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Composition and stratigraphy of late quaternary sediments from the northern end of Juan de Fuca Ridge 1981

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COMPOSITION AND STRATIGRAPHY OF LATE QUATERNARY SEDIMENTS FROM THE NORTHERN END OF JUAN DE FUCA RIDGE RAYMOND ARNOLD COOK B. S c , The University of Alberta, 1973 A THESIS"SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n THE DEPARTMENT OF GEOLOGY We accept t h i s thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA May 1981 (c) Raymond Arnold Cook, 1981 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 o f the requirements f o r an advanced degree a t the U n i v e r s i t y o f B r i t i s h Columbia, I agree t h a t the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and study. I f u r t h e r 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 o f t h i s t h e s i s f o r s c h o l a r l y purposes may be granted by the head o f my department o r by h i s o r her r e p r e s e n t a t i v e s . I t 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 g a i n s h a l l not be allowed without my w r i t t e n p e r m i s s i o n . Department of The U n i v e r s i t y o f B r i t i s h Columbia 2075 Wesbrook P l a c e Vancouver, Canada V6T 1W5 Date ( 9 /1Q\ ABSTRACT Sediments from the northern end of Juan de Fuca Ridge are Late Quaternary i n age and contain widely c o r r e l a t a b l e cycles of t u r b i d i t y current and hemipelagic sedimentation. Sediments from the Ridge were examined for t h e i r mineralogy, structure, components of the sand f r a c t i o n , rates of s e d i - mentation and grain s i z e d i s t r i b u t i o n to e s t a b l i s h processes of sedimentation, stratigraphy, c o r r e l a t i o n and l o c a l hydrothermal r e l a t i o n s h i p s . Ten gravity and Phleger core s i t e s along two p r o f i l e s of the Ridge were examined in d e t a i l , one section was perpendicular to West Valley, the main spreading centre, and one section was within and p a r a l l e l to West Valley. Sediment from Cascadia Basin was compared to the r e s u l t s of the Ridge study. Changes i n sedimentation defined by core X-radiograph structure, components of the sand f r a c t i o n and grain s i z e d i s t r i b u t i o n , indicated cycles of r e l a t i v e l y coarse sediment o v e r l a i n by f i n e r bioturbated sediment with a repeated s t r a t i g r a p h i c r e l a t i o n s h i p in a l l but one Juan de Fuca Ridge core. Changes i n sediment composition are a t t r i b u t e d to b r i e f , episodic, continent derived t u r b i d i t y current deposition followed by lengthy periods of hemipelagic sedimentation for each cy c l e . Differences i n composition e x i s t between sediment of ridges and v a l l e y s , with a greater winnowed foraminiferal-hemipelagic and a l e s s e r t u r b i d i t y current influence i n the former area. Radiocarbon dated f o r a m i n i f e r a l - r i c h i n t e r v a l s from ridge sediments were ex c l u s i v e l y Late Pleistocene with Middle Ridge sediment having an i n f e r r e d 9000-9500 B.P. Late Pleistocene-Holocene boundary. Similar sedimentation cycles between Middle Ridge and v a l l e y l o c a l i t i e s enabled c o r r e l a t i o n of ridge and v a l l e y stratigraphy and the Late Pleistocene-Holocene boundary. A s t r a t i g r a p h i c r e l a t i o n s h i p based on the episodic deposition of continent derived t u r b i d i t e s i i i e x i s t s between the northern end of Juan de Fuca Ridge and the continental P a c i f i c Northwest. Pulses of t u r b i d i t y current sedimentation coincide with i n i t i a l i n t e r g l a c i a l warming trends during the Late Pleistocene. Holocene sedimentation f o r Juan de Fuca Ridge i s of hemipelagic o r i g i n with rare l o c a l t u r b i d i t y current deposition. Hydrothermal minerals were not detected. i v TABLE OF CONTENTS ABSTRACT ± LIST OF ILLUSTRATIONS v i ACKNOWLEDGMENT i x LIST OF PLATES x I. INTRODUCTION INTRODUCTION 1 TECTONIC SETTING 3 PREVIOUS WORK 4 HYDROGRAPHY 6 I I . SEDIMENT TEXTURE AND STRATIGRAPHY INTRODUCTION 7 METHODS 7 RESULTS 12 Sedimentary Structures 12 Grain Size D i s t r i b u t i o n 13 S t a t i s t i c a l V a r i a t i o n 14 Va r i a t i o n Of Grain Size D i s t r i b u t i o n Between Ridges And Valleys 15 Changes In Colour And Grain Size Downcore 17 Radiocarbon Dates And Rates Of Sedimentation 25 DISCUSSION 28 Var i a t i o n In Structure And Size D i s t r i b u t i o n 28 Generalized Turbidite Sequence 28 Tu r b i d i t e Correlation 30 Hemipelagic Sediment 31 Winnowed Sediment 33 Stratigraphy 34 Hydrography 35 C i r c u l a t i o n Patterns A f f e c t i n g The Juan de Fuca Ridge 38 Relationship Of Faunal Preservation And Hydrography On Stratigraphy 38 Stratigraphy Of Middle Ridge 44 Correlation Of Juan de Fuca Ridge Sediment 4 5 Correlation With Continental G l a c i a t i o n 4 6 Source Of Late Pleistocene Turbidites 48 CONCLUSION 49 V I I I . MINERALOGY INTRODUCTION 51 METHODS 52 Analysis Of Bulk Sediment 52 Preparation And X-Ray Analysis Of Clays 52 Analysis Of Unknown Minerals 54 Quantitative Analysis 54 RESULTS 55 Mineralogy Of Bulk Samples 55 Clay Mineralogy 55 Montmorillonite 55 Mica ' 55 C h l o r i t e And K a o l i n i t e 58 Clay Sized Minerals 61 Unknown Minerals 62 DISCUSSION 62 General Mineral D i s t r i b u t i o n 62 d a y Mineral Abundances: Relation To Topography 66 Temporal V a r i a t i o n In Clay Mineral Abundances 69 CONCLUSION 75 Provenance Of Minerals 75 IV. SUMMARY AND CONCLUSIONS 79 BIBLIOGRAPHY 82 APPENDIX I: Location, Bathymetric Depth And Length Of Analyzed Cores 88 APPENDIX I I : Core Structure And Clay Size D i s t r i b u t i o n 89 APPENDIX I I I : Radiocarbon Data 101 APPENDIX IV: Grain Size D i s t r i b u t i o n 103 APPENDIX V: P h i l i p s X-Ray Diffractometer Settings For Sediment Analysis 106 APPENDIX VI: Relative Clay Mineral Proportions 107 yi LIST OF ILLUSTRATIONS FIGURE 1. Bathymetric contour map of the Western Canadian continental margin and seafloor adapted from the Juan de Fuca Plate R e l i e f Map (1978) compiled by the Earth Physics Branch, Canada. The Juan de Fuca Ridge study area i s outlined, Cascadia Basin core 77-14-61 and the major geographic features and deep-sea channels (Carson, 1971) are located. 2 2. Bathymetric contour map (100 metre i n t e r v a l ) and shiptrack of the northern end of Juan de Fuca Ridge. Navigation i s by Loran A - C . F. A. V. Endeavour, 1977. Spreading axes i s West Valley and possibly Middle Valley. 8 3. Bathymetric contour map (100 metre i n t e r v a l ) of the northern end of Juan de Fuca Ridge showing cores and studied sections AA' and BB' . 9 4. Bathymetric p r o f i l e AA' from spreading axis (West Valley) south- eastward showing studied core l o c a t i o n s . Core s i t e 51 i s projected northeast along West Ridge, and s i t e 47 i s projected southwest along East Valley onto p r o f i l e . Bathymetric p r o f i l e BB' i s a northwest to southeast l o n g i t u d i n a l section along West Valley showing studied core loca t i o n s , cores 56 and 63 are projected northeast onto p r o f i l e . 10 5. Ternary plot f r a c t i o n s i l l u s t r a t i n g grain s i z e d i s t r i b u t i o n s by region along sections AA' and BB' from Juan de Fuca Ridge. Cas- cadia Basin core 77-14-61 i s also i l l u s t r a t e d as i s Folk's (1974) c l a s s i f i c a t i o n nomenclature. 16 6. Grain s i z e composition for sand, s i l t and clay i n core 77-14-45 from Middle Ridge. The sand component r e s u l t s i n an obvious symmetry for s i l t and clay. 18 7. Components of the sand s i z e f r a c t i o n i n r e l a t i v e percent are i l l u s t r a t e d for cores of p r o f i l e AA' from Figure 4. The symbols are described i n Figure 8. 20 8. Components of the sand s i z e f r a c t i o n i n r e l a t i v e percent are i l l u s t r a t e d f o r cores of p r o f i l e BB' from Figure 4. 21 9. Generalized sequences from cores of the northern end of Juan de Fuca Ridge based on X-radiograph structure and sand s i z e f r a c t i o n components for A. Valley, B. Ridge and C. Idealized t u r b i d i t e sequence o v e r l a i n by hemipelagic sediment. 23 10. A. Complete t u r b i d i t e sequence of Bouma (1962). B. Ty p i c a l sequence, Juan de Fuca Ridge. C-F. T u r b i d i t e sequence of Cascadia Channel (Griggs and Kulm,1970) 29 v i i FIGURE 11. Generalized s t y l e s of sedimentation for the northern end of Juan de Fuca Ridge. Nomenclature zones a f t e r Folk (1974) as i n Figure 5. 32 12. Location map of hydrographic survey adapted from Thomson (1973) showing: Line P with odd numbered stat i o n s , zone of l a t e r a l mixing between oceanic and coastal domain waters (dashed l i n e ) , and Juan de Fuca Ridge study area ( s o l i d colour). 36 13. Hydrographic p r o f i l e above the northern end of Juan de Fuca Ridge. P r o f i l e A, i s based on hydrographic s t a t i o n 5 (Thomson, 1973), and p r o f i l e B, i s the r e s u l t of hydrographic measure- ments from d i r e c t l y above the seafloor (E. V. G r i l l , U.B.C., 1977). 37 14. Core 45 from Middle Ridge with i l l u s t r a t e d structure, components from the sand s i z e f r a c t i o n , clay percentages, f o r a m i n i f e r a l to r a d i o l a r i a n r a t i o s and radiocarbon dates. Symbols as i n Figure 8 and Appendix I I . 40 15. Correlation of Juan de Fuca Ridge sediments based on the proposed Late Pleistocene-Holocene boundary and apparent cycles of s e d i - S ^ u & A mentation. i n pe-ek-ee- CalkijiVtu 16. Stratigraphy of core 45 from Middle Ridge with sediment and percentage clay fluctuations compared to continental B r i t i s h Columbia and Washington Late Pleistocene to Recent geologic- climate units from Armstrong et a l , (1965), and Late Quaternary temperature changes based on pal y n o l o g i c a l studies from Heusser (1977). 47 17. A. Diffractogram i l l u s t r a t i n g r e f l e c t i o n s from the three dominant ubiquitous minerals i n bulk sediment samples, oc-quartz, p l a g i o - clase feldspar and c h l o r i t e (West Valley core 77-14-43). B. Diffractogram i l l u s t r a t i n g peak traces from the mineral c a l c i t e which i s common to ridge bulk sediments (West Ridge core 77- 14-51). 56 18. A. Diffractogram of the surface sediment (0 to 2 centimetres) from West Valley core 77-14-43 i l l u s t r a t i n g the clay minerals and clay sized minerals common to a l l samples studied. B. Diffractogram peak traces of clay sized c a l c i t e from West Ridge core 77-14-51. 57 19. A. Diffractogram trace from West Valley core 77-14-43 showing untreated Fe-r i c h c h l o r i t e . B. C h l o r i t e peak removal a f t e r twelve hours of d i s s o l u t i o n by warm (80°C) d i l u t e (10%) hydrochloric a c i d . 60 20. Magnetite (mineral "A") diffractogram trace. Minor <x-quartz and p l a g i o c l a s e were c o l l e c t e d u n i n t e n t i o n a l l y with the magnetite concentrate. 63 v i i i FIGURE 21. Authigenic p y r i t e (mineral "B") diffractogram trace. Minor <x-quartz was c o l l e c t e d with the concentrate. 64 22. Bathymetric p r o f i l e s of the northern end of Juan de Fuca Ridge sections AA' and BB' a f t e r Figure 4, showing with small numbers the r e l a t i v e percentage of montmorillonite i n surface samples and averaged through core ( i n parenthesis), large numbers show average r e l a t i v e percent montmorillonite i n Holocene samples (H) and i n Late Pleistocene samples (LP). Cascadia Basin core 77-14-61 i s separately i l l u s t r a t e d . 67 23. Bathymetric p r o f i l e s AA' and BB' of the northern end of Juan de Fuca Ridge a f t e r Figure 4, showing the d i s t r i b u t i o n of the clay minerals i l l i t e (I) and c h l o r i t e (C), and the r e l a t i v e percent- ages of the clay minerals i n surface samples and averaged through the core ( i n parenthesis). Cascadia Basin core 77-14-61 sample values are separately indicated. 68 24. Relative percentage of cla y minerals montmorillonite, c h l o r i t e and i l l i t e p l otted against depth i n core (centimetres) f o r Juan de Fuca Ridge section AA' and West Valley section BB'. Cascadia Basin core 77-14-61 i s i l l u s t r a t e d with legend. 70 2 5. Ratioed r e l a t i v e percentages of clay minerals, with montmorillonite (lx) / i l l i t e (4x) and c h l o r i t e (2x) / i l l i t e (4x) plotted against depth i n core (centimetres) f o r Juan de Fuca Ridge section AA' and West Valley section BB'. Cascadia Basin core 77-14-61 i s also i l l u s t r a t e d . 71 26. Bathymetric p r o f i l e s AA' and BB' of the northern end of Juan de Fuca Ridge a f t e r Figure 4, showing the d i s t r i b u t i o n of average r e l a t i v e percentage values f o r i l l i t e (I) and c h l o r i t e (C) i n Holocene samples (H) and Late Pleistocene samples (LP). Cascadia Basin core 77-14-61 i s separately i l l u s t r a t e d . 73 27. Ternary plot i l l u s t r a t i n g changes i n r e l a t i v e percentages of clay minerals w i t h i n d i f f e r e n t physiographic areas f o r the Late P l e i s - tocene and Holocene Epochs. 74 ix ACKNOWLEDGMENTS This t h e s i s was i n i t i a t e d under the j o i n t supervision of Drs. R. L. Chase and J. W. Murray to both of whom the author i s greatly indebted. Thanks for assistance on the cr u i s e go to G. Beland, J. Kennedy, R. MacDonald, D. Runkle and S. Thorn. The co-operation and assistance of the captain, o f f i c e r s and crew of the research v e s s e l , C. F. A. V. Endeavour was greatly appreciated. Invaluable technical•assistance and access to the Sedigraph units at P a c i f i c Environmental I n s t i t u t e were made to the author by Dr. C. Pharo and his technician Ms. V. Chamberlain. Similar a id and discussion of pertinent hydrographic and oceanographic factors were r e a d i l y supplied throughout t h i s study by Dr. E. V. G r i l l , Department of Oceanography, U. B. C.. Mr. A. Hay, Department of Oceanography, U. B. C., generously supplied substantial assistance on the grain s i z e studies and generated the necessary computer programming to trea t the study area grain s i z e values. To a l l the above people the author i s extremely indebted. Additional thanks go to Dr. A. E. Burgess, Department of Radiology, U. B. C , for the X-raying of the study area cores and to E. Montgomery for his necessary and often timely assistance during t h i s t h e s i s preparation. F i n a l l y to my wife H a r r i e t , son Matthew and to a l l members of my family we are at the beginning. F i n a n c i a l support f o r t h i s study came from grants to, Drs. R. L. Chase, E. V. G r i l l and J . W. Murray from, the National Science and Engineering Council of Canada, Energy, Mines and Resources Canada, the B r i t i s h Columbia Minis t r y of Energy, Mines and Petroleum Resources, Cominco Ltd, Placer Develop- ment Ltd, and the University of B r i t i s h Columbia. X PLATE 1. Photomicrograph showing the sand component from the coarse basal sediment of a t u r b i d i t e sequence (West Valley core 77-l4-43)(Mag. 20x) . 22 2. Photomicograph showing the. sand component of a biogenic - r i c h and f o r a m i n i f e r a l dominated sample t y p i c a l of cored ridge sediment (Middle Ridge core 77-14-45)(Mag. 20x). 22 3. Photomicrograph showing planktic f o r a m i n i f e r a l s h e l l s from Middle Ridge core 77-14-45 with p y r i t e aggregates found i n contact with the s h e l l surface (upper l e f t ) and within the s h e l l s (dark material l i n i n g the umbilical region)(Mag. 50x). 26 4. Photomicrograph showing massive aggregates (lower centre and r i g h t ) of p y r i t e with no apparent biogenic a s s o c i a t i o n (West Valley core 77-14-43). Arenaceous worm (?) burrows ( l i g h t coloured material) l i n e d with dark coloured p y r i t e aggregates (upper l e f t and upper centre) (Mag. 20x). 27 5. Scanning electron micrograph showing p y r i t e aggregates extern- a l l y attached to f o r a m i n i f e r a l s h e l l i n Plate 3 (Mag. 200x). 65 Chapter I INTRODUCTION INTRODUCTION Three consecutive years of deep-sea cruises were i n i t i t a t e d by the Univ e r s i t y of B r i t i s h Columbia (U.B.C.) i n 1977, to determine the presence and extent of hydrothermal deposits on the Juan de Fuca and Explorer Ridges. Sediment chemistry from the i n i t i a l cruise i n - dicated no obvious hydrothermal concentrations. The r e l a t i o n s h i p of chemistry and sediment composition was unknown, requiring a de t a i l e d examination. This study examined the structure, composition, and stratigraphy of surface sediment recovered i n cores from the northern end of Juan de Fuca Ridge. The study area which l i e s between l a t i t u d e s 48°10' and 48°50' north, and longitudes 128°15' and 129°10' west i s 40 km north-south by 60 km east-west ( F i g . l ) . Deep-sea sedimentation and mineralogy have been investigated since the famous Challenger Expedition (1872-1876). Local investigations on the i n t e r a c t i o n of marine processes and sedimentation have been l a r g e l y confined to coastal areas, which t y p i c a l l y have large f l u v i a l sediment budgets and hydrographic processes which strongly i n t e r a c t , a r e l a t i o n s h i p that can confuse or r e i n f o r c e subtle yet s i g n i f i c a n t s t r a t i g r a p h i c changes i n sedi - mentation and sediment mineralogy. With acceptance of the theory of plate tectonics, deep-sea geo- l o g i c a l research has s h i f t e d to encompass the examination of the i n t e r a c t i n g plate boundaries. S c i e n t i f i c i n t e r e s t i n noneconomic sediments coincident with plate boundaries has been secondary to i n t e r e s t i n mantle-derived hydro- thermal products. The understanding of sedimentation at divergent margins must be preceded by an understanding of l o c a l parameters a f f e c t i n g s e d i - mentation and sediment mineralogy. 2 FIGURE 1. Bathymetric contour man of the Western Canadian continental margin and seafloor adapted from the Juan de Fuca Plate R e l i e f Map (1978) compiled by the Earth Physics Branch, Panada. The Juan de Fuca Ridge study area i s out- l i n e d , Cascadia Basin core 77-14-61 and the major geographic features and deep- sea channels (Carson, 1971) are located. 3 Deep-sea sediment budgets f a r from continental influence are small and p r i m a r i l y of hemipelagic, pelagic and hydrogenous sedimentation, these components are dominated by d i f f e r e n t hydrographic factors than those of the continental terrace. L o c a l i t i e s that express synchronous changes i n patterns of both deep-sea and continental terrace sediments are rare and d i f f i c u l t to cor r e l a t e due to va r i a b l e geography and hydrography. In the northeast P a c i f i c the dominant deep-sea topographic features are ridges, o f f s e t t i n g fracture zones, troughs and seamounts. The Explorer, Juan de Fuca and Gorda Ridges are a l l near the North American continental margin. The northern end of each ridge i s closest to the continental margin and exhibits the greatest r e l i e f (Barr, 1972; McManus, et_ a l , 1972). Major changes i n the rate and s t y l e of sedimentation i n the north- east P a c i f i c during the Late Pleistocene and Holocene epochs are well documented from studies of the continental terrace and adjacent abyssal plains (Duncan and Kulm, 1970; Duncan, Kulm and Griggs, 1970; Griggs and Kulm, 1970; Horn et a l , 1971; Nelson and Kulm, 1973; Windom, 1976). Studies on the correlatable synchronous patterns of deep-sea sedimentation are few and i n - conclusive (Carson and McManus, 1971; Phipps, 1977). The proximity of the northern ends of the northeast P a c i f i c ridges to the continental margin, combined with ridge topography, creates l o c a l i t i e s where sedimentary regimes of the deep-sea and continental terraces intermingle. TECTONIC SETTING The Juan de Fuca Ridge, a spreading ridge segment between the P a c i f i c and Juan de Fuca plates, s t r i k e s north northeast. In east-west cross-section the broad ridge has superimposed p a r a l l e l elongate h i l l s and v a l l e y s of subdued r e l i e f , but lacks an obvious median v a l l e y (Barr, 1972; Barr and Chase, 1973; Wakeham, 1977). The ridge i s characterized by asymmetric 4 spreading with a h a l f spreading rate of 2.9 cm/yr (Atwater, 1970; Wakeham, 1977). Geophysical studies have described r e l a t i v e l y aseismic volcanic basement with high i n t e n s i t y magnetization (Lucas, 1972; Barr, 1972; Wakeham, 1977). High heat flow has been measured at numerous points on the ridge, with the highest values occurring near the northern end of the Juan de Fuca Ridge and i t s contact with the Sovanco Fracture Zone (Davis and L i s t e r , 1977b). At i t s northern end the Juan de Fuca Ridge has three p a r a l l e l grabens: West Val l e y , Middle V a l l e y and East Valley, separated by three p a r a l l e l horsts: West Ridge, Middle Ridge and East Ridge (Fig.2) (Barr, 1972; Davis and L i s t e r , 1977a), formed by t i l t e d , rotated f a u l t blocks. These rids*e? PREVIOUS WORK Pr i o r studies of the northeast P a c i f i c including the Juan de Fuca Ridge were i n i t i a l l y d irected at bathymetry and mapping (Barr, 1972, McManus, et a l , 1972). Regional bathymetric descriptions were published by McManus; Mammerickx and Taylor; Chase, Menard and Mammerickx; and Barr (Barr, 1972). Detailed bathymetry of the northern end of Juan de Fuca Ridge, which includes the study area, was published by Barr (1972) and Davis and L i s t e r (1977a). Research on deep-sea sedimentation i n the northeast P a c i f i c was la r g e l y the r e s u l t of regional reconnaissance. Studies concentrated on i c e - raf t e d material, t u r b i d i t e s , and deep-sea channels of the Cascadia Basin and neighbouring abyssal p l a i n s (Griggs and Kulm, 1970;Horn, Ewing and Ewing, 1971; Horn et a l , 1971; Kent et a l , 1971; L i s t i z i n , 1972; Nelson and Kulm, 1973; Stewart, 1976; vonHuene et a l , 1976). Sediment of the continental terrace and Cascadia Abyssal P l a i n o f f Washington and Oregon were analyzed for Late Quaternary changes i n sediment mineralogy. Chronostratigraphy was dependent on radiocarbon dates, biogenic and volcanogenic s t r a t i g r a p h i c 5 markers (Nelson ejt a l , 1968; Duncan £t a l , 1970; Duncan, Kulm and Griggs, 1970; White, 1970; Kulm et a l , 1975; K a r l i n , 1980). The regional a p p l i c a b i l i t y of biogenic s t r a t i g r a p h i c markers was, however, l o c a l l y l i m i t e d because they are time-transgressive on a regional scale (Barnard and McManus, 1973; Phipps, 1977). Mineralogical studies of the surface sediments include Rateev et a l , (1969), Windom. (1969), L i s i t z i n (1972), Kido (1974), Windom (1976). Studies on the stratigraphy of deep-sea sediments to basement are contained i n the DSDP reports (Kulm et a l , 1973). Gross c o r r e l a t i o n s f o r the Late Quaternary have been made on the basis of nonradiocarbon s t r a t i g r a p h i c marker horizons including Mazama Ash (Nelson et a l , 1968), r a d i o l a r i a to f o r a m i n i f e r a l r a t i o (Duncan, Fowler and Kulm, 1970; Barnard and McManus, 1973) and pulses of g l a c i a l d e t r i t u s (vonHuene, et a l , 1976). Sediments at the northern end of Juan de Fuca Ridge, although influenced by s i m i l a r mineralogic and sedimentation controls documented elsewhere from the northeast P a c i f i c , had not been examined p r i o r to t h i s study. Previous investigations of the present study area have been tectonic, and involved only s u p e r f i c i a l examination of sediments (Lucas, 1972; Barr, 1972; McManus et a l , 1972: Barr and Chase, 1973; Davis and L i s t e r , 1977a; Davis and L i s t e r , 1977b). Using continuous s e i s m i c - r e f l e c t i o n p r o f i l e s (CSP), (McManus et_ a l , 1972) divided the sediments into two un i t s , A and B. Unit A was described as a sequence of t u r b i d i t e s that overlay the ridge basement. Near the end of unit A deposition (0.7 m i l l i o n years B.P.), block f a u l t i n g , u p l i f t and t i l t i n g formed the ridges. Unit B, which un- conformably o v e r l i e s the deformed sediments of unit A has l i t t l e deformation, i s confined to the v a l l e y s and was interpreted to be post-deformational (Barr, 1972; McManus et a l , 1972). A de t a i l e d geophysical study augmented 6 by gravity coring was conducted by Davis and L i s t e r (1977a). The cored sediment was p r i m a r i l y examined to aid i n the i n t e r p r e t a t i o n of the acoustic r e f l e c t i v e character of the sediment column. Davis and L i s t e r (1977a and b) recognized, as did McManus et a l (1972) and Barr (1972) the great thickness of sediment of Middle and East Valleys which contrast with very t h i n sediments of West Valley. The Sovanco Fracture Zone (a ridge and p a r a l l e l trough) and i t s contact with West Ridge was proposed as a b a r r i e r which prevented sedimentation by t u r b i d i t y currents on Juan de Fuca Abyssal P l a i n and West Valley (Barr, 1972; McManus et a l , 1972; Davis and L i s t e r , 1977 a and b). Rates of sedimentation, computed from the age of the outer edge of the c e n t r a l Brunhes magnetic anomaly of the basement (0.69 my: Barr, 1972), range, for the t o t a l thickness of Middle Valley sediment, from 55 to 170 cm/lOOOyr (McManus et a l , 1972) or 670 to 1000 cm/lOOOyr (Davis and L i s t e r , 1977a) with n e g l i g i b l e sedimentation from 10,000 yr B.P. to the present (Davis and L i s t e r , 1977a). HYDROGRAPHY Limited data i s a v a i l a b l e for the water column above the northern end of Juan de Fuca Ridge. In the most detai l e d study, Thomson (1973) discussed the v a r i a t i o n and d i s t r i b u t i o n of phy s i c a l properties of seawater to depths of 1500 metres along Line P, which consisted of a number of hydrographic stations stretching from the mouth of the S t r a i t of Juan de Fuca to ocean weather s t a t i o n P ( l a t i t u d e 50°00'N and longitude 145°00'W). Some of the hydrographic stations measured l i e above the study area. In conjunction with the U.B.C. study (1977) bottomwater measure- ments were made at several coring s t a t i o n s by Dr. E. V. G r i l l (U.B.C). The r e s u l t s of Dr. G r i l l ' s work and that of Thomson (1973), w i l l c o l l e c t - i v e l y be discussed i n Chapter II i n r e l a t i o n to the influence of hydro- graphy on Juan de Fuca Ridge sedimentation. 7 Chapter II SEDIMENT TEXTURE AND STRATIGRAPHY INTRODUCTION Research on sediments from oceanic ridges i n the northeast P a c i f i c has aided i n the i n t e r p r e t a t i o n of the deep-sea s t r a t i g r a p h i c record and helped unravel the complex i n t e r r e l a t i o n s h i p of biogenous, hydrogenous, h a l m y r o l i t i c and terrigenous components (Selk, 1977; Phipps, 1977; Be"land i n prep.; Hanson i n prep.; Pric e i n prep.;). The bathymetry f or t h i s study of Juan de Fuca Ridge was recorded by a 3.5 kHz echo sounding system along eight p a r a l l e l northwest-southeast shiptracks (Fig.2). Continuous s e i s m i c - r e f l e c t i o n p r o f i l e s were recorded along some of the same shiptracks. The resultant bathymetry was used to select core s i t e s i n the various l o c a l sedimentary environments. Cores selected for sedimentological analysis were s i t e d on dominant physiographic features of Juan de Fuca Ridge. Cores along two l i n e s were studied, one perpendicular to the ridge axis and the other para- l l e l to West Valley, the ac t i v e spreading r i f t (Figs.3 and 4). METHODS One hundred and twenty samples were analyzed from eight 6.5 cm diameter gravity and three 3.5 cm diameter Phleger cores (Appendix I ) . Seven of the cores were X-radiographed to i l l u s t r a t e s t r u c t u r a l features. The samples for sediment analysis were taken at f i v e centimetre i n t e r v a l s i n the Phleger cores and at ten to f i f t e e n centimetres i n the gravity cores. West Valley, West Ridge, Middle Valley, Middle Ridge, East Valley and Cascadia Basin cores y i e l d e d 64, 9, 7, 17, 15 and 7 samples re s p e c t i v e l y . 8 JUAN DE FUCA RIDGE SHIPTRACK FIGURE 2. Bathymetric map (.100 metre i n t e r v a l ) and shiptrack of the northern end of Juan de Fuca Ridge. Navigation i s by Loran A - C . F. A. V. Endeavour, 1977. Spreading axes are West Valley and possibly Middle Valley. 9 JUAN DE FUCA RIDGE A63 CORE <$>54 CORE AND HYDROCAST A57 HYDROCAST AND VOLCANIC ROCKS FIGURE 3. Bathymetric contour map (100 metre i n t e r v a l ) of the northern end of Juan de Fuca Ridge showing cores and studied sections AA' and BB'. J U A N D E F U C A R I D G E X - S E C T I O N D e p t h b e l o w s e a l e v e l ( m e t r e a - u n c o r r e c l o d ) A 2 1 0 0 WEST RIDQE M I D D L E R I D Q E 2 3 0 0 2 5 0 0 2 7 0 0 2 9 0 0 H 3 1 0 0 WEST VALLEY S c a l e 0 5 K m 1 ' t «-1 I D e p t h b e l o w s e a l e v e l ( m e t r e s ) A ' 2100 D e p t h b e l o w s e a l o v e l ( m e t r e s - u n c o r r e c t e d ) B 2 7 0 0 2 8 0 0 H 2 9 0 0 3 0 0 0 3 1 0 0 W E S T V A L L E Y L O N G I T U D I N A L S E C T I O N 6 6 0 S c a , e 6 K m 1 I I I t I D o p l h b e l o w s e a l e v e l ( m e t r e a ) B' r 2 7 0 0 A — C O R E S O N OR A D J A C E N T S E C T I O N A _ C O R E S N E A R A N D P R O J E C T E D T O S E C T I O N FIGURE 4. Bathymetric p r o f i l e AA' from spreading axis (West Valley) southeastward showing studied core l o c a t i o n s . Core s i t e 51 i s projected northeast along West Ridge, and s i t e 47 i s projected southwest along East Valley onto p r o f i l e . Bathymetric p r o f i l e BB1 i s a northwest to southeast l o n g i t u d i n a l s e c t i o n along West Valley showing studied core l o c a t i o n s , cores 56 and 63 are projected northeast onto p r o f i l e . 11 Examination of X-radiographs v e r i f i e d that repeated major s t r u c t u r a l features were sampled within each core. Analyses of p a r t i c l e s i z e d i s t r i b u t i o n were performed on 1.25 gram sediment samples using both a Micromeritics Sedigraph 5000, and a 5000D P a r t i c l e Size Analyzer (Micromeritics Instruction Manual., 1975). Each sample was prepared from a 2.5 gram aliquot of a i r - d r i e d sediment. Carbonate was removed by reaction with d i l u t e a c e t i c acid on selected samples from cores 45 and 51. Other core samples, which contain less than 3% CaC03 as indicated by p r i o r chemical analyses, were not so treated. Salt was removed from each sample, including those a c i d i f i e d , by repeated washing with d i s t i l l e d water as described below. Samples were wet-sieved with d i s t i l l e d water through a 63 fiva mesh, then mixed and centrifuged for 1.5 hrs i n 100 ml polyethylene test tubes with approximately 90 ml of d i s t i l l e d water at 2100 rpm using an I.E.C. centrifuge with a #240 head, a radius of 23 cm and distance of 8.5 cm from headcentre to the test tube opening. Samples were washed and centrifuged twice, the supernatant l i q u i d was decanted o f f , and the remaining sediment mixed into a s l u r r y with a 40 ml s o l u t i o n of 5 grams of Calgon per l i t r e of d i s t i l l e d water. The s l u r r y was homogenized using a magnetic s t i r r e r and 20 ml was pipeted off and placed i n 25 ml b o t t l e s for Sedigraph a n a l y s i s . Garnet standards and a baseline s o l u t i o n of 5 gram/litre calgon were run p r i o r to every ten samples analyzed. T r i p l i c a t e runs of cumulative curves for the same sample plotted with t 1.5% of the i n i t i a l trace. Computer processing of data points at 1/4 0 i n t e r v a l s from the cumulative curve produced by the Sedigraph enabled the determination of s i z e - d i s t r i b u t i o n s t a t i s t i c s and construction of bargraphs and arithmetic and logarithmic cumulative curves for each analyzed sample. The sand f r a c t i o n was examined under the binocular 12 microscope at 60 to 80 times magnification to determine proportions of i t s components. The sand sized f r a c t i o n was divided into four major components: biogenic ( r a d i o l a r i a n , f o r a m i n i f e r a l , diatom and ostracod t e s t s ) ; d e t r i t a l minerals; carbonaceous material (degraded terrigenous plant de b r i s ) ; and authigenic material (framboidal p y r i t e ) . The i d e n t i t i e s of d e t r i t a l and authigenic components were determined by X-ray d i f f r a c t i o n and scanning electron microscopy. V i s u a l estimates, expressed as percentages were made of proportions of each component. The l a t t e r are only approximate, but are meaningful when combined with quantitative measurements to i l l u s t r a t e sedimentation patterns. A graphic depiction of proportions of r a d i o l a r i a to foraminifera was used to indi c a t e r e l a t i v e changes i n plank t i c s and i l l u s t r a t e which organism most strongly dominates the biogenic component. Four radiocarbon dates were obtained from f o r a m i n i f e r a l - r i c h ridge-top cores. X-radiographs of these cores show l i t t l e disturbance of the sediment over dated i n t e r v a l s . Samples for radiocarbon dating were removed with a s t a i n l e s s s t e e l spatula, the outer two millimetres of sediment being discarded. The sample was then washed onto a 63 pm brass sieve with d i s t i l l e d water, cleaned u l t r a s o n i c a l l y i n glass beakers, sieved again, o p t i c a l l y examined at 60 to 100 times magnification, picked clean of organic contaminants, packaged i n aluminum f o i l and sent f o r analysis to Irene S t e h l i of Dicarb Radioisotope Laboratory, Chagrin F a l l s , Ohio, U.S.A. RESULTS Sedimentary Structures X-radiographs of gravity cores from West Val l e y (Appendix II) each show numerous zones of c l o s e l y spaced laminae, which o v e r l i e a d i s t i n c t (scoured) surface. The laminae are o v e r l a i n by sediment which appears 13 massive except f o r burrows, possibly of holothurians, and c o l l e c t i v e l y forms a sequence of zones. The frequency of burrows generally decreases upsection within a sequence of zones. Large i n t e r v a l s e x i s t that i n - d i v i d u a l l y contain a d i s t i n c t basal erosional contact, o v e r l a i n by several c l o s e l y spaced t h i n sequences of zoned laminated and massive sediment, o v e r l a i n by a f i n a l sequence that c o n s i s t e n t l y contains massive sediment more than 20 cm thick. These i n t e r v a l s are commonly repeated two to three times i n each gravity core and appear c y c l i c a l . Sediment cycles that are s t r u c t u r a l l y s i m i l a r are found i n four of the X-radiographed cores i l l u s - t rated, cores 45, 62, 63 and 67 (Appendix I I ) , three of which, 62, 63 and 67 are located within 7 kilometres of each other, at approximately the same depth i n West Valley. The remaining core, 45, i s from a much shallower depth on Middle Ridge, 28 kilometres southeast of the others, but c l e a r l y contains s t r u c t u r a l cycles s t r i k i n g l y s i m i l a r to those i n the West Valley cores. Three other X-radiographs (56, 66 and 51) are i l l u s t r a t e d to show s t r u c t u r a l v a r i a t i o n . Core 66 i s a 46 cm long Phleger core from West Valley, i n which the s i n g l e cycle observed may be the analogue of the shallowest cycle i n cores 62, 63 and 67. Core 56, from the west scarp of West Valley, a p o t e n t i a l l y unstable area affected by l o c a l slumping and t u r b i d i t y currents, has two main cycles, with thinner sequences that are more highly bioturbated than any other core. The most homogenous and massive of a l l X-radiographed cores i s core 51 from West Ridge, which lacks the sediment sequences described above. Grain Size D i s t r i b u t i o n Except f o r the c l a y - s i l t boundary, the boundaries between sand, s i l t and clay used i n t h i s study are those of Folk and Ward (1957) and Folk (1974). 14 An i n f l e c t i o n at approximately 90, observed i n a l l cumulative curves, prompted the use of 90 for the c l a y - s i l t boundary, rather than Folk's preferred 80. S t a t i s t i c a l V a r i a t i o n Due to the abundance of clay i n the sediment, conclusive r e s o l u t i o n of mean, standard deviation, skewness and kurtosi s i s d i f f i c u l t using conventional s t a t i s t i c methods (Folk and Ward, 1957; Folk, 1974). Projection of the slope of the graphic clay t a i l , obtaining 100% cumulative weight percent, r e s u l t s i n conventionally unacceptable clay weight per- centages and sizes f i n e r than 180 for most samples. The graphic r e s u l t was probably due to post-depositional reworking and experimental d i s - aggregation of clay that i n i t i a l l y deposited as aggregates such as f e c a l p e l l e t s , p a r t i c u l a t e matter and coatings on sand and s i l t grains. Inherent d i f f i c u l t y e x i s t s f o r s t a t i s t i c a l i n t e r p r e t a t i o n of cumulative curve r e s u l t s on c l a y - r i c h sediments. Stokes law of s e t t l i n g i s considered v a l i d for clay to s i l t sized p a r t i c l e s where sediment i s assigned workable density values and sp h e r i c a l diameters. Sediments from the Juan de Fuca Ridge and Cascadia Basin are dominantly mud with at least 40 and commonly greater than 60 percent clay. Clay minerals are not sp h e r i c a l , but platy and i r r e g u l a r i n shape, possess a p o s i t i v e l a t t i c e charge that may r e s u l t i n cohesion between clays, and have v a r i a b l e d e n s i t i e s . A l l of these f a c t o r s , and the small s i z e of the p a r t i c l e s , make measurement and s t a t i s t i c a l treatment based on Stokes law suspect ( B l a t t , Middleton, and Murray, 1972). S t a t i s t i c s based on an i n f e r r e d normal d i s t r i b u t i o n , which accurately r e l a t e experimental to natural r e l a t i o n s h i p s require s e l e c t i o n of an experimental mean coincident with the natural mean. A clay t a i l on the p r o b a b i l i t y curve that r e f l e c t s the experimental and not 15 the n atural composition w i l l s h i f t the experimental mean away from the n atural mean. Standard deviation, skewness and kurtosis values used to deduce environment are then based on experimental mean value and therefore include the mean bias. Correction of the experimental mean to overlap with the natural mean, and s t a t i s t i c a l t e s t i n g of t h i s re- l a t i o n s h i p , must precede a conventional s t a t i s t i c a l examination of sediment environment. No attempt to do t h i s has been made for t h i s study. In describing changes i n texture t h i s study does not determine the experimental and natural s t a t i s t i c a l r e l a t i o n s h i p but depends s o l e l y on grain s i z e d i s t r i b u t i o n boundaries that v a l i d l y f a l l within Stokes law determination. V a r i a t i o n Of Grain Size D i s t r i b u t i o n Between Ridges And Valleys Three dominant grain s i z e ranges include a l l the Juan de Fuca Ridge sediment; sandy s i l t to s i l t , mud and clay (Folk, 1974) (Fig.5). It i s apparent from Figure 5, that the v a l l e y s contain sediment both f i n e r and coarser than that found from the ridges. Cores from West Valley contained the largest proportion of coarse sediment, which could r e f l e c t e ither the sedimentation pe c u l i a r to the l o c a l i t y or simply a bias due to more de t a i l e d areal and depth sampling than that performed on the other physiographic regions. Middle Valley and East V a l l e y contain the f i n e s t sediment i n the area, and several samples are s i m i l a r to or f i n e r than sediment analyzed from the Cascadia Basin. West Ridge sediment tends to be massive with more sand, more clay and less s i l t than Middle Ridge and v a l l e y sediments. In conclusion, the grain s i z e d i s t r i b u t i o n of sediment throughout the area shows differences that suggest varying sedimentation processes(Appendix IV). LEGEND JUAN DE FUCA RIDGE X-SECTION CASCADIA BASIN A WEST V A I L E V A ' E A S T V A L L E Y T f - 1 4 - o S • _ 8 a o t p U point FIGURE 5. Ternary plot f r a c t i o n s i l l u s t r a t i n g grain s i z e d i s t r i b u t i o n by region along studied sections AA' and BB' from Juan de Fuca Ridge. Cascadia Basin core 77-14-61 i s also i l l u s t r a t e d as i s Folk's (1974) c l a s s i f i c a t i o n nomenclature. 17 Changes Of Colour And Grain Size Downcore (Appendix II) The colour of the Juan de Fuca Ridge muds varies widely from a dark to medium gray (N3, N4, N5) for the coarser grain sizes and dusky yellowgreen to l i g h t olivegray (5GY5/2 to 5Y5/2) for the f i n e r sediments. Fluctuations i n clay s i z e p a r a l l e l those s t r u c t u r a l changes described from the X-radiographs. Core 45 from Middle Ridge t y p i c a l l y i l l u s t r a t e s the trends (Fig.6). The sand component comprises less than one percent of each sample analyzed from core 45. Figure 6 shows that a t e x t u r a l change i n clay i s q u a n t i t a t i v e l y and symmetrically r e f l e c t e d i n the s i l t trace. The grain s i z e analyses showed very l i t t l e sand i n any of the cores. One sample contains 22 weight percent sand, th i r t e e n samples ranged between 3 and 11 weight percent sand and the re- maining 106 samples each contain l e s s than 3 weight percent sand. It i s therefore considered v a l i d to use clay f l u c t u a t i o n s to i l l u s t r a t e changes i n sediment within and between analyzed cores. An examination of the clay changes i n core 45 show three gradational f i n i n g upward cycles. Changes from f i n e to coarse sediment are abrupt suggesting a rapid rather than gradational sedimentation process. Changes from coarse to f i n e sediment and from f i n e to coarse sediment appear to be c y c l i c a l i n core 45 as with a l l the Juan de Fuca Ridge cores. An obvious feature between v a l l e y and Middle Ridge cores i s that v a l l e y cores show a decided drop i n clay content with sediment depth while Middle Ridge sediment demonstrates an increase. This r e l a t i o n s h i p based s o l e l y on grain s i z e i n i t i a l l y appears inversely r e l a t e d . Sand Frac t i o n O p t i c a l examination of the f r a c t i o n greater than 62.5 îm from each sample revealed four components based on composition and source: (1) A biogenic component that includes r a d i o l a r i a n , foraminifera, diatom 18 CORE 7 7 - 1 4 - 4 5 GRAIN SIZE COMPOSITION % 0 10 20 3 0 4 0 5 0 6 0 70 8 0 90 1! O-l I I I I U J I L Ul a o o H 100 120H 14CH 160 TI—i—i—i—r 10 2 0 3 0 4 0 5 0 6 0 70 8 0 9 0 100 % SAND ( < 0 . 7 ) -SILT | |-CLAY FIGURE 6. Grain s i z e composition for percentage sand, s i l t and clay i n core 77-14-45 from Middle Ridge. The small sand component r e s u l t s i n an obvious symmetry for s i l t and clay. 19 and ostracod t e s t s ; (2) a d e t r i t a l component that includes quartz, mica, b a s a l t , p l a g i o c l a s e , obsidian and le s s common minerals; (3) carbon- aceous and (4) authigenic components which include decayed terrigenous plant debris and framboidal p y r i t e r e s p e c t i v e l y . Results are i l l u s t r a t e d i n Figures 7 and 8, which demonstrate the changes along West Valley and across Juan de Fuca Ridge. The r e l a t i v e abundances of r a d i o l a r i a and foraminifera also shown, i l l u s t r a t e which organism dominated a given biogenic component (Duncan, Fowler and Kulm, 1970; Barnard and McManus, 1973; Phipps, 1977). C l e a r l y the components are not as s e n s i t i v e as grain s i z e or s t r u c t u r a l changes i n defining c y c l i c a l periods of sedimentation. D i f f i c u l t y e x i s t s when one component i s so r e l a t i v e l y abundant that i t masks the subtle changes i n sedimentation r e f l e c t e d by the other components (Plates 1 and 2). This problem i s most evident i n cores that contained a high f o r a m i n i f e r a l content although even here a major i n f l u x of d e t r i t a l material i s apparent. The gross changes i n sand components roughly p a r a l l e l s the previously described sedimentation sequences noted from the X-radiographs and grain s i z e analyses. An exception to t h i s i s West Valley core 62 which contains eroded and laminated horizons on the X-radiograph (Appendix II) that were not sampled. The resultant record of changes i n grain s i z e with structure changes i s incomplete when compared to other more favourably sampled cores. Composite proportions of the sand s i z e components are plotted alongside the previously described sedimentation sequences i n Figure 9. Sediments immediately overlying buried eroded surfaces have up to 80 to 90 percent as d e t r i t a l component, with mica > quartz > plagioclase > basalt * obsidian. A l l n o n d e t r i t a l components are c o l l e c t i v e l y reduced to 20 percent by d i l u t i o n i n such i n t e r v a l s of d e t r i t a l dominated sediment. JUAN DE FUCA RIDGE X-SECTION F I G U R E 7. Components of the sand siz e f r a c t i o n i n r e l a t i v e percent are i l l u s t r a t e d for cores of p r o f i l e AA' from Figure 4. The symbols are described i n Figure 8. WEST VALLEY LONGITUDINAL SECTION B B' 7 7 - 1 4 - 4 3 7 7 - 1 4 - 6 7 7 7 - 1 4 - 6 3 7 7 - 1 4 - 6 2 7 7 - 1 4 - 6 6 7 7 - 1 4 - 5 6 FIGURE 8. Components of the sand siz e f r a c t i o n i n r e l a t i v e percent are i l l u s t r a t e d for cores of p r o f i l e BB' from Figure 4. 22 PLATE 2. Photomicrograph showing the sand component of a b i o g e n i c - r i c h and fo r a m i n i f e r a l dominated sample t y p i c a l of cored ridge sediment (Middle Ridge core 77-14-45)(Mag. 20x). 23 LEGEND o e> R F 100 %100 NO y / / ^ 0«* ^ ^° ^ ^ > — S a m p l e point B VALLEY CORE RIDGE CORE S A N D S I Z E D C O M P O N E N T S S A N D S I Z E D C O M P O N E N T S S T R U C T U R E R F S T R U C T U R E R F ( X - R A D I O G R A P H ) 100% 100 0 % 100 ( X - R A D I Q G R A P H ) 100%100 0 % 10C - O o •O — 0 TURBIDITE SEQUENCE (GENERALIZED) S T R U C T U R E C O L O U R ( X - R A D I O G R A P H ) 5 Y 5 / 2 1 0 Y 4 / 2 6 G Y 5 / 2 5GY4/ 1 N3 NT N5 — _e _ o. H e m i p e l a g i c s e d i m e n t ( b i o g e n i c - r i c h ) Z o n e of t r a n s i t i o n ( p e l i t e - h e m i p e l a g i c ) — - Z o n e of b u r r o w e d p e l i t e Z o n e of l a m i n a e C o a r s e g r a i n e d b a s a l s e d i m e n t S u r f a c e due to e r o s i o n ( s c o u r ) FIGURE 9. Generalized sequences from cores of the northern end of Juan de Fuca Ridge based on y.-radio^raph structure and sand s i z e f r a c t i o n components for A. Valley, B. Ridge and C. Idealized t u r b i d i t e sequence o v e r l a i n by hemipelagic sediment. 24 The biogenic component i n d e t r i t a l dominated sediment may exhibit a s l i g h t increase i n foraminifera, a feature recognized elsewhere as an entrained t u r b i d i t e fauna (Plate 1) (Griggs and Kulm, 1970). In the overlying laminated and massive sediments a gradational increase i n the amount of biogenic and carbonaceous components at the expense of the d e t r i t a l component takes place with f i n i n g of sediment. In a l l of the sequences the uppermost, f i n e s t grained sediment with reduced burrowing e x h i b i t s the l a r g e s t biogenic component, with p l a n k t i c s much greater than benthics. The same f i n e grained sediment contains a much reduced d e t r i t a l sand component and often lacks carbonaceous or authigenic components. S l i g h t v a r i a t i o n of the previously described sequence i n each core can be a t t r i b u t e d to l o c a l physiography and hydrography. Biogenic materials i n ridge cores d i f f e r from those i n v a l l e y cores. West Valley sediments, the deepest i n the study area, are dominated almost e x c l u s i v e l y by r a d i o l a r i a n t e s t s , except where foraminifera occur i n the coarsest of samples. Frequently these samples contain more robust benthic forms than p l a n k t i c forms. These foraminifera are believed to have been transported, from shallower regions. In Middle and East Valley also, the biogenic component i s dominated by r a d i o l a r i a . In sediments from West and Middle Ridges foraminifera dominate the biogenic component (Plate 2). Occurrence of the authigenic component does not appear to be physiographically c o n t r o l l e d . Framboidal p y r i t e occurs i n both the ridge and West Val l e y sediments (Figs. 7 and 8). West Valley cores 62 and es- p e c i a l l y 43 contain s i g n i f i c a n t proportions of authigenic p y r i t e i n the sand s i z e material. The ridge sediment also contains s u b s t a n t i a l a u t h i - genic p y r i t e although the abundant f o r a m i n i f e r a l component diminishes i t s absolute percentage. The source of the p y r i t e i s conjectural: Studies of 25 anaerobic sediments with high organic content suggest that anaerobic b a c t e r i a decomposing protoplasm provides s i g n i f i c a n t q uantities of sulphur which combines with dissolved i r o n to produce intermediate minerals that with a l t e r a t i o n r e s u l t i n authigenic p y r i t e (Farrand, 1970; Siesser and Rogers, 1976). In the present study, o p t i c a l examination of biogenic material revealed r a d i o l a r i a n t e s t s , f o r a m i n i f e r a l s h e l l s and worm tubes l i n e d or i n f i l l e d with abundant framboidal p y r i t e (Plate 3). Large i r - regular aggregates of framboidal p y r i t e were also observed with no apparent b i o l o g i c a l a s s o c i a t i o n (Plate 4). I d e n t i c a l occurrences i n reduced sediments o f f the northwest coast of A f r i c a were att r i b u t e d to p y r i t e replacement of i r r e g u l a r masses of decomposed organic tissue i n the sediment (Siesser and Rogers, 1976). Ridge sediment, r e l a t i v e l y abundant i n p y r i t e as discussed i n l a t e r sections, exhibits reworking by bottom currents, a mechanism that apparently concentrates the mineral. Radiocarbon Dates And Rates Of Sedimentation Four radiocarbon dates were obtained from foraminifera picked from two ridge cores: Core 51 (West Ridge), sampled over the i n t e r v a l s of 0 to 12 centimetres and 79 to 87 centimetres, yielded dates of 19,000 B.P. plus 840 to minus 930 years and 23,660 B.P. plus 1350 to minus 1620 years re s p e c t i v e l y ; Core 45 (Middle Ridge), sampled over the i n t e r v a l 33 to 54 centimetres and 85 to 109 centimetres, yielded dates of 10,170 B.P. plus 630 to minus 690 years and 14,970 plus 620 to minus 680 years r e s p e c t i v e l y (Appendix I I I ) . The s e l e c t i o n of radiocarbon sample i n t e r v a l s were de- 14 pendent on s u f f i c i e n t biogenic C to produce detectable ages from un- disturbed sediment which, for Middle Ridge, preceded periods of t u r b i d i t e deposition. O p t i c a l examination of the same i n t e r v a l s shows a r a t i o of p l a n k t i c to benthic foraminifera greater than 100:1. Sedimentation rates PLATE 3. Photomicrograph showing planktic f o r a m i n i f e r a l s h e l l s from Middle Ridge core 77-14-45 with p y r i t e aggregates found i n contact with the s h e l l surface (upper l e f t of photo) and within the s h e l l s (dark material l i n i n g the umbilical region)(Mag. 50x). 2 7 PLATE 4. Photomicrograph showing massive aggregates (lower centre and r i g h t of photo) of p y r i t e with no apparent biogenic association (West Valley core 77-14-43). Arenaceous worm (?) burrows ( l i g h t coloured material) l i n e d with dark coloured p y r i t e aggregates (upper l e f t and upper centre of photo)(Mag. 20x). 28 based on sample i n t e r v a l midpoints and age differences are 11.1 cm/1000 years f o r core 45 and 16.5 cm/1000 years for core 51 (Turekian and Stuiver, 1964). DISCUSSION Va r i a t i o n In Structure And Size D i s t r i b u t i o n Sediment structure and s i z e d i s t r i b u t i o n , although dependant on physiographic l o c a t i o n , can show widespread c y c l i c changes. Griggs and Kulm (1970), Horn et a l , (1971) and Nelson and Kulm (1973), i n regional studies, recognized such cycles i n cores from the northeast P a c i f i c and from Cascadia Deep-sea Channel, and att r i b u t e d them to t u r b i d i t y current i n f l u x e s , a l t e r n a t i n g with periods of hemipelagic sedimentation. The Juan de Fuca Ridge sediments correspond to the ra p i d l y and slowly deposited d i s t a l t u r b i d i t e s of Horn et a l , (1971), Bouma and H o l l i s t e r (1973), Nelson and Kulm (1973) and Walker and Mutti (1973). Generalized Tu r b i d i t e Sequence A t u r b i d i t e , f o r the purpose of t h i s study, i s the deposit of a t u r b i d i t y current (Walker and Mutti, 1973), a form of sediment gravity flow, i n which the sediment i s p r i m a r i l y supported by the upward component of f l u i d turbulence (Middleton and Hampton, 1973). The i d e a l i z e d sequence of a t u r b i d i t e was subdivided into f i v e d i v i s i o n s c a l l e d A, B, C, D, and E by Bouma (1962). A generalized t u r b i d i t e sequence characterizing the cored sediment from Juan de Fuca Ridge begins with a scoured contact o v e r l a i n by p a r a l l e l laminae, followed by massive mud (Fig.10). The sequence fines up- ward from sandy s i l t to s i l t y clay. The laminae are d i s t i n c t , and the laminated sediment ranges i n thickness from 0.1 to 1.0 centimetres. The colour (wet) ranges from dark gray (N3) for the coarsest sections to dark greenish-gray (5GY4/1) f or the f i n e r laminae. A massive highly bioturbated 29 B COMPLETE TURBIDITE SEQUENCE JUAN DE FUCA RIDGE CASCADIA CHANNEL TURBIDITY CURRENT SEQUENCES SEQUENCE Pelitic Interva! Upper Interval of Parallel Lamination Interval of Current Ripple Lamination — Lower Interval of Parallel Lamination Graded Interval Ta-e 5£> Tde annus o o o _ Tae Tb-e Tde Te FIGURE 10. A. Complete t u r b i d i t e sequence of Bouma (1962). B. Typical sequence, Juan de Fuca Ridge. C-F. T u r b i d i t e sequences of Cascadia Channel (Griggs and Kulm, 1970). 30 layer of mud a few to several tens of centimetres thick o v e r l i e s the laminated sediment, i s usually dusky yellow-green (5GY5/2) to grayish o l i v e (10Y4/2) and fines upward. The Juan de Fuca Ridge t u r b i d i t e sequence resembles the upper d i v i s i o n of p a r a l l e l lamination (D) and p e l i t i c d i v i s i o n (E) of Bouma (1962) (Fig.16). The top i s a zone of b i o g e n i c - r i c h , l i g h t olive-gray (5Y5/2), clay dominated mud which commonly caps the sequence, appears hemipelagic i n o r i g i n and may be absent due to scour by the next t u r b i d i t y current. Tu r b i d i t e C o r r e l a t i o n Three cycles ( I , I I , III) containing p o t e n t i a l l y c o r r e l a t a b l e t u r b i d i t e s are found i n West V a l l e y sediment (Fig.15). The cycles are best seen i n X-radiograph structures. Each cycle i s composed of one or more c l o s e l y spaced t u r b i d i t e s with intervening massive sediment. Cycles are generally located at depths between 0 and 25cm ( I ) , 25 and 85cm(II) and 80 and 120cm(III). A consistent 50 to 60 cm of massive ( t u r b i d i t e and hemipelagic) sediment separates laminated sequences of cycle I from I I , and 20 to 30 cm separates laminated sequences of cycle II from I I I . Grain s i z e d i s t r i b u t i o n values p a r a l l e l the s t r u c t u r a l changes. Superimposed on the West Val l e y t u r b i d i t e cycles are changes i n sediment c h a r a c t e r i s t i c s above and below an approximate 40 to 50 cm sediment depth. Sediment below 40 to 50 cm contains stronger scouring, thicker laminae, more coarse and less f i n e sediment and more entrained foraminifera i n the t u r b i d i t e s . The massive sediment below 40 to 50 cm also contains more coarse and les s f i n e sediment, as much or more carbon- aceous and authigenic material, and more foraminifera than sediment above the 40 to 50 cm l e v e l . Although X-radiograph p r o f i l e s are lacking for East V a l l e y core 47, a l l of the other sediment changes described downcore 31 i n West Valley occur i n East Valley. Middle Valley sediment was not sampled deep enough to determine cycles II and I I I . The change i n v a l l e y sediment c h a r a c t e r i s t i c s below and above 40 to 50 cm for Juan de Fuca Ridge was observed f o r the sediment i n and adjacent to the Cascadia Deep-Sea Channel by Griggs and Kulm (1970) f or the Late Pleistocene and Holocene r e s p e c t i v e l y . Hemipelagic Sediment Hemipelagic sedimentation was widespread and continuous through- out the area but was modified by processes dependent upon l o c a l physio- graphy. T y p i c a l l y the resultant sediment (1) i s composed of s i l t y clay, but, when winnowed, clayey s i l t , (2) has a high biogenic component with r a d i o l a r i a dominant i n the v a l l e y s and foraminifera dominant on the ridges, (3) contains minor authigenic p y r i t e which, when reworked may be concentrated, (4) contains few holothurian burrows and (5) has a colour (wet) ranging from grayish-olive (10Y4/2) to l i g h t olive-gray (5Y5/2). D i f f i c u l t y e x i s t s i n di s t i n g u i s h i n g hemipelagic sediment from the f i n e t u r b i d i t e sediment of p e l i t i c d i v i s i o n (E) of Bouma (1962), produced from the " d i l u t e cloud" of the t u r b i d i t y current described by Middleton and Hampton (1973). Generally a greater terrigenous component distinguishes a t u r b i d i t e "cloud" p e l i t i c sediment from hemipelagic sediment. Massive sediment d i r e c t l y above the laminated (D) t u r b i d i t e sequence, containing dominantly s i l t to s i l t y mud, more abundant carbonaceous material (terrigenous plant d e b r i s ) , frequent bioturbation, and a moderate biogenic and authigenic component i s p e l i t i c t u r b i d i t e . A t r a n s i t i o n e x i s t s i n most massive sequences between t u r b i d i t e p e l i t e and hemipelagic sediment (Fig.11). Few compositional differences e x i s t at a core s i t e for hemipelagic 32 C L A Y TURBIDITE FIGURE 11. Generalized s t y l e s of sedimentation for the northern end of Juan de Fuca Ridge. Nomenclature zones a f t e r Folk (1974) as i n Figure 5. 33 sediment between t u r b i d i t e cycles. In the v a l l e y s , the massive sediment below 40 to 50 cm possess a larger t u r b i d i t e p e l i t e component than massive sediment above t h i s i n t e r v a l . Winnowed Sediment The ridges are dominated by hemipelagic-pelite sediment which d i f f e r s from that i n the v a l l e y s . The postulate that the difference i s pa r t l y due to winnowing i s discussed below. Reworking of sediment by currents that move sediment ( L i s i t z i n , 1972; Bouma and H o l l i s t e r , 1973), i s not confined to ridges although i t i s w e l l developed there. West and Middle Ridges are the shallowest bathy- metric features of the study area, being much higher than the adjacent v a l l e y f l o o r s . West Ridge contains massive f o r a m i n i f e r a l - r i c h sediment that i s dominated by sand and clay, with low s i l t . The sediment, based on radiocarbon dates, i s Late Pleistocene. The sand i s dominated by pla n k t i c foraminifera and i c e - r a f t e d d e t r i t u s . Authigenic p y r i t e i s abundant when compared to most v a l l e y sediment. In the mineralogy chapter, the concentration of well c r y s t a l l i z e d coarse clay and the absence of poorly c r y s t a l l i n e f i n e clay from the ridges i s pointed out. Middle Ridge sediments are compositionally s i m i l a r to those of West Ridge except that the lower elevation has resulted i n a more sub s t a n t i a l contribution of sediment from the " d i l u t e cloud" of v a l l e y t u r b i d i t y currents. The grain s i z e composition, d i s t r i b u t i o n and abundance of clay minerals and con- centration of authigenic p y r i t e i n West and Middle Ridge sediments a l l suggest sediment reworking. P r e l l (1977) described reworked (winnowed) sediment from the Colombia Basin, Caribbean Sea, based on re l a t i o n s h i p s that appear s i m i l a r to West and Middle Ridges. Winnowed Colombia Basin sediment was i d e n t i f i e d by bottom photography and comparison of proportions 34 of f o r a m i n i f e r a l , c o c c o l i t h and clay components and concentration of the f o r a m i n i f e r a l and sand components. Bottom photographs of t r a n q u i l and current-smoothed seafloor sediments, led P r e l l (1977) to postulate that l o c a l i t i e s such as ridges, major escarpments and other seafloor obstacles lead to streamlining and a c c e l e r a t i o n of watermasses with an associated s e l e c t i v e erosion of f i n e s . West and Middle Ridges possess sediment c h a r a c t e r i s t i c s and physiographic r e l a t i o n s h i p s s i m i l a r to those described by P r e l l (1977) for winnowed sediment. Stratigraphy The s t r a t i g r a p h i c r e l a t i o n s h i p s i n sediment from the Juan de Fuca Ridge were based on radiocarbon dates and sedimentation cycles i n cores from Middle and West Ridge. C o r r e l a t i o n between ridge and v a l l e y stratigraphy i s based s o l e l y on p a r a l l e l changes i n sedimentation patterns and c h a r a c t e r i s t i c s . Chronologic datum l e v e l s within marine sediments are commonly defined by index f o s s i l s or radiocarbon dates, a l l of which are dependent on preserved biogenic material. Factors a f f e c t i n g the biogenic component i n dateable sediment must be understood p r i o r to the e s t a b l i s h - ment of such datum l e v e l s for c o r r e l a t i o n . Changes i n the p o s i t i o n and chemistry of ocean watermasses with time can s i g n i f i c a n t l y vary both the p r o d u c t i v i t y of a s h e l l y organism i n surface water and the preserved fauna i n the sediment (Peterson, 1966; Berger, 1967, 1971, 1976). Conversely, marked changes i n the preserved faunal record through a core may suggest temporal s h i f t s and changes i n watermasses. 35 Hydrography Documentation of p e r i o d i c a l l y repeated hydrographic measure- ments were i n i t i a t e d i n the northeast P a c i f i c at s t a t i o n P i n 1952 and along Line P i n 1959 (Thomson, 1973). Additional hydrographic data was added from stations located 1.5° of l a t i t u d e north and south of Line P i n 1972 (Fig.12). Observations at the stations included salinity-temp- erature-depth (STD) p r o f i l e s and temperature-depth p r o f i l e s measured with expendable bathythermographs. The r e s u l t s of the study demonstrate a northeast-trending zone of mixing watermasses that divides the oceanic from the coastal domain (Fig.12). Seaward of the zone a rapid decrease i n parameter v a r i a t i o n and s t a t i s t i c a l variance occurs while coastward the opposite i s evident. The zone of t r a n s i t i o n or mixed water i s best centered between l a t i t u d e s 48° to 50°N and longitudes 128° to 129°W. The t r a n s i t i o n zone coincides most d i r e c t l y with s t a t i o n 5 of Line P, ( l a t i t u d e s 48°45'N, longitude 128°40'W) which l i e s i n the area of the present study (Figs.12 and 13). Station 5 i s interpreted as c e n t r a l to the area of t r a n s i t i o n or mixed water between the northward flowing coastal current and the eastward flowing West Wind D r i f t (Thomson, 1973). Near-bottomwater hydrographic measurements were made at several stations i n conjunction with t h i s study by Dr. E. V. G r i l l (U.B.C.) (Fig.13). Measurements were made 20 and 50 metres o f f bottom with one 500 metres o f f bottom. The hydrocasts ranged i n depth from 1816 to 2980 metres based on thermometric measurements. Temperature values ranged from 1.71 to 2.03°C, and decreased with depth. Oxygen and s a l i n i t y values i n - creased with depth. Oxygen values ranged from 1.75 ml/1 at 2945 m depth. S a l i n i t y values ranged from 34.588°/oo at 1816 m to 34.647°/oo at 2758 m (deeper values were within 0.002 of 34.645°/oo). 36 LONGITUDE FIGURE 12. Location map of hydrographic survey adapted from Thomson (1973) showing: Line P with odd numbered st a t i o n s , zone of l a t e r a l mixing between oceanic and coastal domain waters (dashed l i n e ) , and Juan de Fuca Ridge study area ( s o l i d c o l o u r ) . 37 T E M P E R A T U R E ( ° C ) CO UJ DC I- Ui 2 Ul > Ul < UJ CO o _l Ul CO X 0 . Ul o 3004 600+ 900+ 1200+ 1500 + 1800 + 2100+ 2400+ 2700 + 3000 S .L . 31 32 33 - 34 SALINITY (%o) FIGURE 13. Hydrographic p r o f i l e above the northern end of Juan de Fuca Ridge. P r o f i l e A, i s based on hydrographic s t a t i o n 5 (Thomson, 1973), and p r o f i l e B, i s the r e s u l t of hydrographic measurements from d i r e c t l y above the seafloor (E.V.Grill,U.B.C.,1977) 38 The lowest temperature and the highest s a l i n i t y and oxygen content occurred i n the deepest part of West Valley, highest temperatures and lowest s a l i n i t y and oxygen contents occurred above Middle Ridge (measurements were not made above West Ridge). Hydrographic measure- ments within Middle and East Valleys had intermediate values. C i r c u l a t i o n Patterns A f f e c t i n g The Juan de Fuca Ridge Based on the ar e a l d i s t r i b u t i o n of the bottomwater hydrographic parameters i t appears that the flow of colder, more s a l i n e and thus denser watermass which contains the highest oxygen content, i s affected by bottom topography. Streamlining of bottom watermasses although un- detected by hydrographic measurements, may have been widespread due to the e f f e c t s of basement r e l i e f on ocean water movement (Thomson, 1973). The water column above the study area was described e a r l i e r as a zone of l a t e r a l mixing of the West Wind D r i f t and the northern continental current. The l a t e r a l mixing, e s p e c i a l l y of surface waters, may a f f e c t the d i s t r i - bution of pelagic and p l a n k t i c components i n the underlying sediments. Relationship Of Faunal Preservation And Hydrography On Stratigraphy The i n t e r r e l a t i o n s h i p of microfaunal p r o d u c t i v i t y and preser- vation, and watermass chemistry has been used by many workers i n the i n - te r p r e t a t i o n of marine stratigraphy (Frerichs, 1968; Duncan, Fowler and Kulm, 1970; Berger and Winterer, 1974; Berger and K i l l i n g s l e y , 1977). Zooplankton with carbonate tests show large f e r t i l i t y and species f l u c - tuations dependent on small changes i n watermass chemistry or temperature (Berger, 1971; E m i l i a n i , 1971; Imbrie and Kipp, 1971). Change i n the r a t i o of foraminifera to r a d i o l a r i a i n sediments has been widely used as an i n d i c a t o r of Late Quaternary c l i m a t i c and 39 oceanographic changes i n the northeast P a c i f i c (Duncan, Fowler and Kulm, 1970; Nelson and Kulm, 1973; Phipps, 1977). This change was l a t e r described as time-transgressive for regional studies but of l o c a l merit (Barnard and McManus, 1973; Phipps, 1977). A s i m i l a r change has been found i n t h i s study. The r e l i e f i n the study area i s 800 metres and the abundance of f o r a m i n i f e r a l s h e l l s decreases with depth (Figs.7 and 8). In cores from West Val l e y , r a d i o l a r i a dominate the biogenic component, except when foraminifera have been introduced by t u r b i d i t y currents. Sediments of West and Middle Ridges, are i n contrast, dominated by p l a n k t i c foraminifera to the r e l a t i v e exclusion of r a d i o l a r i a . Sediments cored from intermediate depths suggest a t r a n s i t i o n of f o r a m i n i f e r a l abundance between the bathymetric extremes. The West and Middle Ridge sediments are dominantly hemipelagic and show evidence of winnowing with a moderate d i l u t i o n of Middle Ridge plankton by t u r b i d i t e f i n e s . T u r b i d i t y current " d i l u t e cloud" sedimen- t a t i o n on Middle Ridge i s apparent during three separate cycles by t u r b i d i t e deposition (Fig.15). The t u r b i d i t e s i n the cycles of Middle Ridge, although s i m i l a r to' those of the v a l l e y s , are d i s s i m i l a r i n some c h a r a c t e r i s t i c s : they do not display scour, but p r i m a r i l y deposition, and the terrigenous sand component i s le s s than one percent. The resultant nonbiogenic sediment i s a l l s i l t and clay. Studies on the Cascadia Deep-Sea Channel ind i c a t e that Holocene t u r b i d i t y currents, which were smaller i n volume than Late Pleistocene t u r b i d i t y currents, may exhibit f i n e sediment plume ( d i l u t e cloud) e f f e c t s 17 kilometres l a t e r a l l y and 120 metres v e r t i c a l l y (Griggs and Kulm, 1970). Middle Ridge sediment i s 135 metres above Middle Valley and West Ridge sediment i s 800 meters above West Valley and 300 meters above 40 CORE 45 MIDDLE RIDGE S T R U C T U R E S A N D SIZED ( X - R A D I O G R A P H ) R p C O M P O N E N T S i p p y o o o % 100 O n ^ 9 . 5 4 0 •^10.170±630/690 - 14,970 ±620/680 3$ 16.320 ££19,500 £S 21,000 35 — T — 40 -+- 45 CLAY 50 55 LEGEND D A T E D INTERVAL ( R A D I O C A R B O N Y E A R S B.P.) INFERRED D A T E ( Y E A R S B.P.) R RADIOLARIA F FORAMINIFERA FIGURE 14. Core 45 from Middle Ridge with i l l u s t r a t e d structure, components from the sand s i z e f r a c t i o n , clay percentages, fo r a m i n i f e r a l to r a d i o l a r i a n r a t i o s and radiocarbon dates. Symbols as i n Figure 8 and Appendix I I . 41 Middle V a l l e y : These large differences i n depth suggest that only major t u r b i d i t y currents such as those of the Late Pleistocene could have contributed to sedimentation on the ridges, which was otherwise dominantly hemipelagic. Abundant p l a n k t i c foraminifera from the ridge-top cores supplied enough CaCC^ for dating. A radiocarbon date indicates that sediment at the top of core 51 from West Ridge i s 19,000 years old. This may imply a hiatus i n sedimentation at the surface of West Ridge. Such a hiatus was not found on Middle Ridge (Fig.14). A comparable hiatus (17,440 B.P. to present) for the surface sediment of core 68PC16 at 2,020 m depth was observed from sediments of the Ontong-Java Plateau (Valencia, 1977). V a r i a t i o n i n hemipelagic sedimentation of the biogenic component between West Ridge and Middle Ridge seems u n l i k e l y due to t h e i r proximity and common hydrography. The f o r a m i n i f e r a l f e r t i l i t y and preservation patterns obtained from the deep-sea sediments east and west of the Juan de Fuca Ridge i n - dicate an abundance of p l a n k t i c foraminifera u n t i l at l e a s t 12,000 B.P. (Nayudu, 1964; Duncan, Fowler and Kulm, 1970; Barnard and McManus, 1973). The reason for the age of the West Ridge surface sediments i s unclear. One possible explanation i s phy s i c a l removal of sediment by l o c a l t u r b i d i t y currents or slumping. Another i s the disturbance of the surface sediment during coring. Yet another, as explained below, involves the p o s i t i o n of sampled sediment at the top of West Ridge and temporal changes i n the chemistry of ocean waters. Extensive work on the d i s s o l u t i o n by seawater of c a l c i t e and the p o s i t i o n of the l y s o c l i n e and carbonate compensation depth (CCD) i n the 42 cen t r a l and north P a c i f i c has aided s i g n i f i c a n t l y i n the i n t e r p r e t a t i o n of carbonate deep-sea stratigraphy (Peterson, 1966; Berger, 1967, 1970, 1976; Berger and Winterer, 1974; Pytkowicz, 1970; Ingle et a l , 1973; Ingle, 1975). North-south hydrographic p r o f i l e s show the l y s o c l i n e at 2600- 200 metres at 46° north l a t i t u d e (Berger, 1970). Projection of Berger's p r o f i l e to 48° north r e s u l t s i n a l y s o c l i n e p o s i t i o n of 2100- 200 metres. During the Late Pleistocene the lowest g l a c i a l - e u s t a t i c sea l e v e l was around 20,000 B.P. (Clague, 1978) and stood approximately 80 to 110 metres deeper than the present l y s o c l i n e thus impinging upon the s i t e of core 51 on West Ridge, and enhancing carbonate preservation i n the water column and sediments (Berger, 1970; Broecker, 1971; Morse and Berner, 1972). A subsequent r i s e i n sea l e v e l and coincident r i s e i n the l y s o c l i n e to i t s present p o s i t i o n would expose the biogenic carbonate of West Ridge surface sediment to enhanced rapid d i s s o l u t i o n of undersaturated waters. It appears that the c r u c i a l r i s e i n the l y s o c l i n e and sea l e v e l began around 18,000 to 19,000 B.P., as evidenced by the 19,000 B.P. surface date of core 51. Middle Ridge sedimented carbonate i s several hundred metres below the l y s o c l i n e , and thus would not be affected by changes i n the l y s o c l i n e depth nor r e f l e c t the magnitude of d i s s o l u t i o n i n f e r r e d f o r core 51 from West Ridge. The complexity of changes i n the sea l e v e l , l y s o c l i n e , and s e d i - mentation processes during the Late Pleistocene make conclusions tentative. Many workers have documented the preservation of f o r a m i n i f e r a l - r i c h Late Pleistocene sediment on the seafloor below the CCD (Berger, 1967; Pytkowicz, 1970). I t was postulated that d i s s o l u t i o n of foraminifera i n seawater undersaturated i n c a l c i t e may be retarded by: (1) An organic coating on the s h e l l s which reduces the number of exchangeable Mg-Ca s i t e s 43 (Lorens et a l , 1977), (2) the formation of a layer of bottomwater saturated i n carbonate adjacent to the carbonate-rich sediment, such that d i s s o l u t i o n i s by slow d i f f u s i o n (Berger, 1967; Pytkowicz, 1970; Lorens et a l , 1977) or (.3) by rapid b u r i a l of carbonate during periods of high carbonate p r o d u c t i v i t y , slumping or sedimentation from t u r b i d i t y currents. Rapid sedimentation would remove the carbonate from corrosive open water c i r c u l a t i o n r e s u l t i n g i n the e q u i l i b r a t i o n of carbonate with pore waters and carbonate preservation. Pla n k t i c p r o d u c t i v i t y throughout the world's oceans was the highest during Late Pleistocene g l a c i a l i n t e r v a l s due to the enhanced atmospheric and corresponding surface water c i r c u l a t i o n (Nayudu, 1964; Broecker, 1971; Thiede, 1973; E m i l i a n i and Shackleton, 1974; Valencia, 1977). Preservation of calcareous plankton i n the water column and surface sediment i s mainly dependent on deepwater chemistry (Berger, 1970). Since 19,000 B.P. pr o d u c t i v i t y and preservation of foraminifera was highest i n the c e n t r a l P a c i f i c during the rapid melting of i c e a f t e r approximately 15,000 B.P. (Berger and K i l l i n g s l e y , 1977). Foraminiferal abundance then decreased gradually u n t i l the end of the Late Pleistocene when pr o d u c t i v i t y again increased around 10,000 B.P. (t h i s study) followed by a major decrease i n eit h e r or both p r o d u c t i v i t y and preservation through- out the Holocene of the west-central and northeast P a c i f i c (Barnard and McManus, 1973; Peng et .al, 1979). Foraminiferal abundance patterns are preserved f o r the Late Quaternary i n Middle Ridge sediment while a post-19,000 B.P. hiatus e x i s t s for West Ridge sediment. The difference i n carbonate stratigraphy between Middle and West Ridge i s p r i m a r i l y a t t r i b u t e d to " d i l u t e cloud" t u r b i d i t e sedimentation on Middle Ridge (absent on West Ridge) which r a p i d l y buries 44 and preserves hemipelagic carbonate and, to a lessor extent, winnowing of West Ridge sediment that may disrupt the formation of carbonate saturated bottom waters and s i g n i f i c a n t l y remove hemipelagic f i n e s . Changes i n the l y s o c l i n e p o s i t i o n dependent on sea l e v e l , as previously discussed, may also have adversely influenced Late Quaternary carbonate sedimentation of West Ridge. Stratigraphy Of Middle Ridge Middle Ridge core 45 contains the best dated record of s e d i - mentation for the northern end of Juan de Fuca Ridge (Fig.14). Based on a sedimentation rate of 11.1 cm/1000 years, determined from dated i n t e r v a l s , the deepest sediment i s i n f e r r e d to be approximately 21,000 years B.P. Three cycles of repeated t u r b i d i t e " d i l u t e cloud" and hemi- pelagic deposition occur throughout core 45. Each cycle i s commonly composed of more than one t u r b i d i t e sequence with a thick f i n a l massive sediment zone and i n t h i s respect i s s i m i l a r to turbidite-hemipelagic cycles discussed previously from adjacent v a l l e y sediments. Inferred dates i n d i c a t e that the oldest (3), medial (2) and youngest (1) tur- bidite-hemipelagic cycles began near 19,500 B.P., 13,620 B.P. and 9,540 B.P. r e s p e c t i v e l y . The top 10 to 15 cm of cored sediment appears hemipelagic i n composition. The age of the surface sediment would be i n f e r r e d at 6,000 B.P. or older i f the sedimentation rate continued to be 11.1 cm/1000 yr. If a zero B.P. surface sediment age i s assumed, a sedimentation rate of 4.3 cm/1000 yr r e s u l t s a f t e r 10,000 B.P. which includes the t u r b i d i t e s of cycle 1. Excluding the t u r b i d i t e s i n cycle 1, a hemipelagic sedimentation rate of 1.0 to 2.3 cm/1000 yrs i s obtained. Based on a 9,000 - 9,540 B.P. Holocene-Late Pleistocene boundary, only the hemipelagic sediment i s Holocene, the remainder of the sediment i s Late Pleistocene. A marked reduction i n f o r a m i n i f e r a l abundance ex i s t s 45 for Holocene sediment compared to Late Pleistocene sediment. Late Pleistocene sedimentation rates on Gorda Ridge and the abyssal p l a i n north of Cobb Seamount are 10.0 and 10.4 cm/1000 years r e s p e c t i v e l y (Nayudu, 1964; Phipps, 1977), i n good agreement with the 11.1 cm/1000 year sedimentation rate obtained from Middle Ridge. Benthic mixing and winnowing of sediment may obscure the actual sediment age (Selk, 1977; Peng et_ a l , 1979). X-radiographs i l l u s t r a t e l i t t l e bioturbation of s u r f i c i a l sediment for Middle Ridge although, as discussed e a r l i e r , some winnowing occurs. In t h i s study sedimentation i s assumed continuous for Middle Ridge and a Holocene hemipelagic s e d i - mentation rate of 1.5 to 2.3 cm/1000 years i s proposed. Correlation Of Juan de Fuca Ridge Sediment Radiocarbon dates are obtainable s o l e l y from ridge sediments. Correlation of ridge and v a l l e y stratigraphy i s therefore based on as- sumption of synchronous sediment compositional changes across the Late Pleistocene-Holocene boundary. On Middle Ridge the boundary occurs at approximately 15 to 20 cm depth and i n the v a l l e y sediments at approxi- mately 40 to 50 cm depth. Late Pleistocene sediment i s expressed i n the v a l l e y s by more than one turbidite-hemipelagic c y c l e , coarser, more erosive (scoured) sediment, t u r b i d i t y current entrained foraminifera, more abundant terrigenous plant debris and thicker p e l i t e dominated pelite-hemipelagic i n t e r v a l s than e x i s t s for Holocene sediment. Middle Ridge Late Pleistocene sediment contains a l l the t u r b i d i t e sequences, coarser sediment, more abundant terrigenous plant debris and s u b s t a n t i a l l y more foraminifera than Holocene sediment. The boundary therefore i s marked by the changing of a l l patterns of sedimentation, t u r b i d i t y current and hemipelagic. 46 Individual Late Pleistocene turbidite-hemipelagic cycles from West Val l e y may cor r e l a t e with turbidite-hemipelagic cycles from Middle Ridge. Continent derived t u r b i d i t y currents entering West Valley are p a r t i a l l y blocked to the northeast by the confluence of the Sovanco Ridge and West Ridge (Davis and L i s t e r , 1977a). Tu r b i d i t y currents entering West Valley would therefore be dominated i n form by " d i l u t e cloud" sedimentation. Common f i n a l sequence thicknesses of t u r b i d i t e and hemipelagic sediment (35 to 40 cm) occur f o r Middle Ridge cycle 2 and West Valley cycle I I I (Fig.15). Middle Ridge t u r b i d i t e s of cycle 1 and West Valley cycle II begin j u s t below the Late P l e i s t o - cene-Holocene boundary and are o v e r l a i n dominantly by Holocene hemipelagic sediments. West Valley Holocene cycle I i s not continuous between cores and i s believed l o c a l l y derived. I t i s proposed that major periods of Late Pleistocene continent derived t u r b i d i t e deposition occurred at the northern end of Juan de Fuca Ridge at 13,620 B.P. then again at 9,540 B.P. each followed by long periods of hemipelagic sedimentation. The 13,620 B.P. and 9,540 B.P. pulses of t u r b i d i t e deposition are recorded as West Valley t u r b i d i t e s i n cycle III and Middle Ridge cycle 2, and i n West Valley cycle II and Middle Ridge cycle 1, respectively. C o r r e l a t i o n With Continental G l a c i a t i o n A comparison of Late Quaternary stratigraphy and sedimentation on the northern end of Juan de Fuca Ridge to the c l i m a t i c g l a c i a l s and i n t e r - g l a c i a l s documented for the same period from the continental P a c i f i c Northwest demonstrates some unique associations (Fig.16). Periods of Late Pleistocene hemipelagic sedimentation on the Ridge are contemporaneous with maximum advances of continental g l a c i a t i o n . The same periods are also characterized LATE PLEISTOCENE GEOLOGIC-CLIMATE UNITS FROM ARMSTRONG (1965) ABSOLUTE TIME THOUSANDS OF YEARS B.P. O-i 6,000 LATE QUATERNARY TEMPERATURE CHANGE BASED ON PALYNOLOGY FROM HEUSSER (1977) JUAN DE FUCA RIDGE LATE QUATERNARY SEDIMENTATION CORE 45 (MIDDLE RIDGE) ( X - R A D K p H ) S E D ^ f N T A T I 0 N C L A Y * + 2 30 35 40 45 50 55 60 10,000 H 15,000-1 20,000 25,000 -»4 FIGURE 16. Stratigraphy of core 45 from Middle Ridge with sediment structure and percentage clay fluctuations compared to continental B r i t i s h Columbia and Washington Lat^ Pleistocene to Recent geologic-climate units from Armstrong et a l , (1965), and Late Quaternary temperature changes based on palynological studies from Heusser (1977). 48 i n marine sediment by abundant w e l l preserved p l a n k t i c and benthic foraminifera. Following maximum advances of the i c e during the Evans Creek, Vashon and Sumas stades, were rapid warming trends as shown by pal y n o l o g i c a l studies i n northwestern Washington (Heusser, 1977), during these times co n t i n e n t a l l y i n i t i a t e d t u r b i d i t y currents deposited t u r b i d i t e s on the northern end of Juan de Fuca Ridge. Thus the Late Pleistocene t u r b i d i t e sequences of Juan de Fuca Ridge c o r r e l a t e d i r e c t l y with periods of maximum p o s t g l a c i a l continental denudation (Mathews, 1979). Late Pleistocene t u r b i d i t y current deposition was replaced by hemipelagic sedimentation during the Holocene along deep-sea channels near Juan de Fuca Ridge (Griggs and Kulm, 1970; Nelson and Kulm, 1973). Coincident Holocene sedimentation at the northern end of Juan de Fuca Ridge was also predominantly hemipelagic. Those t u r b i d i t e s assigned to the Holocene from v a l l e y cores lack the terrigenous character and con- t i n u i t y of the Late Pleistocene t u r b i d i t e s and are considered l o c a l i n source. Source Of Late Pleistocene Turbidites Mineralogy of t u r b i d i t e s and hemipelagic sediments i n the study area i s i d e n t i c a l to that of sediments examined from Explorer Ridge (Beland, i n prep.; Hanson, i n prep.;). Major deep-sea channels nearest to and possibly i n f l u e n c i n g the sedimentation of the study area are Paul Revere Channel, to the north, Juan de Fuca and Vancouver Channels, to the east, a l l of which o r i g i n a t e on the continental slope near Queen Charlotte Sound between Vancouver Island and the Queen Charlotte Islands. It i s proposed that, during the lower sea l e v e l stand of the Late Pleistocene, 49 a large proportion of Queen Charlotte Sound was covered by g l a c i a l i c e with g l a c i a l outwash deposited near the shelf edge (Mathews, 1981, o r a l commun.) Pulses of sediment were b u i l t up and released as t u r b i d i t y currents during periods of major thawing coincident with flooding and abundant g l a c i a l outwash following the onset of g l a c i a l r e t r e a t (Armstrong et a l , 1965; Clague, 1978; Mathews, 1979). Tu r b i d i t y currents along deep-sea channels were s u f f i c i e n t l y intense to strongly a f f e c t the sedimentation of the northern end of Juan de Fuca Ridge. The i n t e r r u p t i o n of f o r a m i n i f e r a l - r i c h hemipelagic deposition over Middle Ridge by " d i l u t e cloud" t u r b i d i t e deposits, preserved a datable s t r a t i - graphic record of deep-sea and associated continental Late Quaternary sedimentation. The presence of major t u r b i d i t y current a c t i v i t y d i r e c t l y following the Sumas stade, which has not been observed i n marine studies o f f the coast of Washington and Oregon, r e f l e c t s the more northerly source of t u r b i d i t e s i n the study area. The post-Sumas t u r b i d i t e sequences of Middle Ridge coincides with the i n i t i a l regression of a world-wide marine transgression (Armstrong et a l , 1965). S u f f i c i e n t sediment build-up on the lower sh e l f as a product of floodwater erosion may have produced the f i n a l t u r b i d i t e sequences documented on Middle Ridge and throughout Juan de Fuca Ridge. CONCLUSION The sediments of the Juan de Fuca Ridge area demonstrate from t h e i r structure, grain s i z e d i s t r i b u t i o n and sand composition several dominant influences: (1) changed patterns i n surface waters affected the hemipelagic-biogenic sediment, possibly dependent on the confluence of the West Wind D r i f t and the Northern Continental Current above the 50 V study area; (2) t u r b i d i t y currents, from the continental terrace eroded, resuspended and d i l u t e d the older sediment and due to the d i s t a l nature of the current, d i l u t e d the terrigenous character of the deposited load; (3) coincident and following the hemipelagic and t u r b i d i t y current sedimentation was the reworking of such sediment by deep and bottomwater currents through winnowing and changes i n flow, dependent on watermass density and seafloor configuration. A l l of these processes produced t r a n s i t i o n a l phases i n the sediment. Middle Ridge sediment best presents the stratigraphy of the whole area. Recognition of synchronous sediment changes from a l l the physiographic areas i s necessary for c o r r e l a t i o n . Detailed c o r r e l a t i o n was achieved p r i m a r i l y by defining the Late Pleistocene-Holocene boundary i n the sediment and periods of synchronous t u r b i d i t e - n o n t u r b i d i t e deposition. Good c o r r e l a t i o n e x i s t s for the Late Quaternary geologic -climate (Armstrong ejt a l , 1965) changes of the continental northwest and the northern end of Juan de Fuca Ridge. 51 Chapter III MINERALOGY INTRODUCTION Detailed studies on the mineralogy of Quaternary sediments i n the northeast P a c i f i c have been mainly directed at fi n d i n g the provenance and s t r a t i g r a p h i c v a r i a t i o n s of mineral species (Duncan et a l , 1970; White, 1970; Stewart, 1976; Phipps, 1977; Selk, 1977). In deep-sea studies, complexity i s introduced by the r e l a t i v e l y great distance from terrigenous sources and by mixing during d i s p e r s a l of sediment, which tends to obscure mineralogical v a r i a t i o n s i n s i l t and clay. Mineralogical investigations have therefore been confined to large regions on or adjacent to the continental terrace (Duncan et_ a l , 1970; White, 1970; S t o f f e r s and Muller, 1972; Stewart, 1976; K a r l i n , 1980). Deep-sea studies of small areas commonly described s t r a t i g r a p h i c changes i n mineralogy but, due to the v a r i e t y of poorly understood se d i - mentation parameters, defined mineralogical provenance with d i f f i c u l t y (Selk, 1977). St r a t i g r a p h i c v a r i a t i o n s i n mineralogy i n the deeper parts of the northeast P a c i f i c are best preserved on i s o l a t e d h i l l s and ridges (Phipps, 1977). In t h i s chapter, d e t a i l e d mineralogy of sediment sampled from Juan de Fuca Ridge and Cascadia Basin i s discussed, the aims being to define and compare gross changes i n r e l a t i v e abundance of minerals which might be products of ridge-type hydrothermal a c t i v i t y (Fryer and Hutchison, 1976; Andrews and Fyfe, 1976). One hundred and twenty samples taken from eleven cores, corres- ponding to those i n t e r v a l s analyzed for grain s i z e , were analyzed i n bulk. 52 Clay minerals were studied i n t h i r t y - n i n e subsamples selected at f i f t y centimetre i n t e r v a l s . Each gravity core produced three to f i v e subsamples and Phleger cores t y p i c a l l y yielded two subsamples. METHODS Bulk sediment samples of approximately one to two cubic centimetres were placed i n Whirlpak bags with a s t a i n l e s s s t e e l spatula, dried overnight at 70°C, gently crushed i n an agate mortar, and stored i n l a b e l l e d glass v i a l s u n t i l analyzed. Bulk sediment and s l i d e s for clay analysis were i n i t i a l l y analyzed untreated. No attempt was made to remove organic components, carbonate, i r o n oxide or hydroxide on the premise that any modification of the sediment could a l t e r the in s i t u mineralogy. Analysis Of Bulk Sediment A small amount of mixed dried sediment from a given sample was placed on a glass s l i d e and mixed with several drops of acetone to form a quickly drying s l u r r y . Each sample was analyzed on a P h i l i p s X-Ray Diffractometer (Appendix V). The scanning speed was changed to l°20/min., for a l l duplicate runs of samples from top surfaces of cores, and selected samples were also run to c l a r i f y mineral peak positions at a time constant of two. Preparation And X-Ray Analysis Of Clays Subsamples of the bulk sediment samples were placed i n 50 ml glass beakers and mixed with 40 ml of d i s t i l l e d water to remove s a l t s . The mixed sediment was l e f t undisturbed for 72 hours to allow most of the clay s i z e material to s e t t l e , the supernatant l i q u i d was removed by pipete. This procedure was repeated, a f t e r which the beakers were f i l l e d with d i s - 53 t i l l e d water, thoroughly mixed with a glass s t i r r i n g rod, and l e f t un- disturbed for eight hours u n t i l only the clay component (<9.70) remained i n suspension (Folk, 1974). Several m i l l i l i t r e s of suspension were removed from d i r e c t l y above the surface of s e t t l e d sediment, pipeted onto a glass s l i d e and allowed to a i r dry at room temperature. The process was repeated u n t i l oriented cl a y minerals with discernable peaks were evident on t r i a l diffractograms. Each oriented clay s l i d e was X-rayed untreated, glycolated with ethylene g l y c o l vapour i n a humidity-controlled vacuum sealed j a r at room temperature, heated i n a muffle furnace at 300°C for two hours and re- heated i n a high temperature furnace at 550°C for two hours (MacEwan, 1961; Brindley, 1961; Biscaye, 1965; C a r r o l l , 1970). X-ray diffractograms were obtained a f t e r each separate s l i d e treatment. Ad d i t i o n a l s l i d e s of oriented clays were prepared from sediment s t i r r e d then s e t t l e d i n 10% hydrochloric acid at 80°C (Brindley, 1961; Rateev et_ a l , 1969; C a r r o l l , 1970). A f t e r settlement periods of 3, 8, 12, and 72 hours, sediment-acid mixtures were washed i n 100 ml of d i s t i l l e d water, centrifuged, as described i n Chapter II methods for s a l t removal, for two hours and the supernatant decanted o f f . The procedure was r e - peated three times u n t i l the samples were w e l l washed a f t e r which oriented s l i d e s were prepared and X-rayed before and a f t e r g l y c o l a t i o n and heating. Oriented clay diffractograms were run with the same d i f f r a c t o - meter settings as previously described f o r the bulk sediment analysis except the scanning speed was a l t e r e d to 1°20 /min., (Appendix V). Selected samples were run with time constants of both one and two. Non-acidified s l i d e s were scanned from a 20 of 30° to 3.0° and 3.5°. A c i d i f i e d s l i d e s were scanned from 40° to 3.5°. 54 Analysis Of Unknown Minerals Two unknown minerals were separated and analyzed as follows: Mineral "A" was a magnetic black s i l t sized mineral that coated the t e f l o n surface of the magnetic s t i r r i n g bar when sediment was prepared for grain s i z e a n a lysis. I t occurred i n a l l samples studied, inc l u d i n g those of Cascadia Basin ranging from le s s than one percent to eight percent by weight. A concentrate was c o l l e c t e d from the samples of one ridge core, washed i n d i s t i l l e d water to remove excess sediment, a i r - d r i e d , mixed with acetone, placed on a glass s l i d e and x-rayed. Mineral "B", commonly observed during o p t i c a l analysis of the 63 jim sand f r a c t i o n , occured i n mineral aggregates with biogenic material i n some cores and as i r r e g u l a r masses i n others. The mineral was commonly brown, had a m e t a l l i c to submetallic l u s t r e and r e a d i l y disaggregated into smaller c l u s t e r s when disturbed. Aggregates of the material were hand- picked under a binocular microscope u n t i l a s u f f i c i e n t concentrate was a v a i l a b l e to produce i d e n t i f i a b l e mineral peaks on diffractograms. Quantitative Analysis The r e l a t i v e proportion of d i f f e r e n t groups of clay minerals i n each sample was estimated by the method of Biscaye (1965). Peak areas were measured from the diffractograms of glycolated clay minerals using a Koizumi polar compensating planimeter. The clay mineral peak traces measured • • • were at 17 A, 10 A and 7 A f o r montmorillonite, i l l i t e and c h l o r i t e group minerals r e s p e c t i v e l y . The areas were measured three to f i v e times per peak and averaged. Biscaye's method requires the use of c a l i b r a t i o n factors with one times the montmorillonite peak area, four times the i l l i t e peak area and two times the c h l o r i t e peak area. The clay minerals are assumed to compose one hundred percent of the clay s i z e f r a c t i o n and the scaled mineral areas are adjusted to percentages. 55 RESULTS Mineralogy Of Bulk Samples Three minerals «<-quartz, plagioclase feldspar and c h l o r i t e dominate each bulk sample (Fig.17). Diffractograms of samples from West and Middle Ridges contain prominent c a l c i t e peaks (Fig.17). Minor h a l i t e peaks i n a few diffractograms r e f l e c t c r y s t a l formation during sample preparation. Any other minerals present do not produce peaks above the r a d i a t i o n background. Clay Mineralogy Three clay minerals and f i v e other clay s i z e minerals were determined i n t h i s study (Fig. 18). The clay minerals are montmorillonite, mica and c h l o r i t e . The other clay s i z e minerals are <x-quartz, plagioclase feldspar, c a l c i t e , c r i s t o b a l i t e and amphibole. Montmorillonite In t h i s study, montmorillonite i s described i n the sense of MacEwan (.1961) Biscaye (1965), Rateev et a l , (1969) and C a r r o l l (1970). I d e n t i f i c a t i o n i s based on movement of the 12.5-13.5 A d(001) r e f l e c t i o n to a 17.0-17.2 A p o s i t i o n following g l y c o l a t i o n . The peak i s wide at the base and i r r e g u l a r , demonstrating poor c r y s t a l l i n i t y , amorphous nature of the clay, or both (Biscaye,1965; C a r r o l l , 1970). Heating to 300°C resulted i n disappearance of the 17.0-17.2 A r e f l e c t i o n , but the 9 A peak that replaces i t cannot be observed due to overlap by the d(001) mica peak. Mica The d(00jj) sequence of 10.2 A and 5.0 A are considered to be i l l i t e or mica, following Biscaye (1965), Duncan et a l , (1970), C a r r o l l (1970) and Selk (.1977). Biscaye (1965) described i d e n t i f i a b l e 3.3 A and 2.5 A diffractogram peaks from A t l a n t i c sediments i n addition to the more co ro cu F-3 ro 3 rt CO ro CO rt H- Cu 09 ro o H , ro I i—• i CO 1̂ ro M Cu o H-3 ro 3 rt 1—» cn Cu • 3 •3 > • le a cn a H- H' l-h Hi Hi Hi i-l ? H Co n o rt CU rt O 1-1 O CW rt era M N H >• Cu 3 *o 3 H- i—1 H* H- Co t-1 CT9 I - 1 C H- c CO O CO rt o rt I-! M i-t CO Cu Cu rt cn rt p- ro H-3 3 CW Hi ro TO •a H ro Cu ro CU CO Hi • d l - 1 cu ro rt i-l o l-l CO rt Co o 3 o ro Cu 3 CO o CO Hi 3* Hi H. t - 1 H O O o 3 i-l H- 3 rt rt rt 3" ro 3* ro ro 3 rt H" ro 3* 3 CO H ro rt ro i-t ro CU <: I-1 CU Cu 1—1 o o M 3 CO ro H* 3 n CU n 3 rt o rt ro re "* t C 3* •^J a* H- - J O i 3* I—* c .o H-H< i rt CO .£> o C O cn o • 3 3 3 o 3 3 er rt Co O Is H. H" H- Cu 3 TO ro c r c a* c 7̂ S a m 3J m m w OH cn 03 • C H L O R I T E <*.!«*> CD = — Q U A R T Z f * - F E L D S P A R (PLA<3.) & - F E L D S P A R (PLAG.)<S-*»A1 • F E L D S P A R ( P L A G . ) *T ( 3 . 6 8 * ) C A L C I T E u.oaX) - Q U A R T Z " " * ) - F E L D S P A R ( P L A G . ) ( 3 . J O * ) ° _ <>_ F E L D S P A R (J.SJA) CALC ITE < 3 o s i ) CO' Q U A R T Z (J.4«A) °> -CALCITE<*-"A> Q U A R T Z ( 2 . 2 8 * ) - Q U A R T Z (».i3A> CALCITE<*-'o*> CALCITE<t .»2*) • C A L C I T E ( i . s e i ) - Q U A R T Z F E L D S P A R ( P L A G . ) 01 A^>-CALCITE<I-«IA> ' co. - Q U A R T Z <i.»»*> 9g 57 < lO o CO < LU CO r- 2 0 ( D E G R E E S ) FIGURE 18. A. Diffractogram of the surface sediment (0 to 2 centimetres) from West Valley core 77-14-43 i l l u s t r a t i n g the clay minerals and clay sized minerals common to a l l samples studied. B. Diffractogram peak traces of c l a y sized c a l c i t e from West Ridge core 77-14-51. 58 intense 10.0 A and 5.0 A peaks. Clays from Juan de Fuca Ridge contain cx-quartz, which has an intense peak that obscures the 3.3 A peak of i l l i t e . The 2.5 A i l l i t e peak, although suggested where intense 001 i l l i t e diffractogram traces occur, i s too weak and near background to be diagnostic. The e f f e c t of g l y c o l a t i o n , heating and acid treatment are n e g l i g i b l e f o r the i l l i t e diffractogram peak traces. C h l o r i t e And K a o l i n i t e The peak at the 7.0-7.2 A p o s i t i o n , previously described i n the section on mineralogy of bulk sediment, could be eit h e r c h l o r i t e or k a o l i n i t e . Basal spacings of c h l o r i t e are 14 A (001), 7 A (002), 4.7 k (003) and 3.5 A (004) (Brindley, 1961; Biscaye, 1964, 1965; C a r r o l l , 1970), and of k a o l i n i t e , 7.15 A (001), 3.57 A (002), 2.35 A (003) and 1.79 A (004) ( C a r r o l l , 1970). Dominance of either clay mineral i n oriented samples, obscures the presence of the other group i n the resultant d i f - fractogram. In diffractograms of deep-sea clay mineral assemblages, low i n t e n s i t i e s of the d(003) and d(004) k a o l i n i t e r e f r a c t i o n s ( C a r r o l l , 1970) make d i f f e r e n t i a t i o n of the two groups even more d i f f i c u l t . Biscaye (1964) developed an ultraslow X-ray d i f f r a c t i o n scanning technique for oriented clay minerals that divides the 7 A and 3.5 A peaks int o t h e i r c h l o r i t e and k a o l i n i t e components but t h i s technique was not used f o r t h i s study. Instead, samples were heated and treated with hydro- c h l o r i c a c i d (Brindley, 1961 ; Biscaye, 1964; C a r r o l l , 1970). Rateev et a l , (1969) s u c c e s s f u l l y applied the same procedure i n t h e i r studies on north- east P a c i f i c and Indian Ocean sediments. The c h l o r i t e group minerals are s e l e c t i v e l y dissolved by warm d i l u t e hydrochloric acid (Brindley, 1961; C a r r o l l , 1970). Diffractograms 59 of acid-treated oriented samples i l l u s t r a t e decreased d(00l) peak i n t e n s i t i e s (Fig.19). Weak v e s t i g i a l 7 A and 3.5 A peaks p e r s i s t i n diffractograms of clay material treated with acid f o r 72 hours. The weak 7 A and 3.5 A peaks may be due to small amounts of k a o l i n i t e or w e l l c r y s t a l l i z e d c h l o r i t e that r e s i s t s rapid a c i d d i s s o l u t i o n . Sediments of the Blanco Trough, Cascadia Basin and the continental terrace o f f Washington and Oregon, when analyzed by the method of Biscaye (1964), were c h l o r i t e - r i c h and kaolinite-poor (Duncan et^ a l , 1970; Selk, 1977). Heat and acid treatments on the Juan de Fuca Ridge clays suggest the presence of either minor coarsely c r y s t a l l i n e c h l o r i t e or minor k a o l i n i t e . K a o l i n i t e , i n the untreated Juan de Fuca Ridge diffractograms, i s strongly i f not completely dominated by the mineral c h l o r i t e . Glycolation of the clay samples exposes the d(001) c h l o r i t e peak a f t e r the movement of the coincident montmorillonite d(001) spacing to 17 A on the diffractogram. Examination of the c h l o r i t e peak i n - t e n s i t i e s demonstrates strong d(002) and d(004) spacings with weaker d(001) and d(003) spacings, a r e l a t i o n s h i p c h a r a c t e r i s t i c of i r o n - r i c h c h l o r i t e s (Brindley, 1961; C a r r o l l , 1970) (Fig. 19). Rateev et a l , (1969 )also observed i r o n - r i c h c h l o r i t e i n the deep northeast P a c i f i c . Heating of clays to 300°C and 550°C produced marked reductions i n s i z e of the d(002), d(003) and d(004) c h l o r i t e peaks with the charac- t e r i s t i c i n t e n s i f i c a t i o n of the d(001) c h l o r i t e peak at 14 A a f t e r the 500°C heat treatment. I d e n t i c a l c h l o r i t e s were i d e n t i f i e d from Cascadia Basin (core 61). 60 B. CM O O UJ H E o CO o o LU H EC o o o U l r - E o 1 1 1 1 1 ' , ' I 10 12 14 4, 18 20 20 (DEGREES) I* I ' I 24 26 FIGURE 19. A. Diffractogram trace from West Valley core 77-14-43 showing untreated F e - r i c h c h l o r i t e . B. C h l o r i t e peak removal a f t e r twelve hours of d i s s o l u t i o n by warm (80'C) d i l u t e (10%) hydrochloric a c i d . 61 Clay Sized Minerals The dominant minerals described i n the bulk sediment mineralogy are also present i n the clay sized f r a c t i o n , ex.-quartz and plagioclase feldspar produced prominent peaks i n a l l oriented clay diffractograms (Fig.18). Weak peaks occur at 8.5 to 8.6 A and 4.0 to 4.1 A i n a l l clay X-ray traces. The 8.5 to 8.6 A peak i s due to the (110) plane of amphibole (Biscaye, 1965). Abundant amphibole should produce a weak 2.82 A peak for the (330) plane. Although a 2.82 A (330) peak j u s t above back- ground may exi s t i n oriented clay diffractograms i t s presence cannot be strongly supported. An unoriented clay sample might better in d i c a t e the amphibole 330 c r y s t a l plane. The 4.0 to 4.1 A peak i s produced by c r i s t o b a l i t e ( C a r r o l l , 1970), which i s widespread i n the clays of the northeast P a c i f i c and has been observed from Explorer Ridge, Juan de Fuca Ridge, Cascadia Basin and l a t i t u d e 35°00'N, longitude 165°00'W ( C a r r o l l , 1970; Blland, i n prep.; P r i c e , i n prep.). Clay sized c a l c i t e i s indicated by diffractogram peaks at 3.04 A and 3.87 A with the former peak being the largest (Fig.18). Samples from West and Middle Ridges have prominent c a l c i t e peaks, whereas West, Middle and East Valleys lack them. Clay sized c a l c i t e occurs wherever c a l c i t e i s present i n bulk sediment. Treatment of the clay sediments by g l y c o l a t i o n , heating and hydrochloric acid produced no change i n the peak i n t e n s i t i e s or positions i for any of the clay sized minerals except c a l c i t e . Heating to 550°C collapses the c a l c i t e peaks to the r a d i a t i o n background although heating to 300°C has no observable a f f e c t . Treatment of s l i d e s by warm d i l u t e hydrochloric acid e f f e c t s removal of c a l c i t e peaks. 62 Unknown Minerals Diffractograms of mineral "A" indi c a t e i t i s magnetite (Fig.20). A d d i t i o n a l peaks are the r e s u l t of minor amounts of quartz and feldspar i n the concentrate. The diffractogram of mineral "B" shows that the mineral i s p y r i t e (Fig.21). Scanning electron microscophy i l l u s t r a t e s the fram- b o i d a l habit of the p y r i t e aggregates (Plate 5). Mineral "B" i s most abundant i n sediments from West Valley, West Ridge and Middle Ridge. P y r i t e tends to be concentrated as a heavy mineral i n the sediments when a d i r e c t association with the biogenic component i s unclear. Its association was described i n d e t a i l i n Chapter I I . The presence of magnetite and p y r i t e i n bulk sediment and clay sized samples i s d i f f i c u l t to detect based on unconcentrated sample preparation p r i o r to X-ray d i f f r a c t i o n analysis. X-ray d i f f r a c t i o n determination by a CuK»* compared with an FeK<x r a d i a t i o n source de- emphasizes the peaks of i r o n - r i c h minerals ( C a r r o l l , 1970), due to high mass absorption c o e f f i c i e n t s . DISCUSSION General Mineral D i s t r i b u t i o n Except for c a l c i t e , the minerals i n the bulk sediment samples and oriented clay subsamples are common to both the northern end of Juan de Fuca Ridge and Cascadia Basin. C a l c i t e occurs most commonly on the ridges of the Juan de Fuca Ridge area and i s noticeable absent from the v a l l e y sediment. Factors c o n t r o l l i n g occurrence of c a l c i t e are discussed i n the preceding chapter. C >x| 3 M H- O 3 a rt <pa Q FJ H- O O • 3 • » I-1 era S 3 H* fD 3* fD 00 3 3 fD l-t fD DJ rr h-> H- - rt > fD - O O 3 n a. rh fD i-h 3 H rr Bo i-t O DJ rt rr O fD CW • H DJ 3 r-t DJ o ro 3 O r( I i-i rr N DJ 3 a. DJ 05 P- o n DJ IA m K fD H ro r> o ro o rr ro a. ro OH ro a ro m O co m S 3 « . ro" cn cn CD" cn C D " o" 05 JO" cn *." QUARTZ FELDSPAR (PLAG.) FELDSPAR (PLAG.) QUARTZ FELDSPAR (PL AG.) hk l MAGMETTTE (220)(*.««*> • MAGNETITE (3 1 1 )«*•««*> QUARTZ MAGNETITE (400)<*-'«A> MAGNETITE (422)<i.»**> MAGNETITE (5 1 1)o «A> MAGNETITE(440)t i . -»*) £ 9 20(DEGREES) FIGURE 21. Authigenic p y r i t e (mineral"B") diffractogram trace. Minor <<-quartz was c o l l e c t e d with the concentrate. PLATE 5. Scanning electron micrograph showing p y r i t e aggregates externally attached to f o r a m i n i f e r a l s h e l l i n Plate 3 (Mag. 200x). 66 Changes i n the peak i n t e n s i t i e s of quartz and plagioclase feldspar occurred between samples, but no attempt at q u a n t i f i c a t i o n was made. Clay Mineral Abundances: Relation To Topography The geographic l o c a t i o n and small s i z e of the area studied severely handicaps any conclusions on mineral provenance. Temporal changes i n the d i s t r i b u t i o n of clay minerals are discussed below based on the s t r a t i g r a p h i c c o r r e l a t i o n of the ridge and v a l l e y sediments outlined i n the preceding chapter. The most obvious v a r i a t i o n e x i s t s between ridges and v a l l e y s , based on the semiquantitative estimation of average r e l a t i v e abundance i n each core; montmorillonite i s depleted on ridges and concentrated i n v a l l e y s (Fig.22), whereas i l l i t e and to a lesser extent c h l o r i t e are concentrated on ridges and d i l u t e d i n the va l l e y s by montmorillonite (Fig.23). C h l o r i t e does not vary as widely i n abundance as do montmorillonite and i l l i t e . The same v a r i a t i o n s ex i s t for surface sediments (Figs.22 and 23). Studies on the clay minerals dominating the various clay sizes of deep-sea sediment from Explorer Ridge show that montmorillonite dominates the f i n e s t clay sizes and i s progressively depleted i n the coarser clay sizes whereas c h l o r i t e and i l l i t e are least abundant i n the very f i n e clay f r a c t i o n with the abundance of i l l i t e greater than c h l o r i t e with increased clay s i z e (Hanson, o r a l commun., 1981). In diffractograms of t h i s study, mont- m o r i l l o n i t e peaks have wide bases and i r r e g u l a r boundaries, whereas i l l i t e and c h l o r i t e peaks have narrow bases and sharp boundaries. The character of peak boundaries and width of base r e f l e c t the degree of 67 JUAN DE F U C A RIDGE X - S E C T I O N Oept h b elo w • e • l e v e l ( m e t r e a - u n c o r r e c l e d ) A 2 100 -, W E S T V A L L E Y ,sr H42 4<°>LP37 W E S T RIDGE 21 H 2 1 MIOOLE V A L L E Y MIDDLE RIDOE i t H22 «?evLP14 E A S T V A L L E Y C A S C A D I A B A S I N 4 6 H44 A «1 D e o l h be low » • a l e v e l ( m e t r e e - u n c o r r e c t e d ) W E S T V A L L E Y LONGITUDINAL S E C T I O N H25 (2o>LP 14 A se n H18 (is)LP18 ST H42 „ H 4 1 ( " » L P 3 7 ?»'LP36 A u ~ 7 f. s« , " 3 7 87 H50 " oe)LP4 1 (50) S C A L E 0 5Km t~I—I I l | A _ C O R E S ON OR A O J A C E N T S E C T I O N A _ C O R E S N E A R AND P R O J E C T E D T O S E C T I O N 6* H _ H O L O C E N E V A L U E L P — L A T E P L E I S T O C E N E V A L U E FIGURE 22. Bathymetric p r o f i l e s of the northern end of Juan de Fuca Ridge AA' and BB' a f t e r Figure 4 , showing with small numbers the r e l a t i v e percentage of montmorillonite i n surface samples.and averaged through core ( i n parenthesis), large numbers show average r e l a t i v e percent montmorillonite i n Holocene samples (H) and i n Late P l e i s t o c e n e samples (LP). Cascadia Basin core 77-14-61 i s separate- l y i l l u s t r a t e d . 68 JUAN DE FUCA RIDGE X-SECTION D . D . h b . l o . W " T RIDQE C A S C A D I A B A S I N I C SO 24 (31>(20> A e i WEST VALLEY LONGITUDINAL SECTION O t p t h b t l o w • • a It v • I ( m « t r * « - u n c o r r * c t t t f ) B 270O-, I C 36 ii I c 36 30 (4 D O C ) A S t 2»)(32> I C I c « , 36 30 23 20 8 3 ( 3 2 X 3 0 ) (2 7 X 2 * ) . S C A L E 0 I K K 1 ' ' I I 1 A _ 64 B' - 3 1 0 0 C O R E S O K OR A D J A C E N T S E C T I O N _ C O R E S N E A R A N D P R O J E C T E D TO S E C T I O N I I L L I T E V A L U E S C — C H L O R I T E V A L U E S FIGURE 23. Bathymetric p r o f i l e s AA' and BB 1 of the northern end of Juan de Fuca Ridge a f t e r Figure 4 , showing the d i s t r i b u t i o n of the clay minerals i l l i t e (I) and c h l o r i t e (C), and the r e l a t i v e percentages of the clay minerals i n surface samples and averaged through core ( i n parenthesis). Cascadia Basin core 77-14-61 sample values are separately i n d i c a t e d . 69 c r y s t a l l i n i t y of the clay mineral: the sharper the peak and the narrower the base the better c r y s t a l l i z e d the clay mineral species (Brindley, 1961; C a r r o l l , 1970). Thus, montmorillonite i s not as w e l l c r y s t a l l i z e d as c h l o r i t e or i l l i t e . Dominance of f i n e poorly c r y s t a l l i n e montmorillonite i n v a l l e y s and of coarser better c r y s t a l l i z e d i l l i t e and c h l o r i t e on ridges could be the r e s u l t of winnowing. The occurrence of winnowed sediment on the topographic highs was observed i n the previous chapter. Winnowing removes the f i n e r sized clay component to the v a l l e y s , while a r e s i d u a l concentration of the coarser clay sizes remains on the ridges. A gradation e x i s t s between v a l l e y s and ridges. Temporal V a r i a t i o n In Clay Mineral Abundances A change i n the abundance of clay minerals from the Late Pleistocene to the Holocene has been observed i n the northeast P a c i f i c by Duncan, Kulm and Griggs (1970), and Duncan and Kulm (1970). A s i m i l a r change i s observed i n t h i s study. Core length p l o t s of r e l a t i v e clay mineral abundances and r a t i o s of montmorillonite to i l l i t e and c h l o r i t e to i l l i t e demonstrate consistent temporal clay mineral f l u c t u a t i o n s (Figs.24 and 25). The Late Pleistocene-Holocene boundary, as discussed i n Chapter II for t h i s study, at 9,000 to 9,540 years B.P., i s shown on the p l o t s . In general the montmorillonite to i l l i t e r a t i o increases from the basal cored sediment to the approximated boundary, then decreases above i t . The average percentage of montmorillonite increases for a l l physiographic areas of the Juan de Fuca Ridge from the Late Pleistocene to the Holocene (Fig.22). A s i m i l a r r e s u l t was found for the r a t i o of montmorillonite to i l l i t e i n the northeast P a c i f i c by Duncan, Kulm and Griggs, (1970). A corresponding change i n the abundance of c h l o r i t e and WEST VALLEY LONGITUDINAL SECTION 7 7 - 1 4 - 6 7 7 7 - 1 4 - 6 3 7 7 - 1 4 - 6 2 7 7 - 1 4 - 6 6 B' 7 7 - 1 4 - 5 6 H O L O C E N E lllhFFFFhllllllllUI L A T E P L E I S T O C E N E W E S T V A L L E Y 7 7 - 1 4 - 6 3 JUAN DE FUCA RIDGE X - S E C T I O N A» CASCADIA BASIN " 7 7 - 1 4 - 6 1 ( L E G E N D ) W E S T R I D G E M I D D L E V A L L E Y M I D D L E R I D G E E A S T V A L L E Y 7 7 - 1 4 - 4 5 7 7 - 1 4 - 4 7 0 * 1 0 0 7 7 - 1 4 - 5 1 7 7 - 1 4 - 5 4 miii'im i n n - B O U N D A R Y ( O B S E R V E D ) - B O U N D A R Y ( I N F E R R E D ) FIGURE 24. Relative percentage of clay minerals montmorillonite, c h l o r i t e and i l l i t e plotted against depth i n core (centimetres) for Juan de Fuca Ridge section AA' and West Valley section BB'. Cascadia Basin core 77-14-61 i s i l l u s t r a t e d with legend. WEST VALLEY LONGITUDINAL SECTION B 2 0-, S 50 ° 100H I 150-1 E 200-J 7 7 - 1 4 - 4 3 0.5 1.0 I. I 7 7 - 1 4 - 6 3 7 7 - 1 4 - 6 2 7 7 - 1 4 - 6 6 B' 7 7 - 1 4 - 5 6 I I I 1.0 1.6 2.0 7 7 - 1 4 - 6 7 0.5 1 0 1.5 0.5 1.0 1.5 0.5 1.0 1.5 0.6 1.0 1.6 0.6 1.0 ,1 I % I _,. I 1 I -, . I , 1 ' -i 1 I _ . I , I l!o lis 2I0 1.0 1̂ 5 2!o llo l.'s 2.0 1.0 lis 2.0 1.0 1.5 2.0 ii\iiiii/m,\ui>Hii,mi I m n 1 1 1 1 1 1 N v / H O L O C E N E imi 11111111111 L A T E P L E I S T O C E N E I . I_ . 1 . JUAN DE FUCA RIDGE X-SECTION . CASCADIA BASIN A A W E S T V A L L E Y W E S T RIDGE MIDDLE V A L L E Y MIDDLE RIDGE E A S T V A L L E Y - 7 7 - 1 4 - 6 1 7 7 - 1 4 - 6 3 7 7 - 1 4 - 5 1 7 7 - 1 4 - 5 4 7 7 - 1 4 - 4 5 7 7 - 1 4 - 4 7 MONTMORILLONITE ( I X ) / ILLITE (4X) 0.5 1.0 1.5 0,6 1.0 0.6 1.0 1.5 0.5 1 f 0 1.5 0.6 1.0 1.5 > . O.& .  .0 O o ,  1.0 u.o i . u 1. 0.5 1.0 1.6 / / / / / ? / / / / / —' I I I — 1 1 1 1 1 1.0 1.5 2.0 1.0 1.5 2.0 1 .01 .5 i i .1 ]\ / i i i 1.0 1.5 2.0 C H L O R I T E (2X)/ ILLITE (4X> LEGEND • - MONTMORILLONITE (1X)/ ILLITE (4X) C H L O R I T E (2X)/ ILLITE (4X) 11111 - B O U N D A R Y ( O B S E R V E D ) inn - B O U N D A R Y ( I N F E R R E D ) FIGURE 25. Ratioed r e l a t i v e percentage of clay minerals, with montmorillonite (lx) / i l l i t e (4x) and c h l o r i t e (2x) / i l l i t e (4x) plotted against depth in core (centimetres) for Juan de Fuca Ridge section AA' and West Valley section BB'. Cascadia Basin core 77-14-61 i s also i l l u s t r a t e d . 72 i l l i t e occurs from the Late Pleistocene to the Holocene for the Juan de Fuca Ridge area but the changes are physiographically v a r i a b l e (Fig.26). C h l o r i t e decreased i n abundance i n the v a l l e y s and increased on the ridges from the Late Pleistocene to the Holocene whereas i l l i t e shows the opposite trend. The i n t e r r e l a t i o n s h i p of the three clay minerals during the Late Pleistocene i s explained by the widespread reduction i n mont- m o r i l l o n i t e discussed e a r l i e r . The observed decrease i n montmorillonite and corresponding increase i n i l l i t e and c h l o r i t e may p r i m a r i l y r e f l e c t the dominance of sedimentation by t u r b i d i t y currents during the Late Pleistocene. Sediments, as discussed i n Chapter I I , are dominated by terrigenous t u r b i d i t e s which contain abundant micaceous and c h l o r i t i c minerals. Moreover, during the Late Pleistocene, winnowed c h l o r i t e appears to have d i l u t e d the clay minerals of the topographic lows leaving a residuum of i l l i t e on the ridges and topographic highs (Fig.26). During the Holocene, montmorillonite abundance generally increased, or c h l o r i t e and i l l i t e abundance decreased compared to Late Pleistocene abundances, and montmorillonite was p r e f e r e n t i a l l y winnowed from ridges to d i l u t e the sediment of the v a l l e y s , c h l o r i t e remained with i l l i t e as a lag deposit on the ridges (Figs.26 and 27). Is the observed change i n the r e l a t i v e clay mineral d i s t r i b u t i o n diagenetic? The shortness of the cores sampled for t h i s study, the radio- carbon ages and the general moist unconsolidated character of the sediment indicates that only the e a r l i e s t stage of diagenesis can have taken place. The early stage of marine diagenesis i s marked by the s t a b i l i t y of the clay minerals (DeSegonzac, 1970; Eberl and Hower, 1976). A diagenetic 73 JUAN DE FUCA RIDGE X-SECTIONl O . p l b b . l o . * « T R I D G E I I I I I I C A S C A D I A B A S I N I C HS 1 H 2 6 A e i WEST VALLEY LONGITUDINAL SECTION D t p l h be low a • a 11 v • I ( m t t r a a - u n c o r r a c l a d ) B 2 700-1 I C H 3 4 Hit H 2 0 H 3 0 . L P 2 7 L P 3 7 A I C „ , H34 H2S • C 0 3 L P 2 ( L P 3 0 H J 7 H 2 4 1 C H3 7 M3 9 LP4 3 LP< 4 A se S C A L E 0 {Km 1 I I I I I _ C O R E S O N OR A D J A C E N T S E C T I O N A _ C O R E S N E A R AND P R O J E C T E D TO S E C T I O N H H O L O C E N E V A L U E LP — L A T E P L E I S T O C E N E V A L U E C — C H L O R I T E V A L U E S I — I L L I T E V A L U E S FIGURE 26. Sathymetric p r o f i l e s AA' and BB 1 of the northern end of Juan de Fuca Ridge a f t e r Figure 4 , showing the d i s t r i b u t i o n of average r e l a t i v e percentage values f o r i l l i t e (I) and c h l o r i t e (C) i n Holocene samples (H) and Late Pleistocene samples (LP). Cascadia Basin core 77-14-61 i s separately i l l u s t r a t e d . ILLITE (100%) LEGEND LATE HOLOCENE PLEISTOCENE O D A V (100%) CHLORITE PHYSIOGRAPHIC AREA WEST VALLEY WEST RIDGE MIDDLE VALLEY MIDDLE RIDGE EAST VALLEY CASCADIA BASIN (100%) MONTMORILLONITE FIGURE 27. Ternary plot i l l u s t r a t i n g changes i n r e l a t i v e percentages of clay minerals within d i f f e r e n t physiographic areas for the Late Pleistocene and Holocene Enochs. 75 explanation for the observed Late Pleistocene to Holocene deep-sea clay mineral f l u c t u a t i o n s was discounted by Duncan, Kulm and Griggs (1970), and t h i s w r i t e r holds the same opinion. In summary, the observed downcore changes i n mineral abun- dance are believed the r e s u l t of i n t e r a c t i n g l o c a l and regional hydro- graphic and sedimentation factors e f f e c t i v e during the Late Quaternary. CONCLUSION Provenance Of Minerals The d e t r i t a l minerals detected from each sample are ubiquitous to a l l the analyzed sediment from the study area. Certain minerals have d i s t i n c t r e l a t i o n s h i p s : c a l c i t e , abundant i n the tests of pl a n k t i c and benthic foraminifera, i s biogenic, while framboidal p y r i t e has a biogenic association. The same sui t e of clay minerals, except for c a l c i t e , was detected both from Juan de Fuca Ridge and Cascadia Basin. Cascadia Basin sediments contain abundant montmorillonite, a feature that characterizes Holocene rather than Late Pleistocene sediments. The change i n clay abundance from the Late Pleistocene to the Holocene suggests a r e l a t i v e increase i n supply of montmorillonite, a r e l a t i v e decrease i n supply of c h l o r i t e and i l l i t e , or both. Clay mineral abundances throughout the world's oceans demonstrate strong l a t i t u d i n a l - c l i m a t i c zonations, a feature p r i m a r i l y the r e s u l t of aeolian and f l u v i a l d i s t r i b u t i o n patterns (Biscaye, 1965; Rateev et_ a l , 1969; K e l l e r , 1970). C h l o r i t i c and i l l i t i c clays are most p l e n t i f u l i n northern l a t i t u d e s . C h l o r i t e and i l l i t e dominate temperate high l a t i t u d e s o i l s where chemical weathering i s of le s s e r i n t e n s i t y than i n lower 76 l a t i t u d e s (Rateev et a l , 1969). Montmorillonite i n the deep-sea may be an a l t e r a t i o n product of: volcanic ash where occurrence with p y r o c l a s t i c minerals and p h i l l i p s i t e suggests a volcanic association, basalts associated with hydrothermal c i r c u l a t i o n (Seyfried and Bischoff, 1981) and low l a t i t u d e , a r i d , a c i d i c , poorly drained, t e r r e s t r i a l l a t e r i t i c s o i l s . P y r o c l a s t i c minerals and p h i l l i p s i t e were not detected i n the clays or the bulk sediments of t h i s study, so a volcanic source i s not apparent and the wide a r e a l d i s t r i b u t i o n and abundance changes for montmorillonite both for the study area and Cascadia Basin lend doubt to a ridge-type hydrothermal source. A temporal v a r i a t i o n i n mont- m o r i l l o n i t e for deep-sea sediments i n the northeast P a c i f i c was proposed by Duncan, Kulm and Griggs (1970), and was a t t r i b u t e d to f l u c t u a t i o n s i n the Columbia River sediment load. C h l o r i t e and i l l i t e - r i c h sediments come from the northern part of the r i v e r basin. The increase i n sediment from the northern basin and i t s domination of the montmorillonite-rich southern Columbia drainage basin was the r e s u l t of severe g l a c i a l erosion to the north i n the Late Pleistocene. Subsequent g l a c i a l recession has caused the Columbia River system to produce a load with higher montmoril- l o n i t e and lower c h l o r i t e and i l l i t e abundances during the Holocene. The influence of such a change i n clay mineral abundance i n the load of the Columbia River may be s u f f i c i e n t l y large to a f f e c t the observed clay mineral abundances at the northern end of Juan de Fuca Ridge. However, the proposed source for t u r b i d i t y currents a f f e c t i n g the study area i s Queen Charlotte Sound. No known mineralogical studies on the sediments of the Sound have been conducted. Rivers presently contributing sediment to the Sound, drain basins that during the Late Pleistocene experienced g l a c i a l erosion and deposition. Sediment source areas contain outcrops 77 of p r i m a r i l y quartz d i o r i t e , granodiorite and d i o r i t e of the Coast Plutonic Complex to the east and basalts, p i l l o w lavas and grano- d i o r i t e s of Vancouver Island to the south (G.S.C. Map 1386A, 1979). The Coast Plutonic Complex covers far more area than the mafic rocks of Vancouver Island, and should thus have been the major contribution to the Late Pleistocene g l a c i a l outwash. Clay minerals from the weathered i n t r u s i v e s would be dominated by muscovite and to a l e s s e r extent c h l o r i t e derived from s e r i c i t i c and p r o p y l i t i c a l t e r a t i o n products ( S i l l i t o e , 1973). T u r b i d i t y currents i n i t i a t e d from Queen Charlotte Sound, generated during g l a c i a l recession, would carry clays whose proportions would r e f l e c t provenance from the Coast Plutonic Complex. In conjunction with or as an a l t e r n a t i v e to the preceding scenarios i s one involving a change i n clay mineral sedimentation dependent on differences i n climate and s o i l mineralogy between the Late Pleistocene and Holocene. The c o r r e l a t i o n between t e r r e s t r i a l and marine c h l o r i t e and i l l i t e clay minerals at high l a t i t u d e s was previously mentioned, while a comparable abundance e x i s t s for montmorillonite at lower l a t i t u d e s . The Late Pleistocene was colder than the Holocene and the isotherms were further south (Clague, 1978). Possibly during the Late Pleistocene, s o i l s from mid-latitudes that presently weather under warm, dry conditions experienced higher humidity and cooler climates that emphasized an increased production of c h l o r i t e and i l l i t e at the expense of montmorillonite clays. The r e s u l t of a l a t i t u d i n a l s h i f t i n s o i l clay mineralogy between the Late Pleistocene and Holocene would be r e f l e c t e d i n the neighbouring deep-sea environment. It can be concluded that the s h i f t i n r e l a t i v e clay mineral abundances between the Late Pleistocene and Holocene epochs for the northern 78 end of Juan de Fuca Ridge p r i m a r i l y r e f l e c t s changes from t u r b i d i t y current deposition i n i t i a t e d from Queen Charlotte Sound to nonturbidity current deposition with possible secondary influence from changing continental s o i l weathering patterns and Columbia River sediment discharge. Minerals described i n t h i s study are biogenic, authigenic or terrigenous. Minerals of a c l e a r l y hydrothermal a f f i n i t y were not discovered i n any of the samples analyzed. It i s believed that due to the l o c a l character of known hydrothermal occurrences, surface vessels without deep-diving submersibles or d r i l l i n g c a p a b i l i t y are u n l i k e l y to discover hydrothermal deposits (Hekinian et a l , 1978, Franchteau et a l , 1979). Detection of hydrothermal minerals w i l l be complicated i n an area such as the northern end of Juan de Fuca Ridge by d i l u t i o n with non- hydrothermal sediment. CHAPTER IV SUMMARY AND CONCLUSIONS Sediments from the northern end of Juan de Fuca Ridge possess c h a r a c t e r i s t i c s as summarized below. 1. Gravity cores at a l l s i t e s penetrate the Late Pleistocene-Holocene boundary. Late Pleistocene sediment i s dominantly t u r b i d i t e , whereas Holocene sediment i s c h i e f l y hemipelagic, with minor t u r b i d i t e . 2. The Late Pleistocene t u r b i d i t e s are of the d i s t a l type, are t e r r i g e n - ous i n character and are dominated by " d i l u t e cloud 11 p e l i t e . Turbidites and hemipelagic sediments are present at a l l physiographic s i t e s studied except West Ridge. The v a l l e y sediments possess a stronger t u r b i d i t e and weaker r e - worked hemipelagic character than do the ridges. Excluding the biogenic com- ponent, the differences i n sediment between va l l e y s and ridges are small. 3. The Late Pleistocene-Holocene boundary i s not marked by a t r a n s i t i o n from f o r a m i n i f e r a l to r a d i o l a r i a n dominated sediment, which was therefore time- transgress ive. Interbedded hemipelagic sediments and t u r b i d i t e s of the v a l l e y s contain more r a d i o l a r i a than foraminifera except where entrained foraminifera occur i n the basal coarse sediment of the t u r b i d i t e sequences. Foraminifera are dominant throughout the sediment of the ridges, with a decreased abundance from the Late Pleistocene to the Holocene. 4. Sedimentation rates f o r the Late Pleistocene based on radiocarbon dates, are 11.1 cm/1000 years f o r Middle Ridge and 16.5 cm/1000 years for West Ridge. Holocene sedimentation rates of 1.5 to 2.3 cm/1000 years are inferred for Middle Ridge. 5. Ubiquitous minerals for the Juan de Fuca Ridge and Cascadia Basin as determined by X-ray d i f f r a c t i o n are: ex-quartz, plagioclase, montmorillonite, i l l i t e , i r o n - r i c h c h l o r i t e , amphibole and c r i s t o b a l i t e . C a l c i t e was found i n a l l analyzed samples from West and Middle Ridges. Magnetite i s ubiquitous, and 80 p y r i t e was i d e n t i f i e d i n concentrates from West Valley, West Ridge and Middle Ridge sediments. 6. Montmorillonite i s r e l a t i v e l y more abundant in the v a l l e y s and c h l o r - i t e and i l l i t e on the ridges, the probable r e s u l t of ridge sediment reworking. Montmorillonite shows a widespread r e l a t i v e increase and c h l o r i t e and i l l i t e a corresponding decrease from the Late Pleistocene to the Holocene. 7. Radiocarbon dates, i n f e r r e d ages and cycles of sedimentation enables the stratigraphy of Juan de Fuca Ridge to be determined. Three cycles of i n t e r - bedded turbidite-hemipelagic sediment were recognized from Middle Ridge and si m i l a r cycles are present i n v a l l e y sediments. Turbidity current deposition appears episodic. Cycles i n v a l l e y sediment contain compositional changes, recognized as Late Pleistocene, Holocene and t r a n s i t i o n a l Late Pleistocene- Holocene i n studies of the Cascadia Abyssal P l a i n and i n c l u s i v e deep-sea channels (Griggs and Kulm, 1970). Postulation of a Late Pleistocene-Holocene boundary in the sediment of the v a l l e y s enables c o r r e l a t i o n of sedimentation cycles throughout the study area. Coincident changes in the r e l a t i v e abundances of clay minerals agree with the postulated boundary p o s i t i o n . 8. A radiocarbon date of 19,000 years B.P. from surface sediment and a date of 23,660 years B.P. from deeper sediment, places stratigraphy of a core from West Ridge wholly within the Late Pleistocene. The hiatus since 19,000 years B.P. i n f o r a m i n i f e r a l - r i c h sediment i n t h i s core from West Ridge may be explained by: (a) Reworking of hemipelagic sediment, (b) lack of deposition from t u r b i d i t y currents or (c) changes i n both the fo r a m i n i f e r a l f e r t i l i t y patterns of surface waters and the p o s i t i o n of the l y s o c l i n e r e l a t i v e to the core s i t e during the Late Quaternary. 9. Enhanced preservation of Middle Ridge pl a n k t i c foraminifera by e p i - sodic deposition of t u r b i d i t e s from " d i l u t e clouds ", associated with t u r b i d - i t y currents o r i g i n a t i n g at the continental terrace, has enabled good c o r r e l a t i o n 81 of geologic-climate events for Juan de Fuca Ridge and the continental P a c i f i c Northwest. 10. The source area for Late Pleistocene t u r b i d i t e s on the Juan de Fuca Ridge was Queen Charlotte Sound. This conclusion i s based on (a) the mineralogy of the t u r b i d i t e s which indicates provenance from a t e r r a i n of intermediate plutons i e . , the Coast Plutonic Complex (b) the fa c t that deep-sea channels nearest the study area o r i g i n a t e on the continental slope immediately west of Queen Charlotte Sound and (c) the presence, in ridge sediments, of post- Sumas stade t u r b i d i t e s not reported i n studies of sediments from Cascadia Abyssal P l a i n . It i s concluded, based on structure, grain s i z e d i s t r i b u t i o n , r a d i o - carbon dates and mineralogy that the sediments from the northern end of Juan de Fuca Ridge contain the Late Pleistocene-Holocene boundary, are c o r r e l a t a b l e between physiographic s i t e s , and are c o r r e l a t a b l e with synchronous continental geologic-climate changes. A hydrothermal input into the sediments was not detected. 82 BIBLIOGRAPHY Andrews, A. J . , and W. S. Fyfe. 1976. 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Academic Press, 5: 103-135. 88 APPENDIX I Location, Bathymetric Depth And Length Of Analyzed Cores Location Depth Length Core No. Latitude Longitude (m) (cm) 77-14-43 48° 39.8 128° 55.9 2935 172 77-14-45 48° 27.5 128° 37.0 2350 160 77-14-47 48° 28.9 128° 25.6 2585 150 77-14-51 48° 30.6 128° 52.0 2180 124 77_14_54 48° 30.0 128° 45.5 2520 53 77-14-56 48° 29.6 129° 04.5 2700 69 77-14-61 48° 34.0 127° 44.6 2600 68 77-14-62 48° 33.4* 128° 52.4 3025 172 77-14-63 48° 34.6' 129° 00.2 2925 148 77_14_66 48° 31.2 128° 58.8* 3010 46 77-14-67 48° 36.4* 128° 55.7 2975 164 89 APPENDIX I Core Structure And Clay Size Distribution LEGEND S T R U C T U R E ( X - R A D I O G R A P H ) s> __<=> _ o _ — o - O — O H o — — H e m i p e l a g i c sed iment ( b i o g e n i c - r i c h ) — Zone of t r a n s i t i o n ( p e l i t e - h e m i p e l a g i c ) — Zone of b u r r o w e d pe l i te Zone of laminae C o a r s e g r a i n e d b a s a l sed iment S u r f a c e due to e r o s i o n ( s c o u r ) Trrrrr-rctSZ Burrow (benth ic o rgan ism) WEST VALLEY CORE 77 -14 -43 MIDDLE RIDGE CORE 77-14-45 —i 1 1 1 1 — 35 40 45 50 55 CLAY % EAST VALLEY CORE 77-14-47 WEST RIDGE CORE 77-14-51 | 1 1 1 1 1 1 1 1 1 1 1 1 1 • 1 50 52 54 56 58 60 62 64 CLAY % MIDDLE VALLEY CORE 77-14-54 15 ' • ' 1 ' I' I' I I I I I l I I ' I I I I I I I I [ I I I I I I I I I I I I I I I | I I 2 5 30 35 40 45 50 55 60 65 CLAY% WEST VALLEY CORE 7 7 - 1 4 - 5 6 CLAY % DEPTH IN CORE (CM) 0 > 4> o o ' ' L ro o _!_ O J Ao \0 5 ^ 1 1  I 1 O o) o > 2 z m N z m —I o CO cn CO o o 0 ) o > -< to' CO CO A' ct> cn' o o J3 m i I 0) O > CO o > > > 96 DEPTH IN CORE (CM) o _ l _ x J> ro o o J ! L, 11 lo1 o y0\<>{ \°. 1 1 'o 1 i o 1 i 1 0 lo' I 0 I i0| o ot> o> *>• o o o o t • i t I I L 0 1 0 1 0 16 i f 01 10 0 I .0, ... 11 o i i p t H to o I o J 1 1 0 1 ' 0 1 1 1 0 1 , i 0 i , 0 ' 0 1 ,0 . 0 1 1 I 0 I I 0 I I 0 I , |o, Cn CO o 1— > -< cn cn cn O) cn cn cn co O 0 1> 0 < J3 m m c o 1 > L6 WEST VALLEY CORE 77-14-63 CLAY % WEST VALLEY CORE 77 -14 -66 C LAY % WEST VALLEY CORE 77-14-67 CLAY % APPENDIX III Radiocarbon Data Core 77-14-45 Sample Interval (centimetres) 33-54 Combustion Calcu l a t i o n Amount C02 (inches Hg) Amount Lithium (grams) Weight Benzene (grams) Weight Carbon (grams) Background Modern Standard Sample Counts/min. 6 Counts/min. d Counts/min. a S p e c i f i c A c t i v i t y (c/m.g.) A iMod^Std.) "Q" r a t i o . „ , x A Sample cfQ + Age: 8035 In ("Q" rat i o ) Age S t a t i s t i c s + Sample Age (B.P.) 20 @ IT 4 .2900 .2675 3.166 .024 8.054 .024 3.773 .043 2.2710 + .185 3.544 .289 10170 B.P. 10800-10170 = 630 10170- 9480 = 690 10170 + 630/690 85-109 20 @ 2T 5 .4550 .4197 3.155 .024 8.054 .024 3.679 .034 1.250 + .100 6.441 .519 14970 15590-14970 = 620 14970-14290 = 680 14970 + 620/680 APPENDIX III continued. Radiocarbon Data Core 77-14-51 Sample Inte r v a l (centimetres) Amount C02 (inches Hg) Amount Lithium (grams) Weight Benzene (grams) Weight Carbon (grams) Counts/min. Combustion C a l c u l a t i o n Background Modern Standard Sample I Counts/min. 1°* Counts/min. d Special A c t i v i t y (c/m.g.) "Q" r a t i o A (Mod. Std.) A Sample dQ + Age: 8035 In ("Q" r a t i o ) Age S t a t i s t i c s + Sample Age (B.P.) 0-12 20 @ 2T 5 .5980 .5517 3.155 .024 8.054 .024 3.572 .038 .756 f .082 10.639 1.167 19000 B.P. 19840-19000 = 340 19000-18070 = 930 19000 + 840/930 79-87 15 @ IT 5 .6000 .5535 3.155 .024 8.054 .024 3.389 .035 .423 + .077 19.004 3.467 23660 B.P. 25010-23660 = 1350 23660-22040 = 1620 23660 + 1350/1620 103 APPENDIX IV Grain Size D i s t r i b u t i o n Core j l e I n t e r v a l Sand S i l t Clay 2ntimetres) (%) (%) (%) 0-2 3 58 39 10-12 2 53 45 20-22 3 52 45 29-31 3 53 44 39-41 3 53 44 50-51 3 52 45 59-61 6 51 43 69-71 0 54 46 80-81 1 54 46 90-91 0 52 48 100-101 0 59 41 109-111 2 58 40 125-126 22 57 21 129-131 0 57 43 139-141 2 57 41 149-151 1 58 41 159-161 1 56 43 170-171 1 58 41 0-2 0 55 45 9-11 0 52 48 19-21 0 55 45 30-32 0 60 40 39-41 1 54 45 49-50 1 51 48 59-61 0 64 36 70-72 0 63 37 80-82 0 62 38 90-92 1 42 57 100-102 0 42 58 109-111 0 47 53 119-121 0 45 55 129-131 1 58 41 139-141 0 53 47 149-151 0 45 55 159-160 1 42 57 0-2 1 33 66 10-11 1 33 66 20-21 1 33 66 30-31 1 32 67 40-41 0 35 65 50-51 0 33 67 60-61 1 35 64 70-71 0 33 67 80-81 1 31 68 95-96 0 33 67 105-106 1 43 56 110-111 0 47 53 77-14-43 77_14_45 77-14-47 104 APPENDIX IV Grain Size D i s t r i b u t i o n continued. Sample Interval Sand S i l t Clay Core (centimetres) (%) (%) (%) 77_14_47 C O n t . 120-121 0 47 53 130-131 0 50 50 135-137 0 64 36 77-14-51 0-2 3 39 58 15-17 3 3 9 58 30-32 3 36 61 45-47 3 38 59 60-61 5 37 58 75-77 2 37 61 90-92 2 37 61 105-107 1 48 51 120-122 0 35 65 77-14-54 0-2 1 36 63 13-15 1 32 67 19- 20 1 34 65 24-26 0 35 65 29- 31 0 3 6 64 35-3 6 1 37 62 39- 41 0 38 62 45-46 1 38 61 49- 51 2 70 28 77-14-56 0-2 6 41 53 10-12 7 65 28 20- 22 1 56 43 30- 32 0 61 39 40- 42 0 73 27 50- 52 2 59 39 55-57 2 72 26 65-67 0 69 31 77-14-61 0-2 1 34 65 20-22 1 37 62 30-32 0 36 64 40-42 0 34 66 50-52 0 41 59 - 60-62 0 37 63 77-14-62 0-3 -1 46 53 15-17 1 42 57 30-32 1 43 56 44-46 0 47 53 60-62 0 43 57 75-77 0 43 57 90-92 0 40 60 105-107 0 41 59 105 APPENDIX IV Grain Size D i s t r i b u t i o n continued. Sample Interval Sand S i l t Clay Core (centimetres (%) (%) (%)_ 77-14-62 cont. 120-122 0 40 60 148-150 0 42 58 157-159 0 41 59 166-168 1 43 56 77_14_63 0-2 0 36 64 15-17 0 42 58 30-32 0 33 67 45-47 0 37 63 60-62 0 38 62 75-77 0 42 58 90-92 0 40 60 105-107 0 43 57 120-122 2 51 47 135-137 0 42 58 77_14_66 0-2 1 45 54 10-12 11 46 43 19-21 1 43 56 29-31 1 45 54 39-41 1 45 54 44- 46 0 46 54 77-14-67 0-2 1 38 61 15-16 0 40 60 45- 46 1 39 60 59-61 0 44 56 75-76 0 41 59 89-91 0 45 55 105-106 0 47 53 119-120 1 37 62 135-136 0 44 56 150-152 0 46 54 106 APPENDIX V P h i l i p s X-ray Diffractometer Settings For Sediment Analysis Radiation source CuK«x F i l t e r Ni Scanning speed 2° 20/min. Scale expansion 4 x 10 2 Time constant 1 Voltage 40 kV Current 20 mA Bas e l ine/Window 150/120 Divergence s l i t 1° Receiving s l i t 0.2° Scatter s l i t 1° Chart speed 20 mm/min. 29 range 60° to 4.5° 107 APPENDIX VI Relative Clay Mineral Proportions Sample Montmorillonite I l l i t e C h l o r i t e Interval Rel. Std. Rel. Std. Rel. Std.* Core (centimetres) % Dev. % Dev. % Dev. 77-14-43 0-2 15 (12) 41 (5) 44 (3) 50-52 18 (8) 36 (4) 46 (3) 100-102 20 (7) 35 (4) 45 (1) 150-152 21 (2) 34 (1) 45 (4) 170-172 15 (3) 31 (4) 54 (4) 77_14_A5 0-2 22 (6) 22 (13) 56 (3) 49-51 13 (8) 56 (3) 31 (4) 100-102 15 (5) 43 (8) 42 (1) 149-151 15 (18) 40 (5) 45 (5) 77-14-47 0-2 33 (3) 45 (14) 22 (8) 50-52 43 (2) 29 (18) 28 (5) 105-107 24 (6) 46 (6) 30 (4) 149-151 17 (1) 43 (1) 40 (2) 77-14-51 0-2 21 (6) 40 (13) 39 (1) 44-46 26 (5) 47 (6) 27 (6) 90-92 13 (6) 44 (2) 43 . (2) 105-107 6 (22) 64 (4) 30 (2) 120-122 12 (6) 56 (7) 32 (4) 77-14-54 0-2 27 (4) 24 (7) 49 (2) 49-51 15 (8) 48 (6) 37 (4) 77-14-56 0-2 32 (6) 38 (7) 30 (4) 50-52 18 (10) 35 (17) 47 (5) 65-67 10 (9) 50 (7) 40 (1) 77-14-61 0-2 46 (4) 30 (6) 24 (5) 50-52 41 (2) 31 (4) 28 (2) 77-14-62 0-2 34 (6) 36 (5) 30, (1) 44-46 34 (4) 35 (2) 31 (3) 90-92 42 (7) 31 (6) 27 (3) 120-122 45 (5) 28 (8) 27 (3) 166-168 35 (4) 29 (8) 37 (2) 77-14-63 0-2 37 (3) 39 (4) 25 (2) 45-47 47 (4) 28 (5) 25 (3) 134-136 37 (2) 29 (2) 33 (1) 77_14_66 0-2 57 (1) 23 (7) 20 (1) 44-46 42 (6) 30 (2) 28 (2) 77-14-67 0-2 39 (1) 33 (2) 28 (2) 45-47 46 (5) 30 (3) 24 (6) 89-91 39 (4) 23 (10) 38 (2) 150-152 33 (3) 30 (2) 36 (3) * - Relative Standard Deviation

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