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A study of sediments from the Juan de Fuca Ridge, Northeast Pacific ocean: with special reference to… Price, Michael Glyn 1981

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A STUDY OF SEDIMENTS FROM THE JUAN DE FUCA RIDGE, NORTHEAST PACIFIC OCEAN: WITH SPECIAL REFERENCE TO HYDROTHERMAL AND DIAGENETIC COMPONENTS by MICHAEL GLYN PRICE B.Sc, The University of B r i t i s h Columbia, 1977 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in THE FACULTY OF GRADUATE STUDIES Department of Geological Sciences and Department of Oceanography We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA February 1981 © Michael Glyn Price, 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 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 gran t e d 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 c o p y i n g o r 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 o f Gcolgj ' iCctl S c v € * 6 a s 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 of 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 DE-6 (2/79) ABSTRACT A regional survey of the sedimentology, geochemistry and miner-alogy of the Pleistocene and Holocene deep-sea sediments from the Juan de Fuca Ridge between 47°00' and 48°15' North latitude and the adjacent Cascadia P l a i n indicates a mainly terrigenous, t u r b i d i t i c source for most sediments i n the area, with some admixture of biogenic material (mainly planktonic debris) throughout. Small hydrogenous and hydrothermal compo-nents may also be present. Sedimentation rates during the Pleistocene of about 100 cm/1000 yr are indicated for the Ridge area. Excess MnO i n the oxidised upper few cm of sediment i s ascribed to diagenetic remobilization. Systematic variations i n the S i 0 2 , A1 20 3 and CaO content of the sediments appear to r e f l e c t a t r a n s i t i o n from a dominantly t u r b i d i t i c sedimentary regime during the late Pleistocene, to a hemipelagic Holocene regime in the uppermost 50 cm of sediment. Extensive deposits of metalliferous sediments with a s i g n i f i c a n t hydrothermal component, such as have been reported from the East P a c i f i c . Rise and other parts of the P a c i f i c Ocean, appear to be absent from the area, due probably to extensive d i l u t i o n by sediments of terrigenous o r i g i n . TABLE OF CONTENTS • Page ABSTRACT i i LIST OF TABLES • v LIST OF FIGURES v i LIST OF PLATES v i i ACKNOWLEDGEMENTS v i i i 1. INTRODUCTION 1 Regional context 1 Ocean fl o o r metallogenesis 1 Heat flow anomalies at ocean ridges 2 The hydrothermal model 3 Experimental investigations 6 Other metalliferous deposits 7 2. PURPOSES OF THIS STUDY 9 Introduction 9 Location of study area 10 Previous work 12 Geophysics . 12 Sedimentology 14 3. METHODS AND IMPLEMENTATION 17 Fieldwork 17 Laboratory work 21 4. RESULTS 24 Bathymetry 24 Structural geology 24 Coring 27 Geochemistry .\ . 27 Core 78-6-18 29 Mineralogy 41 Clay minerals 42 Minor components 46 Estimation of non-clay minerals 47 i i i Page Sedimentology 50 General characteristics 50 Type A 51 Type B 51 Type C 55 Type B/C 55 Non-terrigenous components 58 Core 78-6-18 . .. 58 5. DISCUSSION 60 Similar sediments i n adjacent areas . 60 The present area - broad correlations 61 Sedimentary regimes 62 Sedimentation rates 63 Other evidence 66 Trace elements 69 Sources of sediments . . 70 Core 78-6-18 75 Other metallogenic processes 75 Hydrogenous 76 Diagenetic . 76 Biogenic 79 Feldspar diagenesis 79 6. SUMMARY AND CONCLUSIONS 81 Introduction 81 Overall sedimentary regime 82 Recommendations for future work 85 Economic implications 87 REFERENCES 88 APPENDIX 1. Seismic p r o f i l e s and interpretations * 97 APPENDIX 2. Geochemistry - major oxides (%) ..- 113 APPENDIX 3. .Geochemistry - trace elements (ppm) 121 APPENDIX 4. Mineralogy, from XRD data 126 APPENDIX 5. Sedimentology, from X-ray radiographs and visua l examination, and geochemical units, from data in F i g . 6 130 APPENDIX 6. A note on a n a l y t i c a l precision 138 iv LIST OF TABLES Table Page I Core Locations and Lengths 22 I I Average values for selected components i n units 1, 2, and 3, and cores 78-6-18 and 40, compared with other pelagic and hydrothermal sediments 40 I I I The f i v e samples having lowest CaO/Al 20 3 r a t i o s ; data from Appendix 2 48 IV Comparison of measured and calculated CaCO values, core 78-6-18 49 V Sedimentation rates at selected locations (see F i g . 3) 66 VI Comparison of chemical analyses performed by Cominco Research Laboratories Ltd., and (in parentheses) by Dr. E.V. G r i l l , on samples from core 774-14-55 ...... 140 v LIST OF FIGURES Fi g . Page 1 The convective hydrothermal model for ocean f l o o r metallogenesis 5 2 Location map of study area 11 3 1978 study area showing bathymetry, seismic l i n e positions, In > core locations and locations of sediment depth estimations pn&ked^ 1*-gcfiOv 4 Magnetic p r o f i l e s across the northern Juan de Fuca Ridge 19 5 Map of study area showing core locations 20 6 Variation with sediment depth of selected major oxides and trace elements from the ten longest cores 30 7 Representative X-ray diffractograms, showing effect of glycola-t i o n , heating, and acid treatments 43 8 Variation with sample depth of clay minerals in the ten longest cores 44 9 Covariation between CaO and (Al 20 3+Si0 2) in Juan de Fuca Ridge sediments 52 10 Variation of biogenic component ( i . e . carbonate) with water depth, showing effect of depth on carbonate s o l u b i l i t y 64 11 Covariation of Fe, Mn, and (Ni+Co+Cu)xl0 for Juan de Fuca Ridge geochemical units and Core 78-6-18 71 12 Ratio of Si0 2 to A1 20 3 for deep-sea sediments of hydrothermal, hydrogenous and terrigenous o r i g i n 73 13 Ratio of Fe/Ti to Al/(A1+Fe+Mn) for sediments cored during this study 74 14 Variation i n MnO content and thickness of Unit l a with distance from ridge crest 78 15 Sediment inputs to the Juan de Fuca Ridge area 83 v i LIST OF PLATES Plate Page 1 Sediment Type B 53 2 Sediment Type B, showing sediment-filled burrows believed to be due to Zoophycos 54 3 Sediment Type C 56 4 Sediment Types B/C 57 5 Seismic p r o f i l e s N4.5, E0.5, N3 and E0.25 99 6 Seismic p r o f i l e s E l (west half) and El-2 t i e l i n e 100 7 Seismic p r o f i l e s N3 and E l (east half) ' 101 8 Seismic p r o f i l e s N3.7 and El.5 102 9 Seismic p r o f i l e E2 (west half) 103 10 Seismic p r o f i l e E2 (east half) 104 11 Seismic p r o f i l e E2.5 and 2.5-1.5 t i e l i n e 105 12 Seismic p r o f i l e E3 106 13 Seismic p r o f i l e s E5 (west h a l f ) , N l , and E4 (west half) 107 14 Seismic p r o f i l e s E5 (east h a l f ) , N5, E4, and N4 108 15 Seismic p r o f i l e s E7 and N3.5 109 16 Seismic p r o f i l e E9 110 17 Seismic p r o f i l e s E l l and Nl I l l 18 Seismic p r o f i l e N2 112 v i i ACKNOWLEDGEMENTS This study would not have been possible without the assistance and support of a large number of people and organizations; p a r t i c u l a r thanks are due to the following: My thesis advisor, Dr. R.L. Chase; Dr. E.V. G r i l l , of the Department of Oceanography, who was the source of much sound advice and a vast quantity of reference material; Capt. S. Bowles and the o f f i c e r s and crew of the CFAV Endeavour; Mr. Frank Kiss and the a n a l y t i c a l s t a f f of Cominco Explorations and Research Laboratory; Dr. G. Burgess of the Department of Radiography at Vancouver General H o s p i t a l ; Bob Macdonald, who kept a l l the equipment running; and l a s t l y , but by no means l e a s t , my wife Caroline, whose u n f a i l i n g support I could always count on, even at 2:00 a.m. Funding fq.r the project was provided by the National S c i e n t i f i c and Engineering Research Council of Canada; Cominco Ltd., B.C. Minis t r y of Energy, Mines and Petroleum Resources; and the N.A.H.S. Committee of the University of B r i t i s h Columbia. v i i i 1. INTRODUCTION Regional context The present study forms part of a continuing investigation by the University of B r i t i s h Columbia Departments of Geological Sciences and Oceanography into the sedimentology and tectonics of the Juan de Fuca and Explorer Ridge systems. Results of other phases of the investigation have been, or w i l l be, reported by Barr (1972), Barr and Chase (1974), Piper et a l . (1975), Chase et a l . (1980), G r i l l et al'. (submitted 1980), Beland (in prep.), Cook (in prep.), Malott (in prep.), and Hansen (in prep.). The overall objective of this part of the study i s to investigate the p o s s i b i l i t y that metalliferous hydrothermal deposits form a s i g n i f -icant component of the sediments in the Juan de Fuca Ridge area. Ocean f l o o r metallogenesis The occurrence of metalliferous deposits i n the oceans has been known for almost a century (Murray and R'enard, 1898). These deposits are diverse in character: metal-rich muds, encrustations on seafloor rocks, and nodules, appear to be the commonest forms. Five processes have been proposed for the ori g i n of such depos-i t s (Bonatti, 1975): a) HYDROGENOUS: formed by the slow p r e c i p i t a t i o n of continent-derived metals from normal sea water; this process i s r e s t r i c t e d to areas of low sedimentation rate. 1 2 b) DIAGENETIC: due to the remobilisation of metals during the diagenesis of marine sediments. In the reducing conditions preva-lent below the sediment surface metals may be dissolved, to be redeposited in an oxidised surface zone. c) HALMYROLITIC: due to low-temperature reactions between solids (mainly b a s a l t i c glass) and sea water. This process i s important only i n areas of abundant bas a l t i c pyroclastic deposits. d) MANTLE-DERIVED HYDROTHERMAL: formed by the concentration of metal sulphides in the v o l a t i l e phase of magmatic material. e) CONVECTIVE HYDROTHERMAL: due to the c i r c u l a t i o n of sea water through fractures i n hot ocean f l o o r rocks. This process i s described more f u l l y below. Heat flow anomalies at ocean ridges Von Herzen and Uyeda (1963) f i r s t reported high mean values of heat flow i n sediments on the East P a c i f i c Rise, and inferred that these anomalous values were caused by the upwelling of hot semifluid magma below the Rise crest. Bostrom and Peterson (1966) sampled the sediments in the same area and noted enrichment of several metals, including Fe, Mn, Cu, Cr, Ni and Pb, i n the c r e s t a l sediments as compared with surface sediments at a distance from the Rise crest. They interpreted this enrichment as being due to the p r e c i p i t a t i o n of metallic oxides from "volcanic exhalations," or hydrothermal solutions derived from the v o l a t i l e components of ascending magmas. Corl i s s (1971) showed that the slowly cooled i n t e r i o r s of ba s a l t i c lava flows on the Mid-Atlantic Ridge are depleted i n Fe, Mn and other heavy metals r e l a t i v e to the c h i l l e d margins. The apparent coincidence between this depletion of the basalts and the enrichment 3 of the overlying sediments in the same metals led Cor l i s s to the conclu-sion that the "exhalations" of Bostrom and Peterson (1966) actually con-sisted of 1 sea water, which had reacted with the slowly cooling lavas and dissolved out the metals, transporting them to the sediment surface where they were deposited as oxides in the colder, oxidising environment of the sea f l o o r . L i s t e r (1972) noted that heat flow values along the crest of the Juan de Fuca and Explorer Ridges, while higher than the normal sea f l o o r values, are considerably lower than those measured on the ridge flanks : where the volcanic bedrock i s blanketed by sediments. He interpreted t h i s observation to mean that most of the heat transfer at ridge crests occurs by hydrothermal c i r c u l a t i o n , that i s , by a convective, rather than a conductive process. Where the fractures in the volcanic bedrock which form the hydrothermal c i r c u l a t i o n system are sealed by sediments, heat transfer from below the lithosphere must occur by conduction. The hydrothermal model Bonatti (1975) provides probably the best review of the hydrothermal process. In t h i s model, hot upwelling magma at ridge crests undergoes rapid cooling as i t contacts cold sea water, and extensive f r a c t u r i n g , probably to depths of several kilometres, occurs, as the freshly formed rock moves l a t e r a l l y away from the ridge crest. Sea water •penetrates into these fra c -tures, where under high hydrostatic pressure and strongly reducing condi-tions i t i s heated to 300-500°C, and reacts with the lavas; the following reactions are suggested as examples: 2+ — F e ^ i O ^ + 4H20 —> 2Fe + 40H + H^SiO^ (Fayalite) 4 2Fe 2Si0 l t + 3H20 -> Fe3Si20£(0H) „ + F e 2 + + 20H~ (Serpentine or Talc) The metals thus leached from the rocks are transported, probably as chloride complexes, back into the cool, oxidising environment of the sea f l o o r where they are deposited as oxide and hydroxide precipitates. The whole process i s i l l u s t r a t e d in Fi g . 1. As the solution cools during i t s passage to the sea f l o o r , l e s s -soluble sulphides might also be deposited at lower levels within the frac-3 ture system; v o l a t i l e components from the upper mantle (represented by He in F i g. 1) may be incorporated into the hydrothermal f l u i d , and other compo-nents, such as U , may be lo s t from the sea water and incorporated into the basalt. The resultant Fe-Mn precipitates, on being carried away from the spreading cenntre, would become progressively covered by pelagic and/or. terrigenous sediments. Sampling by the Deep Sea D r i l l i n g Project has re-vealed the presence of an Fe- and Mn-oxide r i c h layer at the base of the sediment column, d i r e c t l y overlying p i l l o w lavas, over large areas of the sea f l o o r ; see, for example, von der Borch and Rex (1970), von der Borch et a l . (1972), and Cronan (1976). Analogous deposits have also been re-ported in sediments of marine o r i g i n on land, such as those associated with the ophiolites of the Troodos Complex, Cyprus (Robertson and Hudson, 1974). Deep-sea analogues of the massive sulphide deposits associated with ophiolites have been reported by Bonatti et a l . (1976) and Francheteau et a l . (1979). Chapman and Spooner (1977) have demonstrated, using Sr-isotope r a t i o s , that the sulphide deposits of the Troodos Complex were formed by sea water c i r c u l a t i o n . 5 F i g . 1. The convective hydrothermal model for ocean f l o o r metallogenesis. See text f o r explanation. Modified from Bonatti (1975). 6 Experimental investigations Several laboratory investigations have been carried out with the objective of testing the hydrothermal model. Bischoff and Dickson (1975) reacted normal sea water with fresh sea f l o o r basalts at 200°C and 500 bars, and noted an increase of sea water a c i d i t y from pH 7.9 to 3.9 after only 72 hours, together with increases i n dissolved Ca, K, Cu, and Ni and de-creases i n Mg and Soi,. Fe and Mn also increased i n i t i a l l y , but then showed a steady decrease. Seyfried and Bischoff (1977) hypothesize that the i n -crease i n a c i d i t y i s a factor in the high metal s o l u b i l i t y . They also noted that on mixing "enriched" sea water with normal sea water, precipitates of varied composition were formed, the composition being strongly influenced by the mixing r a t i o ; with high ratios of enriched to normal sea water a precipitate r i c h in Mg and Si0 2 was formed, while with low ratios a pure Fe hydroxide was produced. These and other studies, including those by Mottl and Holland (1978) and Humphris and Thompson (1978 a and b) seem to confirm that the i n t e r -actions between ocean f l o o r basalts and normal sea water, at high tempera-ture and pressure, are capable of producing solutions which on cooling under oxidising conditions might result i n precipitates having the composi-tions found i n t y p i c a l sea f l o o r deposits. Bonatti (1975) remarked that hydrothermal deposits show a very wide range of Fe/Mn r a t i o s , varying from >10 to <0.1, in contrast to sediments of hydrogenous o r i g i n whose Fe/Mn ratios are close tov.unity (see F i g . 11, p. 71). This va r i a t i o n i s attributed to the more rapid oxidation of Fe, and thus faster p r e c i p i t a t i o n , when the hydrothermal f l u i d s mix with cold sea water. Fe hydroxides would therefore tend to be deposited close to the hydrothermal vent, while Mn oxides would be deposited at a greater distance. 7 Rona (1978) l i s t s geochemical, mineralogical and geophysical c r i t e r i a for the recognition of th i s type of deposit. Other metalliferous deposits Hydrothermal deposits are r e s t r i c t e d , i n general, to the base of the sediment column, as has been outlined above. Other types of m e t a l l i -ferous deposit occur at the sediment/sea water interface, probably the best known being manganiferous nodules. These have been widely studied, and are believed to be of hydrogenous o r i g i n ; for reviews of the current'.state , of knowledge i n th i s f i e l d , see Glasby (1977), Burns and Burns (1977), Morgenstein (1973), and Horn (1972). Metal-rich muds also occur at the sediment surface over wide regions of the ocean f l o o r ; their o r i g i n has been the subject of considerable debate,. .and can probably not be traced to a single cause. Extensive thick deposits of red, brown or yellow muds r i c h in Mn and trace elements were described by Murray and Renard (1898) as "pelagic red clays;" Bramlette (1961) and Horn et a l . (1970) have proposed an authigenic ( i . e . hydrogenous) or i g i n for these deposits. In Bramlette's words: Pelagic sediment i s precipitated and/or settled from the over-lying waters of regions where rates of accumulation are slow enough to cause l i t t l e change i n the great volume of c i r c u l a t i n g bottom waters, and the l i t t l e sediment thus accumulates, and normally remains, in a highly oxidised state." Dymond and Veeh (1975), Bischoff and Rosenbauer (1977), and others, report surface sediments of inferred hydrothermal o r i g i n i n the Bauer .Deep and other s i t e s i n .the equatorial P a c i f i c Ocean. Lynn and Bonatti (1965), and Bonatti et a l . (1971), following on from the work of Krauskopf (1957), have proposed a diagenetic process where-by Mn and other trace elements are remobilised under reducing conditions at depth i n the sediment column. These elements are then transported u > 8 upwards, mainly by ionic and/or molecular d i f f u s i o n along a concentration gradient in the pore water (but also to some extent by the upward flow of pore water expressed from the sediments by compaction), and reprecipitated in the oxidising environment at, or close to, the sediment surface. The process i s thus seen to be analogous to the convective hydrothermal process, except that i t obviously operates at a lower temperature. Oxidation poten-t i a l (Eh) rather than temperature, would seem to be the important c r i t e r i o n for remobilisation. Some doubt has been cast on this model by Bender (1971), who has calculated that ionic or molecular d i f f u s i o n would be i n s u f f i c i e n t to trans-port dissolved Mn at the rate of accumulation judged to be necessary over a v e r t i c a l distance of'greater than lm; thus, some other process must be invoked to account for accumulations of Mn-rich sediment thicker than about lm. However, i t seems certain that remobilisation does occur i n many oceanic areas, at least of Mn and possibly of other .metals ( L i et a l . , 1969; Calvert and Pri c e , 1972; Pedersen,"1979; Hartmann, 1979). Certainly, where only a thin Mh-rich layer e x i s t s , remobilisation processes are probably dominant ( G r i l l , 1978). 2. PURPOSES OF THIS STUDY Introduction I t seems highly probable that many, i f not a l l , of the processes discussed i n Chapter 1 may occur, either together or i n any of several possible sequences, in the v i c i n i t y of an active oceanic spreading centre. The elucidation of the history and provenance of the sediments in such an area thus involves consideration of a number of important questions, including the r e l a t i v e importance of each process in the overall history (which w i l l of course be different from area to area), and the relationship of present mineralogy and geochemistry to the history of the sediments; this l a t t e r should, in theory, show some pattern which could be applied to the study of sediments in other areas. The Juan de Fuca Ridge, an active spreading centre i n the north-east P a c i f i c Ocean, has the added complication of heavy terrigenous sedimentation due to the proximity of the coasts of B r i t i s h Columbia, Washington and Oregon. Two major r i v e r s , the Fraser and the Columbia, between them deliver 20-60 m i l l i o n metric tons of sediment per year into the marine environment (Gross, 1977), and numerous smaller streams also contribute to the t o t a l sediment input. 9 10 Accordingly, the main purposes of the present study are three-f o l d : a) To describe the sediments in the study area in terms of mineral-o g i c a l , geochemical and sedimentological parameters; b) To determine as far as possible the provenance and depositional environment of the sediments, and s p e c i f i c a l l y to determine whether a s i g n i f i c a n t hydrothermal component i s present; and c) To determine whether post-depositional changes in either the mineralogy or the geochemistry of the sediments have occurred, and i f so, the reasons for any such changes. Location of study area The area under investigation i s located i n the northeast P a c i f i c Ocean, between 47°00' and 48°15' north l a t i t u d e , and between 128°15' and 130°00' west longitude (Fig. 2).. Topographically the area includes part of the northern end of the Juan de Fuca Ridge, and a small part of the Casdadia Pl a i n to the east of the ridge. The Juan de Fuca Ridge i s presently an active spreading centre, with a half-rate of between 2.9 and 3.1 cm y r - 1 (Vine, 1966; Chase et a l . , 1975; Riddihough, 1977), and forms the margin between the P a c i f i c Plate to the west, and the Juan de Fuca Plate to the east. The term "ridge" i s , in a sense, misleading in this context, since the Juan de Fuca Ridge consists esse n t i a l l y of a system of p a r a l l e l ranges sepa-rated by deep, often wide, v a l l e y s , together with associated seamount chains. The term "ridge complex" w i l l be generally used in place of "ridge" in the course of this study. Within the study area the ridge crest i s offset at i t s i n t e r -section with the Cobb Fracture Zone by a r i g h t - l a t e r a l transform f a u l t 11 F i g . 2. Location map of study area. Spreading ridge segments are shown as double s o l i d l i n e s , and transform f a u l t s as single s o l i d l i n e s . The edge of the Continental Shelf i s shown as a l i g h t dashed l i n e ; arrows show locations of major submarine canyons. 12 showing a displacement of approximately 25 km. The higher parts of the ridge complex are essenti a l l y bare bas a l t i c "oceanic basement," but the eastern flank i s blanketed by the sediments of the Cascadia P l a i n , which are considered by Horn et a l . (1970) and others to be almost wholly t u r b i d i t i c in character, and derived from the North American landmass to the east. The numer-ous valleys within the ridge complex are also sites of sediment deposi-tion. Water depths in the area range from greater than 2800 m, on the west flank, to less than 1600 m on some of the higher seamounts (Fig. 3). Relief within the ridge complex i s l o c a l l y in excess of 700 m. The Cascadia Plain i s essentially horizontal, and l i e s at a general depth of 2700 m. Previous work Geophysics Work on the tectonics and geophysics of the Juan de Fuca and Explorer ridge system has been extensive. This was the area described by Raff and Mason (1961) in their c l a s s i c paper on the "magnetic s t r i p e s " of the ocean f l o o r , which, interpreted by Vine and Wilson (1965) and Vine (1966) became one of the key pieces of evidence for the whole concept of plate tectonics. The pattern of magnetic anomalies shows a generally symmetrical spreading of oceanic lithosphere away from the ridge crest, but more recently i t has been pointed out that the anomaly pattern i s not en t i r e l y symmetrical (Elvers et a l . , 1973). The small Juan de Fuca Plate, subjected to the stresses of subduction under North America, has undergone considerable internal deformation, 13 s p l i t t i n g into several smaller blocks with movement rates r e l a t i v e to each other of up to 3.5 cm yr 1 ( S i l v e r , 1971). McManus et a l . (1972) suggested that the northern salient of the Juan de Fuca Plate, adjacent to the Explorer Ridge, may be i n the process of s p l i t t i n g away from the rest of the plate. The work of Riddihough (1977) has confirmed this view; thus the c l a s s i c a l l y simple concept of the Juan de Fuca Plate as a single entity has given way to a complex, but un-doubtedly much more r e a l i s t i c , system of small " p l a t e l e t s , " a l l moving semi-independently at different rates and i n different directions. Barr and Chase (1974) have found evidence for a westward migra-tion of the spreading centre at the northern end of the Juan de Fuca Ridge; such a migration, and the existence of dominantly r i g h t - l a t e r a l transform f a u l t s throughout the area, can be accounted for by a rota-tion in the spreading direction of the Ridge about 5 m i l l i o n years ago, as proposed by Menard and Atwater (1968) and Atwater (1970). The spreading dire c t i o n of the Juan de Fuca-Explorer ridge system appears to be gradually rotating into p a r a l l e l i s m with the s t r i k e - s l i p motion of the San Andreas and Queen Charlotte f a u l t zones. Tobin and Sykes (1968) found that, while the Explorer and Gorda Ridges and the Sovan'co and Blanco Fracture Zones are a l l seismically highly active, only a single poorly located seismic event occurred over the whole of the Juan de Fuca Ridge during the ten-year period 1954-1963, and t h i s one event probably occurred on the Cobb Fracture Zone. They drew attention to the observation that r e l a t i v e l y f a s t -spreading ridges which lack a prominent median r i f t , such as the East P a c i f i c Rise, are generally aseismic along the crest; apparently only those ridges having a prominent median valley e x i b i t c r e s t a l seismicity. 14 However, the spreading rate of the Juan de Fuca Ridge i s , by contrast with the East P a c i f i c Rise, r e l a t i v e l y slow (approximately 3 cm y r - 1 , compared with rates of up to 9 cm y r - 1 for the East P a c i f i c Rise, reported by Le Pichon et a l . (1976)), and there i s some indication of incipient r i f t formation, as can be seen in some of the seismic p r o f i l e s (appendix 1). The Juan de Fuca Ridge i s comparable i n this respect to the Galapagos Rise, which has a half-rate of 2.1-3.6 cm y r - 1 and also lacks a prominent r i f t valley in places (Hey, 1977). These ridges are probably t r a n s i t i o n a l in type between the fast-spreading non-rifted and slow-spreading, r i f t e d ridge types, the l a t t e r t y p i f i e d by the Mid-Atlantic Ridge. The reasons for the association between fast spreading rate, lack of a r i f t valley and aseismicity are apparent-ly unknown. The Juan de Fuca Ridge, again unlike the East P a c i f i c Rise, i s extensively block-faulted (McManus et a l . , 1972; Davis and L i s t e r , 1977a). Heat flow studies ( L i s t e r , 1972; Davis and L i s t e r , 1977b) have shown that the rate of geothermal heat flow close to the ridge complex is too high and too variable to be accounted for simply by conduction through the lithosphere; hydrothermal c i r c u l a t i o n , as described in Chapter 1, must be active in the area, and may well contribute a hydro-thermal component to the sediments. Sedimentology It i s perhaps surprising that sedimentological studies in the area have been much less thorough than those related to tectonics. Duncan et a l . (197) studied the clay minerals of the Cascadia Plain sediments and reported montmorillonite, i l l i t e and c h l o r i t e to 15 be the major components. Horn et a l . (1970), in a regional study of the North P a c i f i c , examined a number of cores from the Juan de Fuca and Cascadia P l a i n areas obtained by ships of the Lamont-Doherty Geolo-g i c a l Observatory, and concluded that the sediments are predominantly t u r b i d i t i c . Kulm and Fowler (1974) reported turbidites intercalated with pelagic and hemipelagic sediments in the Cascadia P l a i n . Previous reports of hydrothermal deposits are sparse. Piper et a l . (1975) reported a hydrothermal deposit from Dellwood Seamount, off Vancouver Island; this was es s e n t i a l l y a basal crust, dredged up with samples of basalt, and though i t was obtained somewhat to the north of the present area, i t at least establishes the presence of hydrothermal a c t i v i t y close to the area of present interest. T i f f i n et a l . (1978) and Bornhold et a l . (in prep.), examined a number of cores obtained on a transect of the Juan de Fuca Ridge, again s l i g h t l y to the north of the present area, and reported a pale grey surface layer somewhat depleted in trace elements overlying a thin metal-enriched dark brown layer, which in turn overlies a depleted olive-grey unit. Their dark brown unit (Unit 2) shows a tenfold enrich-ment in Mn compared with the underlying sediments, together with s l i g h t enrichment in Cu and N i . They also report, i n a core obtained to the west of Explorer Ridge, a dark brown unit underlying a l l the others which shows considerable enrichment i n Mn, Cu, Zn, Pb, Ni and Co. This unit they interpret as a basal hydrothermal deposit. Thus i t can be stated that a hydrothermal component in the sediments in the area of the present study i s at least a p o s s i b i l i t y . The large i n f l u x of terrigenous t u r b i d i t i c material, however, may d i l u t e the hydrothermal component, i f i t e x i s t s , beyong the l i m i t s 16 of detection. Undiluted hydrothermal deposits may be found, i f at a l l , oh topographic highs close to the ridge c r e s t where terrigenous sedimen-tation may be absent or much reduced. 3. METHODS AND INSTRUMENTATION Fieldwork The fieldwork for this study was carried out between 5th and 25th June 1978, on board the Canadian Government research ship CFAV  Endeavour, as part of Cruise No. 78-6, organised j o i n t l y by the Depart-ments of Geological Sciences and Oceanography at the University of B r i t i s h Columbia, and the P a c i f i c Geosciences Centre Earth Physics Branch. Navigational positions were obtained by LORAN C, using an Inter-nav LC 204 receiver, i n conjunction with the Endeavour's own LORAN A and s a t e l l i t e navigation systems. The LORAN co-ordinates were converted to geographic co-ordinates by means of a computer program devised by the technical staff of the P a c i f i c Geosciences Centre, run on a Tek-tronix 4051 minicomputer. LORAN C, under favourable conditions, i s understood to provide positional accuracy to within better than 30m. Positions were recorded every ten minutes; a Hewlett Packard K22-5321 d i g i t a l clock was used to provide accurate time readings. Continuous seismic p r o f i l e s were run at 5-10 km intervals in a di r e c t i o n approximately perpendicular to the ridge crest, together with a few p r o f i l e s p a r a l l e l to the ridge. A Bolt PAR airgun with 18 either a 300 i n 3 (4900 cm3) or a 20 i n 3 (330 cm3) a i r chamber was used as a seismic source, and seismic data were recorded using an EPC graphic recorder. Seismic tracks are shown in F i g . 3, and the p r o f i l e s are reproduced, as Appendix 1. Magnetic p r o f i l e s were run concurrently with the seismic p r o f i l e s , using a proton-precession magnetometer towed astern of the ship. The magnetic p r o f i l e s were used i n this study only to define the position of the ridge crest. Two representative pro-f i l e s are presented here as F i g . 4. Sediment samples were obtained by means of a 2£ inch (6.35 cm) internal diameter gravity corer or, in a few cases, a Phleger corer. Attempts to use a new 8 cm diameter gravity corer developed by Geolog-? i c a l Sciences Department technical staff were unsuccessful due to the lack of a suitable core catcher. A t o t a l of 20 cores were obtained (of which 18 were used in t h i s study), at locations shown in F i g . 5 and l i s t e d i n Table I. Most of the cores were taken on a single WNW-ESE transect of the Juan de Fuca Ridge crest along seismic l i n e E2, although a few were taken in other locations. A single Phleger core, No. 78-6-40, was taken i n the Cascadia Plain about 150 km away from the ridge crest, to provide a standard having l i t t l e or no hydrothermal component, against which the other cores could be compared. On recovery, each core was capped, measured and examined v i s u a l -ly for broad sediment type. The cores were then stored upright in the Endeavour's cold store at 4°C. Further sampling was not possible, due to time r e s t r i c t i o n s and the requirements of the P a c i f i c Geoscience Centre's concurrent heat probe and magnetic survey projects. 19 11 June 1978 Time 555 x 545 16 June | 15 June Time F i g . 4. Magnetic p r o f i l e s across the northern Juan de Fuca Ridge; p r o f i l e locations are shown i n F i g . 3. The ridge crest i s assumed to l i e at the cen t r a l point of the major p o s i t i v e anomaly. 20 F i g . 5. Map of study area showing core locations. 'Contours in meters (uncorrected) . • - Core lo c a t i o n (successful). 0 - " " (unsuccessful). 21 Laboratory work After being brought ashore the cores were s p l i t longitudinally and the s p l i t surfaces smoothed with a p l a s t i c spatula. Immediately after s p l i t t i n g , the cores were photographed to provide a record of their fresh appearance. One half of each core was subsampled at 10 cm in t e r v a l s , and in one case (No. 78-6-15) additional samples were taken of layers found to be especially r i c h i n organic remains (mainly foraminifera). Core no. 78-6-18, which seemed to be of special interest, was subsampled at 5 cm int e r v a l s . The remaining half of each core was retained un-disturbed and sealed i n a p l a s t i c sleeve. The subsamples were a i r dried at 25°C, ground in a ceramic mortar to pass through a no. 80 mesh sieve, and analyzed chemically by Cominco Research Laboratories Ltd., of Vancouver (except for those from core no. 78-6-18 which were analyzed by Dr. E.V. G r i l l of the U.B.C. Department of Oceanography). Analyses were performed by means of X-ray fluorescence for the major oxides ( S i 0 2 , A1 20 3, CaO, MgO, Fe 20 3, K 20, Na 20, MnO, T i 0 2 , and P 20s), and by atomic absorption spectro-photometry following dissolution with hydrofluoric acid for the trace elements (Cu, Pb., Zn, Co and Ni) . The results of these analyses are presented in Appendix 2 (major oxides), and Appendix 3 (trace elements); selected data are also presented in Fi g . 6. Further subsamples were taken at 20 cm intervals and analyzed mineralogically by X-ray d i f f r a c t i o n , in general following the proce-dure outlined by C a r r o l l (1969), using a P h i l l i p s PW 1050 diffractometer. The following diffractometer conditions were found to give good r e s u l t s : CuKa radiation; Station No. N. Latitude W. Longitude Water Depth (m) Type Length (cm) ;.. Remarks 6-1 47° 49.98' 129° 3.75" 2677 Gravity 119 2 47° 49.73' 129° 4.76' 2677 132 4 48° 05.26' 129° 44.93" 2827 New grav. _ 5 48° 04.83' 129° 42.59' 2797 II M -6 48° 04.66' 129° 42.20' 2790' Gravity 145 7 48? 03.27' 129° 36.12' 2703 I I 118 8 47° 59.56' 129° 21.37' 2455 i i 166 9 47? 56.35' 129° 10.08' 2442 I I 114 11) hl° 50.48' 128° 37.83' 2633 I I 99 12 47° 54.94' 128° 51.79' 2602 I I 123 15 47° 55.31' 129° 01.38' 2560 i t 145 16 47° 53.94' 128° 58.18' 2542 I I 132 17 47° 54.95' 129° 03.64' 2348 I I -18 47° 55.04' 129° 02.33' 2258 I I 44 19 47° 53.14' 128° 55.37' 2645 I I 175 20 47° 52.58' 128° 54.37' 2553 I I 167 23- 47° 54.18 ' 129° 00.88' 2755 Phleger 27 24 47° 55.30' 129° 04.45' 2347 I I -25 47° 55.01' 129° 02.52* 2609 I I 22 27 47° 57.23' 128° 48.66' 2595 New grav. -29 47° 54.85' 129° 03.06' 2336 Gravity 51 30 47° 55.95' 129° 02.55' 2342 I I -32 47° 57.10' 128° 49.74' 2606 I I 25 35 47° 41.69' 128° 59.04' 2623 II -36 47° 42.47' 128° 59.24* 2738 n -37 47° 43.61' 129° 00.02' 2741 i i -38 47° 07.24' 129° 41.24' 2798 Phleger 29 39 46° 55.29' 128° 57.74' 2692 I I 19 40 46° 33.16' 127° 31.03' 2826 II 27 To Dr. E.V. G r i l l for pore water analysis. No recovery Used by P a c i f i c Geosciences Centre. No recovery No recovery, 23 Cathode potential 40 kV, current 20 mA; Beam s l i t 1°, col l e c t o r s l i t 0.02°; _ i - _ i Chart speed 2 cm min , scan speed 2°26: min Chart range 4 x l 0 2 . time constant 4 sec. The semi-quantitative technique described by Biscaye (1965), as modified by Heath and Pi s i a s (1979) was used to gain some idea of the proportions of the various clay minerals present. Typical d i f f r a c t i o n p r o f i l e s are i l l u s t r a t e d i n F i g . 7, and the mineralogical data are presented i n Appendix 4 and F i g . 8. A descriptive log of each core was prepared, noting sediment colour (using the Munsell rock colour chart), v i s u a l grain siz e , and any d i s t i n c t i v e features such as foraminifera-rich layers, volcanic glass shards or important sedimentary structures. X-ray radiographs of each core were also prepared i n order to reveal sedimentary structures not otherwise v i s i b l e . The core logs and X-ray interpretations are presented i n Appendix 5. 4. RESULTS Bathymetry The bathymetry shown in the main map (Fig. 3) i s based in part on the seismic p r o f i l e s obtained during the Endeavour cruise, and in part on the published bathymetry of Mammerickx and Taylor (1971) and Wilde et a l . (1977). The agreement between the older data and the Endeavour p r o f i l e s i s generally good, although a small elevated area centred at 129°00' west and 47°37' north, v i s i b l e on seismic p r o f i l e s E4 and N3, does not appear on either of the two published charts. None of the seismic lines passes over the centre of the area, so i t s detailed bathymetry and maximum elevation are unknown; the minimum depth recorded was approximately 2280 m. This area seems to be d i r e c t l y in l i n e with the section of the Juan de Fuca Ridge crest south of the Cobb Fracture zone, but exhibits no positive magnetic anomaly. I t i s probably a small, hitherto undiscovered seamount. Structural geology The seismic p r o f i l e s (see Appendix 1) show, to the east of the ridge complex, a thick wedge of generally f l a t - l y i n g sediments with numerous prominent internal r e f l e c t o r s ; these r e f l e c t o r s are. v i s i b l e throughout the sediment column, and indicate c y c l i c , most 24 25 probably t u r b i d i t i c , sedimentation rather than continuous pelagic deposi-ti o n . This contrasts with the "seismically transparent" sediments reported by Kulm and Fowler (1974) to underlie the t u r b i d i t i c deposits in seismic p r o f i l e s from the same area. The p r o f i l e s reproduced in Kulm and Fowler's paper appear to be of rather poor quality. They do not state what kind of seismic source was used; a low-power source might give a strong basement r e f l e c t i o n but miss ref l e c t o r s having low velocity contrast within the sediments. The sediments overlie a presumably ba s a l t i c basement which exhi-b i t s considerable r e l i e f ; extensive block f a u l t i n g , with some t i l t i n g of individual blocks (reported also by Davis and L i s t e r , 1977a) has re-sulted in a series of horst- and graben-like structures, the long axes of which run p a r a l l e l to the ridge crest. Seamount chains, r e s t r i c t e d largely, for some reason, to the west flank of the ridge, cut across this block-faulted pattern at about 90°, resulting in an extremely complex and irregular topography. Sediment deposition within the ridge complex is r e s t r i c t e d almost e n t i r e l y to the "grabens," but on the east flank the whole basement topography i s masked by the tu r b i d i t e wedge of the Cascadia P l a i n . Horn et a l . (1971) place the Cascadia P l a i n within their North-east P a c i f i c Turbidite sedimentary province. The ridge complex they place i n a province of i t s own, the Ridge and Trough Province; however, the sediments in the area, although r e s t r i c t e d to the troughs or grabens, have a similar seismic character to the Cascadia P l a i n t u r b i d i t e s . The troughs probably act as channels for tu r b i d i t y currents with a source to the northeast. Another l i k e l y source for sediments in the troughs may be slumping of hemipelagic material from the neighbouring "horsts," 26 which might be expected to give r i s e to very thin t u r b i d i t e layers or "microturbidites," probably no more than a few cm thick. The offset of the ridge crest mentioned previously i s shown, in most published sources, to be due to the Cobb Fracture Zone, which trends approximately NE and ENE (Vine, 1966; Vogt and Byerly, 1976; etc.). This trend i s consistent with the magnetic data of Raff and Mason (1961), but there seems to be l i t t l e j u s t i f i c a t i o n for assuming that the ridge offset p a r a l l e l s this trend, since i t i s not p a r a l l e l to the direction of r e l a t i v e motion of the P a c i f i c and Juan de Fuca Plates at that point, and therefore could not be a normal ridge-ridge transform. The ridge offset has been shown as orthogonal i n F i g . 2, perhaps for no better .. reason than that i s the way i t theor e t i c a l l y "should" be. I t i s worth pointing out, however, that the Cobb Fracture Zone i s apparently v i r t u a l -ly aseismic (Tobin and Sykes, 1968), and thus i s not t y p i c a l of ridge-ridge transforms i n general. I t should also be noted that the sections of the Cobb Fracture zone east and west of the Juan de Fuce ridge are not p a r a l l e l to each other. These two sections have been given a single name but they may i n fact be two completely independent fracture zones which coincidentally intersect close to the Juan de Fuca Ridge offset. I t i s possible that Hey et al.'s (1980) concept of a "propagating f r a c -ture zone" may be applicable here; the situation in the area i s obviously complex, and further geophysical investigation would seem to be j u s t i f i e d . I t i s unfortunate that the Endeavour seismic p r o f i l e E7, which crosses the trend of the Cobb Fracture Zone, i s of much poorer quality than the other p r o f i l e s , and provides almost no r e l i a b l e information. 27 Coring A t o t a l of 29 coring stations were occupied during the 78-6 cruise, and 20 cores, of an average length of 93 cm, were recovered. The station locations are l i s t e d in Table I, and shown i n F i g . 5. Of the nine unsuccessful coring attempts, three (78-6-4, 5 and 27) were f e l t to be due to equipment deficiencies, as described in Chapter 3, and the remaining six (78-6-17, 24, 30, 35, 36 and 37) due to a lack of s u f f i c i e n t depth of sediment at the station location. In most of these cases the core cutter was observed to be chipped or scratched on recovery, and a few chips of black b a s a l t i c glass were recovered form the core catch-er on a few occasions. On the f i n a l unsuccessful attempt with the 2\ inch gravity corer (78-6-37), the pullout tension on the winch wire was extremely high and on recovery the corer b r i d l e was found to be bent. I t i s suspected that the corer barrel became trapped in a fissure in the bedrock. The cores are described on the following pages under the headings of geochemistry (pp. 27-41), mineralogy (pp.'41-50), and sedimentology (pp..50-59). Geochemistry Analyses of the major oxides are presented in Appendix 2 (pp. 113-120), and trace elements in Appendix 3 (pp.121-125). Selected elements of the ten longest cores are plotted against sample depth in F i g . 6. I t i s possible, on the basis of the geochemistry of these ten cores, to recognise three d i s t i n c t "geochemical u n i t s , " here designated Units 1, 2 and 3; the uppermost of which, Unit 1, can be further sub-divided.into three subunits, designated l a , lb and l c . Unit 2 can also be subdivided, into subunits 2a and 2b. The chemical characteristics 28 used to define the units and subunits are as follows: Unit 1: this unit i s characterised by low S i 0 2 , A1 20 3 , K 20 and T i 0 2 , and high MnO, Cu, Zn, Pb and N i . CaO and LOI (loss on ignition) are usually, though not invariably, high; Co seems to covary to some ex-tent with CaO. The t o t a l thickness of this unit varies from less than 5 cm to greater than 110 cm. The pattern of enrichment of the trace elements and MnO within the unit i s used to define the three subunits. Subunit l a , present in nine of the long cores (78-6-15 i s the sole exception), shows considerable enrichment in MnO, in a few cases by over an order of magnitude, but frequently a s l i g h t decrease in Cu, Zn and Ni compared with subunit l b . This subunit varies from 2 to 9 cm in thickness, and i s invariably brown in colour. Subunit lb shows a progressive upward enrichment of Cu, Pb, Zn and Ni, but MnO i s not enriched. The thickness of this subunit ranges from possibly as l i t t l e as 1 cm to 45 cm. Subunit l c i s the lowermost subdivision of Unit 1, and i t s upper l i m i t .is defined, somewhat subjectively, as the l e v e l at which the trace elements other than Co begin to show substantial enrichment; i t s base i s defined as the depth at which Si0 2 and A1 20 3 f i r s t become depleted, and this l e v e l usually, though not invariably, coincides with the depth at which most trace elements f i r s t become enriched. This subunit, where present, ranges from 10 to 40 cm in thickness. Thus, in summary, N i , Zn, Cu and Pb show s l i g h t enrichment from the base of l c upwards and substantially more enrichment from the base of lb upwards, while MnO i s enriched only in l a . 29 Unit 2 with a minimum thickness of 20 cm, shows high concentra-'. tions of Si0 2 , A1 20 3 ,, K 20 and Ti0 2 , compared with Unit 1, and low MnO, Cu, Pb, Zn, Ni and, usually, CaO. Fe 20 3 and Co are usually also s l i g h t l y depleted, though this tendency i s less well marked than that of the other components. In core 78-6-15, MnO shows enrichment close to the top of t h i s u n i t , with f a i r l y constant values throughout the rest of the core. This unit i s somewhat tentatively subdivided into two subunits: Subunit 2a i s , in a sense, t r a n s i t i o n a l between Units 1 and 2, in that i t shows some variation in concentrations of Si0 2 and A1 20 3. I t appears to be present in .only a few cores, and i s most strongly developed in 78-6-16 where i t has a thickness of about 40 cm. Subunit 2b i s "genuine" Unit 2, with high Si0 2 and A1 20 3 through-out, as described above. Unit 3, of i n d e f i n i t e thickness, i s present only in cores 78-6-1, 6, 8, 19 and 20. I t exhibits depletion in S i 0 2 , A1 20 3, K 20 and T i 0 2 , and enrichment in CaO, MnO and a l l trace elements r e l a t i v e to Unit 2. Once again, MnO behaves d i f f e r e n t l y in a single core, showing enrichment at the top of t h i s unit in core 78-6-19, with r e l a t i v e l y constant values below. Core 78-6-18 Most of the shorter cores show the same pattern as that outlined above for Unit 1; there i s , however, one notable exception. Core 78-6-18 shows extremely high CaO, and some enrichment of LOI, MnO, Co and Pb, but most other components show depletion when compared with the average composition of a l l the other cores; this i s most probably simply an ef-fect of d i l u t i o n by CaO, but i t was f e l t that this core might have a 30 S i Q 2 % A l 2 0 3 % F e 2 0 3 % C a O % MnO % LOI % 120 L Cu ppm Pb ppm Zn ppm Co ppm Ni ppm Units 120 L Core 78-6-1 F i g . 6. V a r i a t i o n with sediment depth of selected major oxides and trace elements from the ten longest cores; data from Appendix 2 (major oxides) and Appendix 4 (trace elements). Also shown are the geochemical units derived from t h i s data. F i g . 6. Continued. 32 120L Core 78-6-7 F i g . 6. Continued. 33 F i g . 6. Continued. r 34 Cu ppm Pb ppm Zn ppm Co ppm Ni ppm Units 120L Core 78-6-9 F i g . 6. Continued. 35 Core 78-6-12 F i g . 6. Continued. 36 Cu ppm Pb ppm Zn ppm Co ppm Ni ppm Units Core 78-6-15 F i g . 6. Continued. 37 Core 78-6-16 F i g . 6. Continued. 38 , o w Core 78-6-19 F i g . 6. Continued. 39 Cu ppm Pb ppm Zn ppm Co ppm Ni ppm Units Core 78-6-20 F i g . 6. Continued. Average values for selected components in units 1, 2, and 3, and cores 78-6-18 and 40, compared with other pelagic and hydrothermal sediments. r o i — l ON r-H m o 00 m CN m <f m CN m m i—l i—i r o o r-H CN r~ 00 O O CN i—i CN CN i-H VO i—l i—l CN O r - l CO 00 CN 1 O m r o i - l CN <r i n ON CN i — l T-f CN CO o co o ON O i 1 i—l i-H CN i n i — i m i n 00 o> 00 ON o o m o o - i n 00 r-H ON .-i O ON m o o m r-H o • • • • • . • a r o r o oo m CO CN CN r-H i - l CO r o 00 00 • • • . • o o o o o 00 <r o m o r-i r o CN i—i CN r o 1—1 • • • . . a a O o o O o rH CM vO 1—1 ON CN CN CN ON CN . . . • a m ON CN ON <f i—l i-H r~ vO CO o CN o r o i — l ON 00 • . . . a • a a ON ON CN m r-H r-H i—i CN r~ o i n 00 CN O 00 r o CO C^ • • • . • . a • CN i n r o ON r o l-H i - l i—i r-H i—i i—i CO o ON o 00 •<)• i n i - l o m CN <r o a . • . a • CN i n r o 00 ON 00 m r o •o- r-H i n ^— m O 60 00 4J ON H-l • H u i n i—l o 14-1 01 ON X • H ,£3 r—t o ^—' o a • cn cd i—i •> cd i — l i - l 1—1 •rH ft o ia CJ cd cd cd pq 00 o CO e P. 6 !-( CN r o i—l o - Z w - H rH H-l Ol rH 1 1 13 CJ 01 Ol CJ +J 4-1 4-> vO M a m o r S P Xi ca • H •rH • H 1 1 Cd -rH x, o H-l rH u 0) / - \ c C C co 00 U 60 U o Ol u o i-H CO !=> 0) Cfl rH 1—1 rH (X 01 u !>. > r - l < r-H •i-l T3 nj ON <3 a) CJ >, PM cd - PH ° 3 P Xi * — pq Xi 41 si g n i f i c a n t hydrothermal component, due to i t s sedimentary characteristics (see p. 58). This point i s discussed more f u l l y at a l a t e r stage. The average values of the most important components in each of the above "geochemical u n i t s " and in cores 78-6-18 and 40 are l i s t e d in Table I I , together with values quoted in a number of publications for vairous pelagic and hydrothermal sediments from the P a c i f i c Ocean, for comparison purposes. Mineralogy The core mineralogy presented here (Appendix 4 and Fig. 8) i s derived from XRD analyses, as previously mentioned (Fig. 7). A very strong peak at 3.35 A, and a smaller peak at 4.26 A, indicate the presence of a-quartz; the 3.35 A quartz peak i s almost invariably the strongest peak present. Another pronounced peak at 3.20 A i s characteristic of the plagioclase feldspars, and the small amplitudes of the other plagioclase peaks (4.04 and 3.66 A) indicate low-temperature a l b i t e as the dominant variety. No trace was found of any of the characteristic peaks of '. . K-feldspar (orthoclase, 3.31, 3.77 and 4.22 A; microcline, 4.22 and 3.26 A; or sanidine, 3.22 and 3.26 A). I t i s possible that a weak 3.22 A sanidine peak could be screened by the adjacent 3.20 A peak of plagioclase; how-ever sanidine i s generally r e s t r i c t e d to potash-rich volcanic rocks such as r h y o l i t e and trachyte (Berry and Mason, 1959), which are uncommon in the adjacent continental areas (Washington and B r i t i s h Columbia). Ortho-clase, the expected variety in view of the composition of the supposed source rocks, appears to be d e f i n i t e l y absent. This point i s discussed further in the next chapter. A prominent peak at 3.04 A (not present in every sample) i s characteristic of c a l c i t e ; t h i s mineral i s thought to be predominantly 42 biogenic in o r i g i n , the major component of foraminiferal tests and other planktonic debris. Clay minerals Clay minerals are i d e n t i f i e d on the basis of the basal (001) re-fle c t i o n s of oriented samples. Strong 10 A and 5 A reflections indicate mica (most probably i l l i t e , the low-K, hydrated form of muscovite), and a rather diffuse peak at about 14 A which expands to about 17 A on glycola-tion indicates montmorillonite (smectite). A weak 14 A peak, unaffected by glycolation, indicates c h l o r i t e ; strong peaks at 7 A and 3.5 A are char-a c t e r i s t i c of either' c h l o r i t e or k a o l i n i t e . K a o l i n i t e i s an unexpected component of temperate-zone marine clays, and i s usually understood to be abundant only in areas of intense t r o p i c a l weathering (Grim, 1958; C a r r o l l , 1969). The 7 A and 3.5 A peaks of the present samples disappear or are much reduced in amplitude on heating to 500°C for 1-2 hours. The ka o l i n i t e structure i s usually reported to be destroyed on heating to 550°C, while c h l o r i t e i s unaffected ( C a r r o l l , 1969); however, Brindley (1961, p. 263) reports that poorly c r y s t a l l i s e d Fe-rich c h l o r i t e s break down at temperatures as low as 450°C. When the samples were heated at 80°C with 2N hydrochloric acid for 1-2 hours before the slides were pre-pared, i t was found that the 7 A and 3.5 A peaks disappeared or were substantially reduced; this i s characteristic of c h l o r i t e (Brindley, 1961). Other evidence in favour of the i d e n t i f i c a t i o n of this mineral as c h l o r i t e rather than k a o l i n i t e or a c h l o r i t e - k a o l i n i t e mixture i s as follows: a) Absence of the 2.38 A peak characteristic of k a o l i n i t e ; b) Presence of a non-expanding 14 A peak which behaves i n the same way as the 7 A and 3.5 A peaks in response to the 43 8 i s 30° 25° 20° 15° 10° 5° —i 1 1 1 i Diffraction angle 26 F i g . 7. Representative X-ray diffractograms, showing effect of various treatments: (a) no treatment (b) Glycolation, 48 hours (c) 2N Hydrochloric acid at 80°C; 2 hours (d) Heating to 500°C, 2 hours. 44 % clays % clays F i g . 8. V a r i a t i o n with sample depth of clay minerals in the ten longest cores; data from Appendix 4. S o l i d l i n e s - montmorillonite. Dashed " - i l l i t e . Dotted " - c h l o r i t e . F i g . 8. Continued. 46 various treatments outlined above; c) Presence of a 4.75 A peak characteristic of c h l o r i t e . The slow-scan technique for distinguishing c h l o r i t e from k a o l i n i t e described by Biscaye (1964) was t r i e d and seemed to indicate the presence of c h l o r i t e and absence of k a o l i n i t e , but i t was f e l t that this technique i s unreliable due to the wide variations reported in the peak positions for various v a r i e t i e s of c h l o r i t e and k a o l i n i t e in the ASTM d i f f r a c t i o n f i l e s . The composition of the clay mineral fraction of the sediments as shown in Appendix 4 i s based on measurements of the areas of the 7 A ( c h l o r i t e ) , 10 A ( i l l i t e ) and glycol-expanded 17 A (montmorillonite) peaks, multiplied by the factors proposed by Heath and P i s i a s (1979), i . e . 1.0, 9.4 and 1.1 for montmorillonite, i l l i t e and c h l o r i t e respectively. Unfor-tunately, the XRD analyses for t h i s study had been completed before the publication of Heath and P i s i a s ' paper, so that their t a l c internal stan-dard technique for estimating clay mineral proportions could not be used. The values reported here, however, are f e l t to be, i f not p a r t i c u l a r l y accurate, at least self-consistent. Minor components No trace was found in any of the samples of ref l e c t i o n s indicative of the manganese minerals 6-Mn02, manganite and pyrolusite, nor of the species todorokite and bi r n e s s i t e , reported by Co r l i s s et a l . (1978) in crusts from hydrothermal mounds on the Galapagos Ridge. This i s so even where the MnO content of the sediments exceeds 3%, in the surface layers of cores 78-6-38 and 39. This i s probably an indication that Mn minerals are present in an amorphous or cryptocrystalline form. S i m i l a r l y , 47 no trace was found of any of the common Fe oxides or hydroxides. A very small quantity of amphibole is indicated in most samples by a small peak at about 8.45 A. Estimation of non-clay minerals No satisfactory method yet exists for even a semi-quantitative estimation of the abundances of minerals other than clays (Heath and Pisias (1979) state that "because of ... poor relative analytical precisions for quartz, plagioclase and amphibole, stable factors for these minerals could not be generated."). The technique outlined here, while almost certain to be imprecise, has the virtue of simplicity and rapidity of calculation. F i r s t i t was assumed that, since the characteristic diffractogram peaks are absent, no K-feldspar was present in any of the samples. This permitted the further assumption that a l l the potassium in the samples was contained in the clays, an assumption supported by the work of Goldberg and Arrhenius (1958), who report that most of the potassium in their samples of Pacific Ocean pelagic sediments was incorporated in clays. Figures for the average concentration of K 20 in clay minerals were taken from Grim (1958); a figure of 5.95% was obtained for i l l i t e (average of 11 published analyses), and 0.31% for montmorillonite (average of 7 analyses). No K 20 was reported in any of 7 analyses of chlorite. Thus, using the K 20 values for the bulk sediments listed in Appendix 2, i t is possible to calculate the percentage of total clays in each sedi-ment sample: % Total clay = K s X 1 0  (5.95 C. + 0.31 C ) I m 48 where K = % K,0 i n sediments, from Appendix 2, s i C\ = % i l l i t e in t o t a l clay, C = % montmorillonite in t o t a l clay, m It i s then a straightforward matter to calculate the percentage of each clay mineral i n the t o t a l sediment, e.g. % i l l i t e i n seds. = C. x % t o t a l clay 6 I etc. 100 It i s further assumed that material of biogenic o r i g i n i s repre-sented by: CaC03 = (CaO - 0.19 (A1 20 3)) x 1.78. This equation i s derived as follows. It can be seen that the r a t i o of CaO to A1 20 3 in the samples (Appendix 2) shows a well defined minimum value of about 0.19 (Table I I I ) ; i t has been suggested ( G r i l l , pers. comm., 1980) that those samples having this minimum Ca0/Al 20 3 r a t i o are without biogenic CaO, i . e . : CaO,, . . v = CaO, >. - 0.19 (A1,0 3). (biogenic) (total) 2 3 Then: Mol. Wt. CaCO, 100.09 = 1.78 Mol. Wt. CaO 56.08 Table I I I . The f i v e samples having lowest Ca0/Al 20 3 r a t i o s ; data from Appendix 2. Sample No. CaO/Al 20 3 78-6-12/50-52 0.184 15/0-2 0.190 16/70-72 0.193 25/10-14 0.195 40/0-5 0.188 Average 0.190 There i s , perhaps, less j u s t i f i c a t i o n for this assumption/than for those made previously; other components of the sediments are almost certain l y biogenic, notably P 2 0 5 a n c* possibly some of the trace elements. Part of the loss on i g n i t i o n (LOI) i s most probably due to loss of C02 from carbon-ate species; i t i s obvious from F i g . 6 that CaO and LOI covaryy i n some cores, notably 78-6-8 and 20. However, there i s f e l t to be i n s u f f i c i e n t j u s t i f i c a t i o n for regarding the whole of the LOI as biogenic, since a si g n i f i c a n t (and variable) part of the LOI may be due to loss of adsorbed and interlayer water and OH groups from the clays, since the samples were only ai r - d r i e d at room temperature before being sent for analysis. In addi t i o n , some Si 0 2 may be biogenic, in the form of diatom and radiolarian tests However., this factor i s probably of small magnitude; Si0 2 and A1 20 3 show very strong covariance (see Fig. 6), which suggests that both are of sub-s t a n t i a l l y the same origin, ( i . e . terrigenous), and these two elements seem to show a s i g n i f i c a n t negative correlation with CaO, especially in cores 78-6-6, 8, 19 and 20 (Fig. 8). A check on the accuracy of this procedure i s possible, since the samples from core 78-6-18 were analyzed for CaC02 as well as CaO; a com-parison of these results with those obtained by the method outlined above i s presented i n Table IV. Table IV. Comparison of measured and calculated CaCO values, core 78-6-18 Sample no. 78-6-18A/0-1 5-6 10-11 115-16 CC* B/6-V. 5-6 15-16 % CaC03  (measured) 26.1 31.6 40.9 35.9 36.9 36.0 33.7 28.3 %JCaC03  (calculated) 24.35 30.94 38.81 32.71 33.83 32.70 31.63 26.11 Error % of meas. value) -6.7 -2.1 -5.1 -7.8 -8.3 -9.2 -6.1 -7.7 *Note: CC = sample recovered from core catcher. 50 (Measured CaC03 values i n Table IV are based on the difference be-tween the i n i t i a l weight of each sample and i t s weight after leaching with ammonium acetate at a pH of 4.5; G r i l l , pers. comm., 1980.) Thus i t i s seen that the calculated values are systematically low, by an average of 6.6%. I t i s probable that those samples having the minimum Ca0/Al 20 3 values, previously mentioned, s t i l l contain a small amount of carbonate; thus the correction factor 0.19 in the equation on p. 48 i s probably too high. This leaves between 25 and 40% of the sediment weight unaccounted fo r , after subtraction of loss on Ignition (see Appendix 4). The very strong a-quartz and plagioclase peaks present in the diffractograms, and the absence of s i g n i f i c a n t peaks corresponding to other minerals, leads to the conclusion that t h i s remaining material must consist predominantly of those two minerals. These proportions seem reasonable i n view of the close proximity of the source area for terrigenous sediments. Thus i t can be seen that Duncan et al.'s (1970) assumption that clay minerals represent 100% of Cascadia P l a i n sediments i s u n j u s t i f i a b l e and may lead to results that are seriously in error. Sedimentology General characteristics The sedimentology of the 10 longest cores used in this study, and core 78-6-18, i s i l l u s t r a t e d in Appendix 5. The interpretations are based on both v i s u a l and X-ray radiographic examination of the cores. In most cores (the exception i s , once again, 78-6-18), three d i s t i n c t sediment types, and a fourth, t r a n s i t i o n a l type, can be recognised. For conven-ience, these are designated here as Types A, B, C and B/C. 51 Type A This type occurs invariably at the top of each core (except 78-6-15, where i t i s absent), and consists of a thin (2-10 cm, average 3 cm) layer of very fine grained, very soft to semi-fluid, medium to dark yellowish bEown l u t i t e (Munsell 10YR 5/4 to 10YR 2/2). In many cases part of th i s surface layer was lo s t during s p l i t t i n g and examination of i the cores due to i t s semi-fluid nature, and the thicknesses quoted are thus minimum values; i t s absence from core 78-6-15 may be due to i t a l l having been lo s t in this way. In a l l cores in which t h i s unit i s present, a strong positive MnO anomaly i s also present i n the uppermost (0-2 cm) geochemical sample, amounting i n a few cases to over 20 times the average for the rest of the core. The dark brown colour i s thought to be due to the presence of amorphous or cryptocrystalline Mn oxides (Hartmann, 1979). Type B Sediment Type B consists of a l i g h t to medium ol i v e grey or greenish grey clayey to s i l t y l u t i t e (Munsell 5Y 5/1, 5Y 5/2, 5GY 5/1), which i s v i s u a l l y almost structureless but in the X-ray radiographs shows evidence of extensive bioturbation, i n the form of strong mottling and the absence of any pre-existing sedimentary structures (see Type C, below). Also present are sediment-filled burrows, 8-15 mm in diameter and generally horizontal or subhorizontal, and numerous randomly oriented f i l l e d burrows 2-3 mm in diameter (Plates 1 and 2). Farrow (pers. comm., 1979) has suggested that the larger burrows were produced by Zoophycos (Ha'ntzschel, 1962; Seilacher, 1964; Simpson, 1970). The burrows are indeed v i s u a l l y very similar to the published i l l u s t r a t i o n s of Zoophycos burrows, however most sources report Zoophycos burrows to be only 1-4 mm in diameter. . 9. Covariation between CaO and ( A l 2 0 3 + S i 0 2 ) in Juan de Fuca Ridg sediments. Plate 1. Sediment Type B; part of core 78-6-19, showing typ i c a l mottling and small scale bioturbation. F u l l size. 54 Plate 2. Sediment Type B; part of core 78-6-20, showing sediment-filled burrows believed to be due to Zoophycos. 55 This sediment type appears to be the commonest of the three types, and frequently comprises 80% or more of individual cores; for example, 78-6-19. Type C Sediment Type C i s v i s u a l l y very similar to Type B, but often exhibits small-scale colour variations, individual layers ranging from a few mm to 2-3 cm i n thickness, and varying in colour from medium ol i v e grey or greenish grey to pale yellowish grey (Munsell 5Y 4/1 to 5Y 5/2). The material i s predominantly clayey or s i l t y l u t i t e , but with a few thin (2-3 cm) layers of s i l t y sand. In the X-ray radiographs this sediment type i s seen to have a f i n e l y laminated structure (Plate 3); t y p i c a l l y , a layer of sediment 5-30 cm thick, averaging about 10 cm, consists of fine (2 mm or less) horizon-t a l laminations at the base, grading upwards into poorly laminated or almost structureless sediment. Wavy or distorted laminae are present l o c a l l y , and occasionally the contacts between layers show evidence of erosion, in the form of truncated laminae and irregular contacts. This i s especially well shown i n core 78-6-12, at about 44 cm depth (Plate 4). Bioturbation i n t h i s sediment type i s r e s t r i c t e d to occasional 8-15 mm diameter f i l l e d burrows. Where Types B and C are both present i n a core, Type B almost invariably overlies Type C. Type B/C A type intermediate between Types B and C, showing sig n i f i c a n t mottling and bioturbation but also having poorly defined layering, i s present in some cores, and i s designated Type B/C (Plate 4). 56 99.7 cm 120.0 cm ate 3. Sediment Type C. Base of core 78-6-12, showing t y p i c a l coarse-and fine-layered structure. The section shown grades from clay down-wards to fine sand. Curved laminae at base are due to d i s t o r t i n g effect of core catcher. Plate 4. Sediment Types B/C (top) and C (bottom); part of core 78-6-12. Also shown (arrowed) i s an eroded contact between two Type C layers. A single sediment-filled burrow (?Zoophycos) i s v i s i b l e at the lower extremity of this section. 58 Non-terrigenous components Calcareous organic remains, mainly foraminiferal tests, are pres-ent i n most cores, in abundances estimated to be about 5-15%, and a few very thin (2-5 mm) layers of extremely foraminifera-rich sediment are present, notably i n cores 78-6-15, 16 and 20. These layers frequently coincide with the contacts between Type C sediment layers, and seem to be entirely r e s t r i c t e d to Type C. Any such layers which might have been present i n Type B sediments would most probably have been disrupted by subsequent bioturbation. Small angular shards of volcanic glass, averaging about 1 mm in diameter, are present i n a few cores, and are notably abundant in 78-6-9, where they may form up to 2-3% of the t o t a l sediment over a 30 cm length of the core. These are undoubtedly of l o c a l o r i g i n . Core 78-6-18 This core, i n contrast to a l l the others, consists en t i r e l y of rather soft, foraminefera-rich yellowish brown s i l t y l u t i t e (Munsell 10YR 5/2) containing abundant angular fragments of black b a s a l t i c glass of up to 5 mm in diameter. The X-ray radiographs of this core show l i t t l e discernable sedimentary structure. A single angular irregularly-shaped fragment of highly fractured ba s a l t i c material measuring approximately 3 cm x 3 cm x 5 cm was found on top of t h i s core on recovery. I t was extremely b r i t t l e , and shat-tered on being diamond-sawn for a thin section. However, a section was made of some of the pieces, which revealed i t to consist of glassy to very f i n e l y c r y s t a l l i n e , almost opaque, dark brown to black material in which individual mineral grains could not be i d e n t i f i e d . I t s colour 59 and opacity suggest a mafic composition. A coating of medium to dark brown, amorphous material covered most of the outer surface. 5. DISCUSSION Similar sediments in Adjacent areas The geochemical units described above show certain s i m i l a r i t i e s to those reported to occur somewhat to the north of the present area by Bornhold et a l . (in prep.). Unit l a , as described here, seems similar in a l l respects to Bornhold et al.'s Unit 2; the i r " t r a n s i t i o n u n i t , " Unit 3, seems similar to the present Unit 1, subunits b and c, and their Unit 4 corresponds to the present Units 2 and 3. Bornhold et a l . define their units on the basis of v i s u a l sedimentary characteristics (mainly colour); their sampling procedure differed from that used i n the present study, i n that only one or two samples were taken from each unit, at irregular intervals (Bornhold, pers. comm. 1980). A more meaningful comparison might be made had similar sampling procedures been used. No trace of the l i g h t grey surface layer designated by Bornhold et a l . as Unit 1 was found i n any of the cores examined i n the present study. A similar l i g h t grey surface deposit has been previously re-ported by Bramlette (1961) i n deep sea samples, and was designated by Horn et a l . (1970) as being characteristic of the i r Central North P a c i f i c sedimentary province. However, the area of the present study and much of the area cored by Bornhold et a l . i s within the areas 60 61 designated by Horn et a l . as the Northeast P a c i f i c Turbidite Province and the Ridge and Trough Province, where no l i g h t grey surface sediment would be expected. I t i s possible that some of these province boundaries might require adjustment as new evidence i s forthcoming. The present area - broad correlations In order to make a meaningful interpretation of the data collected during the 1978 cruise, i t must be assumed that the contacts between the geochemical units described above can be regarded as synchronous, and that the characteristics of these units are solely or predominantly a function of the prevailing sedimentary regime at the time of the deposi-t i o n ; also, that the sedimentary regime was essent i a l l y the same through-out the region at any given time. I t i s apparent that the boundaries between the geochemical units and the sedimentary types i n the present area do not, in general, coin-cide, except that subunit l a invariably consists of sediment Type A. However, there seems to be a tendency for Unit 1 to have a higher propor-tion of sediment Type B than either Units 2 or 3; this tendency can be seen from Appendix 5, and i s especially true of cores 78-6-12, 15 and 16. Also Unit 1 (subunits b and c) seems to be generally more uniform in colour and type (though not i n chemical composition) than the other units; a possible r e f l e c t i o n of a greater degree of homogenisation by bioturbation, which may be related to a lower sedimentation rate. This supposition gains support from the work of Arrhenius (1952), who, after examining cores from the east P a c i f i c Ocean, concluded that: The occurrence of digging structures ... may be taken as a characteristic of normal pelagic deposits. The lack of such structures indicates abnormal conditions, probably a very high rate of sedimentation. 62 Ericson et a l . (1961), working with cores from the A t l a n t i c Ocean, concurred with this view, and concluded that " s i g n i f i c a n t mixing of sedi-ment by burrowers i s confined to the uppermost 5 cm" of sediment. The lack of chemical,uniformity i n Unit 1 trace element abundances may be due to diagenesis, i.e. a process of chemical "de-homogenisation" whose e a r l i e s t stages would ha/e been masked by the bioturbation, but which continued after the cessation of b i o l o g i c a l a c t i v i t y . Indeed, subunit l a seems to be similar to surface sediments described by Lynn and Bonatti (1965), to which they ascribe a diagenetic o r i g i n ; i t seems a reasonable supposition that si m i l a r diagenetic processes have occurred in the present area. This supposition i s discussed further below. Sedimentary regimes The question next arises: what, i f anything, does the composition of the individual geochemical units indicate about the sedimentary regime at the time of the deposition? I n t u i t i v e l y , i t would seem that a sediment high i n Si0 2 and A1 20 3 and low i n CaO would indicate predominantly t e r r i -genous sedimentation, r i c h i n quartz, feldspar and d e t r i t a l clays, whereas a sediment with the opposite c h a r a c t e r i s t i c s , i.e. low Si0 2 and A1 20 3 and high CaO, indicates a more pelagic regime, dominated by biogenic material. This d i s t i n c t i o n i s , of course, v a l i d only for sedimentation above the carbonate compensation depth (Berner, 1971). Thus the lower-most unit, Unit 3, which averages 9.8% CaO (10-20% biogenic material; see Appendix 4), represents a regime with a high pelagic component, while Unit 2, which has less CaO and correspondingly more Si0 2 and A1 20 3, results from a sedimentary regime dominated by continent-derived de-t r i t a l material. Unit 1, on this basis, i s rather less well characterised; 63 i t s S i0 2 and A1 20 3 content i s comparable to that of Unit 3, but i t s CaO content i s more variable and usually much lower than Unit 3 and, occasion-a l l y , lower than Unit 2 (see F i g . 6, especially cores 78-6-1, 6, 9, 15 and 16). I t i s noticeable that the biogenic content of the sediments seems to be an inverse function of water depth (Fig. 10). Hamilton (1967) and Horn et a l . (1970) propose that the depositional regime i n the north-east P a c i f i c Ocean changed from predominantly t u r b i d i t i c to predominantly pelagic at the Pleistocene/Holocene boundary, arguing that the near cessation of g l a c i a l erosion at t h i s time resulted i n a considerable reduction i n terrigenous sediment volume, thus allowing pelagic sedimenta-tion to become more dominant. If t h i s hypothesis i s accepted in the present area, the Si0 2 and A l 2 0 3 - r i c h deposits of Unit 2 may represent sedimentation during the f i n a l (Wisconsin) stage of the Pleistocene g l a c i -ation, while the CaO-rich sediments of Unit 3 belong to the Sangamon Interglaciation (230,000 to 110,000 years B.P.; Douglas et a l . , 1976, p. 678), and Unit 1 consists of post-glacial deposits. The r e l a t i v e lack of biogenic material ( i . e . carbonate) i n the most recent sediments could be due to the post-Glacial r i s e in sea l e v e l and the corresponding r i s e i n the carbonate compensation depth; although i f t h i s i s the case, Unit 3 should be s i m i l a r l y affected. No radioactive age dating was done on the sediments i n t h i s study; i t would have given precise answers to the problems outlined above. In absence of t h i s , a more qu a l i t a t i v e approach i s indicated. Sedimentation rates Opdyke and Foster (1970), Kulm and Fowler (1974) and other workers have reported an average Peistocene sedimentation rate of 10 cm/1000 yr 64 Water depth, m x 100 Fig. 10. Variation of biogenic component ( i . e . carbonate) with water depth, showing effect of depth on carbonate s o l u b i l i t y . Core 78-6-6 appears to be anomalous. 65 for the Cascadia P l a i n . If this rate i s assumed to apply also to the area of the present study, then the longest core obtained (78-6-19, 175 cm) should represent about 17,000 years of sedimentation, and should penetrate the Pleistocone/Holocene boundary at somewhat less than 70 cm depth (since sedimentation rates during the Holocene have presumably been less than 10 cm/1000 y r ) . Thus the thickness of Unit 1, at least, i s of the right order of magnitude, but Unit 2 i s much too thin to represent the whole of the Wisconsin stage. In any case the figure of 10 cm/1000 yr may even be too low; Barr (1972) reported evidence for sedimentation rates of up to 170 cm/1000 yr i n places on the northern end of the Juan de Fuca Ridge, and Davis et a l . (1976) have calculated that rates i n a few locations at the northern end of the Ridge may be as high as 600 cm/1000 yr. Accordingly, estimates were made of sediment thicknesses in the study area using the seismic p r o f i l e s obtained during the 1978 cruise (Appendix 1), and sedimentation rates were calculated by assuming a spreading half-rate of 3.0 cm yr 1, a seismic vel o c i t y in unconsolidated sediments equal to that i n sea water (1490 m s 1; McQuillin and Ardus, 1977), and no allowance for compaction (Table V); they thus represent minimum average rates. At the f i v e chosen locations (see F i g . 3) the calculated sedi- „ mentation rates range from 40 to 233 cm/1000 yr, and average 116 cm/1000 yr, i .e. an order of magnitude higher than the rates proposed by Opdyke and Foster (1970) and Kulm and Fowler (1974) for the Cascadia P l a i n Pleistocene sediments. I t i s apparent from these figures that sedimentation rates vary widely even within a f a i r l y r e s t r i c t e d area of the ridge complex; the f i v e locations were chosen quite a r b i t r a r i l y as points at which a f a i r l y 66 Table V. Sedimentation rates at selected locations (see F i g . 3) Location (fig.3) P r o f i l e Distance from ridge crest (km) Time (yr) Sediment thickness (jn) Sedimenta-tion rate (cm/1000 yr) (1) (2) (3) (4) (5) E2 E3 E5 Tl IT 8.5 E 10.75 W 27.5 W 28.75 E 6.5 W 283,000 355,000 907,500 949,000 214,500 182 272 363 1583 500 65 76 40 167 233 average 116 strong basement r e f l e c t i o n allowed easy estimates to be made of sediment thickness, and i t seems certain that a much wider range of sedimentation rates exists than was actually found. The maximum rate calculated here (233 cm/1000 yr) occurs i n a 5 km wide, branching valley (see F i g . 3), which probably receives slumped sediments from a wide area of the ridge complex and may be a channel for t u r b i d i t y currents coming from the Explorer Plate, to the north of the Sovanco Fracture Zone. The lower rates are c h a r a c t e r i s t i c of smaller valleys and hollows, which probably receive sediments from a much more r e s t r i c t e d area. Other evidence Sediment Type C, described i n Chapter 4, consists of layers of an average thickness of 10 cm, occasionally with erosional contacts, each layer consisting t y p i c a l l y of f i n e l y laminated s i l t y l u t i t e grading upwards into structureless c l a y - r i c h l u t i t e . In a few cases wavy laminae are present, generally towards the base of a layer, and foramini-f e r a l remains also seem i n general to be concentrated at the bases of individual layers. These structures seem i d e n t i c a l to the uppermost units (D and E, or i n a few cases possibly C, D and E) of the Bouma tur b i d i t e sequence (Bouma, 1962). This suggests that Type C sediments 67 are d i s t a l t u r b i d i t e s , or possibly proximal "microturbidites" of l o c a l l y -derived fine-grained material. In an individual flow, the larger p a r t i -cles (in t h i s case, foraminiferal tests) would s e t t l e out f i r s t , followed by f i n e l y laminated s i l t y l u t i t e (Bouma d i v i s i o n D or C-D); the f i n e s t , clay-size p a r t i c l e s would then s e t t l e r e l a t i v e l y slowly as an almost structureless " i n t e r t u r b i d i t e " (Bouma d i v i s i o n E). This whole deposi-t i o n a l process might be completed in a matter of a few days, or possibly even hours - an i l l u s t r a t i o n of the fact that to speak of "average" sedi-mentation rates may be misleading i n t u r b i d i t e areas. If Opdyke and Foster's (1970) figure of 10 cm/1000 yr i s taken as representative of sedimentation rates in the area during the P l e i s t o -cene, this would necessitate a single turbidity-current event every 1000 years, on average. In view of the almost continuous seismic a c t i v i t y i n the area (260 seismic events i n a ten year period, reported by Tobin and Sykes, 1968), this i s f e l t to be u n r e a l i s t i c . Griggs and Kulm (1970) present evidence f o r an i n t e r v a l of about 500 years between t u r b i d i t y current events i n Cascadia Channel during the Holocene; the in t e r v a l during the Pleistocene would almost cert a i n l y have been much shorter. Duncan et a l . (1970) report that Pleistocene l u t i t e s in the Cascadia P l a i n contain more i l l i t e and less montlmorillonite than those of the Holocene. However, their figures are not d i r e c t l y comparable to those presented here, since they use Biscaye's (1965) unmodified semi-quantitative method for estimating clay abundances. They also assume that the clays constitute 100% of the sediments i n the area, an assump-tion which i s t o t a l l y unwarranted, as has been seen. In any case, the use of this observation as a c r i t e r i o n for recognising the Pleistocene/Holocene boundary i s probably only v a l i d 68 for that part of the Cascadia P l a i n which receives sediments from the Astoria Fan, since Duncan et a l . (1970) i n f e r that the change i n clay mineral proportions results from a change in the r e l a t i v e importance of the Snake River and Upper Columbia River sediments to the t o t a l sedi-ment load of the lower Columbia, and thus of the Astoria Fan. Similar conditions almost cert a i n l y do not apply to other areas. The clay mineral abundances found i n t h i s study (Appendix 4 and F i g . 8) seem to bear this out; while some cores, notably 78-6-1, 15, 16 and 19, do i n fact show a t r a n s i t i o n from low- to h i g h - i l l i t e at the base of Unit 1, others (78-6-6, 8 and 12) seem to show the opposite tendency. I t would seem that, while Unit 1 almost certainly represents Holocene sedimentation, and the t r a n s i t i o n to Unit 2 defines the P l e i s t o -cene/Holocene boundary, Unit 3 cannot be as early as Sangamon. The f o l -lowing explanation i s proposed, purely as speculation. The Si0 2 and A l 2 0 3 - r i c h deposits of Unit 2 represent sedimentation close to the end of the Pleistocene, when extremely large quantities of d e t r i t a l material were released catastrophically over a r e l a t i v e l y short period of time as the glaciers retreated, resulting i n substantial increase i n the terrigenous component compared with Unit 3; the l a t t e r , which represents sediment deposited during the Wisconsin g l a c i a l stage, i s much richer in pelagic ( i . e . biogenic) material, f i r s t l y because continent-derived d e t r i t a l material was largely immobilised by ice cover, and secondly because the lower sea l e v e l resulted in less carbonate dissolution before deposition. The r e l a t i v e l y CaO-depleted sediments of Unit 1 were depos-ited i n deeper water during the Holocene, with the result that more CaC03 tended to dissolve i n the seawater column. Other factors (e.g. pH and temperature) are also involved i n carbonate d i s s o l u t i o n , but the 69 above outline, while tentative, would seem to account for the observations. If the r e l a t i v e absence of extensive bioturbation i n Units 2 and 3 i s accepted as further evidence of rapid deposition, as proposed by Arrhenius (1952), the above explanation would seem at least plausible. Trace elements The trace element concentrations (Appendix 3 and F i g . 6), for the most part, show a strong negative correlation with Si0 2 and A1 20 3. MnO, Cu, Pb, Zn and Ni a l l show enrichment i n Units 1 and 3, and deple-tion i n Unit 2. Co seems also to show s l i g h t enrighment i n Units 1 and 3, on average (see Table I I ) , but unlike the other trace elements i t seems to exhibit no consistent pattern of enrichment and depletion. (The abundances of Co and Pb i n these samples are i n many cases, close to the l i m i t of detection (approximately 4 ppm); the apparently unsystematic variations i n these elements v i s i b l e in F i g . 6 can probably be attributed to a n a l y t i c a l errors.) The general indication seems to be that the trace elements, for the most part, are either derived from a non-terrigenous source, or have been diagenetically remobilised since th e i r o r i g i n a l time of deposition -or possibly both. A hydrothermal source would be one p o s s i b i l i t y . Hydrothermal sediments vary widely i n chemical composition. Rona (1978) tabulates ranges of values found for both major and trace elements of a t o t a l of twenty-one examples of hydrothermal encrustations, concre-tions and sediments from seventeen locations, including the East P a c i f i c Rise, Mid-Atlantic Ridge, Red Sea, Afar R i f t , Indian Ocean Ridge, and basal sediments from both A t l a n t i c and P a c i f i c Oceans. A few examples of the ranges of compositions found are as follows: 70 Si0 2 , 0.4 - 55%; A1 20 3 , 0 - 23%; Fe 20 3 , 0 - 73%; MnO, 0 - 75%; Fe/Mn r a t i o , 0.0002" 884; Co, 5 - 330 ppm; Cu, <5 - 33,400 ppm; N i , <5 - 1680 ppm; Zn, 33 - 200,000 ppm. I t i s clear that, using a n a l y t i c a l c r i t e r i a alone, almost anything could be regarded as hydrothermal. The situation i s further complicated, since "metalliferous sediments of hydrothermal o r i g i n may mix with and/or exhibit t r a n s i t i o n a l characteristics with metalliferous sediments of hydrogenous o r i g i n " (Rona, 1978) - and, presumably, also with non-metallif-erous sediments of d e t r i t a l or biogenic o r i g i n . Sources of sediments Several composition diagrams have been published which purport to distinguish sediments of hydrothermal o r i g i n from other types, the best known of which i s probably the Fe - Mn - (Co+Cu+Ni)xl0 triangular diagram published by Bonatti et a l . (1972), and used by Rona (1978) and many other authors. However, this diagram does not d i f f e r e n t i a t e be-tween i r o n - r i c h hydrothermal sediments and normal non-metalliferous pelagic sediments (see Fig. 11). I t does, however, serve to emphasize the wide va r i a t i o n found in Unit 1 sediments; also, the sediments of Unit 1 seem, i n general, to have trace element concentrations higher than those usual i n hydrothermal deposits, and may have a hydrogenous component. 71 (Ni+Co+Cu) xlO Fig. 11. Covariation of Fe, Mn, and (Ni+Co+Cu)xlO for Juan de Fuca Ridge geochemical units and Core 78-6-18. Note the wide va r i a t i o n in composition of Unit 1, suggesting that this unit i s at least in part of hydrogenous o r i g i n . Note also that this diagram does not d i f f e r e n t i a t e between ir o n - r i c h hydrothermal sediments and normal non-metalliferous deep-sea sediments. (a) Average P a c i f i c pelagic sediments (Goldberg and Arrhe-nius, 1958). (b) Average shale (Turekian and Wedepohl, 1961). M.S. = metalliferous sediments. Modified from Bonatti, 1975. 72 Hydrothermal sediments also seem to have r e l a t i v e l y high ratios of S i0 2 to A1 20 3 (Bonatti et a l . , 1972). A plot of these two components (Fig. 12) indicates that the sediments of the study area are predominantly terrigenous; the S i 0 2 / A l 2 0 3 ratios for a l l cores are substantially the same, but the amounts of both these components show a progressive decrease from Unit 2, through Units 1 and 3, to the Si0 2 and Al 20 3-poor sediments of Core 78-6-18. This decrease i s f e l t to be due p r i n c i p a l l y to d i l u t i o n by biogenic or hydrogenous material. A hydrothermal source for Core 78-6-18 i s not indicated. Bostrom et a l . (1969) use the r a t i o of Al to T i to distinguish terrigenous sediments from those derived from oceanic volcanic rocks ( i . e . hydrothermally or by weathering). The A l / T i r a t i o found i n average continental rock i s close to 20, whereas the weathering products of oceanic rock should have an A l / T i r a t i o of about 5. Of the sediments analyzed i n the present study, Units 1, 2 and 3 have average A l / T i ratios of 16.73, 15.94 and 18.38 respectively, and core 78-6-40 (which should have l i t t l e or no hydrothermal component) has an A l / T i r a t i o of 17.27; the r a t i o for core 78-6-18 i s 16.41. This seems to confirm that 78-6-18 i s e s s e n t i a l l y non-hydrothermal, as i s suggested by the S i 0 2 / A l 2 0 3 r a t i o . A graph of the r a t i o of F e / t i to Al/(Al+Fe+Mn) i s shown i n Fig. 13; according to Bostrom (1970), normal pelagic sediments consist of mixtures of terrigenous and hydrothermal sediments and tend to f a l l close to curve (b). A l l of the sediments analyzed i n this study f a l l close to the right hand (terrigenous) end of t h i s curve; however, a small hydro-thermal component for Unit 1 and for core 78-6-18 remains a p o s s i b i l i t y , i f a remote one. 60, 8 IO % A I 2 0 3 . 12. Ratio of Si0 2 to A1 20 3 for deep-sea sediments of hydrothermal, hydrogenous and terrigenous o r i g i n . • - Sediments sampled during this study O - Average compositions of various sediment types: (a) Average deep-sea sediment (Turekian and Wedepohl, 1961) . (b) Average P a c i f i c pelagic sediments (Goldberg and Arrhenius, 1958). (c) Average shale (Turekian and Wedepohl, 1961). Modified from Bonatti, 1975. 74 1000 78-6-40/1 b / Terrigenous Al + Fe + Mn . 13. Ratio of Fe/Ti to Al/(Al+Fe+Mn) for sediments cored during this study. Curve (a) results from mixing of sediments derived hydrotherm-a l l y or from weathering of volcanic rocks with volcanic material; curve (b) i s produced when hydrothermal sediments are mixed with material of terrigenous o r i g i n . Modified from Bostrom, 1970. 75 Core 78-6-18 The evidence outlined above seems to show that core 78-6-18, contrary to i n i t i a l expectations, does not have a s i g n i f i c a n t hydrothermal component. This core was obtained at a distance of about 6.8 km east of the ridge crest, and i s oxidised throughout, i n contrast to a l l the other cores studied (including those obtained i n the immediate v i c i n i t y of 78-6-18) which exhibit only a thin oxidised layer overlying predomi-nantly reduced sediment. This core also has a high CaO content, which r e f l e c t s a high biogenic component; i f the average rate of biogenic sedimentation i s assumed constant throughout the study area, then the high biogenic compo-nent of this core suggests a low overall sedimentation rate. However, 78-6-18 was obtained at a shallower depth than a l l the other cores (2258 m), 78 m shallower than the nearby core 78-6-29 (which also has a high content of CaO), and several hundred metres shallower than 78-6-15 and 25 (2560 m and 2609 m, respectively), the two other cores closest in location to 78-6-18; this factor may also contribute to the high CaO content i n t h i s core, since CaCo3 dissolution in the water column i s an inverse function of depth (see Fig. 10). The Xv-iray d i f f r a c t i o n results (Appendix 4) show strong indica-tions of quartz and a l b i t e , and suggest that the terrigenous material i s the dominant component of this core. Other metallogenic processes Other processes which may be of importance to the t o t a l picture of trace metal concentrations i n the study area are discussed b r i e f l y below. 76 Hydrogenous Hydrogenous sediments are "formed by slow p r e c i p i t a t i o n of metals from normal sea water, in which the metals are provided primarily by weathering of the continents" (Bonatti, 1975). They are quantitatively important only where sedimentation rates are low, but the range of trace element abundances found i n Unit 1 (Fig. 11) seem to indicate that a si g n i f i c a n t proportion of the trace elements in t h i s unit are of hydro-genous o r i g i n . Other processes, however, have redistributed these elements since deposition. Diagenetic Bonatti et a l . (1971) have proposed a process whereby Mn, Co, Ni and to a s l i g h t extent Cu, are dissolved under reducing conditions at depth i n the sediment column and reprecipitated i n an upper, oxidised zone. It has been shown experimentally (Hartmann, 1979) that Mn, Co and Ni are remobilised simultaneously when an oxidised sediment i s treated with an acidic reducing solvent, but that Cu i s dissolved much more slowly. Surface sediments r i c h i n Mn and trace elements are of wide occurrence throughout the oceans, increasing in thickness with increasing distance from land (Lynn and Bonatti, 1965); enrichment in Mn i s usually found to be much more intense and more loc a l i s e d close to the sediment surface, than the other elements, an observation explained by Bonatti et a l . (1971) as being due to the fact that most trace elements do not form d i s t i n c t minerals i n low-temperature sedimentary environments but are hosted in Mn and Fe minerals (Goldberg, 1954). Hartmann (1979) proposes that Ni and Co are incorporated into carbonate or phosphate minerals soon after being remobilised and so tend to be reprecipitated more rapidly than Mn. 77 Cu also tends to be bound or adsorbed to clay minerals (Goldberg and Arrhenius, 1958), and thus i s remobilised with much lower efficiency than Mn, Ni and Co. The results of this study (Fig. 6) seem i n general to support the above analysis; Mn enrichment i s r e s t r i c t e d to only the upper few cm of sediment (the uppermost geochemical sample, 0-2 cm, has on average 6.4 times and may have up to 20 times as much Mn as samples from the remainder of the core), while the other trace elements tend to show a progressive decrease i n concentration from the top of each core to the base of Unit 1. Co, however, seems not to follow this pattern, although a s l i g h t enrichment i n Unit 1 i s seen (Table I I ) , Co shows some degree of covariance with CaO (see below); Hartmann (1979) proposes that Co is incorporated into carbonates by diagenetic processes. I t i s also possible that Co i s being l o s t from the sediments due, perhaps, to l o c a l pH or Eh conditions; Garrels and Christ (1965) note that the s t a b i l i t y f i e l d s of higher oxides of Co occur at a much higher Eh than do Mn oxides, so that i n the absence of a suitable host species Co may remain i n solu-ti o n . I t should also be noted that both the Mn concentration in subunit l a , and the thickness of the Mn-rich layer, appear to increase with distance from the ridge crest, and thus with the time available for diagenesis (Fig. 14), which lends further support to a diagenetic or.igin for t h i s unit. A diagenetic process such as that discussed above should, i n theory, result i n a constant Mn concentration below the oxidised zone; however, i n many cores Mn i s enriched to some extent i n Unit 3 (Fig. 6, especially cores 78-6-1, 8 and 20). I t may be that the Mn i n th i s unit i s present, not as easily reducible oxides, but as some more stable 78 F i g . 14. V a r i a t i o n in MnO content and thickness of Unit l a with distance from ridge crest (and thus with time a v a i l a b l e for diagenesis). Note, however, that an unknown quantity of Unit l a was l o s t from each core on i n i t i a l treatment. 79 species, such as cabonates. L i t t l e published information seems to exist regarding the diagene-t i c behaviour of Zn and Pb. In this study, the behaviour of Zn seems to follow that of Cu, while the behaviour of Pb i s somewhat e r r a t i c but generally close to that of Ni. Biogenic Heath and Dymond (1977) and Leinen and Stakes (1979) have shown that the biogenic component of P a c i f i c pelagic sediments i s an important source of trace metals i n the sediments. This i s hardly surprising i n view of the known tendency for marine organisms to concentrate trace elements (Riley and Roth, 1971; Brewer, 1975). In this study, as noted above, only Co shows any s i g n i f i c a n t degree of covariance with CaO (Fig. 6), and this i s interpreted to mean either that most of this element i s of biogenic o r i g i n , or that i t has been incorporated into the carbonate fr a c t i o n soon after mobilisation (Hartmann, 1979). Co also shows consistently high values i n cores 78-6-18 and 29, both of which are CaO-rich. Incidentally, i t should be mentioned that t h i s covariance of Co with CaO i s an argument against the proposal of Heath and Dymond (1977) that "Co would be a better choice" than Ni as a standard "non-biogenic" element in t h e i r analysis of sediment provenance. Feldspar diagenesis Some explanation seems warranted for the apparent lack of K-feldspar in the sediments i n the study area. I t seems reasonable to assume that K-feldspar would have been present, i n an amount at least of the same order of magnitude as that of plagioclase, i n the o r i g i n a l 80 terrigenous sediments, supposing them to derive from the K-feldspar-bearing rocks of the B r i t i s h Columbia coast (Douglas et a l . , 1976). There-fore, some diagenetic process must be operating to remove K-feldspar, a process which has l i t t l e or no effect on plagioclase. Weaver (1967) has suggested a process whereby K + i s released from K-feldspar and incorporated into clays (mainly i l l i t e ) . I l l i t e s i n marine sediments often appear to be younger than the stratigraphic age of the sediments, by. up to 100 m i l l i o n years (Hawkins and Roy, 1963), suggesting that some, at least, of the i l l i t e s form diagenetically, from reactions involving K + in the i n t e r s t i t i a l waters of the sediments. This c o n f l i c t s with the observation that K-feldspars appear to be thermodynamic-a l l y stable in normal oceanic waters; however, solution could occur, with possible conversion to i l l i t e , under conditions of low pH and low: dissolved Si0 2 (Hess, 1966; Garrels and Mackenzie, 1971). Goldberg and Arrhenius (1958) report that most of the K 20 in P a c i f i c pelagic sediments i s incor-porated i n clays, which suggests that t h i s i s not merely a l o c a l phenomenon. Most of the terrigenous sediments i n the study area have probably been reworked at least once, giving more opportunity for diagenetic + reactions of this type to occur. The much greater concentration of Na than K + in ocean water might tend to i n h i b i t the diagenesis of a l b i t e , and sea water appears to be supersaturated i n Ca + i n the upper layers (Broecker and Oversby, 1971), which would tend to increase the s t a b i l i t y of Ca-bearing feldspars. There seems to be a tendency for more Na + than K + to be removed from seawater by c l a y - r i c h sediments (Weaver, 1967), which would further tend to s t a b i l i s e a l b i t e at the expense of K-feldspar. 6. SUMMARY AND CONCLUSIONS Introduction Geothermal heat flow measurements over the Juan de Fuca Ridge ( L i s t e r , 1972; Davis and Lister,1977b) show that the rate of heat transfer from the mantle through the ba s a l t i c oceanic crust i s too high to be accounted for solely by conductive processes. A convective hydrothermal system, i n which sea water circulates through fractures in hot, freshly formed basalt close to the ridge crest, seems to provide the most probable means of transporting this excess heat (Bonatti, 1975). The sea water, on i t s passage through the system, reacts with the hot rock and dissolves out Mn, Fe and several trace metals, which are re-deposited i n the cool, oxidising environment of the seafloor as Fe-and Mn-rich crusts and metalliferous muds. Fractionation of Mn from Fe also occurs, due to the difference i n s o l u b i l i t y between the two metals; this gives the resultant sediments a characteristic range of compositions. The main purpose of t h i s study was to determine whether hydro-thermal sediments of t h i s type are present on or adjacent to the northern end of the Juan de Fuca Ridge. Samples obtained on a transect of the Ridge complex during June 1978 indicate a predominantly terrigenous source for most of the sedi-ments i n the area, with t u r b i d i t y currents playing the major role in 81 82 sediment transport. Biogenic and hydrogenous material i s also present in the sediments, but no compelling evidence was found for the presence of a s i g n i f i c a n t hydrothermal component. However, a layer of hydrothermal sediment has been reported at the base of the sediment column from other nearby l o c a t i o n s , and i t most probably also exists i n the present area. Overall sedimentary regime This study reveals a complex pi c t u r e of sedimentation in the area ( F i g . 15). A broad outline of the o v e r a l l sedimentary regime would include the following f a c t o r s , i n more or l e s s chronological order: 1) Deposition of Fe-and Mn-rich, highly oxidised hydrothermal sediment from vents and f i s s u r e s on or close to the ridge c r e s t , in a r e l a t i v e l y t h i n layer, probably nowhere more than 1 m thick, overlying b a s a l t i c basement. 2) Deposition of terrigenous sediment, i n i t i a l l y on the continental shelf and i n the N i t i n a t and A s t o r i a fans off the Juan de Fuca S t r a i t and the mouth of the Columbia River. Continual low-level seismic a c t i v i t y along the shelf edge would r e s u l t in t h i s sediment being p e r i o d i c a l l y disturbed and remobilised i n the form of t u r b i d -i t y currents. Most of these currents t r a v e l by way of the Cascadia Channel or the Vancouver V a l l e y , through a gap i n the Blanco Fracture Zone and out onto the Tufts Abyssal P l a i n (Griggs and Kulm, 1970), but occasional larger currents overflow these channels and spread out over the Cascadia P l a i n and into the Ridge complex. The quantity of t h i s material released into the marine environment increases considerably during periods of g l a c i a l r e t r e a t , when vast quantities of sediments are c a t a s t r o p h i c a l l y released over a SEDIMENT INPUTS F i g . 15. Sediment inputs to the Juan de Fuca Ridge area. CO 84 r e l a t i v e l y short time period. 3) A steady " r a i n " of pelagic sediment, including planktonic debris and very fine grained terrigenous material, over the whole area. This pelagic sediment becomes intimately mixed with material of t u r b i d i t i c and hydrothermal o r i g i n , but some of the planktonic debris may become segretated into occasional thin layers due to reworking by tu r b i d i t y currents. 4) P r e c i p i t a t i o n of trace metal-rich material d i r e c t l y from seawater, also over the whole area. 5) Local volcanic a c t i v i t y may add pyroclastic debris, i n the form of glass shards, to the sediments i n certain areas. 6) Slumping of pelagic, hydrogenous and possibly some t u r b i d i t i c and volcanic material from topographic highs into valleys and hollows within the ridge complex, giving r i s e to "microturbidites" a few cm thick. 7) The terrigenous sediment described i n (2) above would be deposited i n i t i a l l y i n an oxidised state, but would quickly be-come reduced due to the decay of organic matter. Diagenetic remobilisation would then occur of Mn and possibly some trace elements i n the reduced zone; these elements then travel upwards by d i f f u s i o n through the i n t e r s t i t i a l water and are redeposited in the s t i l l - o x i d i s e d upper few cm of the sediment column, giving r i s e to a Mn-rich surface layer and a progressive upward enrich-ment of most trace elements. Within this broad framework, the ridge topography exerts consider-able control over sedimentation rates and patterns; each valley within the ridge complex appears to have i t s own individual sedimentation 85 regime, the f a s t e r sedimentation rates being associated with the larger v a l l e y s , as might be expected. Sedimentation rates appear to be approx-imately an order of magnitude f a s t e r i n the ridge complex than has been reported for the Cascadia P l a i n , no doubt due l a r g e l y to the concentra-t i o n of sedimentation into a r e a l l y r e s t r i c t e d v a l l e y s . Recommendations f o r future work This study i s regional in scope rather than l o c a l , and there i s opportunity f o r much more d e t a i l e d work in the area. Even the basic bathymetry has not yet been f u l l y delineated, which, in view of the con-siderable academic i n t e r e s t the area has generated, i s perhaps s u r p r i s i n g . This s i t u a t i o n w i l l undoubtedly improve as fur t h e r seismic p r o f i l e s become a v a i l a b l e . S p e c i f i c recommendations for further work might include the following: 1) More magnetic measurements should be obtained around the o f f s e t of the ridge crest at i t s i n t e r s e c t i o n with the Cobb Fracture Zone, in order to determine the exact nature and trend of the o f f s e t . This could probably best be achieved by using a deep-towed magneto-meter . 2) Samples should be obtained of possible hydrothermal sediment from topographic highs close to the spreading centre. This might be d i f f i c u l t i f a conventional corer was used, since the sediment depth w i l l be minimal and the material may well be in the form of encrustations on b a s a l t i c pillows or as fracture i n f i l l i n g s . Dredging would probably be an acceptable method; the id e a l would, of course, be to use a manned submersible. 86 It would also be useful to obtain one or more cores which include the whole postulated sedimentary sequence, i.e. Units 1, 2 and 3 and the basal hydrothermal unit. This would help, to con-firm the sedimentary scheme outlined above. Piston coring would probably be the most suitable technique for this purpose. 3) Radioactive age dating of the sediments would seem to be of great importance, if only as a check on sedimentation rates. 1IfC would probably be the most suitable method. It should be emphasized, however, that this method would date only the biogenic component of the sediments; mixing of in-situ pelagic sediment with reworked pelagic material transported by turbidity currents might give rise to ambiguous results. Radioactive dating of clay minerals (notably montmorillonite), should i t prove feasible, would serve to distinguish detrital from hydrothermal and/or authigenic components in the sediments. 4) A Q-mode vector analysis of the geochemical data (Imbrie and van Andel, 1964), as was used by Leinen and Stakes (1979) to categorise pelagic sediments, would allow hypothetical end-members (i.e. geochemical factors that may have some significance in terms of sediment provenance) to be defined, as a test of the sedimentary scheme outlined above. It is expected that factors rich in Si0 2, A1203, K20 and Ti0 2 (terrigenous); CaO and Co (biogenic); a l l other trace elements (hydrogenous); and MnO and Fe 20 3 (hydrothermal) would be found. 5) Further experimental work is needed in the field of sediment diagenesis; in particular, the reactions of K-felspar in the marine environment needs to be investigated, and the diagenetic reactions 87 of clays are s t i l l far from being f u l l y understood. I t i s reported, for example (Bonatti and Joensuu, 1968) that d e t r i t a l montmorillonite can be altered to palygorskite by Mg-rich hydrothermal solutions; other reactions undoubtedly remain to be discovered. Economic implications Extensive metalliferous deposits such as are found on the East P a c i f i c Rise, i n Bauer Deep and other areas (Dymond and Veeh, 1975; Bischoff and Rosenbauer, 1977; etc.) do not appear to be present in the area of the present study, c h i e f l y due to d i l u t i o n and blanketing by terrigenous sediments. Massive sulphides, such as those reported by Bonatti et a l . (1976) and Francheteau et a l . (1979), from the Mid-A t l a n t i c Ridge and the East P a c i f i c Rise respectively, have not been found, although they may well exist at depth. Such metal-rich deposits as have been found are of low grade and of small extent, rendering economic exploitation unlikely in the foreseeable future. REFERENCES Arrhenius, G. (1952). 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Geochim. et Cosmochim. Acta, 31, 2181-2196. Wilde, P., Chase, T.E., Holmes, M.L., Normark, W.R., and Thomas, J.A. (1977). Oceanographic data off Washington 46° to 49° north, including the N i t i n a t deep-sea fan. L.B.L. Publ. 223. APPENDIX 1 Seismic p r o f i l e s and interpretations 98 CONTINUOUS SEISMIC REFLECTION PROFILES (CSP) AND INTERPRETATIVE SECTIONS LEGEND Interpretations are shown below the o r i g i n a l CSP traces i n each case. Figures at right-hand end of the CSP traces are 2-way travel times (seconds). Figures at r.h. end of interpretative sections are metres _ i depth, assuming a sound velocity i n sea water of 1490 m s . CSP loca-tions are shown i n Fig. 3. Strong r e f l e c t o r i n sediments - — Weak or discontinuous r e f l e c t o r - — Bedrock -Inferred faults -Plate 5. Seismic p r o f i l e s N 4.5, E0.5, N 3 and E0.25 -z.s -3.0 -3.5 10 k m PROFILE E1 WEST HALF E1-2 TIE LINE Plate 6. Seismic p r o f i l e s E l (west h a l f ) and El-2 t i e l i n e . o o 101 280Q PROFILE M3  I i > i 1 PROFILE E l w r n i i Plate 7. Seismic p r o f i l e s N3 and E l (east h a l f ) . 1 0 2 ' PROFILE E1.5 Plate 8. Seismic p r o f i l e s N3.7 and El.5. Plate 9. Seismic p r o f i l e E2 (west h a l f ) . ,_. o 10 km PROFILE E2 EAST HALF P l a t e 10. Seismic p r o f i l e E2 (east h a l f ) . o -p-10 km , PROFILE E 2.5 2.5-1.5 TIE LINE Plate 11. Seismic p r o f i l e E2.5 and 2.5-1.5 t i e l i n e . o . HWFM.E E3 P l a t e 12. Seismic p r o f i l e E3. o ON Plate 15. Seismic p r o f i l e s E7 and N3.5. o . 20 • PROFILE E9 Plate 16. Seismic p r o f i l e E9. - 3 . 0 —is Jfe; —4.0 —<r.f 2 0 K m ' PROFILE E t l Plate 17. Seismic p r o f i l e s E l l and Nl. M t *> K M P B O W J H2 Plate 18. Seismic p r o f i l e N2. APPENDIX 2 Geochemistry - major oxides Appendix 2: Major oxides (%) Sample no. SiO, A120, Fe 20 3 MgO CaO Na20 K20 TiO„ P 20 5 MnO LOI Ca0/Al 20 3 -1/0-2* 46.69 11.79 6.31 3.24 4.19 4.92 1.87 .61 .31 1.48 19.18 1/10-12 48.16 12.85 6.78 3.47 3.30 4.93 2.14 .66 .34 .33 16.91 1/20-22 48.87 13.17 6.98 3.47 2.92 4.78 2.16 .67 .52 .29 16.36 1/30-32 47.71 13.10 7.41 3.63 4.58 4.63 2.10 .66 .37 .31 16.86 1/40-42 46.69 13.53 7.31 3.48 6.37 4.26 1.93 .63 .38 .24 16.46 1/50-52 53.44 15.79 7.07 3.57 4.38 3.50 2.45 .77 .37 .18 10.62 1/60-62 51.87 15.55 8.07 3.64 3.21 3.88 2.51 .78 .34 .16 11.13 1/70-72 54.02 16.18 7.16 3.42 3.92 3.49 2.41 .80 .35 .15 9.57 1/80-82 55.69 16.11 7.02 3.28 3.70 3.37 2.30 .85 .34 .13 8.73 1/90-92 55.44 15.88 7.08 3.27 3.76 3.08 2.28 .85 .35 .13 8.57 1/100-102 56.64 15.56 6.70 2.96 3.84 3.22 2.11 .81 .36 .12 7.83 1/110-112 49.39 14.33 6.89 3.14 6.98 3.39 2.05 .71 .40 .59 13.33 •6/0-2 46.49 11.97 6.86 3.15 4.71 4.58 1.93 .62 .38 .61 18.57 6/10-12 48.28 12.79 7.30 3.42 3.87 4.51 2.22 .66 .36 .28 16.37 6/20-22 46.07 12.36 7.45 3.36 6.07 3.87 2.01 .62 .37 .24 17.74 6/30-32 44.76 12.85 6.69 3.32 8.07 3.83 1.86 .61 .42 .22 18.04 6/40-42 42.79 12.34 6.31 3.11 11.43 2.93 1.52 .60 .70 .20 18.44 6/50-52 51.01 14.82 6.62 2.96 6.84 3.13 2.64 .81 .50 .15 12.05 6/60-62 49.23 14.43 6.57 2.86 7.04 3.10 2.41 .84 .42 .29 14.03 6/70-72 50.77 14.69 7.11 2.88 5.77 3.10 2.71 .83 .40 .15 13.10 6/80-82 58.35 15.07 6.32 2.79 5.03 3.38 1.72 .85 .39 .13 6.83 6/90-92 50.78 15.07 6.45 2.89 6.27 3.31 2.60 .79 .36 .16 12.90 6/100-102 46.55 13.53 5.68 2.82 11.09 3.09 2.05 .69 .42 .20 15.40 6/110-112 50.18 14.86 5.85 2.82 8.04 2.74 2.53 .76 .39 .22 13.47 6/120-122 41.63 12.02 5.33 2.58 16.01 2.42 1.49 .56 .48 .32 17.68 6/130-132 47.31 14.16 7.20 3.44 9.46 3.33 1.74 .75 .42 .22 12.41 0.222 *Note: Samples are numbered in cm from top of core imple no. S i 0 2 Al, 2 0 3 Fe, 2o 3 MgO .-7/0-2 44 .13 11 .34 6 .54 2 .82 7/10-12 46 .94 12 .16 7 .35 3 .11 7/20-22 48 .57 12 .95 7 .53 3 .26 7/30-32 47 .42 12, .62 7 .58 3 .09 7/40-42 44 .86 12, .21 7 .73 3 .25 7/50-52 44 .66 12, .15 7 .89 3 .39 7/60-62 44 .01 12, .24 7 .20 3 .03 7/70-72 43 .52 12, .71 6 .35 3 .22 7/80-82 47, .OS 12, .37 7 .68 3, .62 7B/0-3 45, .58 12, .06 8, .09 3, .62 7B/10-12 44, .77 12, .23 7, .36 3, .48 7B/20-22 44, .26 12. ,23 7, .47 3. .66 -8/0-2 46, .98 11. 58 7. 79 3, .08 8/10-12 43. ,52 11. ,32 8. ,14 3, .36 8/20-22 42. ,89 12. 41 6. ,59 3, .30 8/30-32 43. ,67 12. 78 5. ,86 2. ,89 8/40-42 51. ,26 15. 09 7. ,00 2. ,94 8-50-52 52. ,52 15. 11 7. 07 2. ,93 8-60-62 52. ,40 15. 69 6. 71 2. ,83 8/70-72 47. 82 13. 92 6. 32 2. 87 8/80-82 49. 17 14. 44 5. 97 2. 77 8/90-92 49. 18 14. 51 6. 20 2. 88 8/100-102 42. 17 12. 19 5. 39 2. 92 8/110-112 41. 56 11. 89 5. 61 2. 95 8/120-122 43. 38 12. 51 5. 82 3. 07 8/130-132 49. 33 13. 92 6. 69 3. 54 CaO Na 2 0 K 2 0 T i 0 2 P 2 0 5 MnO LOI 4.37 4.08 1.88 .69 .36 1.58 21.43 4.89 3.77 2.17 .63 .35 .40 17.58 3.62 4.13 2.34 .67 .33 .36 16.39 4.86 3.40 2.21 .66 .33 .30 17.10 6.51 4.20 2.03 .62 .36 .33 17.85 6.67 3.72 1.99 .62 .36 .47 18.06 8.14 3.51 1.93 .60 .40 .27 17.81 11.27 3.52 1.86 .62 .44 .27 17.41 4.30 4.80 2.20 .65 .35 .36 17.38 5.67 4.47 2.13 .63 .38 .32 17.85 5.77 4.61 2.10 .63 .36 .30 17.95 6.10 4.77 2.08 .62 .40 .38 17.91 3.75 4.94 1.90 .63 .38 .45 18.65 9.55 4.00 1.82 .53 .41 .12 18.66 11.04 3.70 1.79 .57 .42 .15 17.98 11.20 3.96 2.18 .66 .43 .12 16.66 4.73 3.57 2.83 .87 .40 .14 12.17 4.51 3.44 2.74 .96 .40 .17 11.78 4.26 3.27 2.84 .87 .39 .12 11.82 8.76 3.04 2.18 .69 .41 .17 14.56 8.85 2.85 2.22 .72 .39 .18 13.98 7.70 2.98 2.38 .72 .39 .20 13.63 14.09 - 3.22 1.62 .56 .46 .30 16.92 14.66 3.48 1.53 . .54 .47 .31 16.99 13.86 3.03 1.59 .57 .47 .20 16.52 8.62 3.33 1.79 .78 .43 .17 12.55 Sample no. A1 20 3 Fe 20 3 MgO CaO Na20 K 20 T i 0 2 P 2 O 5 MnO LOI Ca0/Al 20 3 )-9-/0-2 46.25 10.13 8.74 3.17 3.92 5.63 1.80 .54 .37 .14 19.44 9/10-12 44.64 10.81 8.30 3.33 5.06 5.09 1.97 .58 .38 .11 19.87 9/20-22 46.14 11.58 8.87 3.56 6.15 4.60 2.01 .65 .36 .11 17.26 9/30-32 45.90 12.57 8.45 4.35 8.15 4.44 1.63 .93 .44 .13 13.23 9/40-42 40.54 11.05 7.87 3.83 9.47 4.21 1.55 .78 .44 .13 15.34 9/50-52 44.90 12.88 7.22 3.92 10.58 3.71 1.76 .84 .49 .15 13.80 9/60-62 42.69 11.48 7.88 3.34 10.03 4.05 1.99 .57 .45 .00 17.14 9/70-72 47.28 13.99 6.40 3.10 8.87 3.23 2.28 .82 .46 .13 13.93 9/80-82 52.90 15.40 7.05 3.00 4.91 3.19 2.77 1.00 .43 .10 10.51 9/90-92 49.95 14.81 6.99 3.13 5.80 3.13 2.74 .86 .41 .10 12.43 9/100-102 48.76 14.43 6.69 2.98 7.41 2.94 2.43 .84 .40 .11 13.42 9/110-112 52.16 15.50 6.73 2.82 4.90 3.16 2.70 .87 .31 .09 12.19 •12/0-2 50.33 12.98 6.78 .24 3.66 4.27 2.05 .67 .36 .17 16.26 12/10-12 50.56 14.02 7.44 3.55 4.95 4.11 2.27 .70 .39 .11 13.10 12/20-22 53.90 15.52 6.79 3.42 4.34 3.75 2.35 .77 .39 .12 9.63 12/30-32 50.40 14.72 6.84 3.35 5.31 3.96 2.27 .71 .38 .22 12.28 12/40-42 55.52 15.45 6.63 3.20 3.88 3.52 2.17 .80 .31 .11 8.45 12/50-52 52.67 15.96 7.92 3.47 2.94 3.99 2.51 .83 .34 .12 10.34 12/60-62 54.96 16.06 6.94 3.30 3.51 3.37 2.32 .85 .35 .11 8.47 12/70-72 56.56 15.48 6.63 3.05 3.84 3.60 2.08 .85 .37 .11 7.92 12/80-82 58.02 14.32 6.01 2.61 4.76 3.59 1.91 .78 .36 .18 7.96 12/90-92 53.06 15.34 7.27 3.24 4.20 3.62 2.28 .79 .36 .13 10.44 12/100-102 53.08 15.05 6.92 3.03 4.56 3.69 2.06 .78 .38 .13 10.91 12/110-112 59.27 15.36 6.25 2.76 3.65 3.71 1.84 .83 .36 .10 6.82 0.184 0.238 lple no. Si0 2 A l s »°s Fe, «°s MgO CaO Na L 20 K 20 Ti0 2 P 20 5 MnO LOI •15/0-2 50, .17 12, .59 8, .50 3, .25 2. 39 4. 31 2. 10 .68 .30 .12 15, .88 15/10-12 46, .53 12, .87 7, .21 3, .30 4. 94 4. 92 2. 09 .65 .34 .10 15, .74 15/20-22 49, .78 14. .30 7, .25 3, .24 5. 61 4. 26 2. 30 .70 .38 .12 12, ;83 15/30-32 51, ,10 14. ,85 6, .98 3, .33 5. 31 3. 77 2. 32 .75 .38 .13 11, .90 15/40-42 50. ,02 14. .54 7, .16 3, ,44 5. 85 4. 10 2. 13 .76 .39 .15 12, .34 15/50-52 48, .20 14. .25 6. .43 3, .07 7. 53 3. 71 2. 35 .73 .43 .17 13, .42 15/54-55F 42, .42 11. .95 5, ;37 2, .55 13. 88 3. 50 1. 85 .60 .48 .17 15, .92 15/60-62 47. .42 13. ,69 6. .54 2, .94 8. 21 3. 42 2. 22 .71 .44 .17 13, .71 15/70-72 55. ,22 15. ,30 6, .76 2, .87 3. 74 3. 49 2. 10 .86 .36 .16 8, .87 15/75-76F 50. ,09 13. ,14 5, .85 2. .51 7. 65 3. 19 1. 81 .76 .41 .36 11, .33 15/80-82 49. ,25 13. ,59 6, ,57 2. ,70 6. 35 3. 14 2. 21 .94 .44 .40 11. .79 15/90-92 50. ,72 14. ,75 6. ,99 2. .70 5. 57 3. 05 2. 71 .86 .41 .16 11, .94 15/100-102 49. ,39 14. ,40 6, .63 2, .63 3. 97 2. 66 2. 62 .89 .42 .11 10. .52 15/110-112 53. ,22 14. ,78 6. .36 2, .61 4. 03 2. 91 2. 81 .90 .41 .11 9, .68 15/114-115F 51. ,70 13. ,40 5. ,98 2, .34 6. 19 2. 66 2. 33 .89 .42 .10 10. .87 15/120-122 52. ,61 14. ,97 6. .37 2. .60 5. 27 2. 84 2. 85 .88 .41 .11 11. .12 15/130-132 51. ,40 15. ,05 6. ,87 2. ,80 4. 43 2. 99 2. 69 .87 .38 .12 11. .25 15/140-142 52. ,26 15. ,09 6. ,92 2. .77 4. 54 3. 05 2. 68 .89 .41 .13 10. .95 15/CC * 52. ,56 15. ,01 6. ,95 2. .69 4. 62 2. 76 2. 67 .88 .41 .14 11. .28 Ca0/Al 20 3 0.190 0.244 16/0-2 48.72 12.21 6.85 2.92 3.24 4.75 1.95 .63 .35 .26 17.13 16/10-12 48.59 12.93 7.06 3.16 2.84 4.79 2.18 .67 .33 .13 15.48 0. 220 16/20-22 46.20 12.48 7.50 3.21 4.61 4.68 2.06 .63 .37 .19 15.97 16/30-32. . 46.32 13.00 6.86 3.11 5.97 4.46 2.02 .63 .36 .15 14.64 16/40-42 47.95 13.56 6.92 3.20 6.21 4.26 2.14 .67 .38 .14 13.83 16/50-52 54.03 14.52 6.07 2.82 4.84 3.62 2.02 .73 .38 .14 10.10 16/60-62 48.15 13.86 6.42 2.99 6.68 4.03 2.39 .7.2 .42 .18 13.34 16/70-72 53.66 15.72 7.37 3.17 3.04 3.99 2.22 .85 .37 .13 10.03 0. 193 16/80-82 48.10 13.95 6.30 2.71 8.15 3.03 2.44 .79 .46 .19 13.35 16/90-92 53.09 15.35 6.84 2.74 4.65 2.93 2.95 .93 .43 .15 10.59 *Note: CC = sample retrieved from core catcher. Sample no. Si0 2 A1 20 3 Fe 20 3 MgO CaO Na20 K 20 Ti0 2 P 20 5 MnO LOI CaO/Al, 78-6-16/100-102 52.22 15.21 6.86 2.77 4.86 3.16 2.88 .89 .42 .12 11.16 16/110-112 53.11 15.33 6.91 2.67 4.54 2.84 2.94 .94 .40 .12 10.45 16/120-122 55.31 15.55 6.97 2.74 3.87 3.02 3.01 .93 .40 .10 9.55 0.249 •18A/0-1 36.9 10.62 6.23 2.80 15.7 3.69 1.29 .76 .30 19.71 18A/5-6 34.5 10.10 5.69 2.65 19.3 3.24 1.20 .79 .16 21.39 18A/10-11 29.0 8.40 5.01 2.25 23.4 2.97 1.13 .56 .27 25.69 18A/15-16 32.6 9.07 5.12 2.29 20.1 3.07 1.19 .56 .30 24.37 18 /CC 32.1 9.45 5.21 2.38 20.8 3.13 1.12 .54 .28 24.89 18B/0-1 31.4 9.63 5.18 2.27 20.2 3.02 1.32 .55 .35 24.00 18B/5-6 31.7 9.63 5.38 2.40 19.6 3.26 1.26 .61 .41 24.17 18B/15-16 35.8 10.68 5.72 2.55 16.7 3.26 1.50 .64 .76 21.98 •19/0-2 48.92 14.01 6.44 3.03 8.49 2.86 2.15 .77 .43 .10 14.18 19/10-12 53.14 15.74 6.41 2.90 4.73 3.12 2.66 .81 .38 .12 10.82 19/20-22 54.43 15.66 6.16 2.71 4.70 2.99 2.79 .81 .39 .15 10.65 19/30-32 47.38 13.99 6.23 3.06 8.76 3.46 2.08 .68 .42 .36 13.82 19/40-42 45.76 13.54 6-. 36 3.37 10.37 3.44 1.71 .67 .44 .20 14.07 19/50-52 45.55 13.28 6.17 3.18 10.74 3.38 1.79 .65 .43 .18 14.54 19/60-62 48.15 14.67 6.81 3.39 7.62 3.76 2.17 .73 .40 .17 12.49 19/70-72 49.58 15.15 7.08 3.59 7.52 3.37 2.27 .71 .42 .18 12.38 19/80-82 48.66 14.09 6.57 3.35 8.47 3.16 1.98 .73 .41 .18 12.91 19/90-92 47.02 14.08 6.32 3.22 9.33 3.39 1.99 .67 .40 .22 13.79 19/100-102 48.63 14.81 7.01 3.38 7.36 3.65 2.14 .72 .40 .15 12.45 19/110-112 47.07 14.42 6.76 3.34 8.63 3.48 2.11 .68 .40 .14 12.72 19/120-122 50.00 15.46 7.25 3.53 6.30 3.91 2.27 .74 .38 .14 10.79 19/130-132 52.94 16.27 7.33 3.23 5.50 3.36 2.18 .81 .47 .15 13.85 19/140-142 50.26 15.59 7.20 3.51 6.28 3.62 2.27 .73 .37 .14 10.81 19/150-152 46.52 14.22 6.93 3.39 8.52 3.99 2.14 .61 .40 .12 13.34 19/160-162 45.16 13.68 6.67 3.28 9.39 4.15 2.19 .59 .42 .11 14.84 19/170-172 42.46 12.06 7.63 3.45 11.74 3.61 1.87 .52 .40 .12 16.97 Sample no. SiO, A1 20 3 Fe 20 3 MgO CaO Na20 K 20 TiO„ P 20 MnO LOI Ca0/Al 20 3 1-20/0-2 48 .50 12 .79 8 .41 3. 25 5 .77 3, .89 2. 18 .65 .38 .22 14, .93 20/10-12 54 .58 15, .09 7 .04 3. 14 3 .73 3, .74 2. 16 .84 .39 .09 10 .41 0, .297 20/20-22 50 .62 14, .32 6 .84 3. 06 6 .23 3, .06 2. 26 .79 .41 .10 12 .63 20/30-32 50 .65 14 .66 6, .59 2. 87 6, .31 3, .19 2. 40 .86 .44 .11 12, .15 20/40-42 54, .04 15, .34 6, .97 2. 73 3, .83 3, .22 2. 59 .89 .37 .09 10, .76 0, .250 20/50-52 53, .77 15, .03 6, .31 2. 64 4, .50 3. .11 2. 66 .87 .41 .10 10, .54 20/60-62 55, .90 15, .22 6, .48 2. 74 4, .00 2, .97 2. 68 .84 .40 .10 9, .68 20/70-72 53, .88 14, .94 6, .51 2. 65 4, .47 2. .98 2. 66 .83 .40 .08 10, .54 20/80-82 52, .30 16, .06 6, .38 2. 99 5, .48 3, .52 2. 72 .84 .37 .10 11, .50 20/90-92 51, .97 15, .55 6, .62 3. 03 5, .47 3, .61 2. 55 .82 .46 .11 11, .72 20/100-102 52, .04 15, .77 6, .30 2. 95 5, .25 3. .23 2. 66 .82 .38 .10 11, .51 20/110-112 53, .58 15. ,60 6, • 25 2. 84 4, .95 3. .09 2. 73 .79 .37 .12 10, .60 20/120-122 44. .82 13. .21 6, .32 3. 32 11. .30 4, .04 1. 73 .62 .45 .19 14, ,65 20/130-132 46. .67 13. .85 6. ,33 3. 38 9. .94 3. ,95 1. 88 .65 .45 .19 13, .66 20/140-142 45. .56 13. .13 6. .38 3. 23 10. ,97 3. .84 1. 81 .62 .46 .17 14. .39 20/150-152 46. .34 13. .79 6. ,38 3. 32 10. .45 3. .71 1. 88 .66 .47 .18 13. .74 20/160-162 53. .25 14. .71 7. .47 3. 98 5. ,46 3. .91 1. 94 .94 .45 .14 9. .95 -23/0-5 47. .40 11. ,71 6. ,87 3. 13 2. ,71 5. ,74 1. 90 .62 .38 .92 18. ,08 23/10-13 48. ,62 12. ,53 6. .65 3. 34 3. ,62 5. ,45 2. 06 .65 .33 .15 16. ,75 0. ,267 23/20-23 50. ,02 13. ,50 7. .08 3. 34 2. .89 5. ,03 2. 21 .71 .34 .15 15. ,38 -25/0-4 49. ,98 12. ,58 7. ,21 3. 20 3. ,37 5. ,31 1. 96 .68 .36. .16 16. ,12 0. 268 25/10-14 49. ,86 13. ,10 7. ,88 3. 56 2. ,56 5. 58 2. 26 .70 .34 .12 . 15. ,19 0. 195 -29/0-2 44. 23 12. 50 5. ,82 3. 03 11. 52 3. 73 1. 61 .62 .44 .18 14. ,88 29/10-12 41. 84 12. 17 5. ,66 3. 13 14. ,90 3. 51 1. 50 .58 .46 .08 16. ,19 29/20-22 42. 21 12. 65 6. 18 3. 13 13. ,80 3. 25 1. 61 .55 .49 .08 15. 57 29/30-32 41. 56 12. 54 6. 40 3. 08 14. 21 3. 26 1. 64 .52 .46 .08 16. ,08 29/40-42 35. 39 10. 55 5. 16 2. 90 19. 06 2. 82 1. 38 .44 .49 .06 20. 38 Sample no. S i 0 2 A 1 2 0 3 F e 2 0 3 MgO CaO Na 20 K 20 T i 0 2 P 2 0 5 MnO LOI Ca0/Al 20 3 78-6-38A/0-3 45.29 11.12 6.37 2.99 3.83 5.19 1.81 .58 .38 3.73 18.00 38A/10-13 48.68 12.90 7.34 3.21 • 4.92 4.73 2.09 .65 .40 .24 15.45 38B/3-7 47.81 12.71 7.90 3.34 6.24 4.19 2.08 .62 .39 .16 15.53 78-6-39A/0-5 43.93 11.26 6.64 3.12 3.40 5.56 1.86 .55 .41 3.58 18.67 • 39B/0-5 47.89 12.53 7.03 3.22 4.54 4.66 2.10 .61 .39 .22 16.53 78-6-40/0-5 47.27 12.20 6.38 3.55 2.29 5.43 2.00 .60 .34 1.63 17.91 0.183 40/10-14 49.05 13.58 7.07 3.53 3.61 4.68 2.31 .68 .33 .11 15.81 0.267 40/20-24 49.46 14.28 7.74 3.52 2.98 4.31 2.32 .77 .34 .09 15.25 0.209 APPENDIX 3 Geochemistry - trace elements (ppm) 122 Appendix 3: Geochemistry - trace elements (ppm) Sample no. Cu Pb Zn Co Ni 78-6-1/0-2 * 116 20 349 17 164 1/10-12 108 22 318 19 185 1/20-22 107 21 290 17 150 1/30-32 100 17 247 23 139 1/40-42 82 15 221 18 116 1/50-52 52 11 139 14 69 1/60-62 58 11 142 14 63 1/70-72 52 12 128 16 61 1/80-82 48 12 111 14 51 1/90-92 46 12 112 15 51 1/100-102 40 10 105 14 50 1/110-112 63 12 141 12 59 78-6-6/0-2 143 23 340 23 177 6/10-12 125 20 339 26 196 6/20-22 130 21 300 28 172 6/30-32 110 17 246 25 143 6/40-42 93 11 200 23 116 6/50-52 45 12 124 14 60 6/60-62 50 9 125 14 53 6/70-72 48 11 113 21 49 6/80-82 37 4 87 15 54 6/90-92 52 11 110 17 50 6/100-102 47 10 97 18 43 6/110-112 59 16 110 28 59 6/120-122 71 7 113 25 58 6/130-132 60 6 130 27 73 78-6-7/0-2 148 20 311 23 193 7/10-12 120 20 334 30 181 7/20-22 100 20 291 28 172 7/30-32 154 23 320 29 155 7/40-42 133 23 269 30 148 7/50-52 135 19 253 38 184 7/60-62 107 18 208 28 130 7/70-72 88 13 167 24 100 7/80-82 176 23 301 27 178 7B/0-3 130 21 280 27 160 7B/10-12 138 19 300 27 151 7B/20-22 139 21 263 32 175 * Note: samples are numberd as i n Table I I iple no. Cu Pb 8/0-2 104 21 8/10-12 98 14 8/20-22 76 13 8/30-32 60 <8* 8/40-42 46 9 8/50-52 42 8 8/60-62 50 9 8/70-72 60 9 8/80-82 55 8 8/90-92 40 9 8/100-102 66 5 8/110-112 59 <4 8/120-122 73 8 8/130-132 57 <4 9/0-2 174 30 9/10-12 190 34 9/20-22 119 34 9/30-32 178 19 9/40-42 128 13 9/50-52 83 10 9/60-62 83 12 9/70-72 71 9 9/80-82 45 8 9/90-92 58 10 9/100-102 59 11 9/110-112 47 10 12/0-2 103 6 12/10-12 61 8 12/20-22 55 6 12/30-32 59 15 12/40-42 46 5 12/50-52 54 7 12/60-62 47 <4 12/70-72 43 5 12/80-82 45 <4 12/90-92 50 <4 12/100-102 50 <4 12/110-112 40 <4 15/0-2 102 17 15/10-12 97 13 15/20-22 58 8 15/30-32 60 12 15/40-42 61 9 15/50-52 61 13 15/54-55F 47 13 Zn Co Ni 240 18 115 212 17 127 182 22 107 130 24 35 120 20 51 110 19 46 110 22 50 112 24 53 112 18 47 107 19 51 115 26 64 125 27 73 130 27 73 125 24 82 225 15 100 258 18 102 255 20 109 182 24 83 167 25 92 152 24 77 135 34 84 113 22 54 105 21 51 115 20 46 117 23 48 107 18 42 275 12 124 179 15 101 124 17 69 129 15 62 110 19 64 121 16 63 107 18 61 100 15 55 103 16 57 118 15 54 109 14 53 92 16 50 268 18 138 228 17 118 154 18 86 140 19 84 135 18 73 124 23 61 100 20 46 124 iple no. Cu Pb Zn Co Ni •15/60-62 54 13 119 29 59 15/70-72 45 7 103 19 59 15/75-76F 47 7 104 20 51 15/80-72 37 11 110 23 47 15/90-92 49 13 115 27 47 15/100-102 46 14 112 21 41 15/110-112 42 14 109 19 37 15/114-115F 40 8 97 18 36 15/120-122 44 12 110 18 36 15/130-132 55 11 115 19 52 15/140-142 52 11 111 15 48 15/CC * 50 11 112 16 47 •16/0-2 106 14 300 14 132 16/10-12 110 14 288 15- 135 16/20-22 117 15 266 17 186 16/30-32 75 12 210 22 111 16/40-42 73 11 180 20 100 16/50-52 56 10 127 16 71 16/60-62 48 10 118 17 56 16/70-72 58 6 113 18 67 16/80-82 56 12 126 23 53 16/90-92 44 13 115 16 45 16/100-102 46 12 120 13 44 16/110-112 47 14 120 14 40 16/120-122 37 11 106 12 44 •18A/0-1 60 23 90 25 40 18A/5-6 70 18 80 18 34 18A/10-11 50 20 73 22 35 18A/15-16 51 17 75 22 37 18 / CC * 52 18 78 20 39 18B/0-1 49 17 73 19 40 18B/5-6 54 20 73 20 43 18B/15-16 75 23 82 60 62 •19/0-2 55 10 141 13 67 19/10-12 51 10 116 18 61 19/20-22 58 15 113 18 51 19/30-32 61 8 121 22 63 19/40-42 75 8 135 29 74 19/50-52 81 8 138 29 77 19/60-62 82 11 145 28 82 19/70-72 68 18 146 28 85 19/80-82 86 7 145 27 83 19/90-92 85 7 146 24 77 19/100-102 83 9 144 28 80 19/110-112 66 11 136 20 71 19/120-122 80 8 146 22 71 19/130-132 77 11 140 21 63 * Note: CC = sample recovered from core catcher 125 Sample no. Cu Pb Zn Co Ni 78-6-19/140-142 75 10 142 22 70 19/150-152 *n n n n n 19/160-162 69 15 135 16 64 19/170-172 56 15 135 19 75 78-6-20/0-2 71 8 206 17 100 20/10-12 43 5 112 18 67 20/20-22 70 12 142 17 72 20/30-32 57 12 126 18 53 20/40-42 38 13 105 16 44 20/50-52 48 13 107 15 43 20/60-62 47 10 106 16 46 20/70-72 38 13 104 17 48 20/80-82 45 11 112 16 45 20/90-92 51 13 113 18 49 20/100-102 59 13 114 18 49 20/110-112 46 16 110 18 49 20/120-122 74 10 125 29 70 20/130-132 81 9 140 29 75 220/140-142 84 9 130 31 75 20/150-152 64 10 126 29 72 20/160-162 54 <4 126 23 92 78-6-23/0-5 100 19 277 15 130 23/10-13 100 17 298 14 134 23/20-23 100 17 280 16 135 78-6-25/0-4 115 20 260 14 126 25/10-14 95 20 263 20 140 78-6-29/0-2 65 11 130 22 63 29/10-12 71 7 114 24 60 29/20-22 58 10 111 21 60 29/30-32 60 10 115 20 58 29/40-42 77 11 109 15 55 78-6-38A/0-3 196 23 390 41 334 38A/10-13 112 23 309 23 159 38B/3-7 126 15 290 19 167 78-6-39A/0-5 164 18 380 33 249 39B/0-5 169 19 355 21 161 78-6-40/0-5 110 10 280 23 198 40/10-14 91 10 273 15 148 40/20-24 66 8 172 16 120 * n = no sample available for analysis APPENDIX 4 Mineralogy, from XRD data Appendix 4 Mineralogy Sample no. Clays Mont. as % of 111. t o t a l clay Chlor. Total clay Clays Mont. as % of 111. t o t a l seds. Chlor. Biogenic Remainder (Quartz & 78-6-1/0-2 9.0 78.8 12.6 39.7 3.6 31.3 5.0 3.5 37.6 20-22 17.4 64.1 18.5 55.8 9.7 35.8 10.3 0.7 27.1 40-42 24.0 60.2 15.7 52.8 12.7 31.8 8.3 6.8 23.9 60-62 12.5 73.3 14.2 57.0 7.1 41.8 8.1 0.5 31.4 80-82 11.6 72.9 15.5 52.6 6.1 38.3 8.2 1.1 37.6 78-6-6/0-2 13.6 74.9 11.6 42.9 5.8 32.1 5.0 4.3 34.2 20-22 5.6 87.0 7.4 38.7 2.1 33.7 2.9 6.6 37.0 40-42 18.3 69.4 12.3 36.3 6.6 25.2 4.5 16.2 29.1 60-62 14.2 75.9 10.0 52.9 7.5 40.2 5.3 7.7 25.4 80-82 9.1 75.5 15.3 38.1 3.5 28.7 5.8 3.9 51.2 100-102 11.6 80.5 8.0 42.5 4.9 34.2 3.4 15.2 26.9 120-122 7.2 80.8 11.9 30.9 2.2 25.0 3.7 24.4 27.1 •7/0-2 15.5 70.7 13.8 44.2 6.9 31.2 6.1 3.9 30.5 20-22 8.0 82.2 9.8 47.6 3.8 39.1 4.7 2.1 33.9 40-42 16.4 66.3 17.2 50.8 8.3 33.7 8.7 7.5 23.9 60-62 19.2 69.3 11.6 46.1 8.9 32.0 5.4 10.3 25.8 80-82 23.7 63.4 12.9 57.2 13.6 36.3 7.4 3.5 21.9 8/0-2 9.5 81.2 9.3 39.1 3.7 31.7 3.6 2.8 39.5 20-22 11.4 75.3 13.3 39.6 4.5 29.9 5.3 15.5 26.9 40-42 16.7 73.1 10.2 64.3 10.7 47.0 6.6 3.3 20.2 60-62 12.4 80.4 . 7.3 58.9 7.3 47.4 4.3 2.3 27.0 80-82 6.4 84.5 9.0 44.0 2.8 37.2 4.0 10.9 31.1 100-102 6.2 78.4 15.4 34.6 2.1 27.1 5.3 21.0 27.5 120-122 10.2 72.6 17.6 36.5 3.7 26.5 6.4 20.4 26.6 Sample no. Clays as % of t o t a l clay Total Clays as % of t o t a l seds. Biogenic Remainder - LOI Mont. H i . Chlor. c l a y Mont. 111. Chlor. (Quartz & plag.) 78-6-9/0-2 11.4 80.9 7.7 37.1 4.2 30.0 2.9 3.6 20-22 8.2 81.5 10.3 41.2 3.4 33.6 4.2 5.3 40-42 16.2 67.6 16.3 38.1 6.2 25.7 6.2 13.1 60-62 13.5 73.1 13.4 45.3 6.1 33.1 6.1 14.0 80-82 8.4 83.1 8.5 55.7 4.7 46.3 4.7 3.5 100-102 13.6 75.4 10.9 53.7 7.3 40.5 5.9 8.3 78-6-12/0-2 6.1 80.4 13.5 42.7 2.6 34.3 5.8 2.1 20-22 4.7 83.5 11.8 47.2 2.2 39.4 5.6 2.5 40-42 12.8 72.3 14.9 50.0 6.4 36.1 7.5 1.7 60-62 8.5 73.6 18.0 52.7 4.5 38.8 9.5 0.8 80-82 9.3 78.2 12.5 40.8 3.8 31.9 5.1 3.6 100-102 9.9 70.7 19.4 48.6 4.8 34.4 9.4 3.0 78-6-15/0-2 16.9 74.0 9.1 47.1 8.0 34.9 4.3 0.0 20-22 10.9 73.2 15.9 52.4 5.7 38.4 8.3 5.1 40-42 16.2 69.9 13.9 50.6 8.2 35.4 7.0 5.5 60-62 10.9 75/6 13.5 49 iO 5.3 37.0 6.6 10.0 80-82 14.1 77.0 8.9 47.8 6.7 36.8 4.3 6.7 100-102 8.9 82.4 8.7 53.1 4.7 43.8 4.6 2.2 120-122 11.5 79.6 8.9 59.7 6.9 47.5 5.3 4.3 140-142 10.5 79.4 10.1 56.3 5.9 44.7 5.7 3.0 78-6-16/0-2 21.7 64.1 14.3 50.2 10.9 32.2 7.2 1.6 20-22 16.8 62.7 20.5 54.5 9.1 34.1 11.2 4.0 40-42 13.4 72.6 14.0 49.1 6.6 35.6 6.9 6.5 60-62 13.3 73.8 12.9 53.9 7.2 39.8 7.0 7.2 80-82 8.3 .81.2 10.5 50.2 4.2 40.8 5.3 9.8 100-102 8.9 84.0 14.6 57.3 5.1 48.1 8.4 3.5 .120-122 6.4 91.0 8.6 55.4 3.5 50.4 4.8 1.6 39.9 36.2 33.5 23.6 30.3 24.6 38.9 40.7 39.9 38.0 47.6 37.5 37.0 29.7 31.6 27.3 33.7 34.2 24.9 29.3 31.1 25.5 30.6 25.6 28.2 28.0 33.5 Sample no. Clays as % of t o t a l clay Total Clays as % of t o t a l seds. Biogenic Remainder - LOI Mont. 111. Chlor. c l a y Mont. m . Chlor. (Quarts & plag.) 78-6-18A/0-2 12.3 75.4 12.2 28.5 3.5 21.5 3.5 24.4 25.8 B/0-2 8.8 81.6 9.6 27.0 2.4 22.1 2.6 32.7 17.2 78-6-19/0-2 16.1 71.5 12.4 . 50.0 8.0 35.7 6.2 10.4 25.4 20-22 6.7 85.1 8.2 54.9 3.7 46.7 4.5 3.1 31.4 40-42 3.1 81.5 15.4 35.2 1.1 28.7 5.4 13.9 36.8 60-62 5.5 76.9 17.5 47.2 2.6 36.3 8.3 8.6 31.7 80-82 8.8 74.5 16.7 44.4 3.9 33.1 7.4 10.3 32.4 100-102 4.6 77.1 18.4 46.5 2.1 35.9 8.6 8.1 33.0 120-122 1.8 84.1 14.1 45.3 0.8 38.1 6.4 6.0 37.9 140-142 2.'4 85.'5 12.1 44.6 1.1 38.1 5.4 5.9 38.7 160-162 3.6 85.0 11.4 43.2 1.6 36.7 4.9 12.1 27.7 78-6-20/0-2 14.6 72.6 12.8 49.9 7.3 36.3 6.4 5.9 29.8 20-22 13.0 76.0 11.0 49.5 6.4 37.6 5.4 6.2 31.7 40-42 11.3 80.2 8.5 53.9 6.1 43.2 4.6 1.6 33.7 60-62 10.0 82.5 6.8 54.3 5.4 44.8 3.7 2.0 34.0 80-82 3.6 87.2 9.1 52.3 1.9 45.6 4.8 4.3 31.9 100-102 6.2 85.3 8.5 52.2 3.2 44.5 4.4 4.0 32.3 120-122 13.5 71.3 15.2 40.4 5.5 28.8 6.1 15.6 29.4 140-142 3.9 80.8 15.3 37.6 1.5 30.3 5.8 15.1 32.9 160-162 24.0 58.4 17.6 54.7 13.1 31.9 9.6 4.7 30.7 APPENDIX 5 Sedimentology, from X-ray radiographs and v i s u a l examination, and geochemical u n i t s , from data i n F i g . 6 131 LEGEND Column 1. X-ray radiograph interpretations. 2. Visual sediment types. 3. Munsell colour c lass i f i cat ion. 4. Geochemical units. X-ray radiograph interpretations. No discernable structure. Visual sediment types. Clay. Planar lamination. Silt. Contorted lamination. Sand. « • • Granular or sandy. Volcanic glass shards. Mottling; bioturbation. Digging structures. (? Zoophycos) • 0 o Volcanic glass shards. Planktonic debris (foraminifera). Dark smears - probably organic. 132 10 20j 30 40l 50 o 60 S70J 80 90 100 110 120 0 o o 0 ft O O o — o p o o o 3 4 10YR2O- 1a 5Y5/2 5Y4/1 f 5G4/1 5Y5/2 to 5/1 5Y4/1 to 5GY5/1 hSGY4/l: 5Y5/2 to 5GY6/1 1b Core 78-6-1 10 20 3 0 l 40l 50| 60| 70J E o X 8 0 CL UJ Q 9 0 I 100J 1 1 0 1 1 2 0 1 130J 140] HEEBi 1 • - 0 — o 9 ° • • • • • • . • • • • 0 0 D — e o o -~-o 5Y5& 1 . . — ^ . • • • • • Q • o — - 5Y5/2 and 5Y4/2 - 5Y4/1 • • * • • • • o o — O — p o — 5Y4/2 « ~ 5Y4/2 and 5Y3/2 • • • • • • • • • 0 O O © ft 0 o — o o ~ 0 5Y4/1 2 • • • • • « • • • • o — 0 e O a Q 5Y5/2 • • • • • • • • • • ° a — « o o « — • o 5Y5/1 and 5GY5/1 3 • • o — • Core 78-6-6 133 10 20 30l 40 50 E ° 6 0 X I-Q. LU Q 70 80 90 100J 110! 2 3 4 ' - T n0YR2 /2Tla~ O o O T o \— * 0 9 O 0 o ~ o — 5Y4/2 f=5YR3/2j 5Y5/1 Core disturbed o c o 5Y5/1 1b Core 78-6-7 10 20 30 40 50 60 70 80 E 9 04 o :100 Q. LU Q 110J 120 130] 140 150 160 • • • Cori 4 — o — o  e ~ "o • - - o - o o — « - ~ ° ~ g O O I " - ~ S_ « . o g «"~ o « |5Y5/1,521 5GY5/1 _ - o — O ~ " o | 5Y5/2 1b 5Y5/1 5Y5/1 disturbed 5Y5/2 1c 5Y4/1 and 5Y5/1 5Y4/6 5GY5/1 Core 78-6-8 134 10 20 30 40 50 60 • • * E ° 70 £ 8 0 , 90 100 110 p0YR5flf 1a 0 ~ — \i • — 22— — - o — eT — o o -"u .•^r-i' — _ it - c. 7T"> 0— ca // o I— o — o o 5GY6/1 to 3/1 5GY5/1 5GY6/1 5Y5/1 Core 78-6-9 1b 1c 10 20J 30 40 50 6Q 90 100 110l 120l o — o - a — o — a -L a " — o - ~ tonus1 5Y6/1 to 5GY6/1 5Y6/1 to 5/1 5Y6/1 to 5GY6/1 5GY4/1 4 31" 1b 2a 2b Core 78-6-12 136 X r-Q. •—>r • /<• <» o *~ O \.» o , « „ • 10YR5/2 a n d 10YR4/2 D 1> *A, ~ " o"="o Vv - — ^ — • o: o •« * ' — 0 o • — « * " — « • Core 78-6-18 10 11111111 • 11 rrm 20 30l 401 50! 60 E o 80 90 §100| 110 120 130 140 150j 160 170 O o a 0 Q o 10YR6/2) 1 0 0 o « o o o O o 0 0 a o o 9 0 0 o o 5GY5/1 to 5Y5/1 Core 78-6-H 138 APPENDIX 6 A Note on A n a l y t i c a l P r e c i s i o n 139 A Note on A n a l y t i c a l Precision The following estimates for the precision of chemical analyses performed on material collected during the course of this study, were supplied by Mr. Frank K i s s , of Cominco Research Laboratories Ltd., of Van- . couver. For the major oxides:-Oxide: Si0 2 A1 20 3 Fe 20 3 Ti0 2 MgO CaO Absolute p r e c i - ± 1% ±0.2-0.3% ±0.5% ±0.1% ±0.2 - 0.3% ±0.2 - 0.3% sion: Na20 K 20 LOI ±0.3-0.5% ±0.3-0.5% ±0.1-0.2% For the trace elements:-Element: Cu Pb Zn Co Ni Detection Limit (ppm): 1 4 1 1 1 Precision around detection l i m i t : 100% 100% 100% 100% 100% Precision around working l e v e l 10% 10% 10% 10% 10% (approx.): TABLE VI, on the following page, shows, for comparison purposes, the results of a series of analyses on some similar material (Core 77-14-55) performed by Cominco Research Laboratories Ltd., and (in parentheses) anal-yses of adjacent samples performed by Dr. E.V. G r i l l of the Department of Oceanography, using atomic absorption spectrophotometry. TABLE VI: Comparison of chemical analyses performed by Cominco Research Laboratories Ltd., and (in parentheses) by Dr. E.V. G r i l l , on samples from Core 77-14-55 Sample Depth Si0 2 fl0~2 A1 20 3 FeTO^ MnO MgO CaO Na 20 K 20 Cu Zn (cm) 0-• 2 53.36 (52.5) 0.72 (0.69) 13.45 (12.8) 7.07 (7.06) 0.26 (0.26) 3.19 (3.08) 3.09 (2.66) 3.10 (3.37) 2.01 (1.93) 100 ( 94) 300 (274) 4-• 6 54.11 (52.6) 0.73 (0.72) 13.97 (13.2) 6.80 (6.75) 0.32 (0.30) 3.29 (3.17) 3.34 (3.04) 3.18 (3.25) 2.08 (2.02) 98 ( 88) 305 (281) 8-•11 52.26 (51.4) 0.73 (0.72 13.68 (13.8) 6.95 (6.99) 0.15 (0.15) 3.22 (3.23) 3.56 (2.95) 3.58 (3.60) 2.11 (2.02) 96 308 17-•20 53.07 (53.0) 0.76 (0.72) 14.26 (13.2) 6.89 (6.95) 0.15 (0.14) 3.21 (3.17) 3.81 (3.19) 3.17 (3.23) 2.15 (2.08) 91 ( 89) 309 (343) 29-•32 53.47 (54.7) 0.78 (0.75) 14.53 (13.5) 7.29 (7.52) 0.14 (0.13) 3.33 (3.22) 3.30 (2.56) 3.40 (3.50) 2.27 (2.19) 93 288 35-•38 52.49 (53.2) 0.77 (0.80) 14.51 (13.5) 7.54 (7.56) 0.15 (0.15) 3.39 (3.41) 3.67 (3.03) 3.56 (3.50) 2.24 (2.17) 95 270 44-•47 51.72 (48.9) 0.77 (0.82) 14.92 (14.1) 7.35 (7.33) 0.40 (0.40) 3.54 (3.35) 4.66 (4.35 3.38 (3.41) 2.23 (2.13) 85 (112) 239 (236) 54-•57 56.21 (54.4) 0.85 (0.82) 15.88 (14.6) 7.15 (7.03) 0.12 (0.11) 3.39 (3.23) 3.78 (3.11) 3.07 (3.37) 2.01 (1.90) 52 120 63-•66 62.60 (59.0) 0.83 (0.80) 14.78 (13.6) 5.69 (5.41) 0.10 (0.09) 2.55 (2.30) 4.34 (3.72) 3.52 (3.53) 1.54 (1.47) 30 ( 29) 81 ( 75) TABLE VI (Cont'd.) Sample Depth Si0 2 Ti0 2 A l 2 o 3 Fe 20 3 MnO (cm) 72-75 57.68 0.85 15. 94 6.92 0.11 (55.5) (0.83) (14. 8) (6.67) (0.11) 81-84 60.01 0.78 15. 35 6.42 0.12 (56.5) (0.78) (14. 2) (6.25) (0.11) 90.93 58.82 0.85 15. 76 6.99 0.10 (55.8) (0.78) (14. 7) (6.53) (0.10) Ppm MgO CaO Na20 K 20 Cu Zn 3.37 (3.18) 3.82 (3.47) 3.29 (3.46) 1.98 (1.87 44 105 2.90 (2.77) 4.47 (4.11) 3.42 (3.24) 1.85 (1.78) 40 100 3.19 (3.12) 4.04 (3.68) 3.11 (3.37) 1.93 (1.88) 42 ( 37) 104 (105) 

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