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Photograph of piston core D10688 from the Madeira Abyssal . Lettered units are interpreted as and numbered units are intervening pelagic layers (the numbers refer to oxygen isotope stage determination). Note bioturbation of pelagic units and tops of turbidites; coarser laminated bases of turbidites B, B 1 and G and to a lesser extent in turbidites E and F; structureless make-up of the thick turbidites; distinct colour changes in organic-rich turbidites A 1, E, F and H representing relict oxidation fronts; chemical laminae above colour changes. For more detailed discussion of these see papers by Jarvis & Higgs, De Lange et al. and Weaver & Rothwell. GEOLOGICAL SOCIETY SPECIAL PUBLICATION NO 31

Geology and Geochemistry of Abyssal Plains

EDITED BY P. P. E. WEAVER & J. THOMSON Institute of Oceanographic , Wormley, Godalming

1987

Published for The Geological Society by Blackwell Scientific Publications

OXFORD LONDON EDINBURGH

BOSTON PALOALTO MELBOURNE Geological Society Special Publications Series Editor K. COE

Published for DISTRIBUTORS The Geological Society by USA and Canada Blackwell Scientific Publications Blackwell Scientific Publications Inc Osney Mead, Oxford OX2 0EL PO Box 50009, Palo Alto (Orders:Tel. 0865 240201) California 94303 8 John Street, London WC1 2ES (Orders: Tel. (415) 965-4081) 23 Ainslie Place, Edinburgh EH3 6AJ 52 Beacon Place, Boston 02108, USA Blackwell Scientific Publications 667 Lytton Avenue, Palo Alto (Australia) Pty Ltd California 94301, USA 107 Barry Street, Carlton 107 Barry Street, Carlton Victoria 3053 Victoria 3053, Australia (Orders: Tel. (03) 347 0300)

First published 1987 British Library Cataloguing in Publication Data

1987 The Geological Society. Authorization to Geology and geochemistry of abyssal plains.-- photocopy items for internal or personal use, or the (Geological Society special publications, internal or personal use of specific clients, is granted ISSN 0305-8719; no. 31) by The Geological Society for libraries and other users 1. 2. Chemical registered with the Copyright Clearance Center I. Weaver, P.P.E. and Thomson, J. II. Series (CCC) Transactional Reporting Service, providing 551.46'083 GC87 that a base fee of $02.00 per copy is paid directly to CCC, 27 Congress Street, Salem, MA 01970, USA. ISBN 0-632-01744-9 0305-8719/87/$02.00 Library of Congress Cataloging-in-Publication Data Typeset, printed and bound in Great Britain by William Clowes Limited, Beccles and London. Geology and geochemistry of abyssal plains. (Geological Society special publication; no. 31) Bibliography: p. Includes index. 1. geology. 2. . 3. Abyssal zone. 4. sediments. I. Weaver, P. P. E. and Thomson, J. II. Series. QE39.G454 1987 551.46'08 86-29978 ISBN 0-632-01744-9 Contents

WEAVER, P. P. E., THOMSON, J. & HUNTER, P.M. Introduction vii

PILKEY, O.H. Sedimentology of basin plains 1

KUIJPERS, A., DE LANGE, G. J. & DUIN, E. J. Th. Areal rate patterns of the 13 southern Nares , Western N Atlantic

LEDBETTER, M. T. & KLAUS, A. Influence of bottom currents on texture and - 23 floor morphology in the Argentine Basin

KIDD, R. B., HUNTER, P. M. & SIMM, R.W. -current and debris-flow pathways to 33 the Verde Basin: status of long-range side-scan (GLORIA) surveys

SEARLE, R.C. Regional setting and geophysical characterization of the Great Meteor East 49 area in the

WEAVER, P. P. E. & ROTHWELL, R.G. Sedimentation on the Madeira Abyssal Plain over 71 the last 300 000 years

WILLIAMS, S. R.J. Faulting in abyssal-plain sediments, Great Meteor East, Madeira 87 Abyssal Plain

HUGGETT, Q.J. Mapping of hemipelagic versus turbiditic muds by feeding traces observed 105 in deep-sea photographs

SCHULTHEISS, P. J. & NOEL, M. Evidence of pore- in the Madeira Abyssal 113 Plain from pore- and temperature measurements

SHEPHARD, L. E., RUTLEDGE, A. K., BRYANT, W. R. & MORAN, K.M. Geotechnical 131 characteristics of fine-grained sequences from the Nares Abyssal Plain

DE LANGE, G. J., JARVIS, I. & KUIJPERS, A. Geochemical characteristics and of 147 late Quaternary sediments from the Madeira Abyssal Plain, N Atlantic

THOMSON, J., COLLEY, S., HIGGS, N. C., HYDES, D. J., WILSON, T. R. S. & SORENSEN, J. 167 Geochemical oxidation fronts in NE Atlantic distal turbidites and their effects in the sedimentary record

JARVIS, I. & HIGGS, N. Trace-element mobility during early diagenesis in distal turbidites: 179 late Quaternary of the Madeira Abyssal Plain, N Atlantic

HEGGIE, D., MARLS, C., HUDSON, A., DYMOND, J., , R. & CULLEN, J. Organic carbon 215 oxidation and preservation in NW Atlantic sediments

INDEX 237 Introduction

P. P. E. Weaver, J. Thomson & P. M. Hunter

In this publication is assembled a set of 14 papers teristics of the 'Great Meteor East' (GME) area. from the presentations at a meeting of the Marine This area lies in the centre of the Madeira Abyssal Studies Group of the Geological Society, held on Plain and, as a result of the activities of the the 29th and 30th January 1986. The papers cover Working Group, is probably the most various aspects of the , sedimentology, extensively surveyed area of abyssal plain in the geochemistry and geotechnics of abyssal-plain 's . This volume contains several sediments. papers relating to the GME area. Abyssal plains are among the least studied The distribution of individual turbidites and areas of the 's surface. They are poorly entry points of the turbidity currents into the preserved in the sedimentary record because they GME area is discussed by Weaver & Rothwell. tend to be consumed by in the long Williams describes structures which are term. They were not recognized as distinct common in the sediments of part of the area, and physiographic features of the present sea-floor proposes a model in which differential compac- until the late 1940s, and systematic investigations tion initiates the faults which may then act as of relatively few examples have been made. seals to pore-water flow, leading to normal or During the late 1970s an international research reverse directions of throw. Huggett, in a novel programme began to examine selected areas of approach, shows how the turbidite sediments on the N Atlantic and to the plain can be identified on the basis of assess the feasibility of disposal of radioactive macrofaunal feeding and burrowing traces from in deep-sea sediments. This work was seabed photographs. coordinated through the Seabed Working Group Papers by Shephard et al. and Schultheiss & of the Nuclear Agency (OECD, 1984). Noel concentrate on geotechnical properties of The considerations of sea-floor properties re- abyssal-plain sediments. The former paper de- quired for such studies (Laine et al. 1983; Searle scribes the geotechnical properties of sediments 1984) had the result that some of the N Atlantic from the Nares Abyssal Plain, and the latter study areas were in abyssal plains. The availabil- discusses conflicting evidence of pore-water flow ity of new geological information from this through the GME sediments derived from tem- programme provided the impetus for convening perature and pressure measurements. The heat- this meeting, but the papers are not restricted to flow data suggest large downward advection, those deriving from such studies. whereas the pore-pressure data suggest at most a The first paper by Pilkey sets the scene by small downward movement. summarizing the sedimentological work which The paper by de Lange et al. demonstrates by has been carried out at Duke University on 13 compositional arguments that the turbidites abyssal plains. 12 factors controlling the forma- emplaced on the Madeira Abyssal Plain have at tion and development of abyssal plains are least three distinct sources. Few previous geo- discussed. The paper by Kuijpers et al. tackles chemical studies have contrasted the conditions the difficult problem of estimating accumulation developed in sediment columns containing abys- rates in the Nares Abyssal Plain, where the sal-plain turbidites with those which would sediments consist of pelagic and turbiditic clays otherwise obtain in the pelagics of deep basins containing little and few (Wilson et al. 1985). The papers by Jarvis & dateable fossils. Ledbetter & Klaus show that Higgs and Thomson et al. illustrate that the sediments are supplied to the Argentine Basin by importation of labile organic carbon with turbi- down-slope processes but can be picked up by dites has consequences for the redox status, bottom currents and redistributed. The Argentine sediment colour and post-depositional redistri- Abyssal Plain thus consists of areas of coarse bution of several elements. (A recent edition of terrigenous sediments and areas of mud-. (Vol. 68, 1985) contains further In this, the Argentine Abyssal Plain contrasts papers on the contrasts between turbidites and sharply with the Madeira Abyssal Plain (in the other sediment types in the Basin.) Basin) which is dominated by the The final paper by Heggie et al. compares input of fine-grained turbidites. estimates by different methods of the amount of Kidd et al. show the regional picture of parts organic carbon oxidation in the sediments of the of the Cape Verde Basin using GLORIA sono- Hatteras Abyssal Plain and its environs. It is graphs, and Searle describes in detail the charac- suggested in this paper that dissolved organic vii viii P. P. E. Weaver, J. Thomson & P. M. Hunter compounds may be more important than previ- depressions in the seabed become flattened, and, ously appreciated. although there may be a small regional slope, To place the papers of this Special Publication undulations in the seabed of more than a few in context we present below a brief history of metres are rare. This serves to distinguish abyssal research into abyssal plains and an account of plains from other relatively fiat areas of seabed, their distribution in the . The abyssal such as the central parts of the Pacific, which plains discussed here form a very small proportion have been termed 'archipelagic aprons' by Men- of those listed in Table 1, and are limited almost ard (1958). exclusively to the . This reflects in One early study of sediments on an abyssal part the relative inaccessibility of the abyssal plain was by Belderson & Laughton (1966), who plains in high , and the impetus for obtained a series of sediment cores from the research in specific abyssal plains given by the Madcap area of the Cape Verde Basin which Seabed Working Group's research programme contained turbidites, some with coarse bases, that relating to the feasibility of could be correlated across distances of over disposal in the deep ocean. 65 km. They recognized colour sequences within individual turbidites but did not investigate the geochemical processes responsible. Later studies History of research by Horn et al. (1971) and Horn et al. (1972) Before the late 1920s bathymetric data were revealed the importance of turbidity currents in collected by discontinuous soundings using lines forming abyssal plains in the Atlantic, Pacific lowered to the seabed. These were never taken in and Mediterranean . These workers also sufficient numbers to enable the detailed physiog- showed how turbidity-current entry points into raphy of the world's oceans to be delineated, abyssal plains could be identified by grain-size although maps such as those by Murray & Renard analyses, with the coarsest sizes lying most (1891 ) and Thoulet (1904) did outline other major proximally. Recently, the distribution and thick- features such as the edge of the continental nesses of individual turbidites have been mapped shelves and the Mid-Atlantic Ridge. During the between closely spaced cores on several Atlantic 1920s acoustic sounding equipment was devel- abyssal plains (Bennetts & Pilkey 1976; Ditty et oped which could be operated much more rapidly al. 1977; Elmore et al. 1979; Schorsch 1980; van than the sounding lines, thus enabling the Meteor Tassell 1981; Weaver & Rothwell 1987). Ulti- expedition of 1925-1927 to take soundings every mately, these studies should help to elucidate 20 min on E-W Atlantic transects. Maps pro- characteristics of the turbidity currents, such as duced from these techniques (Maurer & Stocks their velocity, and rates of settling. 1933; Stocks & Wust 1935) show clearly the major One feature which has emerged from studying Atlantic basins, but the depth precision of these individual turbidites is the very large volume of early instruments was not sufficient to reveal the material which can be involved in a single flow. flat featureless floors of the basins, now known as Elmore et al. (1979) estimated the volume of the abyssal plains. As the equipment became more Black Shell turbidite on the Hatteras Abyssal refined the depth precision became greater and Plain as over 100 km 3, and Weaver & Rothwell the profiling became continuous. The accumula- (1987) estimate a volume of over 120 km 3 for the tion of such data allowed accurate and detailed f turbidite on the Madeira Abyssal Plain. Such maps to be drawn of large areas of the ocean- volumes are comparable with those calculated for floor and consequently features such as the abyssal the sediment slides and debris flows along the plains could be recognized. Tolstoy & Ewing NW African margin (Embley 1982), one of which (1949) identified the first abyssal plain to the S of (the Saharan slide) travelled in the direction of Newfoundland--now known as the Sohm Abys- the Madeira Abyssal Plain, reaching almost to sal Plain. Following this discovery many other the plain-lower rise boundary (Simm & Kidd examples were found in all the oceans (Heezen et 1983/84). It is possible that in some cases slides, al. 1954, 1959; Koczy 1954; Menard 1955; Hurley debris flows and turbidites may be generated as 1960; Heezen & Laughton 1963). part of the same event. The initiation of the The first cores taken from abyssal plains turbidity currents reaching the Madeira Abyssal revealed sediments containing , often with Plain has been linked to sea-level changes displaced shallow-water (Locher associated with advances and retreats 1954; Phleger 1954) and it became evident that (Weaver & Kuijpers 1983), and similar explana- abyssal plains were formed by the infilling of tions have been invoked for turbidites in the basins, and other deep areas of the ocean-floor, southern Brazil Basin (Johnson & Rasmussen by turbidity currents (Heezen et al. 1951 ; Heezen 1984). Weaver et al. (1986) speculated that the & Laughton 1963). As a result of this infilling, all Madeira Abyssal Plain was initiated by the onset Introduction ix of major glaciation in the late , and that plains. An indication is given in Table 1 of the this abyssal plain, at least, is a relatively recent area occupied by each abyssal plain, but it should feature. be recognized that such estimates are subject to considerable uncertainty. Errors can be caused by inadequate mapping, especially since some of Distribution of abyssal plains the largest abyssal plains occur in the less-well- Abyssal plains were defined by Heezen et al. known Antarctic Ocean. Other errors occur in (1954) as 'areas of the deep ocean floor in which defining the boundaries of the features, and they the ocean bottom is fiat and the slope of the can only be resolved by detailed studies of each bottom is less than 1:000'. The flat seabed is abyssal plain. The Cape Verde Abyssal Plain, produced by the ponding of transported sedi- which lies to the S of the Madeira Abyssal Plain, ments beyond the bases of slopes, which causes for example, was shown by detailed studies an infilling of the deeper areas between abyssal (Auffret et al. 1984; Kidd & Searle 1984) to have hills. The hills gradually become submerged as more 6f the character of the lower continental the area of the plain extends, although few plains rise than of an abyssal plain sensu stricto. It is have become so mature as to have no protruding therefore omitted from our table. hills left. With the exception of , abyssal The distribution of abyssal plains is not plains often form the deepest parts of the oceans, uniform, with the Pacific, for example, having a and in the Atlantic the largest abyssal plains are total of seven and the Atlantic having 29. The located between the base of the comparatively small Ocean has 10 abyssal and the distal parts of the Mid-Atlantic Ridge, or plains, and the four. Abyssal plains other topographic highs such as the Madeira- develop preferentially on sea-floor which can Tore rise. receive a large sediment input from a nearby Approximately 75 abyssal plains have been or upper rise. They are thus identified in the world's oceans (Fig. 1, Table 1). precluded from forming adjacent to margins This list excludes the fiat areas on the floors of bounded by trenches, the situation common trenches and the flat areas on shelves such as are around most of the Pacific. In the N Pacific the found off California, as well as the numerous only true abyssal plains have formed in the NE, areas of ponded turbidites which occur in very to the N of the Mendocino . In this localized basins throughout the oceans. Emery area sediment supply from N America has infilled (1960) named flat areas of seabed in shallow much of the , thus allowing sediment to water as 'basin plains', although later workers cross the trench axis and pond in the areas of the have used this term interchangeably with abyssal Tufts and Cascadia Abyssal Plains.

120 E 180 W 120 60 0 60 120 E

60

o ~

i060

120 E 180 W 120 60 0 60 120 E FIG. 1. Distributionof abyssalplains in the world'soceans (see Fig. 2 for Arctic abyssalplains). The key to the numbers is given in Table 1. x P.P.E. Weaver, J. Thomson & P. M. Hunter

TABLE 1. List of named abyssal plains by ocean with approximate locations and areas Lat Long Area (km 2) Lat Long Area (km 2)

Antarctic 46 Town 39~ 11 ~ 136 000 1 Amundsen 63~ 128~ 570 000 Caribbean 2 Bellinghausen 65~ 90~ 385 000 47 Colombian 13~ 76~ 168 000 3 Enderby 60~ 35~ 3 703 000 48 Grenada 13~ 62~ 42 000 4 South Indian 58~ 125~ 865 000 49 Jamaican 15~ 79~ 42 000 5 62~ 68~ 420 000 50 Panama 1 I~ 79~ 93 000 6 Weddell 65~ 20~ 1 298 000 51 Venezuela 14~ 67~ 75 000 Arctic 52 Yucatan 20~ 85~ 75 000 7 Barents 85~ 40~ 870 of Mexico 8 Boreas 77~ I~ 1 100 53 Florida 25~ 86~ 18 000 9 Canada 76~ 150~ 8 700 54 Sigsbee 23~ 93~ 135 000 10 Chukchi 77~ 172~ 1 700 11 Dumshaf 70~ 5~ 9 000 Indian 12 Fletcher 87~ 180~ 110 55 N Australian 14~ 117~ 196 000 13 75~ 3~ 4 200 56 Mid Indian 4~ 82~ 1 025 000 14 Mendeleyev 81~ 170~ 1 500 57 Cocos 3~ 93~ 536 000 15 Northwind 76~ 161~ 1 400 58 Cuvier 22~ lll~ 45 000 16 Pole 88~ 90~ 360 59 Gascoyne 16~ 110~ 430 000 17 Wrangel 82~ 177~ 1 800 60 Mascarene 19~ 52~ 496 000 61 Perth 28~ 110~ 398 000 Atlantic (IV) 62 Somali I~ 51~ 542 000 18 Barracuda 17~ 56~ 34 000 63 S Australian 37~ 130~ 436 000 19 Biscay 45~ 7~ 268 000 20 Blake Bahama 76~ 54 000 JapaneseSea 28~ 64 Japan 41~ 135~ 160 000 21 Ceara I~ 38~ 303 000 22 Demerara 10~ 48~ 380 000 Mediterranean 23 Gambia 12~ 28~ 175 000 65 Adriatic 42~ 18~ 13 000 24 Guinea l~ 3~ 508 000 66 Alboran 36~ 4~ 2600 25 Hatteras 31~ 71~ 460 000 67 Balearic 40~ 6~ 238 000 26 Hispaniola 20~ 71~ 11 000 68 Sicilia 36~ 18~ 17 000 27 Horseshoe 36~ 12~ 36 000 69 Sidra 34~ 19~ 3800 28 Iberian 44~ 14~ 107 000 70 Tyrrherian 40~ 12~ 30 000 29 Madeira 32~ 21~ 54 000 30 Nares 23~ 63~ 338 000 71 Norway 65~ 4~ 19 000 31 Para 6~ 41~ 215 000 32 Porcupine 49~ 16~ 165 000 Pacific(N) 33 Seine 34~ 12~ 63 000 72 55~ 143~ 718 000 34 Sierra Leone 5~ 17~ 368 000 73 Aleutian 49~ 160~ 988 000 35 22~ 69~ 71 000 74 Cascadia 47~ 127~ 35 000 36 Sohm 36~ 55~ 309 000 75 Tufts 47~ 140~ 793 000 37 Tagus 37~ 12~ 41 000 Pacific(S) 38 Vidal 15~ 55~ 39 000 76 Mornington 54~ 86~ 9200 Atlantic (S) 77 Raukumara 36~ 179~ 21 000 39 Angola 15~ 2~ 1 001 000 40 Aghulas 46~ 23~ 52 000 78 Okhotsk 52~ 149~ 76 000 41 Argentine 47~ 50~ 140 000 42 Burdwood 54~ 62~ 66 000 S China Sea 43 Cape 35~ 6~ 104 000 79 S China Sea 17~ 117~ 129 000 44 Namibia 31~ 5~ 53 000 45 Pernambuco 7~ 27~ 393 000 80 Tasman 34~ 153~ 303 000 draining into the Atlantic from the large drainage unbroken chain from 50~ to 30~ In the S area of N America have supplied enough sedi- Atlantic abyssal plains are less frequent (Fig. 1). ment to form the very large Hatteras and Sohm Emery & Uchupi (1984) estimated that abyssal Abyssal Plains, with Nares Abyssal Plain receiv- plains in the Atlantic Ocean occupy one-seventh ing its sediment via an overflow channel (the of the area of all physiographic units that are due Vema Gap) from the Hatteras Abyssal Plain to sedimentary processes. (Tucholke 1980). In the eastern Atlantic there is In the polar regions abyssal plains are common, a series of abyssal plains forming an almost with 10 in the (Fig. 2) and six Introduction xi

FIG. 2. Distribution of abyssal plains in the Arctic Ocean. The key to the numbers is given in Table 1. surrounding the Antarctic . Sediment 3.7 x l06 km 2, three larger than the second supply is high in these areas owing to ice largest Weddell Abyssal Plain. These vast abyssal on the adjacent and the absence of plains off the Antarctic continent have been able trenches. The largest abyssal plains of all are to form because of the absence of trenches and those surrounding the Antarctic continent, with the prolonged erosion of the Antarctic continent the Enderby Abyssal Plain occupying an area of by ice (Vanney & Johnson 1976).

References

AUFFRET, G. A., LE SUAVE, R., KERBRAT, R., SICHLER, EMERY, K. O. 1960. Basin plains and aprons off B., ROY, S., LAJ, C. & MULLER, C. 1984. southern California. J. Geol. 68, 464-79. Sedimentation in the southern Cape Verde Basin: -- & UcHuPI, E. 1984. The Geology of the Atlantic seismic and sediment facies. In: STOW D. A. V. & Ocean, Springer, New York. PIPER, D. J. W. (eds) Fine-grained Sediments: HEEZEN, B. C. & LAUGHTON,A. S. 1963. Abyssal plains. Deep-water Processes and Facies. Geol. Soc. Spec. In: HILL, M. N. (ed.) The Sea Vol. 3, pp. 312-64, Publ. 15, pp. 153-67. Wiley-Interscience, New York. BELDERSON,R. H. & LAUGHTON,A. S. 1966. Correlation --, EWlNG, M. & ERICSON, D. B. 1951. Submarine of some Atlantic turbidites. Sedimentology, 7, 103- in the North Atlantic. Geol. Soc. Am. 16. Bull. 62, 1407-9. BENNETTS, K. R. W. & PILKEY,O. H. 1976. Character- --,--& 1954. Further evidence for a turbidity istics of three turbidites, Hispaniola-Caicos Basin. current following the Grand Banks . Geol. Soc. Am. Bull. 82, 1341-54. Deep-sea Res. 1, 193-202. DITTY, P. S., HARMON, C. J., PILKEY, O. H., BALL, M. --, THARP, M. & EWING, M. 1959. The floors of the M. & RICHARDSON,E. S. 1977. Mixed terrigenous- oceans; I. The North Atlantic. Geol. Soc. Am. Bull. carbonate sedimentation in the Hispaniola-Caicos Spec. Pap. 65, 1-122. turbidite basin. Mar. Geol. 24, 1-20. HORN, D. R., EWlNG, M., HORN, B. M. & DELACH, M. ELMORE, R. D., PILKEY, O. H., CLEARY, W. J. & N. 1971. Turbidites of the Hatteras and Sohm CURRAN, H. A. 1979. Black Shell Turbidite, Abyssal Plains, western North Atlantic. Mar. Geol. Hatteras Abyssal Plain, western North Atlantic 11, 287-323. ocean basin. Geol. Soc. Am. Bull. 90, 1165-76. , EWING, J. I. & EWlNG, M. 1972. Graded-bed EMBLEY, R. W. 1982. Anatomy of some Atlantic margin sequences emplaced by turbidity currents north of sediment slides and some comments on ages and 20~ in the Pacific, Atlantic and Mediterranean. mechanisms. In: SAXOV, S. & NIEWE~IS, J. K. Sedimentology, 18, 247-75. (eds) Marine Slides and other Mass Movements, pp. HURLEY, R. J. 1960. The of abyssal 189-213, Plenum, New York. plains in the northeast Pacific Ocean. Unpublished xii P. P. E. Weaver, J. Thomson & P. M. Hunter

work, Scripps Institute of Oceanography, Ref. 60- level radioactive waste on or beneath the ocean 67. floor. Nucl. Technol. 64, 166-74. JOHNSON, D. A. & RASMUSSEN, K. A. 1984. Late SIMM, R. W. & KIDD, R. B. 1983/84. Submarine debris Cenozoic turbidite and in flow deposits detected by long range side-scan

the southern Brazil Basin. Mar. Geol. 58, 225-62. sonar 1000 km from source. Geo-Mar. Lett. 3, 13- KIDD, R. B. & SEARLE, R. C. 1984. Sedimentation in 16. the southern Cape Verde Basin: regional observa- STOCKS, T. & WEST, G. 1935. Die Tiefenverhaltnisse tions by long range side scan sonar. In: STOW, D. des offenen Atlantischen Ozeans: Deutsche Atlan- A. V. & PIPER, D. J. (eds) Fine-grained Sediments, tischen Exped. Meteor, 1925-1927. Wiss. Ergeb. 3, Geol. Soc. Spec. Publ. No. 15, pp. 145-51. 1-31. VAN TASSELL,J. V. 1981. Silver Abyssal Plain carbonate KOCzY, F. F. 1954. A survey on deep-sea features taken turbidite: flow characteristics. J. Geol. 89, 317-33. during the Swedish deep-sea expedition. Deep-sea THOULET, J. 1904. L'Ocean, ses Lois, ses Problkmes. Res. 1, 176-84. Hachette. LAINE, E. P., ANDERSON, D. R. & HOLLISTER, C. D. TOLSTOY, I. & EWlNG, M. 1949. North Atlantic 1983. Site qualification for the Subseabed Disposal and the mid-Atlantic Ridge. Bull. Program. In: PARK, P. K., KESTER, n. R., Geol. Soc. Am. 60, 1527-40. DUEDALL, I. W. & KETCHUM, B. (eds) in TUCHOLKE, B. E. 1980. Acoustic environment of the The Ocean, Vol. 3, Radioactive Wastes in the Oceans, Hatteras and Nares Abyssal Plains, western North pp. 345-58, Wiley, New York. Atlantic Ocean, determined from velocities and LOCHER, F. W. 1954. Ein Beitrag zum Problem der physical properties of sediment cores. J. Acoust. Tiefseesande im westlichen Teil des aquatorialen Soc. Am. 68, 1378-90. Atlantiks. Heidelb. Beitr. Petrogr. 4, 135- VANNEY, J. R. & JOHNSON, G. L. 1976. The Belling- 50. shausen-Amundsen Basins (southeastern Pacific): MAURER, H. & STOCKS, T. 1933. Die Echolotengen des major sea-floor units and problems. Mar. Geol. 22, 'Meteor' Deutschen Atlantischen Exped. Meteor, 71-101. 1925-1927. Wiss. Ergeb. 2, 1-309. WEAVER, P. P. E. & KUIJPERS, A. 1983. Climatic MENARD, H. W. 1955. channels, topography control of turbidite deposition on the Madeira and sedimentation. Bull. Am. Assoc. Petrol. Geol. Abyssal Plain. , Lond. 306, 360-3. 39, 236-55. -- & ROTHWELL, R. G. 1987. Sedimentation on the Madeira Abyssal Plain over the last 300 000 years. -- 1958. Development of median in ocean basins. Geol. Soc. Am. Bull. 69, 1179-86. In: WEAVER,P. P. E. and THOMSON,J.(eds) Geology and Geochemistry of Abyssal Plains. This volume, MURRAY, J. & RENARD, A. F. 1891. Report on the Deep- pp. 71-86. sea Deposits based on the Specimens Collected during --, SEARLE, R. C. & KUIJPERS, A. 1986. Turbidite the Voyage of H.M.S. Challenger in the years 1872 deposition and origin of the Madeira Abyssal to 1876, HMSO, London. Plain. In: SUMMERHAYES,C. P. & SHACKLETON,N. PHLEGER, F. B. 1954. Foraminifera and deep-sea J. (eds) North Atlantic Palaeoceanography, Geol. research. Deep-sea Res. 2, 1-23. Soc. Spec. Publ. No. 20, pp. 131-43. SCnORSCHH, L. 1980. The Orleansville Turbidite, south- WILSON, T. R. S., THOMSON, J., COLLEY, S., HYDES, D. ern Balearic Basin, Western . J., HIGGS, N. C. & SORENSEN, J. 1985. Early M.S. Thesis, Duke University, Durham, NC. organic diagenesis: The significance of progressive SEARLE, R. C. 1984. Guidelines for the selection of sites subsurface oxidation fronts in pelagic sediments. that might prove suitable for the disposal of high- Geochim. cosmochim. Acta, 49, 811-22.

P. P. E. WEAVER, J. THOMSON& P. M. HUNTER, Institute of Oceanographic Sciences, Brook Road, Wormley, Godalming, Surrey GU8 5UB.