  South  ranging  America,  as  far  east  the  Robertson  as  from  Southern Timor  in  5-1).  PACIFIC  In Oregon  of  DISTRIBUTION OF  Northern  Indonesia  in  (Taylor  reconstruction  western  a  tectonic  southern  terranes,  GLOBAL  crust  provinciality  in the  latitudinal  of  paleobiogeography  displacements  Lithiotis  faunas  assessment  Caribbean  demonstrate  ammonite  Canadian the  the  reconstructions  latitudinal  and  presence  oceanic  Ammonite  ancient  constraints  Lithiotis  through  formation  of  tectonics. Paleobiogeography  place  paleobiogeography bivalve  PALEOBIOGEOGRAPHY  1976);  in  1978);  and  the in  Dickinson  Thompson the  occurs  Dunlap  and  Limestone Formation 55  in  Vigrass, in  1965;  California  (Muller  and  Formation  Batten (Batten  Ferguson,  and and  in  West, Taylor,  1939)  and  56  •  Bioherms  •  Biostromes  •  unspecified  •  occurrence  unconfirmed  P  Pliensbachian  T  Toarcian MIGRATION  Figure of  the  5-1:  Paleogeographic  bivalve.  distribution  of  Lithiotis  and  probable  migration  routes  57  Sunrise  Formation  (Silberling,  1959;  Smith,  1981)  in  Nevada.  1939)  Sunrise  Formation  (Silberling  1959,  Smith  1981)  in  Nevada.  In  these  areas  has  Lithiotis eastern  Oregon  lenses  containing  resembled  of  bivalve  Peru  b.  and  In  South  and  Chile  Lithiotis.  from  large  fragments  resembling America  occurs  in  (Bosellini  and  the  age  found  Geyer,  thin  section  than  is  found  in  that  work  abundant  wide  rather  spots  and  1  on algal  cm  thick)  Lithiotis. lower  Toarcian  strata  in  Italy  of  the  Loriga, in  Albania  in  the  Calcari  1971;  Pliensbachian  (Domerian)  grigi  Limestone)  Gohner,  (Grey  1980).  southeastern  Spain,  and  (Loriga  Greece  Occurrences  the  of  south-central  and  Neri,  1976;  1977). There  northern locate  is  France the  verified  suggested  possible (Boehm,  and  Morocco  from  (Dubar,  a  bioherms  (Loriga  In fauna  cm  limestone  and  revealed  oysters  northern  Formation.  Yugoslavia,  and  10  in  from  streaks  (up  Formation  REGION  strata  Apennines,  dark  to  Donovan  originated  has  of  1982).  Toarcian  are  report  lenses  Lithiotis  (Hillebrandt,  the  Examination  these  lower  same  This  all  strata.  from  irregular  CIRCUM-MEDITERRANEAN Lithiotis  to  of  Pliensbachian  reported  1941).  abundant  shells  in  been  (Lupher,  collected  laminations  found  also  sections  samples  is  Lithiotis  and  the  1948; that  1892).  and Neri,  the  Agard  of  Recent  Lithiotis  in  Lithiotis authors  the  have  Sarthe been  identification  has  area  unable not  in to  been  1976).  Lithiotis  Atlas  large  occurrence  has  Mountains and  bivalves  been in  included  the  Jbel  DuDresnay, such  as  Perna  bou  1965). have  in  the  Dahar Other been  Pliensbachian reef authors  complex have  misidentified  as  58  in  Lithiotis and  this  plates  area  of  the  In  Somalia  near  described  including  but  Lithiotis  again  Iran  and  and  in  Iraq  uppermost Geyer,  the  and  Loriga,  1977)  Perna, GerviIleioperna  and  Lithiotis.  occurs  a  and  Middle  Liassic from  Opisoma  positively  Iran,  occurs  strata  The Kioto  TETHYAN  Indonesia  Toarcian  Iraq  and  Oman  in  to  slightly  upper  to  has  (Geyer,  the  1977).  Middle  East.  In  Toarcian  strata  ranging  from  strata  (Benini  been facies  Lithiotis  lower  younger  Toarcian  fauna  the  identified  in P l i e n s b a c h i a n  in  OCEAN  and  Loriga,  1977;  Lithiotis  facies  Spitzbergen An  provided  has in  been  the  verified  has been Island,  in  Timor  mentioned  Himalayas,  (Geyer,  by  Dr.  cm to  long  many  on the outer  included  Norway  examination  misidentification. 1.5  found  in  Pliensbachian  to  in  descriptions  although  of  the  identification  of  1977).  OCCURRENCES  Lithiotis  1981).  is 1923).  facies  has not been  OTHER  OCCURRENCES  Lithiotis  (Krumbeck,  Limestone  Lithiotis  lines  in  1976; Benini  include  has not been  it  Neri,  1977).  In  belong  of  Pliensbachian  EASTERN  and  fauna  Cochlearites  Lithiotis  Oman  and  Mogadiscio  occurs  Lithiotis  d.  reef  but no examples  Opisoma  c.  (Loriga  of  A.  The is  in  the fauna  (Wierzbowski, plates  and  Wierzbowski  small  distinguished  pelecypod Lithiotis  species shells.  a  of by arid  Toarcian  Kulicki cast  have  fragment  of  shown  shell  wavy is  of  less  and  fossil  this than  similar  in  Pugaczewska,  the  growth not  deposits  lines to  to 1  cm that  the  kindly be  a  wide could growth  59  B.  MIGRATION  ROUTES is  Lithiotis producer of  Tethyan  maintained  the  between  Seaway  the  America Tethys.  to  to the  sponge  bivalve  Timor  characteristic  Pacific  in the eastern  during  Morocco  likely  Tethys  Ocean.  middle  Jurassic  bivalve  Europe.  Through  strong  correlations  during  Hallam faunas  between and  endemic  that  during  would  (1983) from  made North  an  similarity  North  American  North  American  Western  t h e central  that  from  to  the eastern  Ocean  1986). T h e  Corridor. to  Wey/a  is  the Toarcian  the early  Pliensbachian  and Mancenido,  its presence analysis  first  of  South  in the  lower  and  America and  coefficients  and  sponge  on occurrences of  and Tipper,  and  in  North  the Tethyan  based  of  migration  centre;  in  or in the  the calcareous  America,  Simpson  between  the  the  been  occurrences  (Damborena  require  and  occurrences  the Hettangian  Ocean  centre  have  along  Tethys  from  (Smith  the Toarcian  route  to in  indicates  the Hispanic  from  Tethyan  the use of  faunas  and Peru  Pacific  b y a southern  Tethyan  This  to migrate  along  had  Toarcian  Pliensbachian  migrated  America  1971 a n d 1981a)  the Western  Corridor  North  occurred  although  has suggested  the early  in the western  Migration  Pliensbachian  1981a)  carbonate  The endemic  a r e n o Lithiotis  areas.  and from  the eastern  and  have  the Pliensbachian  in Y u g o s l a v i a , also  1923),  these  the Hispanic  appears  eastern  from  (1971,  and  1978).  of  prodigious  populations  (Hillebrandt,  (Krumbeck,  America,  used  of  America  in both  South  Weyla  Pliensbachian  There  South  of  continuity  Corridor.  Hillebrant  the East  genetic  or Hispanic  spread  Stylothalamia  strata  must  of  and a  environments.  migration  of  Toarcian  Since  the disjunct  are found  Lithiotis  t o tropical  Pacific,  Pliensbachian  Pliensbachian  bivalve  Pliensbachian  Ocean.  a n d t h e East  Atlantic  Tethyan  restricted  is in t h e upper  Lithiotis  Tethys  LITHIOTIS  an endemic  presumably  Western  OF  he  South European  showed American Toarcian  60  faunas.  He  Corridor  concluded  did  not  intermigration  occur  of  epicontinental  by  corridor  during  the  C.  Hungary  TECTONIC The  Boreal  center  Tethyan  endemic  separated mixed than  by  the  the  a  (Smith  Tipper,  families the  the  In  the  result  American  of  Realm,  The  of  the  Northwest the  craton  the  to  be  and  been  shallow genus  from  the  the  Hispanic  reported  and  east  (Reid,  worldwide  form  The  which  has  a  two is  of  1973;  lower  of  for  Hallam, of  and  form  realms  are by  fauna in  factors  to  the  are  east-west  1973;  Boreal  the  a  fluctuations  1972,  the  Boreal  diversity  greater  reason  distribution  hemisphere  a  a the  distinguished  resources. These the  In  Dactylioceratidae  result  also  delineates  provinciality.  1986).  Realm  food  faunas  Liparoceratidae  boundary  the  are  realms  northern  a  and  through  ammonite  Tipper,  Boreal  and  the  yet  limited  ammonite  ammonite  and  trending  climate  Smith  Realm  Tethyan  is  Realm  globe. Pacific  northward (Taylor  of  and  believed  general  of  European  Hildoceratidae  The  controlled  not  but  along  freboldi  migration  Hispanic  AMERICA  Amaltheidae  between  part  of  (Smith  Bajocian,  The  D.  the  1986).  Realm  faunas.  by  has  NORTH  east-west  latitude  rest  IN  families  center  it  Tipper,  Tethyan  salinity, light,  1986).  northern  and  distribution  broad  boundary  occupies  a  supports  and  Tethyan  extent  trending and  also  Boreal-Tethyan  temperature, some  D. dubari  as  along  occurred  Pliensbachian. Pacific  and  endemic  have  east  Pliensbachian  the  must  the  migration  Toarcian-early  the  geographic  Realm  free  late  faunas  IMPLICATIONS  Pliensbachian,  the  during  from  Tethys  and  until  seaway  western  Italy  relatively  molluscan  known  Dubariceras  that  the  boundary  displacement et  al.,  1984;  of  trends terranes  Smith  and  northwest-southeast relative Tipper,  to 1986).  the  as  North Suspect  61  terranes  of  the  paleomagnetic to  each  evidence  terrane;  evidence  and  yielded  a  faults  et  al,  fauna  northern  their  The  Sonomia the  was  Jurassic  relative and  to  the  Tipper, The  Sonomia  to  that  progressive  based  on  rocks  of  late  but  fauna  during  across  can  be  Inlier  has  yielded  as  data, the  the  in  Boreal the  as  and  south  purely  are  have  biogeographically  Triassic  Sonomia  Wrangellia,  Sonomia  is  a  the  considered  its  in et  Tethyan  (Figure  Tethyan  (Speed,  in  a  cratonal  Stikinia  1984).  (Monger  Wrangellia, and  paleobiogeographic the  data  which  site  of  "polar  bear  principle."  and  1980). can  of  by  and  been  5-2 fauna.  1977)  fixed  and  position  sediments  (Smith  on  the  north  Smith  and  Tipper  help  Boreal  quantify the  the  1300 or  (1986)  late  or  4900  hemisphere  displacement  Amaltheus  are is  from  Triassic km  for  option  suggested by  on  a  displacement  for  have  is  with  outward  of  km  south  paleolatitudes  ammonite  km  it  terranes.  northwards  amount  the  interpretations  passing  1300  and  on  other  structural  the  to  volcanics  to  displaced  from  1980)  comparable  Tertiary  displacement  varied  Irving,  paleoequator The  have  have  fauna  relationship  Estimations  depending  Irving,  surrounded  ammount  data  Tethyan  discontinuities  terranes  the al,  is  a  tectonic  lithologic  paleomagnetic  (Yole  inlier  Canadian  (Taylor  Triassic  chosen  Day  increase  craton  craton  terrane  mixed  contains  and  determine  Paleomagnetic  the  Tethyan  paleobiogeographic terranes  that a  characteristic  1986).  fauna,  indicate  the  and  suspect  contain  stratigraphy;  rotations  suspect  fauna  Sonomia  unique  and  Canadian  a  deposited  craton  John  difficult  to  by  borders  American  and  terrane,  sediments  The  terranes  parts  accreted  terrane  ammonite  Canadian  American  the  the  Pliensbachian The  (A)).  on  and  recognized  displacements  1980).  Quesnellia  differentiated. in  are  showing  major  (Coney  Stikinia  Cordillera  that  determining  based  restricted  on  the  to  the  62  northern  hemisphere,  would  have  border  (Fig.  similarity  5-2  southern  limit  by  the  presence  of  found  in  explored  Stikinia  terranes.  displaced  likely  reason  terranes facies.  is The  Queen  or  that  that  collection most  Offshore marine  is  failure  complete  not  a  of  could  the  to  marginal  the  terranes  and  absence  is of  reveal  occur  that  the  in  the  are  age  Lithiotis  but  in  a  not  the  Canadian  The  Canadian  in  marginal  Wrangellia  Islands is  a  the  basinal  shallow  fully  have  indicator.  Charlotte  in  in  shallow  exposures  and  terranes  latitude  shallow  Pliensbachian  Quesnellia  found  Queen  marine  America.  appropriate  Toarcian  well  low  been  lack  On  of  in  indicate  not  or  of  Sonomia  should  Lithiotis  Pliensbachian  Islands.  exploration  is  Amaltheus  Oregon-California  in  North  exposed  would  has  Pliensbachian  water  not most  suspect marine on  the  Maude facies. marginal  facies.  CONCLUSIONS is  Lithiotis  circum-Mediterranean is  Wrangellia.  Lithiotis  in  poorly  Lithiotis  displacement  regions  strata  absence  and  of  Stikinia.  shoaling  and  and  It's  Charlotte  Formation  D.  scattered  for  occurrences  border  Lithiotis  and  Pliensbachian  are  in  in  southerly  Canada-U.S.A.  The  occurrences  been  the  most  (B)).  is  seas  suspect  the  Quesnellia, Wrangellia  Lithiotis shelf  between  limited in  Lithiotis  been  therefore  found  Ocean  in  and  widespread, region  Pliensbachian elsewhere  Tethyan  bivalve  Lithiotis  could  Gondwanaland;  is  migration have  as  far  strata  in  North  America  Toarcian  strata.  found  in  would  east  to  have South  Africa  east  been  as  in  and  migrated  between  occurring  Timor and  by  East  in  the  a  to  Pacific,  Indonesia.  Because  restricted  America and  the  western it  is  low  Tethyan endemic  paleolatitudes.  southern  India-Antarctica  an  Lithiotis  and  route  around  around  the  n ! . " biogeographic zonation within allochthonous terranes. (B) L a t i t u d i n a l displacement suggested constraints. From Smith and Tipper, 1986. F  i  U  r  5  2  :  (  A  )  N  o  r  t  h  s  o  u  t  h  the by  Pliensbachian biogeographic  64  southern  tip  Corridor  is  Ocean  to  of the  North  it  absence  is  shallow  most  or  route  via for  the  Hispanic  migration  Corridor.  from  the  The  western  Hispanic Tethyan  America.  should likely  water  America; logical  has  Lithiotis although  South  not  yet  exist  in  the  facies.  result  been  found  nearshore of  in  facies  collection  Canadian in  failure  suspect  Pliensbachian or  absence  terranes, strata.  of  Its  suitable  VI. In a  MORPHOLOGY this  chapter  discussion  on  classification  of  A.  the  morphology  taxonomic  and  it  were  possible  (Plates  1-3).  from  float  limestone  and  are  matrix  varies  to  and The  and  complete  shell  extremely  examining  large  1  0.5  m  peels  and  are only  the  LITHIOTIS  described,  bivalve,  free  followed  by  and  the  taxonomic  Formation  are  embedded  is  the  cut  the  were  made  up  seen  in  the  only  as  6  The  cm  Four  slabs  which  the  bottom which  were  slabs,  stick-like in  float  included  attached  remnant  such  photographed  elongate,  robust  some  calcarenite  from  and  In  slabs,  and  found  a  polished  to  top  to  limestone.  taken  was of  extract.  examined  the  specimen  is  4  bioherms. at  The  reef  was  to  mudstone  into  slabs  broken  which  of  were the  crushed  difficult  calcareous  Lithiotis  valve.  valve  extremely  m,  of  Lithiotis  Robertson  blocks  of  usually  free  the  within  one  cavity. thin  the  by  morphology  specimens  specimens  of  from  remove  acetate  bivalves  Lithiotis  is  Lithiotis  OF  LITHIOTIS in  approximately  polished  of  affinities  found  limestone  is  blocks,  bivalves  indurated  the  AFFINITIES  Lithiotis.  Lithiotis  highly  areas  an  the  TAXONOMIC  M O R P H O L O G I C D E S C R I P T I O N OF The  in  AND  a  valve  and  essential  for  fragments  on  float  specimens. The  Lithiotis  recrystallized  and  obscured.  body  The  calcarenite  which  examination bivalves internal  of  have  details  of  chamber  contrasts the  been  structure  bivalves  of  shape studied the  the  internal  or  shell  with  the  of  the in  bivalves  Formation  structure  cavity  of  the  body  available  65  Well  and  from  have  the  are  infilled  with  and  facilitates  preserved  information  work  in  been  bivalves is  carbonate  chamber. Italy  of  bivalves  recrystallized  Northern is  Robertson  these  Lithiotis about  the  areas.  The  66  morphological information  1. S H E L L  descriptions  where  has  a  average  thickness  height  cross-section elliptical, Juvenile  the are  free 4)  which  were  a  to  shell  cm  surface  is  A  this  is  region  of  of  part  flare  of  rapidly  a  additional  to  the  6  less  and  an  round  in  which  is  is  6-1  the  which  cm  shell  (Figure  of  become  shell  shell  from  height  margins  4 the  appearance  At  a  are  thick,  to  cobbles  too  small  sand  and  umbo,  than  6-2).  forming  10  cm  and  a  the  sub-parallel.  outside  made forming of  small  the The ridges  up  of  in  ridges are  are  cemented  on  the  extends the  ridges  Lithiotis often  common.  the  (Plate  is  very  subdued  Occasionally  pioneering bivalves, valve  is  of  the  margin  of  the  7).  The  which  are  and  lines the  shells  surface  5  growth around  in  attached  cardinal  thin,  adult  mature  The  from  shell  to  shells  supported  substrate.  individual  distinct  valve  pelecypod  have  plate  of  ridges  or  mud  area  attached  found  to  or  furrowed  the  robust  commonly  plume-like  intervals.  and  5).  stick-like  width  upper  and  of  the  around  periodicity 2  the  shell  up  in  prominent  1  a  umbonal  (Plate  distinct  6-1).  plate  has  spoon-like  the  umbo  periodically  in  30  anchored by  a  elongated  more,  to  cemented  area  The  The  Juveniles  plume-like  shell.  cm.  and  likely  (Figure  furrowed  3  made  The  characterized valve  with  VALVE  valve.  communities.  or  than  is  and  cm  cone-shaped  ATTACHED  fragile  30  shell  drops  Lithiotis  dorso-ventrally  comparison  greater rate  a  of  in  shells  expansion  (Plate  of  giving  angle  THE  supplemented  appropriate.  reaches  2.  are  Lithiotis  OUTLINE  Lithiotis  an  of  outside  regular  and  resulting thick  of  in  ridges  the  occurs a of  flat up  VENTER A POSTERIOR  body  ANTERIOR  chamber  adductor muscle scar  cardinal  margin  v e n t r a l m a r g i n of furrowed plate  internal  buttress  plume-like furrowed  CARDINAL cone-m-cone internal structure  x - s e c t i o n from A to B with f r e e v a l v e in place  B DORSUM Attached  Figure  6-1:  Morphology  of  Valve  Lithiotis  area  plate  FACE  68  F i g u r e 6 - 2 : H o r i z o n t a l c r o s s - s e c t i o n a l v i e w s of t w o Lithiotis b i v a l v e s (right) and their p o s i t i o n w i t h i n the b i v a l v e s ( l e f t ) . S p e c i m e n s EB 1 - 1 and EB 1 - 2 . B o t t o m right = s k e t c h o f the t w o b i v a l v e s in l i f e p o s i t i o n . ( X 0 . 6 ) S o l i d b l a c k r e p r e s e n t s the b e l o w the b o d y c h a m b e r .  outer  shell.  The  hatched  pattern  represents  the  infilling  69  to  1  cm  ridges 30  height  flare  out  degrees,  Creek  might  growth  lines  also  The  were  and  more  though  characteristic current  If  continued account ridges  are  the  the  and  only  in  Oregon  attached  not  from  specimens  interlayered  robust,  in  the  the  represent lines  is  difference  a  Northern  nacreous  Italy  section  because  are  different  reflected  Northern cross  ridges  of  the  show  in  the  1982).  area  of  Brisbois which  been  is  enough  nearby  Begg rock  it  could  The  thick  Creek  area  environmental  species. The  periodicity  structure  Lithiotis.  of  prominent  which  is  as  environment.  Swamp of  are  they  Creek  shells.  periodically 1982),  thick  conglomerate  effect  shell  specimens  are  Formation  recrystallization. The  (Chinzei,  the  the  Lithiotis  (Chinzei,  Italian  aragonite  in  from  an  by  area  have  Lithiotis  seen  Lithiotis  shells  energy  small  Robertson  ridged  the  Swamp  must  rock  Swamp  however  conglomerate  transport  the  strongly  that  basal  There  to  of  morphological  horizontal  valve  required  a  to  the  ridged  the  higher  overlies  20  Formation  else  the  of  distinguished  in  a  of  the  bivalve,  nowhere  to  accumulate  deposition  indicates do  to  angle  periodicity  Although  bivalves  Member.  The  the  are  contains  specimens  an  Robertson  localities,  adaptation  Begg  of  shell.  Creek  at  degrees.  the  the  Robertson  energy  In  ridged  Swamp  area  the  plumed-growth  laminae  and  this  more  Specimens  the  the  high  which  conditions the  in  the  for  in  plate  bioherms  of  thick  70  shelled  charactersitic of  growth  count.  reflect  reworked  through  bivalves  of  of  action  Member.  may  Formation  even  the  bioherm  The  thin  shells  to  Creek  northern  and  50  outside  In  furrowed  robust  at  to  6).  the  in  Swamp  prevalent.  Robertson  of  out  faint  the  (Plate  thick,  flare  on  robust  Member  the  too  the  edge  cyclicity  the  in  prominent are  reflect  ridges  seen  in  ridges  from  prominent  the  whereas  ridges  developed  from  area, the  bivalves  are  are  outer  made  Lithiotis  up  growth  not  seen  shell of  of  in the  prismatic  specimens  from  70  the  Robertson  calcite shell  which  that  Formation contrasts  is c h a l k y  have with  an  outer  the  shell  Italian  of  t o u g h , dark  specimens  in a p p e a r a n c e . T h i s  probably  which  grey, prismatic  have  reflects  a  soft  differing  outer  diagenetic  histories.  3 . THE  FREE The  VALVE free  valve  attached  v a l v e . The  whereas  the  the plate  free  same  height  and  open  Articulation  shell  between  eroded.  Horizontal  between  study  valve  cavity the  the on  free  b e c a u s e the  valve free  a g a i n s t the  valves  has  2 mm  attached the  cross-sections  lying  the t w o  as  paper-thin  which  1 to  only  and w i d t h  to  free  is  is  Lithiotis  attached valve  valve  difficult  thin  of  valve  free  valve,  covers  through furrowed  and  face  of  Lithiotis plate with  valve  the  attached  extremely  to  t h i c k n e s s of  t h i c k . The  the  is  comparison  an a v e r a g e  cardinal and  in  is  the  3 cm, nearly  furrowed  attached  valve  fragile  is  and  occasionally l e s s than  the  valve. usually  is  easily  show  1 mm  the space  (Figure 6 - 3 ) .  F i g u r e 6 - 3 : T h i n s e c t i o n of c r u s h e d Lithiotis b i v a l v e s h o w i n g against furrowed plate. A r r o w indicates thin, free valve.  thin  free  valve  ly  71  A the  crescent-shaped posterior  specimens  side  1977).  of  free  elastically Several more  The  away  from  valve  inset  (Plate  the  series or  of  on 2)  tube  of  eroded.  the  In  or  the  ball 3,  the  of  A  valve  ventral  margin away  free  of  the  from  furrowed  plate  the  umbonal  region  bivalve  was  purpose  in  still the  and  B).  shell  below. and  the  cavity  umbonal  plate  cavity The  was  living. A s umbonal  shell  the  region  free  probably bivalve but  the  the  6-1  the  broken grew  the  free  is  made  2  the  bivalve  off  of  of  the  into  this  appears valve up  have  in  are is  and point  this  3  mm)  at  when and  area  the open  toward  present while  free  valve  would  would  be  protected  to  farther  valve  occasionally in  easily  is  (approximately  6-4)  a  the  close  and  attached  of  furrow  only  valve mm)  a  to  corresponding  structures  free  a  plate  what  a  parts.  illustrate  preserved  and  only  soft  margin  plate  articulation  is  bent  ridges  (within  with  valve  is  the  valve  snugly  with  region  (Figure  above  The  delicate  examined,  free  fits  plate  articulates  the  end  the  connects  articulation  ventral  furrowed  from  6-7).  the  bioherms  valve  Lithiotis and  bivalve  The  furrowed  which  obviously  the  furrowed  joint  (Figure  The  the  the  The  valve ' articulated furrowed  the  the  to  of  socket  cross-sections to  free  rare  on  (Benini  to  the  mm  in  present  intact  that  valves.  2  is  valve  Formation  The  and  wide  attached  expose  two  valve.  them  plate;  adjacent  The  to  the  cm  completely  concluded  center  valve.  adjacent  absent, 6-4).  of  free  the  has  structures  top  furrowed  all  (Figure  swung  a  the  1.5  attached  are  approximately  in  (Plate  in on  attached  away  and  the  Robertson  attached  be  valve  ridge  center  the  to  presumably  between  inset  on  cavity  the  ridge-and-groove  open  round  the  is  c r o s s - s e c t i o n to attached  shell  articulation  areas  area  (1982)  from  1  which  muscle  the  scar,  cavity  Italy  Chinzei  cross-sections  attached  shell  adductor  valve.  plume-like  in  the  muscle  Northern  elaborate  the  of  from  Loriga, the  adductor  serve by  in the no the  72  Figure 6-4: p o s i t i o n of the b i v a l v e  Horizontal cross-sectioinal view of the free v a l v e (right) and the r e l a t i v e ( l e f t ) , (x 0 . 7 ) S p e c i m e n E B 2-9.  Lithiotis  positions  which of the  illustrates the sections within  73  upper  part  o f the free  often  split  specimens  layers  and fragments  show  distinct  layers.  In t h e R o b e r t s o n  a n d t h e inner  preserved  occasional  granular  body  (Figure  6-2).  A n internal body  on  the inside  is  chamber of  (Figure  not been result  of  not always  function  or  Accessory  it  cavity  layers  the free  the free  Northern  these  on  Italy  is  is  float  layers are  T h e free  aragonite,  (Chinzei,  valve  valve  Formation  is obscured.  from  valve  of  composed  of  interlayered  with  1982).  to 2  Skelton  for  incubation  the  transfer  c m past  6 - 5 ) . This  secondary  stress  (1976,  it  are sometimes  bivalve.  and larvae.  of symbiotic  algae  is known  in several  known  be non-incubatory  of  side in  bivalves,  The secondary  body  as a  present  in  hippuritid  or  from oyster  including  parent  purpose  pouch  is also  rudist  species Crassostrea  which  chamber  rudist  (Stenzel,  vital pouch.  bivalves have  an ideal  a  a  brood  might  t o larvae  although  plate  secondary  d i d not serve  their  of  s o is clearly not  served  brood  a  specimens  have  A  the base  o f the internal  might  that  (Figure  the furrowed  specimens  found  presumably  p. 9 8 ) h a s s u g g e s t e d  of eggs  is  b y other  and therefore that  many  of  near t h e  ventrally  side  margin  cone  o n the growing  is possible  the anterior  o n the posterior  or compressed  present  cross-section  compressed  6 - 1 ) . In  is located  crowded  more  the ventral  (Figure  e n d o f the attached  has a circular  from  chamber  Incubation to  chamber  extends  the shell  cavities  and  is in the ventral  Lithiotis  and becomes  buttress  of the body  buttress  of  The body  the shell  the  the  of  and nacreous  and prismatic  6-1).  of  have  prismatic  chamber  base  cone  structure  section  CHAMBER  The valve  of  shell  specimens  Lithiotis  layers  BODY  cross  several  alternating  4.  In h o r i z o n t a l  into  recrystallized better  valve.  been  site f o r  (Cowen,  1983).  f e w genera are 1971),  which  is  74  closely  related As  and  elongate.  The  specimens  same or  in  in  originally  considered  in  Northern  Italy  the  be the  An  a  can  be  faintly  bivalves  from  the  Robertson  The  which  Benini  umbo grooves  (Chinzei, form  face  Italy  remnant  to  and  shell  calcite  quite  assumed  in  A  (Figure  altered  1982).  Chalky  material  which  the  for  the  of  to  to  irregular  the  chalky  a  from  infilling  similar  sections  granular  specimens  Lithiotis  The  believed  similar  smoothen  structure  longitudinal  is  and  1977).  calcite. of  In  shell  structure  shell  is  outer  blocky  (Chinzei,  through  Loriga,  the  porous  fill  internal  carbonate.  consists  The  function  sections  in  grey,  Konbostrea  rapidly  with  more  area  cone-in-cone few  Lithiotis  Formation.  of  structure and  ridge-and-groove  seen  light  soft,  became  between  material,  of  cavity  moved  PLATE  cardinal  ridge-and-groove  as  analogous  (Benini  space  Lithiotis,  chamber  infilled  Northern  shell  cone-in-cone  chamber  shell  chambers).  patches  body  was  shows  body  Longitudinal  exhibit  FURROWED  which  such  are  shell.  from  aragonitic  structure  5. T H E  of  precipitated  Lithiotis.  body  composed  the  oysters shells  to of  deposits  below  of  chamber the  resembles  the  the  Formation  calcite of  closely  upwards  body  is  that  below  specimens  perimeter  oyster  surface  cavity  prismatic  the  the  Robertson  Lithiotis  deposits  deposits  below  shell  recrystallized  inner  region  the  around  are  umbonal  the  sometimes  chalky  vertically  space  space  6-5, be  the  oyster  grew  from  below  an  Konbostrea,  Lithiotis  upwards  and  to  deeper  lying  Loriga  structure 1982)  the  attached parallel  (1977) extends  to  the  pits  at  to  from  end  cardinal the  characterized  long  the  grooves  of  is  the  named  ventral either  valve  axis  of  furrowed on  margin umbo,  either  the  side  is  the shell,  plate.  (Figure which  by  of  The the  6-1).  The  the  only  75  Figure 6-5: Horizontal cross-sectional view of Lithiotis, the body chamber (right) and the relative position of bivalve (left). Specimen EB 2-10. Upper right sketch c h a m b e r b e l o w the v e n t r a l m a r g i n of the f u r r o w e d plate,  i l l u s t r a t i n g the s h a p e of the sections within the = shape of the body (x 0.65)  76  indication  of  a  possible  ridge-and-groove separated  b e referred  mm  high  The  number  on  the  and  and  the  varies  o f the  furrowed  furrow  Italy,  1982)  diameter  assumed  has  and  series  becomes  a  The  grooves  than  groove  top,  are  than  plate  develop  20,  wide.  depending  gets  wider  a furrow  separating  and  up t o 1  0.5t o 1 m m  5 t o more  gradually  which are  o n the  ridges  are  furrowed  1982). T h e  ridges  furrow  6-7).  A s the  and  of  an open  the  less  thicken  and  form  a chevron The  with  furrowed  Individual  tubes  with  o n top,  t w onew  bioherms  information  of  date  about  ridges  They  their  tubes  continuous  position  at t h e  Loriga,  0.2  are  bent  Formation  Plate  valves.  valve  structures  T h e horizontal  t o 0.5  hollow from In  1977; mm  o r calcite i n the  the  edge  longitudinal  o f the  tube  that  Articulation plate,  and  free  was  to  light  from  additional  the ridge-and-groove probably  suggested valve  a n d t h e internal  cross-sections  bring  3 shows  o f thefurrowed  theattached  the  aragonite,  region.  unknown.  two  behind  6-7).  purpose.  the  are  from  and  of theumbo  in the Robertson  margin  between  are  (Benini  arranged The  bivalves  observed  approximately  the ridge-and-groove  been  articulated  t h eventral  lines  (Figure  are  aragonite.  calcite.  Lithiotis  is plate  o f radially  from  growth  function  tubes  t o t h e base  pattern  preserved  of the  sparry  margin  the  has to  structures  6-6).  o f well  internal  arecomposed  infilled  section  Lithiotis  sections  structure  t h e cardinal  distance  a  (Figure  plate.  r o w of  (Figure  cross  at  tube  from  t o be recrystallized  and  tubes  cross  a  ridge-and-groove  of  branch,  horizontal  Northern  center  ridge  wide  o f ridges  of  (Chinzei,  Lithiotis  1982).  In  Chinzei,  Each  t o a s an open  the former  (Chinzei,  in  grooves.  ridges  in  consists  1.5 t o 2 m m  width  growth,  structure  b y deep  can  ligament  active  only  b y t h e increasing  towards  t h e umbonal  and  77  plume-like area  furrowed  plate  internal t u b e s body chamber  Surface features  Longitudinal section  Cross-section of ridge-and-groove structure  1  •a .c  Internal tube  mm  Horizontal section of int. tubes  78  region.  It  fastened  6.  is  possible  t o the free  SUMMARY  that  valve  biostromes  was a  and bioherms  bivalves  cobbles,  b y the attached  t o have  areas  with  indicate  a  that  chamber  well  above  bivalves thin,  free  margin  environment the  between  B.  base  The  of  of  of  the bivalves surface.  took  plate,  a  sedimentation sediment  environments. and probably  anchored  in t h e  lines  the  on only  keeping  of  the soft in  adaptation  valve  mature  at t h e  f o r living  If t h e t w o v a l v e s would  parts  the animal. The  the attached  particles  bivalve  around the  continued  size  necessary rate.  is t o o  adapted f o r  growth  with  area  w a s well  place  vertically,  in t h e b o d y  the furrowed  were  Growth  Upwards  increase  umbo,  which  material grew  water  as shells  Lithiotis  sedimentation.  in l o w d i v e r s i t y  The attachment  bivalves  n e w shell  a high  such  at t h e u m b o .  articulated  the  which  the valves.  vertically  shallow  surfaces,  Lithiotis  with  AFFINITY  OF  bivalve  Lithiotis  trapped  food  animal  that  center  o f Lithiotis  scar  of  grew  marine  the mature  significant  of  between  ligaments  in  articulated  become  jammed  suspension  feeding  the t w o valves.  TAXONOMIC  of  valve  rate  of  marginal  t o hard  the sediment  valve  that  The morphology  a n d that  without  ventral  at  high  accretion  body  an  cemented  or m u d substrate.  contained  articulation  bivalve  in  supported  tubes  MORPHOLOGY  sessile  Juvenile  sand  a n d aided  O F LITHIOTIS  Lithiotis  small  t h e internal  the outer (Chinzei,  shell,  LITHIOTIS w a s almost  in i t s gills.  certainly  Longitudinal  cross-sections  reveal  that  the growth  reach  only  o n e or t w o c m beyond  1982).  There  is  not enough  lines,  a  which  space  in  indicate  through the the position  the adductor the shell  muscle  cavity  for  79  accommodating  gills  lamellae  probably  marginal  extensions  inside  the  extended in  shell  around  living  and  the  oysters  a  fringe  ventral and  of  margin,  conchiolin  rich  comparable  t o the  bivalves  (Chinzei,  pteriomorph  1982). Suspension sedimentation  feeding  because  continuous  danger  their  Epifaunal  gills.  matter  between  of  within  communities  However,  such  animals  can  bivalves  order  to  adopted  of  mature  barren  in  well  type"  shells  the same above  are  to habit not  species,  the  of  markedly  water  are frequently  (Chinzei,  water  if  soft  bottom  strategies  to  interface.  soft  Miocene  bottom  juveniles  up  the  sessile  and Seilacher,  elongate, building  and  and the  a  1986).  Several  adopted  Savazzi  suspended  higher  marine,  on  clogging  are actually  Crassostrea life  a r e in  from  plentiful.  have  rapid  particles  material  the sediment  (Chinzei,  trapping  rates  marginal  sessile  of  particles  substrates  is  oyster,  areas  trapped  organic  them  vertically  sediment  juveniles  muddy  water,  Cretaceous  growth  the  food  above  adapted  muddy  act as baffles,  suspended  all  Lithiotis,  have  Lithiotis,  the  interface.  This  found  attached  by 1982).  attach  to  beds  in  shell  strategy  is  to the  also  in situ  bivalves. Elongated  a  on  in  and the bivalves  Sedimentation  shallow  chamber  oyster of  to  the lower  remain with  than  adapted  "relay  shells  action.  environment,  Saccostrea  adult  wave  rare  by  protecting  the  Species  the  and  tolerate  body  Although  shells  are  are scarce  communities  rich  maintain  a  and  are  a n d , like  adopting  suffocation  by  environments  oyster,  burial  areas  have  their  sites  their  removal  bivalves  attachment  bivalve  subsequent the  sessile  "rudist  bottoms  species  type" (Chinzei,  of  morphology Savazzi  Saccostrea which and  a n d the rudist enables  Seilacher,  bivalves  the  bivalves  1982).  The  to  have live  attached  adopted on valve  soft is  80  elongate space  and  the  below  ligament acting  is  as  a  in  upright  carbonate  only  have  to  of  In  gastropods  coral-algal-rudist  Crassostrea  oysters  near-shore  environments  1979).  environment,  The  Caprinids  resemble mutual  coral  (Bein,  The  grows the  vertically  shell.  long, 1986).  and The  carbonate,  from  found  the  achieve  stability  by  rather  shallow  and  reptile however,  In  early  common  developed  which  and  in  the  within  the  area  (Scott,  morphologically  interlocking,  than  barren  Exogyra  shoaling  clusters  be  1979).  are  energy  fan-like  bivalves,  to  Arizona,  are  in  the  grew  rudists;  (Scott,  Nerinea,  high  rudists  remains  Radiolitid  reefs  realm  Cretaceous,  southeastern  gastropod  formed  Tethyan  tended  fish  quantity  Caprinid-algal  oyster,  Chinzei,  upright, majority  2  3  space  cm  thick  below  considered  to  Savazzi  with of  has  Konbostrea  has  Konbostrea  The to  in  small,  rudists  The  the  functional  crowding  attachment  to  and  a  firm  growth  habit  1976).  which  type."  "Lithiotis  of  Cretaceous  Lithiotis  and  and  dominant  from  the  away  heads  the  reefs  from  orbitolinids,  present  with  are  cementation  substrate  as  along  reefs  void  remains  marine,  which  the  The  Radiolitid  Lithiotis,  communities  with  are  by  while  valve  shallow  inhabited  echinoids,  along  free  and  in  shell  partitions.  the  Caprinid  rudist  the  thin  and  Cretaceous  Israel,  found  The  diversity  organisms.  in  septa-like  those  low  upward  growth  early  Cretaceous  lagoonal  by  operculum.  in  been  nerineid  off  the  platform  migrates  upwards  similar  encrusting  bones  or  reefs  vertically  the  lid  environments  body  closed  follows  extensive  of  soft  a  the  and  specimens and the  have  are body  are  restricted 50  densely  chamber  originally  to  been  is very  same  (1982)  dorsoventrally  body  found  the  Seilacher  similar soft  adopted  70  refer  to  elongated to cm  the  infilled porous,  4  together by  the  shell  that  ventral  high,  packed  as  to  end  of  5  cm  (Chinzei,  porcellaneous chalky  material  81  (Chinzei, is  1986).  made  1986).  of  foliated  T h e free  valve  attached  the  internal  the  body  is  lived  are found  intercalated beds  are traces  habitat,  of boring is  Lithiotis however  Lithiotis  nacreous  aragonite  originally  shells  muscle  scar  the  monomyarian their  layers  left  oysters  valve  exist  from  shell  composed  which  (Chinzei,  a n d Lithiotis  (Benini  1982). is  preserved  attached  and Loriga,  by  are  tubes  area w a s  of  1986).  or  brackish  water, oyster  Konbostrea  b y sandstone within  with  the oyster  (Chinzei,  and  1986).  environmental  that  1977;  Chinzei,  calcite.  attach  to  t h e right  Lithiotis  The  right  1982).  adductor  o f the shell  the  Well  prismatic and  indicates  side  to  of  (Chinzei,  contain  which  Oysters  some  the t w o bivalves.  Italy  analogous  6 - 7 ) . In  shells  between  from  shell  morphology  solely  of the  the elasticity  found  o n the posterior is  time  In J a p a n ,  fossils  shell,  by  t o the umbo.  there  underlain  Northern  in t h e outer  is located  valve,  in  valve  T h e ligamental  intertidal  mudstone,  differences  and  the  position.  Konbostrea  (Figure  at w h i c h  in  on well  are c o m m o n l y  attached  bottom  adjacent  area  opened  sponges  specimens  o f Lithiotis  have  other  h a d an aragonite  Oyster  on  to  T h e free  and is continuous  spaces.  T h e only  similar  several  preserved  conical  in sandy  seams.  valve  attached  shell  (Chinzei,  o n the center  is located  subdivided  in a vertical  as lenses  coal  is  maturity,  muddy  in the sediment  area  lenses  o f calcite.  the  is found  the ligamental  reached  a  overlaps  muscle  of  believed  on  and composed  and  cavity  a n d t h e outer  porcellaneous  o n the attached  behind  the bivalve  valve  anchored  thin  ligamental  umbonal  a n d robust  intervening  area  to the number  until  Konbostrea  beds  t o just  the  free  cardinal  is present  cavity  corresponding utilized  with  is extremely  and a small  tube  specimens  is thick  0.5 c m . A n a d d u c t o r  valve  An  valve  calcite  valve  covers  approximately  the  The attached  cavity  valve  the substrate valve.  of by  F o r these  82  reasons of  is  Lithiotis  separates  in  function not  both  as  a  the is  hinge  oysters,  probable and  Lithiotis  bivalve in  similar  to  that  (Benini  and  it  functional  an  oyster.  plate as  that  or  the the  If  the  tooth  internal  is  tube  the  furrowed  structure  ligament  although  Konbostrea,  Cochlearites outcrops it  Loriga, ligament is  Cochlearites attached  by  Lithiotis,  it  the is  environment,  often  1977).  left  adjacent the  been  its  open  valve  composed  although  in  of  by  the  plate  this  also  sole  served  purpose  two  differs  the  not  stages  the  (Chinzei,  is  hinge  a  of  as  similar  the  tube  and  looks in  in  Lithiotis and  of  associated  Lithiotis  no  its  valve  (Chinzei,  1982).  Cochlearites  intermixed  and  outcrop  furrowed  free  so  having  right  communities found  often  Ocean,  from  elasticity  than  Lithiotis are  Tethyan  juvenile  rather  1890)  misidentified  aragonite to  (Tausch, the  Cochlearites  present to  loppianus  throughout  has  believed  communities  1977).  It  c l a s s i f i e d as  certain.  Lithiotis  in  been  from  oysters.  in  The with  not  considered  Lithiotis  structure  is  has  Lithiotis  plate. and  1982). is  a  is Like  found  in  the  same  (Benini  and  Loriga,  83  PLATE  Photographed from Robertson Formation,  1:  HORIZONTAL  CROSS-SECTIONS  acetate peels of slabbed northeast of C o w Creek.  OF  biohermal  Lithiotis  limestone  A  -  Horizontal cross-section through the shell c a v i t y area b e l o w the ventral m a r g i n of the furrowed plate. The free valve is separated f r o m the a t t a c h e d v a l v e . S p e c i m e n EB 1-1, m a g n i f i c a t i o n X 2.  B  -  C r o s s - s e c t i o n through the upper s h e l l c a v i t y . The f r e e v a l v e is r e p r e s e n t e d b y a thin line and l a y e r i n g c a n be s e e n o n the right hand side. S p e c i m e n EB 1-2, magnification X 4.  C  -  Cross  s e c t i o n through the u m b o n a l T h e f r e e v a l v e is a b s e n t . 2-7, magnification X 4.  Lithiotis. EB  region of Specimen  from  the  23a PLATE 1  84  PLATE  Photographed from Robertson Formation,  2:  HORIZONTAL  CROSS-SECTIONS  acetate peels of northeast of C o w  slabbed Creek.  OF  biohermal  Lithiotis  limestone  A1  -  C r o s s - s e c t i o n s h o w i n g the free v a l v e within the indented furrowed plate area. Specimen EB 2 - 8 , magnification X 1.6.  A2  -  Detail of the free valve showing layering within the valve. The free valve is snug against the attached valve, indicating a l o n g i t u d i n a l p o s i t i o n d i r e c t l y b e l o w the shell cavity. Specimen EB 2-8, magnification X 4.2.  B  C  -  C r o s s - s e c t i o n of the s a m e s p e c i m e n as A l , further down in the umbonal region. S p e c i m e n EB 2 - 8 , m a g n i f i c a t i o n X 1.6.  -  Cross-section through Lithiotis. has been crushed and distorted) EB 3-14, magnification X 3.2.  (Specimen Specimen  from  the  85  PLATE  Photographed from Robertson Formation,  A1  -  3:  HORIZONTAL  CROSS-SECTIONS  acetate peels of slabbed northeast of C o w Creek.  Cross-section  through  Lithiotis  OF  biohermal  near  Lithiotis  limestone  the  ventral margin of the furrowed plate. A r t i c u l a t i o n b e t w e e n the v a l v e s is s h o w n in A2 and figured in A3. A4 is an SEM photograph of the articulating ridge of the. attached valve. Specimen EB 2-9, A1 m a g n i f i c a t i o n X 1.9, A 2 m a g n i f i c a t i o n X 5 .  B1  -  Cross-section through Lithiotis showing indented furrowed plate area and remnant fragments of the free valve. Specimen EB 1-3, magnification X 2. B2 Detail of remnant fragments of attached valve, m a g n i f i c a t i o n X 3.  C1  -  Cross-section through Lithiotis near the ventral margin of the furrowed plate. Specimen EB 1-4, magnification X 2. C 2 D e t a i l o f t h e f r e e v a l v e , m a g n i f i c a t i o n X 6.  from  the  %5a  PLATE 3  86  PLATE  Top  Row:  Bottom  Row;  4  float specimens from the Swamp C r e e k area ( l o c a l i t y 2, Fig. 3 - 5 ) with thick, robust, strongly ribbed shells. Specimens 30-F 1, 2 , 3 , 4 .  Lithiotis  float specimens from the area of Pine Creek, with relatively smooth shells. Specimens 7-12 1, 2 .  Lithiotis north outer  87  PLATE  A1,  A2  and  A3;  Lithiotis  float  5  specimens  from  north of Pine Creek, exhibiting plate and plume-like area on f a c e of the b i v a l v e . S p e c i m e n s  B1,  B2  and  B3:  the the F-6,  the  area  furrowed cardinal 7, 8.  Juvenile Lithiotis bivalves. B1 shows the bivalves ability to curve as it grew. B2 shows a juvenile shell flaring rapidly from the umbo. B3 shows two juvenile bivalves cemented onto mature bivalve. Specimens F - 9 , F - 1 0 and 3 0 - F 5.  88  PLATE 6  A1:  shell.  A2:  bivalve Specimen  Lithiotis  Lithiotis  Specimen  bivalve F-11.  with 30-F  a strongly 6.  with  a  flat  ribbed  outer  outer  shell.  PLATE  7  Outer surface of Lithiotis bivalve. specimen from the Swamp Creek Specimen 30-F 6.  Cardinal 30-F 6.  face  of  Lithiotis  Outer surface of Lithiotis specimen from the area Creek. Specimen F-12.  bivalve.  Float area,  Specimen  bivalve. north of  Float Pine  Cardinal face of Lithiotis. bivalve. Note growth lines on p l u m e - l i k e area. S p e c i m e n F-  S93  PLATE 8  Cardinal specimen Specimen  Outer 30-F  face of Lithiotis bivalve. from the Swamp Creek 30-F 7.  surface 7.  of  Outer surface specimen from Creek. S p e c i m e n  Cardinal  face  of  Lithiotis  bivalve.  of Lithiotis the area F-14.  Lithiotis  Specimen  bivalve. north of  bivalve.  Float area,  Float Pine  Specimen  F-  90a PLATE 8  VII. is  Lithiotis 1965.  The  muscle from and  the  three is  and the  oysters.  bivalves  unique  in  its  ligaments  preserved  within  their  Cochlearites.  Benini  Lithiotis  and  families.  Lithiotis  (Chinzei,  1982) or  A.  it  stages  plate,  wide  and  indicate  a  Bakevelliidae  growth  are p r o b a b l y  the  their  related  valve.  valves.  BIVALVIA  Konbostrea  and  Lithiotina  for  belong the  to  different  Isognomonidae  1984).  Order  PTERIOIDA  LITHIOTINA  91  and Loriga,  Benini  LITHIOTIDAE  1871 a m m e n d .  1758  N e w e l l , 1965  Benini  LITHIOTACEA  Family  Gumbel,  Linnaeus,  1977  and Loriga, 1977  Reis, 1903  Reis,  1903, a m m e n d .  If  aragonite  DESCRIPTION Class  the  functional  remnant  to  lower  Lithiotis  right'  left  Suborder  bivalves  the  Konbostrea,  between  the  Lithiotis  Cochlearites  having  with  link  adductor  pattern.  by  by  Newell,  separates  between  both  found  two  (Seilacher,  age  attached  the  Lithiotis,  attachment  established  the  shell  type"  strong  of  Cretaceous  similar,  and being  (1977)  in  lower  and  Pterioida,  position  between  "Lithiotis  more  Order  the  gap  the  plate  although  of  exist  were  Cochlearites  Superfamily  LITHIOTIS  Bivalvia,  oysters  would  Suborder  Genus  a  are  and Loriga  and  is  furrowed  Cochlearites,  SYSTEMATIC  there  Konbostrea  LITHIOTIS  composition  characteristic  juvenile  shells,  Class  similarities  Konbostrea  in their  better  a  OF  furrowed  Cochlearites  hinged  and  Cochlearites  the  Striking  have  the  aragonitic  and  Lithiotis  in  of  Although  Konbostrea.  Jurassic  included  articulation  scar  TAXONOMY  Benini  and  92  L o r i g a , 1977. SYNONYMS  1930  Type  Lupher  Plicatostylus  Species:  Lithiotis  problematica  A  comprehensive  description  in  the work  of  Benini  and Packard;  Gumbel, of  1 8 7 1 , p. 4 8  6-1  -  6 - 6 , tables  Lithiotis  problematica  Gumbel;  GUMBEL,  1879  Lithiotis  problematica  Gumbel;  DE  p. 4 1 , p l a t e  ZIGNO,  p.  129 -  1890  Lithiotis  ostreacina  Gumbel;  1890  Trichites  loppianus  T a u s c h ; T A U S C H , p . 18 -  1892  Ostrea  1903  Lithiotis  problematica  1923  Lithiotis  aff.  1923  Lithiotis  timorensis  1930  Plicatostylus  1962  Lithiotis  Gumbel;  included  2 , f i g . 13, 14. 135,  problematica  10, f i g . 1 -  Type  locality:  Rotzo  Type  formation:  p.  REIS,  plate  Gumbel;  p.  p. 8 0 -  71  19, f i g . -  1.  73, plate  6 , f i g . 17 -  80  -  1 7 6 , f i g . 9.  176, f i g . 9.  and Packard,  p. 2 0 4 , p l a t e  DE C A S T R O ,  p . 13 - 1 4 ,  2, fig.  1977; Plate  1, f i g . 2 , c o l l e c t e d  by  1.  Gumbel,  fig.-l. (Vicenza),  Calcari  fig. 1  22.  8 1 , plate  8 1 , plate  3,  6.  and Loriga, 67,  Lupher  p . 6 7 , f i g . 1.  BOEHM,  Krumbeck,  Krumbeck,  gregarius  p . 6 7 , f i g . 1.  GUMBEL,  Gumbel;  problematica  p.  GUMBEL,  Gumbel;  problematica  Benini  1870,  is  1, f i g . 2 , 4 , 5 , 6 .  Ostrea lithiotis  Neotype:  taxonomy  1 - 8  1890  plate  5 1 , f i g . 1 3 , 14.  G u m b e l , 1871  1871  plate  2 , f i g . 1.  (1977).  PROBLEMATICA  Fig.  -  the s u p r a - g e n e r i c  and Loriga  LITHIOTIS  p. 2 0 4 , p l a t e  grigi  Italy. (Grey  Limestone),  Member  of  Rotzo,  -  3.  93  Upper  Pliensbachian  Plastotype:  Reis,  1903,  Geologische Description:  thin,  curved plate  highly  in in  f i g . 8,  the  9,  free  with  valve;  specimens face  valve,  from made  areas  of  lines  extend  prominent thin  and  internal  cavity  to  formed  can  surrounding  Occurrence: rocks  tubular  or  the  and  lacks  western  Southern  Europe,  Timor  Indonesia.  in  9a-9e;  attached  valve  margin  as  to  prominent  free of  the  of  the  from  adductor  the  are  of  plume-like plate  periodically  commonly margin  muscle  scar;  calcite  radially  shell  structure  lower  prismatic  acute,  furrowed  shell,  to  furrowed  valve;  monomyarian;  passing  masses  very  margin  side  of  with  circular  umbone  rear;  on  either  of  valve  ridge-and-groove  ridges  ridges;  together  resemblance  valve,  6,  of  with shell  ostracum  developed  disposed  as  crystals  vesicles.  L. problematica of  each  of  outside  distinct  calcite  layers  General right  in  f i g . 4,  elongated;  or  umbo up  from  the  posterior  lamellar  intercalated  by  form  buttress  below  of  around  thick  front  to  corresponding  valve  robust,  either  with  attached  7,  compressed;  articulates  on  plate  ventrally  which  growth  14;  dorso-ventrally  extends  attached  11,  Vienna.  inequivalve;  cardinal  of  6,  cross-section,  some  on  cavity  plate  fragile  elliptical  Toarcian.  Bundesanstalt,  Large;  and  to  is  to  median reported  continental  North  Africa,  and  Cochlearites groove from  for  fibrous  Pliensbachian  margins the  Konbostrea  of  Middle  North East  but  attached  ligament. and and  and  Toarcian South  as  far  America, east  as  CONCLUSIONS  is  Lithiotis  an epifaunal,  Pliensbachian are  most  extensive  suggesting Mowich up  Robertson  a  three  Assemblage core Death  characterized  is  a  Reef  by  made  brachiopods. in  up  shelly  Formation  deposited  in  water,  intertidal Dunalp  environment.  Formations In  In  Italy  area  in s i m i l a r  Southern  Europe,  the depositional  has been  protected marginal  by  a  marine  is found  barrier  edges  bar. The bioherms marked  by a  are  significant  is  and that  other  reef  t o have  been  marine,  brackish  or  in the Sunrise a n d  marine  environments. grigi  bioherms of  to  indicating  are interpreted  Lithiotis  as the shoaling  conditions,  gastropods  in the Calcari  o f the  parallel  inhibited  marginal  Death  Assemblage  low,  in Nevada  a  bivalves. The  lying  Nerinea  that  are made  represents the  Flank  marginal  found  water,  environment  interpreted  bivalves  area,  across the  (2)  Lithiotis  is extremely  nearshore,  Lithiotis  Suplee-lzee  Assemblage  abundant  Upper  bioherms  The bioherms  action. T h e Reef  bioherms  shallow  the  Lithiotis  the  vertical  abundant  is also  Lithiotis  in  Assemblage;  environment  The Robertson shallow  of  T h e Life  diversity  organisms.  a  Oregon.  a n d east.  debris,  restrictive  found  in a s e a t r a n s g r e s s i n g  in situ  of  T h e reef  a  of  b y current  Lithiotis  part  Flank  Assemblage.  aligned  central  the south  and is comprised  thrived  Lithiotis  in east  environment  (1)  a n d (3) a L i f e  pelecypod  northeastern  biofacies:  and often  terebratulid  the  from  Assemblage  bedding  in  generally  o f the reef  aberrant  Formation  "semi-protected"  Upwarp  of  sessile,  a  Formation.  in the R o t z o  lagoon,  developed decrease  in  which  is  restricted  in  foraminifera  Formation  has shown  fauna. Examination that  the free  series  of  valve  of  of  specimens  Lithiotis  ridge-and-groove  from  the  Robertson  was articulated  structures  on  94  the  to  the a t t a c h e d  cardinal  face  valve  by a  of the attached  95  valve, up  at  in  the  its  however  of  shell  as  adaptation has  top  the  may  the  furrowed  adapted  it  bivalves  were  well  have  plate.  The  living  in  for  been  not a  morphology  similar  to  Upper  Cretaceous  oyster,  Konbostrea.  on  the  basis  presence muscle  of  The  and  lagoonal  in  are  an  similarity  to  The  that  Eastern  Tethys  Hispanic  Corridor  The  the  marginal  the  a  terranes;  terranes  have  Western  the  between  not  thrive  areas  the  Lithiotis  and  the  Given  that  the  that  of  low  aragonite that  many  is  a  Lithiotis,  within  of  Caprinid  diversity  the  environment,  the  which  and  bioherms lagoon  lagoons.  distribution  of  endemic  center  Ocean,  Since  disjunct  Pacific,  the  Tethys  Toarcian. the  East  itself  Lithiotis  has  in  a  is  greater  to  genetic  must  in  South  the  have  East  America  continutiy  Pliensbachian  migration  reveals  Lithiotis  had  occurred  Pacific and to  populations  that  the have  in  the  along  the  Pliensbachian.  Lithiotis  Wrangellia, been  and  differentiated  conclude  that  to  Pliensbachian  the  of  Lithiotis  oysters.  paleogeographic  during  to in  marine  light.  been in  and  to  found  shoaling  for  this  bivalves.  similar  found  and  suspect  related  tend  and  presence  be  is  scar  move  growth,  Cochlearites  have  bivalves  to  sedimentation,  with  Cochlearites.  reasonable  rudists  in  and  both  However,  during  Western  muscle  is  Lithiotis  bivalve  the  bivalve  rapid  competition  bivalves  are  from  maintained  on  the  buried  The  rudists  of  America Tethys,  been  could  of  Jurassic  The  worldwide  North  it  areas  to  Lithiotis  central  of  inshore,  migrated  Lithiotis  be  reefs.  of  both  mineral,  settings.  oysters  found  to  in  Konbostrea  rudist  Lower  placement  environment  Radiolitid  of  tend  unstable  Cochlearites  while  the  aragonite  scars  relatively  of  the  of  continually  response  a  ability  in  Sonomia  Quesnellia  displaced  or  that  and and  its  absence  Stikinia,  Lithiotis  is  in  the  indicates not  a  low  Canadian that  the  latitude  96 indicator. for  its  marginal could  The  environmental  absence marine  reveal  in  the  facies.  Lithiotis  constraints  suspect Offshore  within  of  Lithiotis  terranes exploration  Wrangellia.  is  lack in  the  suggests of  that  the  appropriate  Queen  Charlotte  reason shallow, Islands  BIBLIOGRAPHY  A g a r d , J . and pres de 131-152.  DuDresnay, Beni-Tajje:  R., 1 9 6 5 , L a r e g i o n m i n e r a l i s e e du J . B o u Dahar, Notes Mem. Serv. geol. Maroc., No. 181, p.  Batten, B.L. and Taylor, D.G., 1978, Reassessment of Thompson Limestone, Lower Jurassic, Plumas County, o f P a l e o n t o l o g o y , V . 5 2 , p. 208-209. B a t t e n , B . L . a n d W e s t , R., 1 9 7 6 , A s t u d y County, Oregon: Portland, Oregon: Industry, O M S I Technical Reports, V. Bein,  of the R o b e r t s o n Oregon Museum 4 , p. 1-37.  the age of the California: Journal  Formation, Grant of Science and  A., 1976, Rudistid Fringing Reefs of Cretaceous Shallow Platform of Israel: American Association of Petroleum B u l l i e t e n , V . 6 0 , N o . 2 , p. 258-272.  B e n i n i , C . 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