A Study of Sediments from the Juan De Fuca Ridge, Northeast
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 British 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 presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission.
Department of Gcolgj'iCctl Scv€*6as
The University of British Columbia 2075 Wesbrook Place Vancouver, Canada V6T 1W5
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 Plain indicates a mainly terrigenous, turbiditic source for most sediments in 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 in the oxidised upper few cm of sediment is ascribed to diagenetic remobilization.
Systematic variations in the Si02, A1203 and CaO content of the sediments appear to reflect a transition from a dominantly turbiditic 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 significant hydrothermal component, such as have been reported from the East Pacific .
Rise and other parts of the Pacific Ocean, appear to be absent from the area, due probably to extensive dilution by sediments of terrigenous origin. TABLE OF CONTENTS
• Page
ABSTRACT ii
LIST OF TABLES • v
LIST OF FIGURES vi
LIST OF PLATES vii
ACKNOWLEDGEMENTS viii
1. INTRODUCTION 1 Regional context 1 Ocean floor 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
iii 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 in 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 profiles 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 visual examination, and geochemical units, from data in Fig. 6 130
APPENDIX 6. A note on analytical precision 138
iv LIST OF TABLES
Table Page
I Core Locations and Lengths 22
II 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 40
III The five samples having lowest CaO/Al203 ratios; 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 Fig. 3) 66
VI Comparison of chemical analyses performed by Cominco Research Laboratories Ltd., and (in parentheses) by Dr. E.V. Grill, on samples from core 774-14-55 ...... 140
v LIST OF FIGURES
Fig. Page
1 The convective hydrothermal model for ocean floor metallogenesis 5
2 Location map of study area 11
3 1978 study area showing bathymetry, seismic line positions, In >
core locations and locations of sediment depth estimations pn&ked^ 1*-gcfiOv
4 Magnetic profiles 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- tion, heating, and acid treatments 43
8 Variation with sample depth of clay minerals in the ten longest cores 44
9 Covariation between CaO and (Al203+Si02) in Juan de Fuca Ridge sediments 52
10 Variation of biogenic component (i.e. carbonate) with water depth, showing effect of depth on carbonate solubility 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 Si02 to A1203 for deep-sea sediments of hydrothermal, hydrogenous and terrigenous origin 73
13 Ratio of Fe/Ti to Al/(A1+Fe+Mn) for sediments cored during this study 74
14 Variation in MnO content and thickness of Unit la with distance from ridge crest 78
15 Sediment inputs to the Juan de Fuca Ridge area 83
vi 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 profiles N4.5, E0.5, N3 and E0.25 99
6 Seismic profiles El (west half) and El-2 tie line 100
7 Seismic profiles N3 and El (east half) ' 101
8 Seismic profiles N3.7 and El.5 102
9 Seismic profile E2 (west half) 103
10 Seismic profile E2 (east half) 104
11 Seismic profile E2.5 and 2.5-1.5 tie line 105
12 Seismic profile E3 106
13 Seismic profiles E5 (west half), Nl, and E4 (west half) 107
14 Seismic profiles E5 (east half), N5, E4, and N4 108
15 Seismic profiles E7 and N3.5 109
16 Seismic profile E9 110
17 Seismic profiles Ell and Nl Ill
18 Seismic profile N2 112
vii ACKNOWLEDGEMENTS
This study would not have been possible without the assistance and support of a large number of people and organizations; particular
thanks are due to the following:
My thesis advisor, Dr. R.L. Chase; Dr. E.V. Grill, 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 officers
and crew of the CFAV Endeavour; Mr. Frank Kiss and the analytical staff
of Cominco Explorations and Research Laboratory; Dr. G. Burgess of the
Department of Radiography at Vancouver General Hospital; Bob Macdonald,
who kept all the equipment running; and lastly, but by no means least,
my wife Caroline, whose unfailing support I could always count on, even
at 2:00 a.m.
Funding fq.r the project was provided by the National Scientific
and Engineering Research Council of Canada; Cominco Ltd., B.C. Ministry
of Energy, Mines and Petroleum Resources; and the N.A.H.S. Committee of
the University of British Columbia.
viii 1. INTRODUCTION
Regional context
The present study forms part of a continuing investigation by the University of British 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 will be, reported by Barr (1972), Barr and Chase (1974),
Piper et al. (1975), Chase et al. (1980), Grill 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 is to investigate the possibility that metalliferous hydrothermal deposits form a signif• icant component of the sediments in the Juan de Fuca Ridge area.
Ocean floor metallogenesis
The occurrence of metalliferous deposits in 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 origin of such depos• its (Bonatti, 1975):
a) HYDROGENOUS: formed by the slow precipitation of continent-
derived metals from normal sea water; this process is restricted 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 basaltic glass) and sea water. This process is
important only in areas of abundant basaltic pyroclastic deposits.
d) MANTLE-DERIVED HYDROTHERMAL: formed by the concentration of
metal sulphides in the volatile phase of magmatic material.
e) CONVECTIVE HYDROTHERMAL: due to the circulation of sea
water through fractures in hot ocean floor rocks. This process
is described more fully below.
Heat flow anomalies at ocean ridges
Von Herzen and Uyeda (1963) first reported high mean values of heat flow in sediments on the East Pacific 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, in the crestal sediments as compared with surface sediments at a distance from the Rise crest. They interpreted this enrichment as being due to the precipitation of metallic oxides from
"volcanic exhalations," or hydrothermal solutions derived from the volatile components of ascending magmas.
Corliss (1971) showed that the slowly cooled interiors of basaltic lava flows on the Mid-Atlantic Ridge are depleted in Fe, Mn and other heavy metals relative to the chilled margins. The apparent coincidence between this depletion of the basalts and the enrichment 3 of the overlying sediments in the same metals led Corliss to the conclu• sion that the "exhalations" of Bostrom and Peterson (1966) actually con• sisted of1 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 floor.
Lister (1972) noted that heat flow values along the crest of the
Juan de Fuca and Explorer Ridges, while higher than the normal sea floor values, are considerably lower than those measured on the ridge flanks : where the volcanic bedrock is blanketed by sediments. He interpreted this observation to mean that most of the heat transfer at ridge crests occurs by hydrothermal circulation, that is, by a convective, rather than a conductive process. Where the fractures in the volcanic bedrock which form the hydrothermal circulation 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 this model, hot upwelling magma at ridge crests undergoes rapid cooling as it contacts cold sea water, and extensive fracturing, probably to depths of several kilometres, occurs, as the freshly formed rock moves laterally away from the ridge crest. Sea water •penetrates into these frac• tures, where under high hydrostatic pressure and strongly reducing condi• tions it is heated to 300-500°C, and reacts with the lavas; the following reactions are suggested as examples: 2+ —
Fe^iO^ + 4H20 —> 2Fe + 40H + H^SiO^
(Fayalite) 4
2+ 2Fe2Si0lt + 3H20 -> Fe3Si20£(0H) „ + Fe + 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 floor where they are deposited as oxide and hydroxide precipitates. The whole process is illustrated in Fig. 1.
As the solution cools during its passage to the sea floor, less- soluble sulphides might also be deposited at lower levels within the frac- 3 ture system; volatile components from the upper mantle (represented by He in Fig. 1) may be incorporated into the hydrothermal fluid, and other compo- nents, such as U , may be lost 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 Drilling Project has re• vealed the presence of an Fe- and Mn-oxide rich layer at the base of the sediment column, directly overlying pillow lavas, over large areas of the sea floor; see, for example, von der Borch and Rex (1970), von der Borch et al. (1972), and Cronan (1976). Analogous deposits have also been re• ported in sediments of marine origin 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 al. (1976) and Francheteau et al. (1979). Chapman and Spooner (1977) have demonstrated, using Sr-isotope ratios, that the sulphide deposits of the Troodos Complex were formed by sea water circulation. 5
Fig. 1. The convective hydrothermal model for ocean floor metallogenesis. See text for 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 floor basalts at 200°C and 500 bars, and noted an increase of sea water acidity from pH 7.9 to 3.9 after only
72 hours, together with increases in dissolved Ca, K, Cu, and Ni and de• creases in Mg and Soi,. Fe and Mn also increased initially, but then showed a steady decrease. Seyfried and Bischoff (1977) hypothesize that the in• crease in acidity is a factor in the high metal solubility. 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 ratio; with high ratios of enriched to normal sea water a
precipitate rich in Mg and Si02 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 inter• actions between ocean floor basalts and normal sea water, at high tempera• ture and pressure, are capable of producing solutions which on cooling under oxidising conditions might result in precipitates having the composi• tions found in typical sea floor deposits.
Bonatti (1975) remarked that hydrothermal deposits show a very wide range of Fe/Mn ratios, varying from >10 to <0.1, in contrast to sediments of hydrogenous origin whose Fe/Mn ratios are close tov.unity (see Fig. 11, p. 71). This variation is attributed to the more rapid oxidation of Fe, and thus faster precipitation, when the hydrothermal fluids 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) lists geochemical, mineralogical and geophysical criteria for the recognition of this type of deposit.
Other metalliferous deposits
Hydrothermal deposits are restricted, in general, to the base of the sediment column, as has been outlined above. Other types of metalli• 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 origin; for reviews of the current'.state , of knowledge in this field, 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 floor; their origin 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 rich in Mn and trace elements were described by Murray and Renard (1898) as "pelagic red clays;" Bramlette (1961) and
Horn et al. (1970) have proposed an authigenic (i.e. hydrogenous) origin for these deposits. In Bramlette's words:
Pelagic sediment is precipitated and/or settled from the over• lying waters of regions where rates of accumulation are slow enough to cause little change in the great volume of circulating bottom waters, and the little 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 origin in the Bauer .Deep and other sites in .the equatorial Pacific Ocean.
Lynn and Bonatti (1965), and Bonatti et al. (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 in the sediment column. These elements are then transported u > 8 upwards, mainly by ionic and/or molecular diffusion 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 is thus seen to be analogous to the convective hydrothermal process, except that it obviously operates at a lower temperature. Oxidation poten• tial (Eh) rather than temperature, would seem to be the important criterion for remobilisation.
Some doubt has been cast on this model by Bender (1971), who has calculated that ionic or molecular diffusion would be insufficient to trans• port dissolved Mn at the rate of accumulation judged to be necessary over a vertical 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, it seems certain that remobilisation does occur in many oceanic areas, at least of Mn and possibly of other .metals (Li et al., 1969;
Calvert and Price, 1972; Pedersen,"1979; Hartmann, 1979). Certainly, where only a thin Mh-rich layer exists, remobilisation processes are probably dominant (Grill, 1978). 2. PURPOSES OF THIS STUDY
Introduction
It seems highly probable that many, if not all, of the processes discussed in Chapter 1 may occur, either together or in any of several possible sequences, in the vicinity 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 relative importance of each process in the overall history (which will of course be different from area to area), and the relationship of present mineralogy and geochemistry to the history of the sediments; this latter 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 in the north• east Pacific Ocean, has the added complication of heavy terrigenous sedimentation due to the proximity of the coasts of British Columbia,
Washington and Oregon. Two major rivers, the Fraser and the Columbia, between them deliver 20-60 million metric tons of sediment per year into the marine environment (Gross, 1977), and numerous smaller streams also contribute to the total sediment input.
9 10
Accordingly, the main purposes of the present study are three• fold:
a) To describe the sediments in the study area in terms of mineral-
ogical, geochemical and sedimentological parameters;
b) To determine as far as possible the provenance and depositional
environment of the sediments, and specifically to determine
whether a significant hydrothermal component is present; and
c) To determine whether post-depositional changes in either the
mineralogy or the geochemistry of the sediments have occurred,
and if so, the reasons for any such changes.
Location of study area
The area under investigation is located in the northeast Pacific
Ocean, between 47°00' and 48°15' north latitude, 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 Plain to the east of the ridge.
The Juan de Fuca Ridge is presently an active spreading centre, with a half-rate of between 2.9 and 3.1 cm yr-1 (Vine, 1966; Chase et al., 1975; Riddihough, 1977), and forms the margin between the Pacific
Plate to the west, and the Juan de Fuca Plate to the east. The term
"ridge" is, in a sense, misleading in this context, since the Juan de Fuca Ridge consists essentially of a system of parallel ranges sepa• rated by deep, often wide, valleys, together with associated seamount chains. The term "ridge complex" will be generally used in place of
"ridge" in the course of this study.
Within the study area the ridge crest is offset at its inter• section with the Cobb Fracture Zone by a right-lateral transform fault 11
Fig. 2. Location map of study area. Spreading ridge segments are shown as double solid lines, and transform faults as single solid lines. The edge of the Continental Shelf is shown as a light dashed line; arrows show locations of major submarine canyons. 12 showing a displacement of approximately 25 km.
The higher parts of the ridge complex are essentially bare basaltic "oceanic basement," but the eastern flank is blanketed by the sediments of the Cascadia Plain, which are considered by Horn et al. (1970) and others to be almost wholly turbiditic 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 is locally in excess of
700 m. The Cascadia Plain is essentially horizontal, and lies 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 classic paper on the "magnetic stripes" of the ocean floor, 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 it has been pointed out that the anomaly pattern is not entirely symmetrical (Elvers et al., 1973).
The small Juan de Fuca Plate, subjected to the stresses of subduction under North America, has undergone considerable internal deformation, 13 splitting into several smaller blocks with movement rates relative to each other of up to 3.5 cm yr 1 (Silver, 1971). McManus et al.
(1972) suggested that the northern salient of the Juan de Fuca Plate, adjacent to the Explorer Ridge, may be in the process of splitting away from the rest of the plate. The work of Riddihough (1977) has confirmed this view; thus the classically simple concept of the Juan de Fuca Plate as a single entity has given way to a complex, but un• doubtedly much more realistic, system of small "platelets," all moving semi-independently at different rates and in 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 right-lateral transform faults throughout the area, can be accounted for by a rota• tion in the spreading direction of the Ridge about 5 million years ago, as proposed by Menard and Atwater (1968) and Atwater (1970). The spreading direction of the Juan de Fuca-Explorer ridge system appears to be gradually rotating into parallelism with the strike-slip motion of the San Andreas and Queen Charlotte fault zones.
Tobin and Sykes (1968) found that, while the Explorer and Gorda
Ridges and the Sovan'co and Blanco Fracture Zones are all 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 this one event probably occurred on the Cobb Fracture
Zone. They drew attention to the observation that relatively fast- spreading ridges which lack a prominent median rift, such as the East
Pacific Rise, are generally aseismic along the crest; apparently only those ridges having a prominent median valley exibit crestal seismicity. 14
However, the spreading rate of the Juan de Fuca Ridge is, by contrast with the East Pacific Rise, relatively slow (approximately
3 cm yr-1, compared with rates of up to 9 cm yr-1 for the East Pacific
Rise, reported by Le Pichon et al. (1976)), and there is some indication of incipient rift formation, as can be seen in some of the seismic profiles (appendix 1). The Juan de Fuca Ridge is comparable in this respect to the Galapagos Rise, which has a half-rate of 2.1-3.6 cm yr-1 and also lacks a prominent rift valley in places (Hey, 1977). These ridges are probably transitional in type between the fast-spreading non-rifted and slow-spreading, rifted ridge types, the latter typified by the Mid-Atlantic Ridge. The reasons for the association between fast spreading rate, lack of a rift valley and aseismicity are apparent• ly unknown. The Juan de Fuca Ridge, again unlike the East Pacific
Rise, is extensively block-faulted (McManus et al., 1972; Davis and
Lister, 1977a).
Heat flow studies (Lister, 1972; Davis and Lister, 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 circulation, as described in
Chapter 1, must be active in the area, and may well contribute a hydro- thermal component to the sediments.
Sedimentology
It is perhaps surprising that sedimentological studies in the area have been much less thorough than those related to tectonics.
Duncan et al. (197) studied the clay minerals of the Cascadia
Plain sediments and reported montmorillonite, illite and chlorite to 15 be the major components. Horn et al. (1970), in a regional study of the North Pacific, examined a number of cores from the Juan de Fuca and Cascadia Plain areas obtained by ships of the Lamont-Doherty Geolo• gical Observatory, and concluded that the sediments are predominantly turbiditic. Kulm and Fowler (1974) reported turbidites intercalated with pelagic and hemipelagic sediments in the Cascadia Plain.
Previous reports of hydrothermal deposits are sparse. Piper et al. (1975) reported a hydrothermal deposit from Dellwood Seamount, off Vancouver Island; this was essentially a basal crust, dredged up with samples of basalt, and though it was obtained somewhat to the north of the present area, it at least establishes the presence of hydrothermal activity close to the area of present interest.
Tiffin et al. (1978) and Bornhold et al. (in prep.), examined a number of cores obtained on a transect of the Juan de Fuca Ridge, again slightly 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 slight enrichment in Cu and Ni. They also report, in a core obtained to the west of Explorer Ridge, a dark brown unit underlying all the others which shows considerable enrichment in Mn, Cu, Zn, Pb, Ni and Co. This unit they interpret as a basal hydrothermal deposit.
Thus it can be stated that a hydrothermal component in the sediments in the area of the present study is at least a possibility.
The large influx of terrigenous turbiditic material, however, may dilute the hydrothermal component, if it exists, beyong the limits 16
of detection. Undiluted hydrothermal deposits may be found, if at all, oh topographic highs close to the ridge crest 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 jointly by the Depart• ments of Geological Sciences and Oceanography at the University of
British Columbia, and the Pacific Geosciences Centre Earth Physics
Branch.
Navigational positions were obtained by LORAN C, using an Inter- nav LC 204 receiver, in conjunction with the Endeavour's own LORAN A and satellite 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 Pacific Geosciences Centre, run on a Tek• tronix 4051 minicomputer. LORAN C, under favourable conditions, is understood to provide positional accuracy to within better than 30m.
Positions were recorded every ten minutes; a Hewlett Packard
K22-5321 digital clock was used to provide accurate time readings.
Continuous seismic profiles were run at 5-10 km intervals in a direction approximately perpendicular to the ridge crest, together with a few profiles parallel to the ridge. A Bolt PAR airgun with 18 either a 300 in3 (4900 cm3) or a 20 in3 (330 cm3) air chamber was used as a seismic source, and seismic data were recorded using an EPC graphic recorder. Seismic tracks are shown in Fig. 3, and the profiles are reproduced, as Appendix 1. Magnetic profiles were run concurrently with the seismic profiles, using a proton-precession magnetometer towed astern of the ship. The magnetic profiles were used in this study only to define the position of the ridge crest. Two representative pro• files are presented here as Fig. 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-? ical Sciences Department technical staff were unsuccessful due to the lack of a suitable core catcher. A total of 20 cores were obtained
(of which 18 were used in this study), at locations shown in Fig. 5 and listed in Table I. Most of the cores were taken on a single WNW-
ESE transect of the Juan de Fuca Ridge crest along seismic line E2, although a few were taken in other locations. A single Phleger core,
No. 78-6-40, was taken in the Cascadia Plain about 150 km away from the ridge crest, to provide a standard having little or no hydrothermal component, against which the other cores could be compared.
On recovery, each core was capped, measured and examined visual• 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 restrictions and the requirements of the Pacific Geoscience Centre's concurrent heat probe and magnetic survey projects. 19
11 June 1978 Time
555
x
545
16 June | 15 June Time
Fig. 4. Magnetic profiles across the northern Juan de Fuca Ridge; profile locations are shown in Fig. 3. The ridge crest is assumed to lie at the central point of the major positive anomaly. 20
Fig. 5. Map of study area showing core locations. 'Contours in meters (uncorrected) . • - Core location (successful). 0 - " " (unsuccessful). 21
Laboratory work
After being brought ashore the cores were split longitudinally and the split surfaces smoothed with a plastic spatula. Immediately after splitting, the cores were photographed to provide a record of their fresh appearance.
One half of each core was subsampled at 10 cm intervals, and in one case (No. 78-6-15) additional samples were taken of layers found to be especially rich in organic remains (mainly foraminifera). Core no. 78-6-18, which seemed to be of special interest, was subsampled at 5 cm intervals. The remaining half of each core was retained un• disturbed and sealed in a plastic sleeve.
The subsamples were air 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. Grill of the
U.B.C. Department of Oceanography). Analyses were performed by means
of X-ray fluorescence for the major oxides (Si02, A1203, CaO, MgO,
Fe203, K20, Na20, MnO, Ti02, and P20s), 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 Fig. 6.
Further subsamples were taken at 20 cm intervals and analyzed mineralogically by X-ray diffraction, in general following the proce• dure outlined by Carroll (1969), using a Phillips PW 1050 diffractometer.
The following diffractometer conditions were found to give good results:
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 To Dr. E.V. Grill for pore water analysis. 4 48° 05.26' 129° 44.93" 2827 New grav. _ No recovery 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 II 118 8 47° 59.56' 129° 21.37' 2455 ii 166 II 9 47? 56.35' 129° 10.08' 2442 114 II 11) hl° 50.48' 128° 37.83' 2633 99 Used by Pacific Geosciences Centre. 12 47° 54.94' 128° 51.79' 2602 II 123 15 47° 55.31' 129° 01.38' 2560 it 145 16 47° 53.94' 128° 58.18' 2542 II 132 17 47° 54.95' 129° 03.64' 2348 II - No recovery 18 47° 55.04' 129° 02.33' 2258 II 44 19 47° 53.14' 128° 55.37' 2645 II 175 20 47° 52.58' 128° 54.37' 2553 II 167 23- 47° 54.18 ' 129° 00.88' 2755 Phleger 27 24 47° 55.30' 129° 04.45' 2347 II - No recovery, 25 47° 55.01' 129° 02.52* 2609 II 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 II - 32 47° 57.10' 128° 49.74' 2606 II 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 ii - 38 47° 07.24' 129° 41.24' 2798 Phleger 29 II 39 46° 55.29' 128° 57.74' 2692 19 40 46° 33.16' 127° 31.03' 2826 II 27 23
Cathode potential 40 kV, current 20 mA;
Beam slit 1°, collector slit 0.02°; _i -_i Chart speed 2 cm min , scan speed 2°26: min
Chart range 4xl02. time constant 4 sec.
The semi-quantitative technique described by Biscaye (1965), as modified by Heath and Pisias (1979) was used to gain some idea of the proportions of the various clay minerals present. Typical diffraction profiles are illustrated in Fig. 7, and the mineralogical data are presented in Appendix 4 and Fig. 8.
A descriptive log of each core was prepared, noting sediment colour (using the Munsell rock colour chart), visual grain size, and any distinctive features such as foraminifera-rich layers, volcanic glass shards or important sedimentary structures. X-ray radiographs of each core were also prepared in order to reveal sedimentary structures not otherwise visible. The core logs and X-ray interpretations are presented in
Appendix 5. 4. RESULTS
Bathymetry
The bathymetry shown in the main map (Fig. 3) is based in part on the seismic profiles obtained during the Endeavour cruise, and in part on the published bathymetry of Mammerickx and Taylor (1971) and
Wilde et al. (1977). The agreement between the older data and the
Endeavour profiles is generally good, although a small elevated area centred at 129°00' west and 47°37' north, visible on seismic profiles
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 its detailed bathymetry and maximum elevation are unknown; the minimum depth recorded was approximately 2280 m. This area seems to be directly in line with
the section of the Juan de Fuca Ridge crest south of the Cobb Fracture
zone, but exhibits no positive magnetic anomaly. It is probably a
small, hitherto undiscovered seamount.
Structural geology
The seismic profiles (see Appendix 1) show, to the east of
the ridge complex, a thick wedge of generally flat-lying sediments with numerous prominent internal reflectors; these reflectors are. visible throughout the sediment column, and indicate cyclic, most
24 25 probably turbiditic, sedimentation rather than continuous pelagic deposi• tion. This contrasts with the "seismically transparent" sediments reported by Kulm and Fowler (1974) to underlie the turbiditic deposits in seismic profiles from the same area. The profiles 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 reflection but miss reflectors having low velocity contrast within the sediments.
The sediments overlie a presumably basaltic basement which exhi• bits considerable relief; extensive block faulting, with some tilting of individual blocks (reported also by Davis and Lister, 1977a) has re•
sulted in a series of horst- and graben-like structures, the long axes of which run parallel to the ridge crest. Seamount chains, restricted
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 restricted almost entirely to the "grabens," but on the east flank
the whole basement topography is masked by the turbidite wedge of the
Cascadia Plain.
Horn et al. (1971) place the Cascadia Plain within their North•
east Pacific Turbidite sedimentary province. The ridge complex they
place in a province of its own, the Ridge and Trough Province; however,
the sediments in the area, although restricted to the troughs or grabens,
have a similar seismic character to the Cascadia Plain turbidites. The
troughs probably act as channels for turbidity currents with a source
to the northeast. Another likely source for sediments in the troughs
may be slumping of hemipelagic material from the neighbouring "horsts," 26 which might be expected to give rise to very thin turbidite layers or
"microturbidites," probably no more than a few cm thick.
The offset of the ridge crest mentioned previously is 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 is consistent with the magnetic data of Raff and Mason (1961), but there seems to be little justification for assuming that the ridge offset parallels this trend, since it is not parallel to the direction of relative motion of the Pacific 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 in Fig. 2, perhaps for no better .. reason than that is the way it theoretically "should" be. It is worth pointing out, however, that the Cobb Fracture Zone is apparently virtual• ly aseismic (Tobin and Sykes, 1968), and thus is not typical of ridge- ridge transforms in general. It should also be noted that the sections of the Cobb Fracture zone east and west of the Juan de Fuce ridge are not parallel to each other. These two sections have been given a single name but they may in fact be two completely independent fracture zones which coincidentally intersect close to the Juan de Fuca Ridge offset.
It is possible that Hey et al.'s (1980) concept of a "propagating frac• ture zone" may be applicable here; the situation in the area is obviously complex, and further geophysical investigation would seem to be justified.
It is unfortunate that the Endeavour seismic profile E7, which crosses the trend of the Cobb Fracture Zone, is of much poorer quality than the other profiles, and provides almost no reliable information. 27
Coring
A total 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 listed in Table I, and shown in Fig. 5.
Of the nine unsuccessful coring attempts, three (78-6-4, 5 and 27) were felt 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
sufficient 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 basaltic glass were recovered form the core catch•
er on a few occasions. On the final 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 bridle was found to be bent.
It is 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 Fig. 6.
It is possible, on the basis of the geochemistry of these ten
cores, to recognise three distinct "geochemical units," here designated
Units 1, 2 and 3; the uppermost of which, Unit 1, can be further sub•
divided.into three subunits, designated la, lb and lc. 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 is characterised by low Si02, A1203 , K20 and
Ti02, and high MnO, Cu, Zn, Pb and Ni. CaO and LOI (loss on ignition) are usually, though not invariably, high; Co seems to covary to some ex• tent with CaO. The total 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 is used to define the three subunits.
Subunit la, present in nine of the long cores (78-6-15 is the
sole exception), shows considerable enrichment in MnO, in a few cases by over an order of magnitude, but frequently a slight decrease in Cu,
Zn and Ni compared with subunit lb. This subunit varies from 2 to 9 cm
in thickness, and is invariably brown in colour.
Subunit lb shows a progressive upward enrichment of Cu, Pb, Zn
and Ni, but MnO is not enriched. The thickness of this subunit ranges
from possibly as little as 1 cm to 45 cm.
Subunit lc is the lowermost subdivision of Unit 1, and its upper
limit .is defined, somewhat subjectively, as the level at which the trace
elements other than Co begin to show substantial enrichment; its base
is defined as the depth at which Si02 and A1203 first become depleted,
and this level usually, though not invariably, coincides with the depth
at which most trace elements first become enriched. This subunit, where
present, ranges from 10 to 40 cm in thickness.
Thus, in summary, Ni, Zn, Cu and Pb show slight enrichment from
the base of lc upwards and substantially more enrichment from the base
of lb upwards, while MnO is enriched only in la. 29
Unit 2 with a minimum thickness of 20 cm, shows high concentra-'.
tions of Si02 , A1203 ,, K20 and Ti02 , compared with Unit 1, and low MnO,
Cu, Pb, Zn, Ni and, usually, CaO. Fe203 and Co are usually also slightly depleted, though this tendency is less well marked than that of the other components. In core 78-6-15, MnO shows enrichment close to the top of
this unit, with fairly constant values throughout the rest of the core.
This unit is somewhat tentatively subdivided into two subunits:
Subunit 2a is, in a sense, transitional between Units 1 and 2,
in that it shows some variation in concentrations of Si02 and A1203. It
appears to be present in .only a few cores, and is most strongly developed
in 78-6-16 where it has a thickness of about 40 cm.
Subunit 2b is "genuine" Unit 2, with high Si02 and A1203 through•
out, as described above.
Unit 3, of indefinite thickness, is present only in cores 78-6-1,
6, 8, 19 and 20. It exhibits depletion in Si02, A1203, K20 and Ti02,
and enrichment in CaO, MnO and all trace elements relative to Unit 2.
Once again, MnO behaves differently in a single core, showing enrichment
at the top of this unit in core 78-6-19, with relatively constant values
below.
Core 78-6-18
Most of the shorter cores show the same pattern as that outlined
above for Unit 1; there is, 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 all the other cores; this is most probably simply an ef•
fect of dilution by CaO, but it was felt that this core might have a 30
SiQ2 % Al203% Fe203% CaO% MnO % LOI %
120L
Cu ppm Pb ppm Zn ppm Co ppm Ni ppm Units
120L
Core 78-6-1
Fig. 6. Variation 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 this data. Fig. 6. Continued. 32
120L Core 78-6-7
Fig. 6. Continued. 33
Fig. 6. Continued. r 34
Cu ppm Pb ppm Zn ppm Co ppm Ni ppm Units
120L Core 78-6-9
Fig. 6. Continued. 35
Core 78-6-12
Fig. 6. Continued. 36
Cu ppm Pb ppm Zn ppm Co ppm Ni ppm Units
Core 78-6-15
Fig. 6. Continued. 37
Core 78-6-16
Fig. 6. Continued. 38
,ow Core 78-6-19 Fig. 6. Continued. 39
Cu ppm Pb ppm Zn ppm Co ppm Ni ppm Units
Core 78-6-20
Fig. 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.
ro i—l ON r-H m o 00 m CN m 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 ro i-l CN o co o ON O i 1 i—l i-H CN in i—i m in 00 o> 00 ON o o m o o- in 00 r-H ON .-i O ON m o o m r-H o • • • • • • a ro ro oo m . CO CN CN r-H i-l CO ro 00 00 • • • • o o o o . o 00 vO 1—1 ON CN CN CN ON CN • a . m. ON. CN ON i-H r~ vO CO o CN o ON ro i—l 00 • a • a a . ON. ON. CN m r-H r-H i—i CN r~ o in 00 CN O 00 ro CO C^ • • • • a • CN in ro ON. ro . l-H i-l i—i r-H i—i i—i CO o ON o 00 •<)• in i-l o m CN significant hydrothermal component, due to its sedimentary characteristics (see p. 58). This point is discussed more fully at a later stage. The average values of the most important components in each of the above "geochemical units" and in cores 78-6-18 and 40 are listed in Table II, together with values quoted in a number of publications for vairous pelagic and hydrothermal sediments from the Pacific Ocean, for comparison purposes. Mineralogy The core mineralogy presented here (Appendix 4 and Fig. 8) is 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 is almost invariably the strongest peak present. Another pronounced peak at 3.20 A is characteristic of the plagioclase feldspars, and the small amplitudes of the other plagioclase peaks (4.04 and 3.66 A) indicate low-temperature albite 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). It is possible that a weak 3.22 A sanidine peak could be screened by the adjacent 3.20 A peak of plagioclase; how• ever sanidine is generally restricted to potash-rich volcanic rocks such as rhyolite and trachyte (Berry and Mason, 1959), which are uncommon in the adjacent continental areas (Washington and British Columbia). Ortho• clase, the expected variety in view of the composition of the supposed source rocks, appears to be definitely absent. This point is discussed further in the next chapter. A prominent peak at 3.04 A (not present in every sample) is characteristic of calcite; this mineral is thought to be predominantly 42 biogenic in origin, the major component of foraminiferal tests and other planktonic debris. Clay minerals Clay minerals are identified on the basis of the basal (001) re• flections of oriented samples. Strong 10 A and 5 A reflections indicate mica (most probably illite, 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 chlorite; strong peaks at 7 A and 3.5 A are char• acteristic of either' chlorite or kaolinite. Kaolinite is an unexpected component of temperate-zone marine clays, and is usually understood to be abundant only in areas of intense tropical weathering (Grim, 1958; Carroll, 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 kaolinite structure is usually reported to be destroyed on heating to 550°C, while chlorite is unaffected (Carroll, 1969); however, Brindley (1961, p. 263) reports that poorly crystallised Fe-rich chlorites 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, it was found that the 7 A and 3.5 A peaks disappeared or were substantially reduced; this is characteristic of chlorite (Brindley, 1961). Other evidence in favour of the identification of this mineral as chlorite rather than kaolinite or a chlorite-kaolinite mixture is as follows: a) Absence of the 2.38 A peak characteristic of kaolinite; b) Presence of a non-expanding 14 A peak which behaves in 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 Fig. 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 Fig. 8. Variation with sample depth of clay minerals in the ten longest cores; data from Appendix 4. Solid lines - montmorillonite. Dashed " - illite. Dotted " - chlorite. Fig. 8. Continued. 46 various treatments outlined above; c) Presence of a 4.75 A peak characteristic of chlorite. The slow-scan technique for distinguishing chlorite from kaolinite described by Biscaye (1964) was tried and seemed to indicate the presence of chlorite and absence of kaolinite, but it was felt that this technique is unreliable due to the wide variations reported in the peak positions for various varieties of chlorite and kaolinite in the ASTM diffraction files. The composition of the clay mineral fraction of the sediments as shown in Appendix 4 is based on measurements of the areas of the 7 A (chlorite), 10 A (illite) and glycol-expanded 17 A (montmorillonite) peaks, multiplied by the factors proposed by Heath and Pisias (1979), i.e. 1.0, 9.4 and 1.1 for montmorillonite, illite and chlorite respectively. Unfor• tunately, the XRD analyses for this study had been completed before the publication of Heath and Pisias' paper, so that their talc internal stan• dard technique for estimating clay mineral proportions could not be used. The values reported here, however, are felt to be, if not particularly accurate, at least self-consistent. Minor components No trace was found in any of the samples of reflections indicative of the manganese minerals 6-Mn02, manganite and pyrolusite, nor of the species todorokite and birnessite, reported by Corliss et al. (1978) in crusts from hydrothermal mounds on the Galapagos Ridge. This is so even where the MnO content of the sediments exceeds 3%, in the surface layers of cores 78-6-38 and 39. This is probably an indication that Mn minerals are present in an amorphous or cryptocrystalline form. Similarly, 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. First it 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 all 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 K20 in clay minerals were taken from Grim (1958); a figure of 5.95% was obtained for illite (average of 11 published analyses), and 0.31% for montmorillonite (average of 7 analyses). No K20 was reported in any of 7 analyses of chlorite. Thus, using the K20 values for the bulk sediments listed in Appendix 2, it is possible to calculate the percentage of total clays in each sedi• ment sample: % Total clay = Ks X 10 (5.95 C. + 0.31 C ) I m 48 where K = % K,i 0 in sediments, from Appendix 2, s C\ = % illite in total clay, C = % montmorillonite in total clay, m It is then a straightforward matter to calculate the percentage of each clay mineral in the total sediment, e.g. % illite in seds. = C. x % total clay 6 I etc. 100 It is further assumed that material of biogenic origin is repre• sented by: CaC03 = (CaO - 0.19 (A1203)) x 1.78. This equation is derived as follows. It can be seen that the ratio of CaO to A120 3 in the samples (Appendix 2) shows a well defined minimum value of about 0.19 (Table III); it has been suggested (Grill, pers. comm., 1980) that those samples having this minimum Ca0/Al203 ratio are without biogenic CaO, i.e.: CaO,, . . v = CaO, >. - 0.19 (A1,02 3 3). (biogenic) (total) Then: Mol. Wt. CaCO, 100.09 = 1.78 Mol. Wt. CaO 56.08 Table III. The five samples having lowest Ca0/Al203 ratios; data from Appendix 2. Sample No. CaO/Al203 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 is, perhaps, less justification for this assumption/than for those made previously; other components of the sediments are almost certain anc ly biogenic, notably P205 * possibly some of the trace elements. Part of the loss on ignition (LOI) is most probably due to loss of C02 from carbon• ate species; it is obvious from Fig. 6 that CaO and LOI covaryy in some cores, notably 78-6-8 and 20. However, there is felt to be insufficient justification for regarding the whole of the LOI as biogenic, since a significant (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 air-dried at room temperature before being sent for analysis. In addi tion, some Si02 may be biogenic, in the form of diatom and radiolarian tests However., this factor is probably of small magnitude; Si02 and A1203 show very strong covariance (see Fig. 6), which suggests that both are of sub• stantially the same origin, (i.e. terrigenous), and these two elements seem to show a significant negative correlation with CaO, especially in cores 78-6-6, 8, 19 and 20 (Fig. 8). A check on the accuracy of this procedure is 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 is presented in Table IV. Table IV. Comparison of measured and calculated CaCO values, core 78-6-18 Sample no. % CaC03 %JCaC03 Error (measured) (calculated) % of meas. value) 78-6-18A/0-1 26.1 24.35 -6.7 5-6 31.6 30.94 -2.1 10-11 40.9 38.81 -5.1 115-16 35.9 32.71 -7.8 CC* 36.9 33.83 -8.3 B/6-V. 36.0 32.70 -9.2 5-6 33.7 31.63 -6.1 15-16 28.3 26.11 -7.7 *Note: CC = sample recovered from core catcher. 50 (Measured CaC03 values in Table IV are based on the difference be• tween the initial weight of each sample and its weight after leaching with ammonium acetate at a pH of 4.5; Grill, pers. comm., 1980.) Thus it is seen that the calculated values are systematically low, by an average of 6.6%. It is probable that those samples having the minimum Ca0/Al203 values, previously mentioned, still contain a small amount of carbonate; thus the correction factor 0.19 in the equation on p. 48 is probably too high. This leaves between 25 and 40% of the sediment weight unaccounted for, 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 significant peaks corresponding to other minerals, leads to the conclusion that this remaining material must consist predominantly of those two minerals. These proportions seem reasonable in view of the close proximity of the source area for terrigenous sediments. Thus it can be seen that Duncan et al.'s (1970) assumption that clay minerals represent 100% of Cascadia Plain sediments is unjustifiable 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, is illustrated in Appendix 5. The interpretations are based on both visual and X-ray radiographic examination of the cores. In most cores (the exception is, once again, 78-6-18), three distinct sediment types, and a fourth, transitional 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 it is 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 lutite (Munsell 10YR 5/4 to 10YR 2/2). In many cases part of this surface layer was lost during splitting and examination of i the cores due to its semi-fluid nature, and the thicknesses quoted are thus minimum values; its absence from core 78-6-15 may be due to it all having been lost in this way. In all cores in which this unit is present, a strong positive MnO anomaly is also present in the uppermost (0-2 cm) geochemical sample, amounting in a few cases to over 20 times the average for the rest of the core. The dark brown colour is thought to be due to the presence of amorphous or cryptocrystalline Mn oxides (Hartmann, 1979). Type B Sediment Type B consists of a light to medium olive grey or greenish grey clayey to silty lutite (Munsell 5Y 5/1, 5Y 5/2, 5GY 5/1), which is visually almost structureless but in the X-ray radiographs shows evidence of extensive bioturbation, in 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 filled 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 visually very similar to the published illustrations of Zoophycos burrows, however most sources report Zoophycos burrows to be only 1-4 mm in diameter. . 9. Covariation between CaO and (Al203+Si02) in Juan de Fuca Ridg sediments. Plate 1. Sediment Type B; part of core 78-6-19, showing typical mottling and small scale bioturbation. Full 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 is visually very similar to Type B, but often exhibits small-scale colour variations, individual layers ranging from a few mm to 2-3 cm in thickness, and varying in colour from medium olive grey or greenish grey to pale yellowish grey (Munsell 5Y 4/1 to 5Y 5/2). The material is predominantly clayey or silty lutite, but with a few thin (2-3 cm) layers of silty sand. In the X-ray radiographs this sediment type is seen to have a finely laminated structure (Plate 3); typically, a layer of sediment 5-30 cm thick, averaging about 10 cm, consists of fine (2 mm or less) horizon• tal laminations at the base, grading upwards into poorly laminated or almost structureless sediment. Wavy or distorted laminae are present locally, and occasionally the contacts between layers show evidence of erosion, in the form of truncated laminae and irregular contacts. This is especially well shown in core 78-6-12, at about 44 cm depth (Plate 4). Bioturbation in this sediment type is restricted to occasional 8-15 mm diameter filled burrows. Where Types B and C are both present in a core, Type B almost invariably overlies Type C. Type B/C A type intermediate between Types B and C, showing significant mottling and bioturbation but also having poorly defined layering, is present in some cores, and is 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 typical coarse- and fine-layered structure. The section shown grades from clay down• wards to fine sand. Curved laminae at base are due to distorting effect of core catcher. Plate 4. Sediment Types B/C (top) and C (bottom); part of core 78-6-12. Also shown (arrowed) is an eroded contact between two Type C layers. A single sediment-filled burrow (?Zoophycos) is visible at the lower extremity of this section. 58 Non-terrigenous components Calcareous organic remains, mainly foraminiferal tests, are pres• ent in 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 in cores 78-6-15, 16 and 20. These layers frequently coincide with the contacts between Type C sediment layers, and seem to be entirely restricted to Type C. Any such layers which might have been present in 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 in a few cores, and are notably abundant in 78-6-9, where they may form up to 2-3% of the total sediment over a 30 cm length of the core. These are undoubtedly of local origin. Core 78-6-18 This core, in contrast to all the others, consists entirely of rather soft, foraminefera-rich yellowish brown silty lutite (Munsell 10YR 5/2) containing abundant angular fragments of black basaltic glass of up to 5 mm in diameter. The X-ray radiographs of this core show little discernable sedimentary structure. A single angular irregularly-shaped fragment of highly fractured basaltic material measuring approximately 3 cm x 3 cm x 5 cm was found on top of this core on recovery. It was extremely brittle, and shat• tered on being diamond-sawn for a thin section. However, a section was made of some of the pieces, which revealed it to consist of glassy to very finely crystalline, almost opaque, dark brown to black material in which individual mineral grains could not be identified. Its 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 similarities to those reported to occur somewhat to the north of the present area by Bornhold et al. (in prep.). Unit la, as described here, seems similar in all respects to Bornhold et al.'s Unit 2; their "transition unit," 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 al. define their units on the basis of visual sedimentary characteristics (mainly colour); their sampling procedure differed from that used in the present study, in 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 light grey surface layer designated by Bornhold et al. as Unit 1 was found in any of the cores examined in the present study. A similar light grey surface deposit has been previously re• ported by Bramlette (1961) in deep sea samples, and was designated by Horn et al. (1970) as being characteristic of their Central North Pacific sedimentary province. However, the area of the present study and much of the area cored by Bornhold et al. is within the areas 60 61 designated by Horn et al. as the Northeast Pacific Turbidite Province and the Ridge and Trough Province, where no light grey surface sediment would be expected. It is possible that some of these province boundaries might require adjustment as new evidence is forthcoming. The present area - broad correlations In order to make a meaningful interpretation of the data collected during the 1978 cruise, it 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• tion; also, that the sedimentary regime was essentially the same through• out the region at any given time. It is apparent that the boundaries between the geochemical units and the sedimentary types in the present area do not, in general, coin• cide, except that subunit la 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 is 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 in chemical composition) than the other units; a possible reflection 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 Pacific 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 al. (1961), working with cores from the Atlantic Ocean, concurred with this view, and concluded that "significant mixing of sedi• ment by burrowers is confined to the uppermost 5 cm" of sediment. The lack of chemical,uniformity in Unit 1 trace element abundances may be due to diagenesis, i.e. a process of chemical "de-homogenisation" whose earliest stages would ha/e been masked by the bioturbation, but which continued after the cessation of biological activity. Indeed, subunit la seems to be similar to surface sediments described by Lynn and Bonatti (1965), to which they ascribe a diagenetic origin; it seems a reasonable supposition that similar diagenetic processes have occurred in the present area. This supposition is discussed further below. Sedimentary regimes The question next arises: what, if anything, does the composition of the individual geochemical units indicate about the sedimentary regime at the time of the deposition? Intuitively, it would seem that a sediment high in Si02 and A1203 and low in CaO would indicate predominantly terri• genous sedimentation, rich in quartz, feldspar and detrital clays, whereas a sediment with the opposite characteristics, i.e. low Si02 and A1203 and high CaO, indicates a more pelagic regime, dominated by biogenic material. This distinction is, of course, valid 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 Si02 and A1203, results from a sedimentary regime dominated by continent-derived de• trital material. Unit 1, on this basis, is rather less well characterised; 63 its Si02 and A1203 content is comparable to that of Unit 3, but its CaO content is more variable and usually much lower than Unit 3 and, occasion• ally, lower than Unit 2 (see Fig. 6, especially cores 78-6-1, 6, 9, 15 and 16). It is noticeable that the biogenic content of the sediments seems to be an inverse function of water depth (Fig. 10). Hamilton (1967) and Horn et al. (1970) propose that the depositional regime in the north• east Pacific Ocean changed from predominantly turbiditic to predominantly pelagic at the Pleistocene/Holocene boundary, arguing that the near cessation of glacial erosion at this time resulted in a considerable reduction in terrigenous sediment volume, thus allowing pelagic sedimenta• tion to become more dominant. If this hypothesis is accepted in the present area, the Si02 and Al203-rich deposits of Unit 2 may represent sedimentation during the final (Wisconsin) stage of the Pleistocene glaci• ation, while the CaO-rich sediments of Unit 3 belong to the Sangamon Interglaciation (230,000 to 110,000 years B.P.; Douglas et al., 1976, p. 678), and Unit 1 consists of post-glacial deposits. The relative lack of biogenic material (i.e. carbonate) in the most recent sediments could be due to the post-Glacial rise in sea level and the corresponding rise in the carbonate compensation depth; although if this is the case, Unit 3 should be similarly affected. No radioactive age dating was done on the sediments in this study; it would have given precise answers to the problems outlined above. In absence of this, a more qualitative approach is 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 solubility. Core 78-6-6 appears to be anomalous. 65 for the Cascadia Plain. If this rate is 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 yr). Thus the thickness of Unit 1, at least, is of the right order of magnitude, but Unit 2 is 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 in places on the northern end of the Juan de Fuca Ridge, and Davis et al. (1976) have calculated that rates in 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 profiles 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 velocity in unconsolidated sediments equal to that in 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 five chosen locations (see Fig. 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 Plain Pleistocene sediments. It is apparent from these figures that sedimentation rates vary widely even within a fairly restricted area of the ridge complex; the five locations were chosen quite arbitrarily as points at which a fairly 66 Table V. Sedimentation rates at selected locations (see Fig. 3) Location Profile Distance from Time (yr) Sediment Sedimenta• (fig.3) ridge crest (km) thickness (jn) tion rate (cm/1000 yr) (1) E2 8.5 E 283,000 182 65 (2) IT 10.75 W 355,000 272 76 (3) Tl 27.5 W 907,500 363 40 (4) E3 28.75 E 949,000 1583 167 (5) E5 6.5 W 214,500 500 233 average 116 strong basement reflection allowed easy estimates to be made of sediment thickness, and it 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 in a 5 km wide, branching valley (see Fig. 3), which probably receives slumped sediments from a wide area of the ridge complex and may be a channel for turbidity currents coming from the Explorer Plate, to the north of the Sovanco Fracture Zone. The lower rates are characteristic of smaller valleys and hollows, which probably receive sediments from a much more restricted area. Other evidence Sediment Type C, described in Chapter 4, consists of layers of an average thickness of 10 cm, occasionally with erosional contacts, each layer consisting typically of finely laminated silty lutite grading upwards into structureless clay-rich lutite. In a few cases wavy laminae are present, generally towards the base of a layer, and foramini- feral remains also seem in general to be concentrated at the bases of individual layers. These structures seem identical to the uppermost units (D and E, or in a few cases possibly C, D and E) of the Bouma turbidite sequence (Bouma, 1962). This suggests that Type C sediments 67 are distal turbidites, or possibly proximal "microturbidites" of locally- derived fine-grained material. In an individual flow, the larger parti• cles (in this case, foraminiferal tests) would settle out first, followed by finely laminated silty lutite (Bouma division D or C-D); the finest, clay-size particles would then settle relatively slowly as an almost structureless "interturbidite" (Bouma division E). This whole deposi- tional process might be completed in a matter of a few days, or possibly even hours - an illustration of the fact that to speak of "average" sedi• mentation rates may be misleading in turbidite areas. If Opdyke and Foster's (1970) figure of 10 cm/1000 yr is taken as representative of sedimentation rates in the area during the Pleisto• cene, this would necessitate a single turbidity-current event every 1000 years, on average. In view of the almost continuous seismic activity in the area (260 seismic events in a ten year period, reported by Tobin and Sykes, 1968), this is felt to be unrealistic. Griggs and Kulm (1970) present evidence for an interval of about 500 years between turbidity current events in Cascadia Channel during the Holocene; the interval during the Pleistocene would almost certainly have been much shorter. Duncan et al. (1970) report that Pleistocene lutites in the Cascadia Plain contain more illite and less montlmorillonite than those of the Holocene. However, their figures are not directly 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 in the area, an assump• tion which is totally unwarranted, as has been seen. In any case, the use of this observation as a criterion for recognising the Pleistocene/Holocene boundary is probably only valid 68 for that part of the Cascadia Plain which receives sediments from the Astoria Fan, since Duncan et al. (1970) infer that the change in clay mineral proportions results from a change in the relative importance of the Snake River and Upper Columbia River sediments to the total sedi• ment load of the lower Columbia, and thus of the Astoria Fan. Similar conditions almost certainly do not apply to other areas. The clay mineral abundances found in this study (Appendix 4 and Fig. 8) seem to bear this out; while some cores, notably 78-6-1, 15, 16 and 19, do in fact show a transition from low- to high-illite at the base of Unit 1, others (78-6-6, 8 and 12) seem to show the opposite tendency. It would seem that, while Unit 1 almost certainly represents Holocene sedimentation, and the transition to Unit 2 defines the Pleisto- cene/Holocene boundary, Unit 3 cannot be as early as Sangamon. The fol• lowing explanation is proposed, purely as speculation. The Si02 and Al203-rich deposits of Unit 2 represent sedimentation close to the end of the Pleistocene, when extremely large quantities of detrital material were released catastrophically over a relatively short period of time as the glaciers retreated, resulting in substantial increase in the terrigenous component compared with Unit 3; the latter, which represents sediment deposited during the Wisconsin glacial stage, is much richer in pelagic (i.e. biogenic) material, firstly because continent-derived detrital material was largely immobilised by ice cover, and secondly because the lower sea level resulted in less carbonate dissolution before deposition. The relatively CaO-depleted sediments of Unit 1 were depos• ited in deeper water during the Holocene, with the result that more CaC03 tended to dissolve in the seawater column. Other factors (e.g. pH and temperature) are also involved in carbonate dissolution, but the 69 above outline, while tentative, would seem to account for the observations. If the relative absence of extensive bioturbation in Units 2 and 3 is 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 Fig. 6), for the most part, show a strong negative correlation with Si02 and A1203. MnO, Cu, Pb, Zn and Ni all show enrichment in Units 1 and 3, and deple• tion in Unit 2. Co seems also to show slight enrighment in Units 1 and 3, on average (see Table II), but unlike the other trace elements it seems to exhibit no consistent pattern of enrichment and depletion. (The abundances of Co and Pb in these samples are in many cases, close to the limit of detection (approximately 4 ppm); the apparently unsystematic variations in these elements visible in Fig. 6 can probably be attributed to analytical 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 their original time of deposition - or possibly both. A hydrothermal source would be one possibility. Hydrothermal sediments vary widely in chemical composition. Rona (1978) tabulates ranges of values found for both major and trace elements of a total of twenty-one examples of hydrothermal encrustations, concre• tions and sediments from seventeen locations, including the East Pacific Rise, Mid-Atlantic Ridge, Red Sea, Afar Rift, Indian Ocean Ridge, and basal sediments from both Atlantic and Pacific Oceans. A few examples of the ranges of compositions found are as follows: 70 Si02 , 0.4 - 55%; A1203 , 0 - 23%; Fe203 , 0 - 73%; MnO, 0 - 75%; Fe/Mn ratio, 0.0002" 884; Co, 5 - 330 ppm; Cu, <5 - 33,400 ppm; Ni, <5 - 1680 ppm; Zn, 33 - 200,000 ppm. It is clear that, using analytical criteria alone, almost anything could be regarded as hydrothermal. The situation is further complicated, since "metalliferous sediments of hydrothermal origin may mix with and/or exhibit transitional characteristics with metalliferous sediments of hydrogenous origin" (Rona, 1978) - and, presumably, also with non-metallif• erous sediments of detrital or biogenic origin. Sources of sediments Several composition diagrams have been published which purport to distinguish sediments of hydrothermal origin from other types, the best known of which is probably the Fe - Mn - (Co+Cu+Ni)xl0 triangular diagram published by Bonatti et al. (1972), and used by Rona (1978) and many other authors. However, this diagram does not differentiate be• tween iron-rich hydrothermal sediments and normal non-metalliferous pelagic sediments (see Fig. 11). It does, however, serve to emphasize the wide variation found in Unit 1 sediments; also, the sediments of Unit 1 seem, in general, to have trace element concentrations higher than those usual in 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 variation in composition of Unit 1, suggesting that this unit is at least in part of hydrogenous origin. Note also that this diagram does not differentiate between iron-rich hydrothermal sediments and normal non-metalliferous deep-sea sediments. (a) Average Pacific 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 relatively high ratios of Si02 to A1203 (Bonatti et al., 1972). A plot of these two components (Fig. 12) indicates that the sediments of the study area are predominantly terrigenous; the Si02/Al203 ratios for all 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 Si02 and Al203-poor sediments of Core 78-6-18. This decrease is felt to be due principally to dilution by biogenic or hydrogenous material. A hydrothermal source for Core 78-6-18 is not indicated. Bostrom et al. (1969) use the ratio of Al to Ti to distinguish terrigenous sediments from those derived from oceanic volcanic rocks (i.e. hydrothermally or by weathering). The Al/Ti ratio found in average continental rock is close to 20, whereas the weathering products of oceanic rock should have an Al/Ti ratio of about 5. Of the sediments analyzed in the present study, Units 1, 2 and 3 have average Al/Ti ratios of 16.73, 15.94 and 18.38 respectively, and core 78-6-40 (which should have little or no hydrothermal component) has an Al/Ti ratio of 17.27; the ratio for core 78-6-18 is 16.41. This seems to confirm that 78-6-18 is essentially non-hydrothermal, as is suggested by the Si02/Al203 ratio. A graph of the ratio of Fe/ti to Al/(Al+Fe+Mn) is shown in Fig. 13; according to Bostrom (1970), normal pelagic sediments consist of mixtures of terrigenous and hydrothermal sediments and tend to fall close to curve (b). All of the sediments analyzed in this study fall close to the right hand (terrigenous) end of this curve; however, a small hydro- thermal component for Unit 1 and for core 78-6-18 remains a possibility, if a remote one. 60, 8 IO %AI203 . 12. Ratio of Si02 to A1203 for deep-sea sediments of hydrothermal, hydrogenous and terrigenous origin. • - Sediments sampled during this study O - Average compositions of various sediment types: (a) Average deep-sea sediment (Turekian and Wedepohl, 1961) . (b) Average Pacific 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- ally or from weathering of volcanic rocks with volcanic material; curve (b) is produced when hydrothermal sediments are mixed with material of terrigenous origin. Modified from Bostrom, 1970. 75 Core 78-6-18 The evidence outlined above seems to show that core 78-6-18, contrary to initial expectations, does not have a significant hydrothermal component. This core was obtained at a distance of about 6.8 km east of the ridge crest, and is oxidised throughout, in contrast to all the other cores studied (including those obtained in the immediate vicinity 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 reflects a high biogenic component; if the average rate of biogenic sedimentation is 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 all 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 in this core, since CaCo3 dissolution in the water column is an inverse function of depth (see Fig. 10). The Xv-iray diffraction results (Appendix 4) show strong indica• tions of quartz and albite, and suggest that the terrigenous material is the dominant component of this core. Other metallogenic processes Other processes which may be of importance to the total picture of trace metal concentrations in the study area are discussed briefly below. 76 Hydrogenous Hydrogenous sediments are "formed by slow precipitation 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 in Unit 1 (Fig. 11) seem to indicate that a significant proportion of the trace elements in this unit are of hydro• genous origin. Other processes, however, have redistributed these elements since deposition. Diagenetic Bonatti et al. (1971) have proposed a process whereby Mn, Co, Ni and to a slight extent Cu, are dissolved under reducing conditions at depth in the sediment column and reprecipitated in an upper, oxidised zone. It has been shown experimentally (Hartmann, 1979) that Mn, Co and Ni are remobilised simultaneously when an oxidised sediment is treated with an acidic reducing solvent, but that Cu is dissolved much more slowly. Surface sediments rich in 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 is usually found to be much more intense and more localised close to the sediment surface, than the other elements, an observation explained by Bonatti et al. (1971) as being due to the fact that most trace elements do not form distinct minerals in 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 is remobilised with much lower efficiency than Mn, Ni and Co. The results of this study (Fig. 6) seem in general to support the above analysis; Mn enrichment is restricted 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 in concentration from the top of each core to the base of Unit 1. Co, however, seems not to follow this pattern, although a slight enrichment in Unit 1 is seen (Table II), Co shows some degree of covariance with CaO (see below); Hartmann (1979) proposes that Co is incorporated into carbonates by diagenetic processes. It is also possible that Co is being lost from the sediments due, perhaps, to local pH or Eh conditions; Garrels and Christ (1965) note that the stability fields of higher oxides of Co occur at a much higher Eh than do Mn oxides, so that in the absence of a suitable host species Co may remain in solu• tion. It should also be noted that both the Mn concentration in subunit la, 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 this unit. A diagenetic process such as that discussed above should, in theory, result in a constant Mn concentration below the oxidised zone; however, in many cores Mn is enriched to some extent in Unit 3 (Fig. 6, especially cores 78-6-1, 8 and 20). It may be that the Mn in this unit is present, not as easily reducible oxides, but as some more stable 78 Fig. 14. Variation in MnO content and thickness of Unit la with distance from ridge crest (and thus with time available for diagenesis). Note, however, that an unknown quantity of Unit la was lost from each core on initial treatment. 79 species, such as cabonates. Little published information seems to exist regarding the diagene• tic behaviour of Zn and Pb. In this study, the behaviour of Zn seems to follow that of Cu, while the behaviour of Pb is somewhat erratic but generally close to that of Ni. Biogenic Heath and Dymond (1977) and Leinen and Stakes (1979) have shown that the biogenic component of Pacific pelagic sediments is an important source of trace metals in the sediments. This is hardly surprising in 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 significant degree of covariance with CaO (Fig. 6), and this is interpreted to mean either that most of this element is of biogenic origin, or that it has been incorporated into the carbonate fraction soon after mobilisation (Hartmann, 1979). Co also shows consistently high values in cores 78-6-18 and 29, both of which are CaO-rich. Incidentally, it should be mentioned that this covariance of Co with CaO is 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 their analysis of sediment provenance. Feldspar diagenesis Some explanation seems warranted for the apparent lack of K- feldspar in the sediments in the study area. It seems reasonable to assume that K-feldspar would have been present, in an amount at least of the same order of magnitude as that of plagioclase, in the original 80 terrigenous sediments, supposing them to derive from the K-feldspar- bearing rocks of the British Columbia coast (Douglas et al., 1976). There• fore, some diagenetic process must be operating to remove K-feldspar, a process which has little or no effect on plagioclase. Weaver (1967) has suggested a process whereby K+ is released from K-feldspar and incorporated into clays (mainly illite). Illites in marine sediments often appear to be younger than the stratigraphic age of the sediments, by. up to 100 million years (Hawkins and Roy, 1963), suggesting that some, at least, of the illites form diagenetically, from reactions involving K+ in the interstitial waters of the sediments. This conflicts with the observation that K-feldspars appear to be thermodynamic- ally stable in normal oceanic waters; however, solution could occur, with possible conversion to illite, under conditions of low pH and low: dissolved Si02 (Hess, 1966; Garrels and Mackenzie, 1971). Goldberg and Arrhenius (1958) report that most of the K20 in Pacific pelagic sediments is incor• porated in clays, which suggests that this is not merely a local phenomenon. Most of the terrigenous sediments in 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 inhibit the diagenesis of albite, and sea water appears to be supersaturated in Ca+ in the upper layers (Broecker and Oversby, 1971), which would tend to increase the stability of Ca-bearing feldspars. There seems to be a tendency for more Na+ than K+ to be removed from seawater by clay-rich sediments (Weaver, 1967), which would further tend to stabilise albite at the expense of K-feldspar. 6. SUMMARY AND CONCLUSIONS Introduction Geothermal heat flow measurements over the Juan de Fuca Ridge (Lister, 1972; Davis and Lister,1977b) show that the rate of heat transfer from the mantle through the basaltic oceanic crust is too high to be accounted for solely by conductive processes. A convective hydrothermal system, in 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 its passage through the system, reacts with the hot rock and dissolves out Mn, Fe and several trace metals, which are re-deposited in 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 in solubility between the two metals; this gives the resultant sediments a characteristic range of compositions. The main purpose of this study was to determine whether hydro- thermal sediments of this 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 in the area, with turbidity currents playing the major role in 81 82 sediment transport. Biogenic and hydrogenous material is also present in the sediments, but no compelling evidence was found for the presence of a significant hydrothermal component. However, a layer of hydrothermal sediment has been reported at the base of the sediment column from other nearby locations, and it most probably also exists in the present area. Overall sedimentary regime This study reveals a complex picture of sedimentation in the area (Fig. 15). A broad outline of the overall sedimentary regime would include the following factors, in more or less chronological order: 1) Deposition of Fe-and Mn-rich, highly oxidised hydrothermal sediment from vents and fissures on or close to the ridge crest, in a relatively thin layer, probably nowhere more than 1 m thick, overlying basaltic basement. 2) Deposition of terrigenous sediment, initially on the continental shelf and in the Nitinat and Astoria fans off the Juan de Fuca Strait and the mouth of the Columbia River. Continual low-level seismic activity along the shelf edge would result in this sediment being periodically disturbed and remobilised in the form of turbid• ity currents. Most of these currents travel by way of the Cascadia Channel or the Vancouver Valley, through a gap in the Blanco Fracture Zone and out onto the Tufts Abyssal Plain (Griggs and Kulm, 1970), but occasional larger currents overflow these channels and spread out over the Cascadia Plain and into the Ridge complex. The quantity of this material released into the marine environment increases considerably during periods of glacial retreat, when vast quantities of sediments are catastrophically released over a SEDIMENT INPUTS Fig. 15. Sediment inputs to the Juan de Fuca Ridge area. CO 84 relatively short time period. 3) A steady "rain" 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 turbiditic and hydrothermal origin, but some of the planktonic debris may become segretated into occasional thin layers due to reworking by turbidity currents. 4) Precipitation of trace metal-rich material directly from seawater, also over the whole area. 5) Local volcanic activity may add pyroclastic debris, in the form of glass shards, to the sediments in certain areas. 6) Slumping of pelagic, hydrogenous and possibly some turbiditic and volcanic material from topographic highs into valleys and hollows within the ridge complex, giving rise to "microturbidites" a few cm thick. 7) The terrigenous sediment described in (2) above would be deposited initially in 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 in the reduced zone; these elements then travel upwards by diffusion through the interstitial water and are redeposited in the still-oxidised upper few cm of the sediment column, giving rise 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 its own individual sedimentation 85 regime, the faster sedimentation rates being associated with the larger valleys, as might be expected. Sedimentation rates appear to be approx• imately an order of magnitude faster in the ridge complex than has been reported for the Cascadia Plain, no doubt due largely to the concentra• tion of sedimentation into areally restricted valleys. Recommendations for future work This study is regional in scope rather than local, and there is opportunity for much more detailed work in the area. Even the basic bathymetry has not yet been fully delineated, which, in view of the con• siderable academic interest the area has generated, is perhaps surprising. This situation will undoubtedly improve as further seismic profiles become available. Specific recommendations for further work might include the following: 1) More magnetic measurements should be obtained around the offset of the ridge crest at its intersection with the Cobb Fracture Zone, in order to determine the exact nature and trend of the offset. 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 difficult if a conventional corer was used, since the sediment depth will be minimal and the material may well be in the form of encrustations on basaltic pillows or as fracture infillings. Dredging would probably be an acceptable method; the ideal 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 it 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 Si02, A1203, K20 and Ti02 (terrigenous); CaO and Co (biogenic); all other trace elements (hydrogenous); and MnO and Fe203 (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 still far from being fully understood. It is reported, for example (Bonatti and Joensuu, 1968) that detrital 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 Pacific Rise, in 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, chiefly due to dilution and blanketing by terrigenous sediments. 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Iron-rich sediments cored during Leg 8 of the Deep Sea Drilling Project. In: Initial Repts. DSDP., Washington, D.C, Nat. Sci. Found. 8, 829-833. , and Rex, R.W. (1970). Amorphous iron oxide precipitates in sediments cored during Leg 5, Deep Sea Drilling Project. In: Initial Repts. DSDP., Washington, D.C, Nat. Sci. Found. 5_, 541-544. Von Herzen, R.P., and Uyeda, S. (1963). Heat flow through the eastern Pacific Ocean floor. Jour. Geophys. Res. 6_8, 4219-4250. Weaver, C.E. (1967). Potassium, illite and the ocean. 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 Nitinat deep-sea fan. L.B.L. Publ. 223. APPENDIX 1 Seismic profiles and interpretations 98 CONTINUOUS SEISMIC REFLECTION PROFILES (CSP) AND INTERPRETATIVE SECTIONS LEGEND Interpretations are shown below the original CSP traces in 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 in sea water of 1490 m s . CSP loca• tions are shown in Fig. 3. Strong reflector in sediments - — Weak or discontinuous reflector - — Bedrock - Inferred faults - Plate 5. Seismic profiles N4.5, E0.5, N3 and E0.25 -z.s -3.0 -3.5 km 10 PROFILE E1 WEST HALF E1-2 TIE LINE Plate 6. Seismic profiles El (west half) and El-2 tie line. o o 101 280Q PROFILE M3 I i > i 1 PROFILE Elwrnii Plate 7. Seismic profiles N3 and El (east half). 102 ' PROFILE E1.5 Plate 8. Seismic profiles N3.7 and El.5. Plate 9. Seismic profile E2 (west half). ,_. o 10 km PROFILE E2 EAST HALF Plate 10. Seismic profile E2 (east half). o -p- 10 km , PROFILE E 2.5 2.5-1.5 TIE LINE Plate 11. Seismic profile E2.5 and 2.5-1.5 tie line. o . HWFM.E E3 Plate 12. Seismic profile E3. o ON Plate 15. Seismic profiles E7 and N3.5. o . 20 • PROFILE E9 Plate 16. Seismic profile E9. -3.0 —is Jfe; —4.0 — 20 Km ' PROFILE Etl Plate 17. Seismic profiles Ell and Nl. Mt *> KM PBOWJ H2 Plate 18. Seismic profile N2. APPENDIX 2 Geochemistry - major oxides Appendix 2: Major oxides (%) Sample no. 2 3 SiO, A120, Fe 0 MgO CaO Na20 K20 TiO„ P205 MnO LOI Ca0/Al203 -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 0.222 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 *Note: Samples are numbered in cm from top of core no. Si02 203 imple Al, Fe, MgO CaO Na20 K20 Ti02 2o3 P205 MnO LOI .-7/0-2 44 .13 11 .34 6 .54 2 .82 4.37 4.08 1.88 .69 .36 1.58 21.43 7/10-12 46 .94 12 .16 7 .35 3 .11 4.89 3.77 2.17 .63 .35 .40 17.58 7/20-22 48 .57 12 .95 7 .53 3 .26 3.62 4.13 2.34 .67 .33 .36 16.39 7/30-32 47 .42 12,.6 2 7 .58 3 .09 4.86 3.40 2.21 .66 .33 .30 17.10 7/40-42 44 .86 12,.2 1 7 .73 3 .25 6.51 4.20 2.03 .62 .36 .33 17.85 7/50-52 44 .66 12,.1 5 7 .89 3 .39 6.67 3.72 1.99 .62 .36 .47 18.06 7/60-62 44 .01 12,.2 4 7 .20 3 .03 8.14 3.51 1.93 .60 .40 .27 17.81 7/70-72 43 .52 12,.71 6 .35 3 .22 11.27 3.52 1.86 .62 .44 .27 17.41 7/80-82 47,.O S 12,.3 7 7 .68 3,.6 2 4.30 4.80 2.20 .65 .35 .36 17.38 7B/0-3 45,.5 8 12,.0 6 8,.0 9 3,.6 2 5.67 4.47 2.13 .63 .38 .32 17.85 7B/10-12 44,.7 7 12,.2 3 7,.3 6 3,.4 8 5.77 4.61 2.10 .63 .36 .30 17.95 7B/20-22 44,.2 6 12.,2 3 7,.4 7 3..6 6 6.10 4.77 2.08 .62 .40 .38 17.91 -8/0-2 46,.9 8 11. 58 7..7 9 3,.0 8 3.75 4.94 1.90 .63 .38 .45 18.65 8/10-12 43.,5 2 11.,3 2 8.,1 4 3,.3 6 9.55 4.00 1.82 .53 .41 .12 18.66 8/20-22 42.,8 9 12. 41 6.,5 9 3,.3 0 11.04 3.70 1.79 .57 .42 .15 17.98 8/30-32 43.,6 7 12. 78 5.,8 6 2.,8 9 11.20 3.96 2.18 .66 .43 .12 16.66 8/40-42 51.,2 6 15. 09 7.,0 0 2.,9 4 4.73 3.57 2.83 .87 .40 .14 12.17 8-50-52 52.,5 2 15. 11 7. 07 2.,9 3 4.51 3.44 2.74 .96 .40 .17 11.78 8-60-62 52.,4 0 15. 69 6. 71 2.,8 3 4.26 3.27 2.84 .87 .39 .12 11.82 8/70-72 47. 82 13. 92 6. 32 2. 87 8.76 3.04 2.18 .69 .41 .17 14.56 8/80-82 49. 17 14. 44 5. 97 2. 77 8.85 2.85 2.22 .72 .39 .18 13.98 8/90-92 49. 18 14. 51 6. 20 2. 88 7.70 2.98 2.38 .72 .39 .20 13.63 8/100-102 42. 17 12. 19 5. 39 2. 92 14.09 - 3.22 1.62 .56 .46 .30 16.92 8/110-112 41. 56 11. 89 5. 61 2. 95 14.66 3.48 1.53 . .54 .47 .31 16.99 8/120-122 43. 38 12. 51 5. 82 3. 07 13.86 3.03 1.59 .57 .47 .20 16.52 8/130-132 49. 33 13. 92 6. 69 3. 54 8.62 3.33 1.79 .78 .43 .17 12.55 Sample no. A1203 Fe203 MgO CaO Na20 K20 Ti02 P2O5 MnO LOI Ca0/Al203 )-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 0.184 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 0.238 lple no. Si02 Als Fe, MgO CaO NaL 20 K20 Ti02 P205 MnO LOI Ca0/Al203 »°s «°s •15/0-2 50,.1 7 12,.5 9 8,.5 0 3,.2 5 2. 39 4. 31 2. 10 .68 .30 .12 15,.8 8 0.190 15/10-12 46,.5 3 12,.8 7 7,.2 1 3,.3 0 4. 94 4. 92 2. 09 .65 .34 .10 15,.7 4 15/20-22 49,.7 8 14..3 0 7,.2 5 3,.2 4 5. 61 4. 26 2. 30 .70 .38 .12 12,;8 3 15/30-32 51,,1 0 14.,8 5 6,.9 8 3,.3 3 5. 31 3. 77 2. 32 .75 .38 .13 11,.9 0 15/40-42 50.,0 2 14..5 4 7,.1 6 3,,4 4 5. 85 4. 10 2. 13 .76 .39 .15 12,.3 4 15/50-52 48,.2 0 14..2 5 6..4 3 3,.0 7 7. 53 3. 71 2. 35 .73 .43 .17 13,.4 2 15/54-55F 42,.4 2 11..9 5 5,;3 7 2,.5 5 13. 88 3. 50 1. 85 .60 .48 .17 15,.9 2 15/60-62 47..4 2 13.,6 9 6..5 4 2,.9 4 8. 21 3.4 2 2. 22 .71 .44 .17 13,.7 1 15/70-72 55.,2 2 15.,3 0 6,.7 6 2,.8 7 3. 74 3.4 9 2. 10 .86 .36 .16 8,.8 7 0.244 15/75-76F 50.,0 9 13.,1 4 5,.8 5 2..5 1 7. 65 3. 19 1.8 1 .76 .41 .36 11,.3 3 15/80-82 49.,2 5 13.,5 9 6,,5 7 2.,7 0 6. 35 3. 14 2. 21 .94 .44 .40 11..7 9 15/90-92 50.,7 2 14.,7 5 6.,9 9 2..7 0 5. 57 3. 05 2. 71 .86 .41 .16 11,.9 4 15/100-102 49.,3 9 14.,4 0 6,.6 3 2,.6 3 3. 97 2.6 6 2. 62 .89 .42 .11 10..5 2 15/110-112 53.,2 2 14.,7 8 6..3 6 2,.6 1 4. 03 2. 91 2. 81 .90 .41 .11 9,.6 8 15/114-115F 51.,7 0 13.,4 0 5.,9 8 2,.3 4 6. 19 2.6 6 2. 33 .89 .42 .10 10..8 7 15/120-122 52.,6 1 14.,9 7 6..3 7 2..6 0 5. 27 2.8 4 2. 85 .88 .41 .11 11..1 2 15/130-132 51.,4 0 15.,0 5 6.,8 7 2.,8 0 4. 43 2. 99 2. 69 .87 .38 .12 11..2 5 15/140-142 52.,2 6 15.,0 9 6.,9 2 2..7 7 4. 54 3.0 5 2. 68 .89 .41 .13 10..9 5 15/CC * 52.,5 6 15.,0 1 6.,9 5 2..6 9 4. 62 2. 76 2.6 7 .88 .41 .14 11..2 8 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. Si02 2 3 2 3 Sample no. A1 0 Fe 0 MgO CaO Na20 K20 Ti02 P205 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, A1203 Fe203 MgO CaO Na20 K20 TiO„ P20 MnO LOI Ca0/Al203 48 .50 12 .79 8 .41 3. 25 5 .77 3,.8 9 2. 18 .65 .22 1 .38 14,.9 3 -20/0-20/10-12 2 54 .58 15,.0 9 7 .04 3. 14 3 .73 3,.7 4 2. 16 .84 .39 .09 10 .41 0,.29 7 20/20-22 50 .62 14,.3 2 6 .84 3. 06 6 .23 3,.0 6 2. 26 .79 .41 .10 12 .63 20/30-32 50 .65 14 .66 6,.5 9 2. 87 6,.3 1 3,.1 9 2.4 0 .86 .44 .11 12,.1 5 20/40-42 54,.0 4 15,.3 4 6,.9 7 2. 73 3,.8 3 3,.2 2 2. 59 .89 .37 .09 10,.7 6 0,.25 0 20/50-52 53,.7 7 15,.0 3 6,.3 1 2. 64 4,.5 0 3..1 1 2. 66 .87 .41 .10 10,.5 4 20/60-62 55,.9 0 15,.2 2 6,.4 8 2. 74 4,.0 0 2,.9 7 2. 68 .84 .40 .10 9,.6 8 20/70-72 53,.8 8 14,.9 4 6,.5 1 2. 65 4,.4 7 2..9 8 2. 66 .83 .40 .08 10,.5 4 20/80-82 52,.3 0 16,.0 6 6,.3 8 2. 99 5,.4 8 3,.5 2 2. 72 .84 .37 .10 11,.5 0 20/90-92 51,.9 7 15,.5 5 6,.6 2 3.0 3 5,.4 7 3,.6 1 2. 55 .82 .46 .11 11,.7 2 20/100-102 52,.0 4 15,.7 7 6,.3 0 2. 95 5,.2 5 3..2 3 2. 66 .82 .38 .10 11,.5 1 20/110-112 53,.5 8 15.,6 0 6,• 25 2. 84 4,.9 5 3..0 9 2. 73 .79 .37 .12 10,.6 0 20/120-122 44..8 2 13..2 1 6,.3 2 3. 32 11..3 0 4,.0 4 1. 73 .62 .45 .19 14,,6 5 20/130-132 46..6 7 13..8 5 6.,3 3 3. 38 9..9 4 3.,9 5 1. 88 .65 .45 .19 13,.6 6 20/140-142 45..5 6 13..1 3 6..3 8 3. 23 10.,9 7 3..8 4 1.8 1 .62 .46 .17 14..3 9 20/150-152 46..3 4 13..7 9 6.,3 8 3. 32 10..4 5 3..7 1 1. 88 .66 .47 .18 13..7 4 20/160-162 53..2 5 14..7 1 7..4 7 3. 98 5.,4 6 3..9 1 1. 94 .94 .45 .14 9..9 5 -23/0-5 47..4 0 11.,7 1 6.,8 7 3. 13 2.,7 1 5.,7 4 1. 90 .62 .38 .92 18.,0 8 23/10-13 48.,6 2 12.,5 3 6..6 5 3. 34 3.,6 2 5.,4 5 2. 06 .65 .33 .15 16.,7 5 0.,26 7 23/20-23 50.,0 2 13.,5 0 7..0 8 3. 34 2..8 9 5.,0 3 2. 21 .71 .34 .15 15.,3 8 -25/0-4 49.,9 8 12.,5 8 7.,2 1 3. 20 3.,3 7 5.,3 1 1. 96 .68 .36. .16 16.,1 2 0. 268 25/10-14 49.,8 6 13.,1 0 7.,8 8 3. 56 2.,5 6 5. 58 2. 26 .70 .34 .12 . 15.,1 9 0. 195 -29/0-2 44. 23 12. 50 5.,8 2 3. 03 11. 52 3. 73 1. 61 .62 .44 .18 14.,8 8 29/10-12 41. 84 12. 17 5.,6 6 3. 13 14.,9 0 3. 51 1. 50 .58 .46 .08 16.,1 9 29/20-22 42. 21 12. 65 6. 18 3. 13 13.,8 0 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.,0 8 29/40-42 35. 39 10. 55 5. 16 2. 90 19. 06 2. 82 1. 38 .44 .49 .06 20. 38 Sample no. Si02 A1203 Fe203 MgO CaO Na20 K20 Ti02 P205 MnO LOI Ca0/Al203 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 in Table II iple no. Cu Pb Zn Co Ni 8/0-2 104 21 240 18 115 8/10-12 98 14 212 17 127 8/20-22 76 13 182 22 107 8/30-32 60 <8* 130 24 35 8/40-42 46 9 120 20 51 8/50-52 42 8 110 19 46 8/60-62 50 9 110 22 50 8/70-72 60 9 112 24 53 8/80-82 55 8 112 18 47 8/90-92 40 9 107 19 51 8/100-102 66 5 115 26 64 8/110-112 59 <4 125 27 73 8/120-122 73 8 130 27 73 8/130-132 57 <4 125 24 82 9/0-2 174 30 225 15 100 9/10-12 190 34 258 18 102 9/20-22 119 34 255 20 109 9/30-32 178 19 182 24 83 9/40-42 128 13 167 25 92 9/50-52 83 10 152 24 77 9/60-62 83 12 135 34 84 9/70-72 71 9 113 22 54 9/80-82 45 8 105 21 51 9/90-92 58 10 115 20 46 9/100-102 59 11 117 23 48 9/110-112 47 10 107 18 42 12/0-2 103 6 275 12 124 12/10-12 61 8 179 15 101 12/20-22 55 6 124 17 69 12/30-32 59 15 129 15 62 12/40-42 46 5 110 19 64 12/50-52 54 7 121 16 63 12/60-62 47 <4 107 18 61 12/70-72 43 5 100 15 55 12/80-82 45 <4 103 16 57 12/90-92 50 <4 118 15 54 12/100-102 50 <4 109 14 53 12/110-112 40 <4 92 16 50 15/0-2 102 17 268 18 138 15/10-12 97 13 228 17 118 15/20-22 58 8 154 18 86 15/30-32 60 12 140 19 84 15/40-42 61 9 135 18 73 15/50-52 61 13 124 23 61 15/54-55F 47 13 100 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 as % of total clay Total Clays as % of total seds. Biogenic Remainder clay Mont. 111. Chlor. Mont. 111. Chlor. (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 total clay Total Clays as % of total seds. Biogenic Remainder - LOI Mont. Hi. Chlor. clay 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 39.9 20-22 8.2 81.5 10.3 41.2 3.4 33.6 4.2 5.3 36.2 40-42 16.2 67.6 16.3 38.1 6.2 25.7 6.2 13.1 33.5 60-62 13.5 73.1 13.4 45.3 6.1 33.1 6.1 14.0 23.6 80-82 8.4 83.1 8.5 55.7 4.7 46.3 4.7 3.5 30.3 100-102 13.6 75.4 10.9 53.7 7.3 40.5 5.9 8.3 24.6 78-6-12/0-2 6.1 80.4 13.5 42.7 2.6 34.3 5.8 2.1 38.9 20-22 4.7 83.5 11.8 47.2 2.2 39.4 5.6 2.5 40.7 40-42 12.8 72.3 14.9 50.0 6.4 36.1 7.5 1.7 39.9 60-62 8.5 73.6 18.0 52.7 4.5 38.8 9.5 0.8 38.0 80-82 9.3 78.2 12.5 40.8 3.8 31.9 5.1 3.6 47.6 100-102 9.9 70.7 19.4 48.6 4.8 34.4 9.4 3.0 37.5 78-6-15/0-2 16.9 74.0 9.1 47.1 8.0 34.9 4.3 0.0 37.0 20-22 10.9 73.2 15.9 52.4 5.7 38.4 8.3 5.1 29.7 40-42 16.2 69.9 13.9 50.6 8.2 35.4 7.0 5.5 31.6 60-62 10.9 75/6 13.5 49 iO 5.3 37.0 6.6 10.0 27.3 80-82 14.1 77.0 8.9 47.8 6.7 36.8 4.3 6.7 33.7 100-102 8.9 82.4 8.7 53.1 4.7 43.8 4.6 2.2 34.2 120-122 11.5 79.6 8.9 59.7 6.9 47.5 5.3 4.3 24.9 140-142 10.5 79.4 10.1 56.3 5.9 44.7 5.7 3.0 29.3 78-6-16/0-2 21.7 64.1 14.3 50.2 10.9 32.2 7.2 1.6 31.1 20-22 16.8 62.7 20.5 54.5 9.1 34.1 11.2 4.0 25.5 40-42 13.4 72.6 14.0 49.1 6.6 35.6 6.9 6.5 30.6 60-62 13.3 73.8 12.9 53.9 7.2 39.8 7.0 7.2 25.6 80-82 8.3 .81.2 10.5 50.2 4.2 40.8 5.3 9.8 28.2 100-102 8.9 84.0 14.6 57.3 5.1 48.1 8.4 3.5 28.0 .120-122 6.4 91.0 8.6 55.4 3.5 50.4 4.8 1.6 33.5 Sample no. Clays as % of total clay Total Clays as % of total seds. Biogenic Remainder - LOI Mont. 111. Chlor. clay 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 visual examination, and geochemical units, from data in Fig. 6 131 LEGEND Column 1. X-ray radiograph interpretations. 2. Visual sediment types. 3. Munsell colour classification. 4. Geochemical units. X-ray radiograph interpretations. Visual sediment types. No discernable structure. Clay. Planar lamination. Silt. Contorted lamination. Sand. Granular or sandy. Volcanic glass shards. Volcanic glass shards. Planktonic debris • 0 o (foraminifera). « • • Mottling; bioturbation. Dark smears - probably organic. Digging structures. (? Zoophycos) 132 3 4 0 o o 10YR2O- 1a HEEBi 1 0 ft 10 10 • - 0 — o 9 ° 0 • • 0 20j O O o 20 D 5Y5/2 1b • — e 5Y5& 1 • • •. •• o 30 30l • • o -~-o . — o p 40l 40l .— ^ • • • • • Q. • o — - 5Y5/2 50 5Y4/1 50| and 5Y4/2 f 5G4/1 o 60 60| - 5Y4/1 5Y5/2 • • to 5/1 * o o S70J 70J 5Y4/2 • • — O E o • • — p o «— ~ 80 5Y4/2 X 80 and CL 5Y3/2 5Y4/1 UJ to Q 2 90 5GY5/1 90I 0 O • O © • • 5Y4/1 • • ft 0 100 100J • • o — o o ~ • • • o — 110 1101 0 0 : • hSGY4/l • 5Y5/2 • « • e O5Y5/ 2 o o o to • • • • a Q 120 5GY6/1 1201 • • Core 78-6-1 ° a — • « o 130J • • • 5Y5/1 • o « • • and 3 • — • o • • 5GY5/1 140] o — • Core 78-6-6 133 4 — o —o 10 e ~ "o • - - o -o o—« 5Y5/2 1b -~° ~ g O O I 20 " - ~ S_ 2 3 4 « . o g ' -T n0YR2/2Tla~ «"~ o « 30 10 1c 5Y5/1 40 20 |5Y5/1,521 5GY5/1 50 30l 60 40 5Y4/2 5Y5/1 O 70 50 o • • • E 80 °60 1b X I- Q. LU E904 _ - o — Q 70 o f=5YR3/2j O ~ " o | :100 80 O T o Q. 5Y5/2 5Y5/1 LU \— * 0 Q 9 O 0 110J 90 o ~ o — Core disturbed 120 100J 130] 110! 5Y5/1 o c o 5Y4/1 and 140 5Y5/1 Core 78-6-7 Cori disturbed 150 160 5Y4/6 5GY5/1 Core 78-6-8 134 4 31" p0YR5flf 1a o— o - a — o —a- La"—o -~ 1b 10 10 0 ~ 5GY6/1 to 3/1 20 — \i 20J 5Y6/1 to • — 22— 5GY6/1 —- o — eT 1b 30 30 • • * — o o- 2a "u .•^r-i' 5GY5/1 _ it 40 40 — - c. 50 50 7T"> 5GY6/1 5Y6/1 0— ca // o 6Q to 5/1 60 1c tonus1 E ° 70 £80, I— o — o o 5Y5/1 2b 90 90 5Y6/1 to 100 100 5GY6/1 110 110l Core 78-6-9 120l 5GY4/1 Core 78-6-12 136 O o 10YR6/2) 1 10 a 0 Q o 11111111 • 11 rrm 20 /<• <» o 30l •—>r • *~ O \.» o 10YR5/2 , « „ • 401 and X r- 10YR4/2 Q. 0 0 D 1> *A, ~" o"="o Vv - — ^ — 50! • o: o o « o •« * '—0 o • — « * o o "—« 60 O o • 0 0 Core 78-6-18 a o 5GY5/1 o 9 to 0 0 5Y5/1 80 o o E o 90 §100| 110 120 130 140 150j 160 170 Core 78-6- H 138 APPENDIX 6 A Note on Analytical Precision 139 A Note on Analytical 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 Kiss, of Cominco Research Laboratories Ltd., of Van- . couver. For the major oxides:- Oxide: Si02 A1203 Fe203 Ti02 MgO CaO Absolute preci- ± 1% ±0.2-0.3% ±0.5% ±0.1% ±0.2 - 0.3% ±0.2 - 0.3% sion: Na20 K20 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): 14 111 Precision around detection limit: 100% 100% 100% 100% 100% Precision around working level 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. Grill 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. Grill, on samples from Core 77-14-55 Sample Depth Si02 fl0~2 A1203 FeTO^ MnO MgO CaO Na20 K20 Cu Zn (cm) 0-• 2 53.36 0.72 13.45 7.07 0.26 3.19 3.09 3.10 2.01 100 300 (52.5) (0.69) (12.8) (7.06) (0.26) (3.08) (2.66) (3.37) (1.93) ( 94) (274) 4-• 6 54.11 0.73 13.97 6.80 0.32 3.29 3.34 3.18 2.08 98 305 (52.6) (0.72) (13.2) (6.75) (0.30) (3.17) (3.04) (3.25) (2.02) ( 88) (281) 8-•11 52.26 0.73 13.68 6.95 0.15 3.22 3.56 3.58 2.11 96 308 (51.4) (0.72 (13.8) (6.99) (0.15) (3.23) (2.95) (3.60) (2.02) 17-•20 53.07 0.76 14.26 6.89 0.15 3.21 3.81 3.17 2.15 91 309 (53.0) (0.72) (13.2) (6.95) (0.14) (3.17) (3.19) (3.23) (2.08) ( 89) (343) 29-•32 53.47 0.78 14.53 7.29 0.14 3.33 3.30 3.40 2.27 93 288 (54.7) (0.75) (13.5) (7.52) (0.13) (3.22) (2.56) (3.50) (2.19) 35-•38 52.49 0.77 14.51 7.54 0.15 3.39 3.67 3.56 2.24 95 270 (53.2) (0.80) (13.5) (7.56) (0.15) (3.41) (3.03) (3.50) (2.17) 44-•47 51.72 0.77 14.92 7.35 0.40 3.54 4.66 3.38 2.23 85 239 (48.9) (0.82) (14.1) (7.33) (0.40) (3.35) (4.35 (3.41) (2.13) (112) (236) 54-•57 56.21 0.85 15.88 7.15 0.12 3.39 3.78 3.07 2.01 52 120 (54.4) (0.82) (14.6) (7.03) (0.11) (3.23) (3.11) (3.37) (1.90) 63-•66 62.60 0.83 14.78 5.69 0.10 2.55 4.34 3.52 1.54 30 81 (59.0) (0.80) (13.6) (5.41) (0.09) (2.30) (3.72) (3.53) (1.47) ( 29) ( 75) TABLE VI (Cont'd.) Ppm Sample Na20 K20 Cu Zn Depth Si02 Ti02 Al2 o3 Fe203 MnO MgO CaO (cm) 72-75 57.68 0.85 15. 94 6.92 0.11 3.37 3.82 3.29 1.98 44 105 (55.5) (0.83) (14. 8) (6.67) (0.11) (3.18) (3.47) (3.46) (1.87 81-84 60.01 0.78 15. 35 6.42 0.12 2.90 4.47 3.42 1.85 40 100 (56.5) (0.78) (14. 2) (6.25) (0.11) (2.77) (4.11) (3.24) (1.78) 90.93 58.82 0.85 15. 76 6.99 0.10 3.19 4.04 3.11 1.93 42 104 (55.8) (0.78) (14. 7) (6.53) (0.10) (3.12) (3.68) (3.37) (1.88) ( 37) (105)