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Depositional facies and the early phase of ocean basin evolution in the circum-Antarctic region
Marine Geology, 25 (1977) 1--13 o Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands
DEPOSITIONAL FACIES AND THE EARLY EVOLUTION IN THE CIRCUM-ANTARCTIC
PHASE OF OCEAN BASIN REGION*
PETER B. ANDREWS
Sedimentation Laboratory, New Zealand Geological Survey, Christchurch (New Zealand) (Received March 28, 1977)
ABSTRACT Andrews, P.B., 1977. Depositional facies and the early phase of ocean basin evolution in the circum-Antarctic region. Mar. Geol., 25: 1--13. Many Deep Sea Drilling Project drillholes in circum-Antarctic regions penetrated a basal euxinic claystone facies. The facies is dark-coloured, organic carbon and pyrite-rich, very sparsely fossiliferous, massive to burrow-mottled detrital claystone and silty claystone At some sites redeposited silt and sand is intercalated with the facies. The facies accumulated relatively rapidly, under stagnant or restricted circulation b o t t o m conditions. On subsided fragments of continental crust (Falkland Plateau, Campbell Plateau) the euxinic claystone facies succeeds transgressive non-marine to marine sequences; in nearcontinent positions it overlies the oldest oceanic crust. The former relationship appears to mark the rifting phase and the latter the early spreading phase of ocean basin development in circum-Antarctic and other Southern Hemisphere regions. Persistent oceanic biogenic sediment eventually succeeds the claystone facies at each drillsite. In the younger parts of an ocean basin biogenic sediment lies directly on oceanic crust. The change from claystone to biogenic sediment occurs earliest in first-formed oceanic basins and latest in young basins. The change appears to mark the m o m e n t when each basin had grown to sufficient size through sea-floor spreading for a thermohaline circulation to develop.
INTRODUCTION T h e f i r s t s t a g e in t h e e v o l u t i o n o f a n y o c e a n b a s i n f o r m e d b y r i f t i n g a n d spreading of fragments of the Gondwanaland continent should be reflected in t h e c h a r a c t e r o f t h e s e d i m e n t d e p o s i t e d u p o n t h e f i r s t - f o r m e d o c e a n i c c r u s t . I t is r e a s o n e d t h a t a n e m b r y o n i c o c e a n b a s i n w o u l d b e s m a l l , p r o b a b l y narrow, possibly of complex configuration, and therefore characterized by restricted circulation conditions. Sediments consistent with deposition under restricted circulation conditions were encountered during Deep Sea Drilling P r o j e c t ( D S D P ) d r i l l i n g in t h e c i r c u m - A n t a r c t i c r e g i o n . T h e y a r e t h e s u b j e c t of this paper. *Based on a similarly titled paper presented at the Circum-Antarctic Marine Geology Symposium, 25th International Geological Congress, Sydney, August 16--25, 1976.
According to sea-floor magnetic anomaly data and local geological considerations the ocean basins in the circum-Antarctic region originated at different times during the Mesozoic and Cenozoic, viz. Early Cretaceous in the South Atlantic (Larson and Ladd, 1973; Melguen et al., 1975), Early to Middle Cretaceous in the southwest Indian Ocean (Luyendyk, 1974), Late Cretaceous in the southeast and southwest Pacific Ocean (Pitman et al., 1968; Herron, 1971; Christoffel and Falconer, 1972), Late Cretaceous in the Tasman Sea (Hayes and Ringis, 1973), and Late Paleocene in the southeast Indian Ocean (Weissel and Hayes, 1972). In most of these regions one or more DSDP drillholes penetrated the sedimentary sequence and underlying oceanic crust, in near-continental positions (Figs.l--3). At each site the basal sediments gave an age for the oceanic crust similar to or slightly younger than that predicted by the magnetic anomaly data (Table I). Despite the differing ages of the circum-Antarctic ocean basins, the sediments deposited on the first-formed (oldest) oceanic crust in each basin are very similar and very distinctive. They comprise a detrital claystone and silty claystone facies, the characteristics of which indicate accumulation under restricted circulation, even stagnant, conditions (Girdley et al., 1974; Veevers and Johnstone, 1974; Andrews and Ovenshine, 1975; Melguen et al., 1975). The facies is herein called the euxinic claystone facies. EUXINIC CLAYSTONE FACIES
The facies is notably dark-coloured (grey-brown, olive grey, dark brown, olive black and black being common), rich in organic carbon, and contains sparse microfaunas and microfloras of low diversity. The sediments consist of very fine-grained land-derived detritus. X-ray diffraction shows that quartz, micas, montmorillonite, K-feldspar, plagioclase, variable amounts of chlorite and kaolinite, and clinoptilolite are widespread (Cook et al., 1974; Matti et al., 1974; Andrews and Ovenshine, 1975). Petrographic examination of coarser grains shows that the mica recognized by X-ray diffraction occurs as biotite and muscovite, and in schistose rock fragments (Andrews and Ovenshine, 1975). Authigenic pyrite is widespread, and some glauconite occurs. The secondary silica minerals, cristobalite and tridymite, are abundant where the facies is volcanogenic (Site 249), and in the upper part of the facies wherever it is succeeded by biogenic siliceous ooze (Sites 275, 280, 283; see Fig.3). Although generally massive, the facies is burrow-mottled at some sites, some horizons being thoroughly mottled. Andrews and Ovenshine (1975) recognized four distinctive burrow-types in the vicinity of the South Tasman Rise (Sites 280, 283). Primary stratification and sedimentary structures are absent at most sites, particularly deep sites. At shallow sites such as those on the Falkland Plateau, textural variations give a banding to the facies. The banding is at 10--30 cm scale and some finer-grained bands are internally laminated. A few thin beds of sideritic limestone and microsparite are scattered throughout the facies
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1974) and Me!guen et al. (1975).
~'ig.2. Stratigraphy at DSDP Sites 2 4 9 , 2 5 0 , 3 2 7 , 3 3 0 and 361. Data taken from Barker e t a ] . (1974), Davies et a]~ (1 974), Simpso~ et
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~'ig.3. Stratigraphy at DSDP Sites 274, 275, 280, 283, 323. Data taken from Hollister et al. (1974), Andrews and Ovenshine (1975) and {ayes and Frakes (1975).
- I000
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IETRES --0
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;OUTH TASMAN
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2088 5199 2800
4176
4729
5004
2410
2636 4557
249 250 275
280
283
323
327
330 361
not reached (gneiss/ granite expected) gneiss/~ite not reached (basalt just below)
basement }
basalt silt (close to
basalt basalt not reached (schist expected) basalt sill (close to basement) basalt
Nature of basement
Middle--Late Jurassic Earliest Aptian
Late Cretaceous/Early Paleocene Campanian/ Maestrichtian Neocomian
Early--Middle Eocene
Neocomian Coniacian Campanian
Age of basal sediment
Early--Middle Albian Late Paleocene
Danian (very thin) or Oligocene/Early Miocene Early--Middle Albian
Late Eocene
Early Oligocene
Campanian Early--Middle Miocene Campanian/Maestrichtian
Age of lowest biogenic sediment*
50 50
n.d
10 or 60
25
25
40 60 n.d.
Difference** (m.y.)
*Lowest biogenic sediment = earliest formed persistent biogenic sediment anywhere in the basin of deposition. **Difference = difference in age between oldest occurrence of euxinic claystone and oldest persistent biogenic sediments anywhere in the basin of deposition. n.d. = not determinable.
Depth (m)
Drillhole
DSDP stratigraphic drillholes discussed in this report and at which euxinic claystone is the basal sediment (also see Figs.2 and 3).
TABLE I
at Falkland Plateau (Barker et al., 1974). On the shallow Mozambique Plateau (Site 249), the upper part of the facies is commonly laminated, and a few sharp-based graded beds of silt-size ash and volcanic detritus are intercalated with the claystone (Simpson et al., 1974). In the Cape Basin immediately southwest of Africa (Site 361), a local deep-sea fan environment of deposition is indicated by the widespread occurrence of beds of parallel laminated and cross-stratified, carbonaceous siltstone and fine sandstone throughout much of the euxinic claystone facies (Melguen et al., 1975). The features suggest that turbidity currents periodically introduced coarse detrital sediment into a basin where stagnant bottom conditions prevailed. Organic carbon content
The euxinic claystone facies is characterized by unusually high organic carbon values. Measurements are commonly 0.4--1.3 wt.%, and range up to 3.5%. According to Hunt (1975) most of the organic carbon comes from marine plankton, although some comes from spores and pollen of terrestrial origin. Leaf and stem fragments contribute to the very high organic carbon values recorded at some sites (viz. 3.9% and 5.3% at Site 330, and up to 10.0% at site 361). The high organic carbon content has been interpreted to mean accumulation under anaerobic bottom conditions (Girdley et al., 1974; Andrews and Ovenshine, 1975). Fauna and flora
The facies is typically very sparsely fossiliferous, very small numbers of individuals and low faunal diversities being characteristic. A low diversity fauna of arenaceous benthic forams (a "Rhabdammina" fauna according to Webb, 1975) is typical at some localities (Andrews and Ovenshine, 1975). Sparse ostracods, and lagenid and tiny globigerinid forams occur at Site 249, Mozambique Plateau (Simpson et al., 1974). Chitinous fish debris, meagre assemblages of primitive arenaceous forams, and poorly preserved nannofossils occur at Site 250, Mozambique Basin (Davies et al., 1974). In the shallow Falkland Plateau area, the facies is distinguished by small numbers of planktonic and nektonic ammonites, belemnites and thin-shelled bivalves (Ciesielski and Wise, 1976). Dinoflagellates, silicoflagellates, archeomonads, spores and pollens occur in small numbers and varying diversity and preservation at several sites. Spore content is high in some samples, supporting the terrestrial origin of the sediments. Reworked Australian Permian, Triassic, and Early Cretaceous non-marine palynofloras are common at sites near Tasmania (Haskell and Wilson, 1975). Sedimentation rates
Although biostratigraphic control is poor at many sites, it is sufficiently
TABLE II Sedimentation rates for the euxinic claystone facies DSDP site
Rate (m/m.y.)
249
3--5
250
not determinable
275
not determinable
280
35--40 (poor biostratigraphic control)
283
26--28 (fair biostratigraphic control)
323
possibly very low
327
21 }
330
30
361
70
good biostratigraphic control
good at some to show that the facies accumulated at a comparatively high rate (Table II). Representative sedimentation rates of 25--35 m/m.y, are similar to those for biogenic sediment accumulating in areas of high biological productivity; they are extremely high in comparison to typical sedimentation rates for red abyssal clay (1 m/m.y., according to Goodell et al., 1973). DISTRIBUTION OF THE FACIES
The euxinic claystone facies accumulated upon first-formed oceanic crust in many circum-Antarctic basins (Figs.l--3). It also succeeded transgressive non-marine to shallow-marine shelf sequences that accumulated on subsiding blocks of continental crust (viz. Campbell Plateau and Falkland Plateau, Figs.2 and 3). Subsidence and marine transgression over the Falkland Plateau appears to have occurred during Early Jurassic time (Drewry, 1976), probably as the result of pre-spreading rifting. Accumulation of the euxinic claystone facies began in Middle Jurassic time (Barker et al., 1974), well before spreading began early in the Cretaceous, and continued until Middle Cretaceous time. The depositional setting of the euxinic claystone facies thus evidently persists throughout the rifting and early spreading phases of ocean basin evolution. On the Campbell Plateau, the facies occurs at Site 275 (basement not reached), and succeeds a Late Cretaceous non-marine to marine tran~ressive sequence that rests on schistose (Campbell Island) and granitic (Auckland Islands) basement (Summerhayes, 1969). The facies appears to have formed about the time that the Campbell Plateau began to spread away from Antarctica (Late Cretaceous, magnetic anomaly 36). The euxinic claystone facies was n o t drilled into in the Wilkes Coast and Ross Sea region of Antarctica. The oldest sediments recovered were latest
Eocene olive grey, sparsely chertified silty claystone (Site 274, Fig.3), and a thin bed of Late Eocene nanno chalk (Site 267B, Fig.l). Spreading of Australia away from Antarctica began during Late Paleocene--Early Eocene time, and euxinic claystone of Eocene age should occur at sites close to Wilkes Land (viz. Sites 268, 269), as it does close to Australia (Sites 280, 282). It is presumed that if drilling had penetrated to basement at Sites 268 and 269 (Fig. 1), euxinic claystone facies would have been recovered. Drilling was abandoned in Late Oligocene chertified silty clay and clayey silt at Site 268, and in Early Miocene/?Late Oligocene clay, silty clay and silt at Site 269. Nowhere in the circum-Antarctic regions covered by Fig.1 is the oldest oceanic crust known to be overlain by facies other than the euxinic claystone facies. ENVIRONMENT OF DEPOSITION
It is widely agreed that the euxinic claystone facies accumulated under either restricted circulation conditions or stagnant conditions (Barker et al., 1974; Girdley et al., 1974; Andrews and Ovenshine, 1975; Melguen et al., 1975; Ciesielski and Wise, 1976). Certainly, in the South Atlantic area (Cape Basin and its extension the Argentine Basin) and the southwest Indian Ocean (Mozambique Plateau and Mozambique Basin area), where organic carbon values are high, there is negligible evidence of a benthic fauna. Burrowing is largely absent, and the sparse faunal elements present consist almost wholly of planktonic forms. These features are consistent with stagnant bottom waters and oxygenated surface waters of open marine character. In the Bellingshausen Sea, Campbell Plateau area, and in the vicinity ef the South Tasman Rise, burrowing is quite widespread, and despite high organic carbon values, bottom waters were probably oxygenated. However, the absence of primary stratification and the fineness of the sediments suggest that bottom-water circulation was sluggish. The restricted character of the micro-faunas and floras suggests that the bottom conditions were limiting in some respect, perhaps depth. Similarly, the relatively high sedimentation rates (Table II) may have exerted a limiting influence, although their effect is difficult to assess. Webb (1975) concluded from a review of the literature that the arenaceous foram fauna indicates an abyssal environment of deposition. The presence of diverse dinoflagellate palynofloras in the vicinity of the South Tasman Rise suggests that oceanic waters periodically penetrated the depositional basins (Haskell and Wilson, 1975). However, the depth of deposition is difficult to determine. The rarity of calcareous planktonic microfaunas and microfloras suggests deposition below the carbonate compensation depth of the time, yet the few calcareous elements preserved show few signs of dissolution. Barker et al. (1974) concluded that accumulation of the euxinic claystone facies on the Falkland Plateau began when the plateau was quite shallow (perhaps only hundreds of metres deep), and that only when most of the facies had accumulated did the plateau subside (rapidly) to its present depth of 2500 m.
10
Successive studies have demonstrated a direct relationship between age and depth of oceanic crust. The empirical relationship summarized by Le Pichon et al. (1973) showed that oceanic crust generated at spreading ridges forms at a depth of about 2500 m. In their study of depositional environments and the southern Australian continental margin, Deighton et al. (1976, p.29), showed that spreading "ridges as shallow as 1000 m may be typical in y o u n g . . , and n a r r o w . . , spreading ocean basins", for example the Gulf of Aden. Taken together the above considerations show that the euxinic claystone facies accumulated on continental crust during the rifting stage of basin development, at depths measured in hundreds rather than thousands of metres. It also accumulated on oceanic crust formed during the early spreading phase of basin development, at depths that probably ranged from 1000 to 2500 m. S O U T H E R N H E M I S P H E R E D I S T R I B U T I O N O F THE F A C I E S
Although this paper is primarily concerned with circum-Antarctic basins, DSDP results show that the euxinic claystone facies is widespread throughout the Southern Hemisphere as an index of the early phase of an ocean basin's development (Andrews and Ovenshine, 1975). Veevers and Johnstone (1974) viewed the facies as a product of restricted circulation during the early history of the Wharton Basin, northwest of Australia. Similarly, Melguen et al. (1975) regarded the facies as an index of stagnant bottom conditions during the early history of Angola Basin, west of Africa. L A T E R E V E N T S IN BASIN E V O L U T I O N - - E V I D E N C E F R O M B I O G E N I C S E D I M E N T S
At all sites discussed herein, the euxinic claystone facies is succeeded stratigraphically by biogenic sediments. A similar succession is characteristic of the additional sites listed by Andrews and Ovenshine (1975), with the exception that at a few very deep sites (viz., 256, 257), the facies persists unchanged. Further, biogenic sediment, and not euxinic claystone, accumulates on young oceanic crust (middle and later stages in a basin's evolution), as is shown by the sequence of drillholes (265--267) across the southeast Indian Ocean (Hayes and Frakes, 1975), The timing of the change from claystone to persistent biogenic sediments is different in each of the developing basins, occurring earliest in the oldest basins, and latest in the youngest basins, regardless of whether the succeeding biogenic sediment is siliceous or calcareous (Table I). The time interval between first deposition of claystone and first deposition of biogenic sediments anywhere in a basin is approximately 50 m.y. for older basins (Jurassic--Early Cretaceous origin) and 25 m.y. for younger basins (Late Cretaceous--Early Tertiary origin). It is concluded that this systematic succession of claystone by biogenic sediments was closely linked to the gradual increase in size of the ocean
11
basins by sea-floor spreading, and to the related development of the oceanic circulation patterns as they now exist. During the early phase of sea-floor spreading the basins were relatively small and circulation was restricted; fine-grained land-derived detritus was deposited. Only when the continental fragments had drifted far apart did a thermohaline circulation of oceanic waters develop. Organic nutrients increased, an abundant and diverse plankton developed, and biogenic sediments began to accumulate (Veevers and Johnstone, 1974; Andrews and Ovenshine, 1975). In detail, different thermohaline circulation systems developed in the different basins, the older systems becoming modified and some becoming integrated as younger ocean basins developed (cf. Kennett et al., 1974; Drewry, 1976). Although the detail varies from one basin to another, the above generalized sequence of events is characteristic of the Southern Hemisphere basins. ACKNOWLEDGEMENTS
Preparation of this paper has benefited substantially from discussions with several participants at the 25th International Geological Congress, Sydney, 1976. I am particularly indebted to Dr. A.D. Partridge, Esso Australia Ltd.; Dr. D. Falvey, University of Sydney; and Dr. S.W. Wise, Florida State University. I also acknowledge the sterling work of Ms. Lee Leonard, University of Canterbury, who drafted the figures. Mr. G. Warren, New Zealand Geological Survey, kindly reviewed the manuscript.
REFERENCES Andrews, P.B. and Ovenshine, A.T., 1975. Terrigenous silt and clay facies: deposits of the early phase of ocean basin evolution. Initial Reports of the Deep Sea Drilling Project, 29. U.S. Govt. Printing Office, Washington, D.C., pp.1049--1063. Barker, P.F., Dalziel, I.W.D., Elliott, D.H., Von der Borch, C.C., Thompson, R.W., Plafker, G., Tjalsma, R.C., Wise, S.W., Dinkelman, M.G., Gombos, A.M., Lonardi, A. and Tarney, J., 1974. Southwestern Atlantic Leg 36. Geotimes, 19 (11): 16--18. Christoffel, D.A. and Falconer, R.K.H., 197~2. Marine magnetic measurements in the southwest Pacific Ocean and the identification of new tectonic features. In: D.E. Hayes (Editor), Antarctic Oceanology, II: The Australian--New Zealand Sector. Antarct. Res. Ser., 19: 197--209. Ciesielski, P.F. and Wise, S.W., 1976. South Atlantic sector of the Southern Ocean: Mesozoic/Cenozoic paleoenvironments of deposition recorded in sediments of the Falkland Plateau and adjacent basins (abstract). Abstr. 25th Int. Geol. Congr., Sydney, 3: 882--883. Cook, H.E., Zemmels, I. and Matti, J.C., 1974. X-ray mineralogy data, Southern Indian Ocean Leg 26 Deep Sea Drilling Project. Initial Reports of the Deep Sea Drilling Project, 26. U.S. Govt. Printing Office, Washington, D.C., pp.573--592. Davies, T.A., Luyendyk, B., Rodolfo, K.S., Kempe, D.R.C., McKelvey, B.C., Leidy, R.D., Horvath, G.J., Hyndman, R.D., Thierstein, H.R., Herb, R.C., Boltovskoy, E. and Doyle, P., 1974. Initial Reports of the Deep Sea Drilling Project, 26. U.S. Govt. Printing Office, Washington, D.C., 1129 pp. Deighton, I., Falvey, D.A. and Taylor, D.J., 1976. Depositional environments and geotectonic framework: Southern Australian continental margin. J. Aust. Pet. Explor. Assoc., 16: 25--36. -
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~'2 Drewry, D.J., 1976. Deep-sea drilling from Glomar Challenger in the Southern Ocean. The results and geophysical and geological implications. Polar Rec., 18 (112): 47--77. Goodell, H.G., Houtz, R., Ewing, M., Hayes, D., Naini, B., Echols, R.J., Kennett, J.P. and Donahue, J.G., 1973. Marine sediments of the southern oceans. Am. Geogr. Soc., Antarct. Map Folio Set., Folio 17. Girdley, W.A., Leclaire, L., Moore, C., Vallier, T.L. and White, S.M., 1974. Lithologic summary, Leg 25, Deep Sea Drilling Project. Initial Reports of the Deep Sea Drilling Project, 25. U.S. Govt. Printing Office, Washington, D.C., pp.725--741. Haskell, T.R. and Wilson, G.J., 1 975. Palynology of sites 280--284, DSDP Leg 29, off southeastern Australia and western New Zealand. Initial Reports of the Deep Sea Drilling Project, 29. U.S. Govt. Printing Office, Washington, D.C., pp. 723--741. Hayes, D.E. and Frakes, L.A., 1975. General synthesis, Deep Sea Drilling Project, Leg 28. Initial Reports of the Deep Sea Drilling Project, 28. U.S. Govt. Printing Office. Washington, D.C., pp.919--942. Hayes, D.E. and Ringis, a., 1973. Seafloor spreading in the Tasman S~a. Nature, 243: 454--458. Herron, E.M., 1971. Crustal plates and seafloor spreading in the southeastern Pacific. In: J.L. Reid (Editor), Antarctic Oceanology, I. Antarct. Res. Ser., 15: 229--237. Hollister, C.D., Craddock, C., Bogdanov, J.A., Edgar, N.T., Gieskes, J., Haq, B.U., Lawrence, J., RSgl, F., Schrader, H.J., Tucholke, B.E., Vennum, W., Weaver, F.M. and Zhivago, V.N., 1974. Deep drilling in the Southeast Pacific Basin. Geotimes, 19 (8): 16--19. Hunt, J.M., 1975. Hydrocarbon studies. Initial Reports of the Deep Sea Drilling Project, 31. U,S. Govt. Printing Office, Washington, D.C., pp.901--903. Kennett, J.P., Houtz, R.E., Andrews, P.B., Edwards, A.R., Gostin, V.A., Hajos, M., Hampton, M.A., Jenkins, D.G., Margolis, S.V., Ovenshine, A.T. and Perch-Nielsen, K., 1974. Development of the Circum-Antarctic Current. Science, 186: 144--147. Larson, R.L. and Ladd, J.W., 1973. Evidence for the opening of the South Atlantic in the Early Cretaceous. Nature, 246: 210--212. Le Pichon, X., Francheteau, J. and Bonin, J., 1973. Plate Tectonics, Elsevier, Amsterdam, 300 pp. Luyendyk, B.P., 1974. Gondwanaland dispersal and the early formation of the Indian Ocean. Initial Reports of the Deep Sea Drilling Project, 26. U.S. Govt. Printing Office, Washington, D.C., pp.945--952. Matti, J.C., Zemmels, I. and Cook, H.E., 1974. X-ray mineralogy data, western Indian Ocean -- Leg 25, Deep Sea Drilling Project. Initial Reports of the Deep Sea Drilling Project, 25. U.S. Govt. Printing Office, Washington, D.C., pp.843--861. Melguen, M., Bolli, H.M., Ryan, W.B.F., Foresman, J.B., Hottman, W.E., Kagami, H., Longoria, J.F., McKnight, B.K., Natland, J., Protodecima, F. and Siesser, W.G., 1975. Facies evolution and carbonate dissolution cycles in sediments from basins and continental margins of the eastern South Atlantic since early Cretaceous. Int. Cong. Sedimentol., 9th, Nice, 8: 43--50. Pitman, W.C., Herron, E.M. and Heirtzler, J.R., 1968. Magnetic anomalies in the Pacific and sea floor spreading. J. Geophys. Res., 73 (6): 2069--2085. Simpson, E.S.W., Schlich, R,, Gieskes, J.M., Girdley, W.A., Leclaire, L., Marshall, B.V., Moore, C., Muller, C., Sigal, J., Vallier, T.L., White, S.M. and Zobel, B., 1974. Initial Reports of the Deep Sea Drilling Project, 25. U.S. Govt. Printing Office, Washington, D.C., 884 pp. Summerhayes, C., 1969. Marine geology of the New Zealand sub-antarctic seafloor. N.Z. Oceanogr. Inst. Mere., 5 0 : 9 2 pp. Veevers, J.J. and Johnstone, M.H., 1974. Comparative stratigraphy and structure of the western Australian margin and the adjacent deep ocean floor. Initial Reports of the Deep Sea Drilling Project, 27. U.S. Govt. Printing Office, Washington, D,C., pp.571-585.
13 Webb, P.N., 1975. Paleocene foraminifera from DSDP site 283, South Tasman Basin. Initial Reports of the Deep Sea Drilling Project, 29. U.S. Govt. Printing Office, Washington, D.C., pp.833--843. Weissel, J.K. and Hayes, D.E., 1972. Magnetic anomalies in the southeast Indian Ocean. In: D.E. Hayes (Editor), Antarctic Oceanology, II: The Australian--New Zealand Sector. Antarct. Res. Ser., 19: 165--196.
DEPOSITIONAL FACIES AND THE EARLY EVOLUTION IN THE CIRCUM-ANTARCTIC
PHASE OF OCEAN BASIN REGION*
PETER B. ANDREWS
Sedimentation Laboratory, New Zealand Geological Survey, Christchurch (New Zealand) (Received March 28, 1977)
ABSTRACT Andrews, P.B., 1977. Depositional facies and the early phase of ocean basin evolution in the circum-Antarctic region. Mar. Geol., 25: 1--13. Many Deep Sea Drilling Project drillholes in circum-Antarctic regions penetrated a basal euxinic claystone facies. The facies is dark-coloured, organic carbon and pyrite-rich, very sparsely fossiliferous, massive to burrow-mottled detrital claystone and silty claystone At some sites redeposited silt and sand is intercalated with the facies. The facies accumulated relatively rapidly, under stagnant or restricted circulation b o t t o m conditions. On subsided fragments of continental crust (Falkland Plateau, Campbell Plateau) the euxinic claystone facies succeeds transgressive non-marine to marine sequences; in nearcontinent positions it overlies the oldest oceanic crust. The former relationship appears to mark the rifting phase and the latter the early spreading phase of ocean basin development in circum-Antarctic and other Southern Hemisphere regions. Persistent oceanic biogenic sediment eventually succeeds the claystone facies at each drillsite. In the younger parts of an ocean basin biogenic sediment lies directly on oceanic crust. The change from claystone to biogenic sediment occurs earliest in first-formed oceanic basins and latest in young basins. The change appears to mark the m o m e n t when each basin had grown to sufficient size through sea-floor spreading for a thermohaline circulation to develop.
INTRODUCTION T h e f i r s t s t a g e in t h e e v o l u t i o n o f a n y o c e a n b a s i n f o r m e d b y r i f t i n g a n d spreading of fragments of the Gondwanaland continent should be reflected in t h e c h a r a c t e r o f t h e s e d i m e n t d e p o s i t e d u p o n t h e f i r s t - f o r m e d o c e a n i c c r u s t . I t is r e a s o n e d t h a t a n e m b r y o n i c o c e a n b a s i n w o u l d b e s m a l l , p r o b a b l y narrow, possibly of complex configuration, and therefore characterized by restricted circulation conditions. Sediments consistent with deposition under restricted circulation conditions were encountered during Deep Sea Drilling P r o j e c t ( D S D P ) d r i l l i n g in t h e c i r c u m - A n t a r c t i c r e g i o n . T h e y a r e t h e s u b j e c t of this paper. *Based on a similarly titled paper presented at the Circum-Antarctic Marine Geology Symposium, 25th International Geological Congress, Sydney, August 16--25, 1976.
According to sea-floor magnetic anomaly data and local geological considerations the ocean basins in the circum-Antarctic region originated at different times during the Mesozoic and Cenozoic, viz. Early Cretaceous in the South Atlantic (Larson and Ladd, 1973; Melguen et al., 1975), Early to Middle Cretaceous in the southwest Indian Ocean (Luyendyk, 1974), Late Cretaceous in the southeast and southwest Pacific Ocean (Pitman et al., 1968; Herron, 1971; Christoffel and Falconer, 1972), Late Cretaceous in the Tasman Sea (Hayes and Ringis, 1973), and Late Paleocene in the southeast Indian Ocean (Weissel and Hayes, 1972). In most of these regions one or more DSDP drillholes penetrated the sedimentary sequence and underlying oceanic crust, in near-continental positions (Figs.l--3). At each site the basal sediments gave an age for the oceanic crust similar to or slightly younger than that predicted by the magnetic anomaly data (Table I). Despite the differing ages of the circum-Antarctic ocean basins, the sediments deposited on the first-formed (oldest) oceanic crust in each basin are very similar and very distinctive. They comprise a detrital claystone and silty claystone facies, the characteristics of which indicate accumulation under restricted circulation, even stagnant, conditions (Girdley et al., 1974; Veevers and Johnstone, 1974; Andrews and Ovenshine, 1975; Melguen et al., 1975). The facies is herein called the euxinic claystone facies. EUXINIC CLAYSTONE FACIES
The facies is notably dark-coloured (grey-brown, olive grey, dark brown, olive black and black being common), rich in organic carbon, and contains sparse microfaunas and microfloras of low diversity. The sediments consist of very fine-grained land-derived detritus. X-ray diffraction shows that quartz, micas, montmorillonite, K-feldspar, plagioclase, variable amounts of chlorite and kaolinite, and clinoptilolite are widespread (Cook et al., 1974; Matti et al., 1974; Andrews and Ovenshine, 1975). Petrographic examination of coarser grains shows that the mica recognized by X-ray diffraction occurs as biotite and muscovite, and in schistose rock fragments (Andrews and Ovenshine, 1975). Authigenic pyrite is widespread, and some glauconite occurs. The secondary silica minerals, cristobalite and tridymite, are abundant where the facies is volcanogenic (Site 249), and in the upper part of the facies wherever it is succeeded by biogenic siliceous ooze (Sites 275, 280, 283; see Fig.3). Although generally massive, the facies is burrow-mottled at some sites, some horizons being thoroughly mottled. Andrews and Ovenshine (1975) recognized four distinctive burrow-types in the vicinity of the South Tasman Rise (Sites 280, 283). Primary stratification and sedimentary structures are absent at most sites, particularly deep sites. At shallow sites such as those on the Falkland Plateau, textural variations give a banding to the facies. The banding is at 10--30 cm scale and some finer-grained bands are internally laminated. A few thin beds of sideritic limestone and microsparite are scattered throughout the facies
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1974) and Me!guen et al. (1975).
~'ig.2. Stratigraphy at DSDP Sites 2 4 9 , 2 5 0 , 3 2 7 , 3 3 0 and 361. Data taken from Barker e t a ] . (1974), Davies et a]~ (1 974), Simpso~ et
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~'ig.3. Stratigraphy at DSDP Sites 274, 275, 280, 283, 323. Data taken from Hollister et al. (1974), Andrews and Ovenshine (1975) and {ayes and Frakes (1975).
- I000
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IETRES --0
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2088 5199 2800
4176
4729
5004
2410
2636 4557
249 250 275
280
283
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327
330 361
not reached (gneiss/ granite expected) gneiss/~ite not reached (basalt just below)
basement }
basalt silt (close to
basalt basalt not reached (schist expected) basalt sill (close to basement) basalt
Nature of basement
Middle--Late Jurassic Earliest Aptian
Late Cretaceous/Early Paleocene Campanian/ Maestrichtian Neocomian
Early--Middle Eocene
Neocomian Coniacian Campanian
Age of basal sediment
Early--Middle Albian Late Paleocene
Danian (very thin) or Oligocene/Early Miocene Early--Middle Albian
Late Eocene
Early Oligocene
Campanian Early--Middle Miocene Campanian/Maestrichtian
Age of lowest biogenic sediment*
50 50
n.d
10 or 60
25
25
40 60 n.d.
Difference** (m.y.)
*Lowest biogenic sediment = earliest formed persistent biogenic sediment anywhere in the basin of deposition. **Difference = difference in age between oldest occurrence of euxinic claystone and oldest persistent biogenic sediments anywhere in the basin of deposition. n.d. = not determinable.
Depth (m)
Drillhole
DSDP stratigraphic drillholes discussed in this report and at which euxinic claystone is the basal sediment (also see Figs.2 and 3).
TABLE I
at Falkland Plateau (Barker et al., 1974). On the shallow Mozambique Plateau (Site 249), the upper part of the facies is commonly laminated, and a few sharp-based graded beds of silt-size ash and volcanic detritus are intercalated with the claystone (Simpson et al., 1974). In the Cape Basin immediately southwest of Africa (Site 361), a local deep-sea fan environment of deposition is indicated by the widespread occurrence of beds of parallel laminated and cross-stratified, carbonaceous siltstone and fine sandstone throughout much of the euxinic claystone facies (Melguen et al., 1975). The features suggest that turbidity currents periodically introduced coarse detrital sediment into a basin where stagnant bottom conditions prevailed. Organic carbon content
The euxinic claystone facies is characterized by unusually high organic carbon values. Measurements are commonly 0.4--1.3 wt.%, and range up to 3.5%. According to Hunt (1975) most of the organic carbon comes from marine plankton, although some comes from spores and pollen of terrestrial origin. Leaf and stem fragments contribute to the very high organic carbon values recorded at some sites (viz. 3.9% and 5.3% at Site 330, and up to 10.0% at site 361). The high organic carbon content has been interpreted to mean accumulation under anaerobic bottom conditions (Girdley et al., 1974; Andrews and Ovenshine, 1975). Fauna and flora
The facies is typically very sparsely fossiliferous, very small numbers of individuals and low faunal diversities being characteristic. A low diversity fauna of arenaceous benthic forams (a "Rhabdammina" fauna according to Webb, 1975) is typical at some localities (Andrews and Ovenshine, 1975). Sparse ostracods, and lagenid and tiny globigerinid forams occur at Site 249, Mozambique Plateau (Simpson et al., 1974). Chitinous fish debris, meagre assemblages of primitive arenaceous forams, and poorly preserved nannofossils occur at Site 250, Mozambique Basin (Davies et al., 1974). In the shallow Falkland Plateau area, the facies is distinguished by small numbers of planktonic and nektonic ammonites, belemnites and thin-shelled bivalves (Ciesielski and Wise, 1976). Dinoflagellates, silicoflagellates, archeomonads, spores and pollens occur in small numbers and varying diversity and preservation at several sites. Spore content is high in some samples, supporting the terrestrial origin of the sediments. Reworked Australian Permian, Triassic, and Early Cretaceous non-marine palynofloras are common at sites near Tasmania (Haskell and Wilson, 1975). Sedimentation rates
Although biostratigraphic control is poor at many sites, it is sufficiently
TABLE II Sedimentation rates for the euxinic claystone facies DSDP site
Rate (m/m.y.)
249
3--5
250
not determinable
275
not determinable
280
35--40 (poor biostratigraphic control)
283
26--28 (fair biostratigraphic control)
323
possibly very low
327
21 }
330
30
361
70
good biostratigraphic control
good at some to show that the facies accumulated at a comparatively high rate (Table II). Representative sedimentation rates of 25--35 m/m.y, are similar to those for biogenic sediment accumulating in areas of high biological productivity; they are extremely high in comparison to typical sedimentation rates for red abyssal clay (1 m/m.y., according to Goodell et al., 1973). DISTRIBUTION OF THE FACIES
The euxinic claystone facies accumulated upon first-formed oceanic crust in many circum-Antarctic basins (Figs.l--3). It also succeeded transgressive non-marine to shallow-marine shelf sequences that accumulated on subsiding blocks of continental crust (viz. Campbell Plateau and Falkland Plateau, Figs.2 and 3). Subsidence and marine transgression over the Falkland Plateau appears to have occurred during Early Jurassic time (Drewry, 1976), probably as the result of pre-spreading rifting. Accumulation of the euxinic claystone facies began in Middle Jurassic time (Barker et al., 1974), well before spreading began early in the Cretaceous, and continued until Middle Cretaceous time. The depositional setting of the euxinic claystone facies thus evidently persists throughout the rifting and early spreading phases of ocean basin evolution. On the Campbell Plateau, the facies occurs at Site 275 (basement not reached), and succeeds a Late Cretaceous non-marine to marine tran~ressive sequence that rests on schistose (Campbell Island) and granitic (Auckland Islands) basement (Summerhayes, 1969). The facies appears to have formed about the time that the Campbell Plateau began to spread away from Antarctica (Late Cretaceous, magnetic anomaly 36). The euxinic claystone facies was n o t drilled into in the Wilkes Coast and Ross Sea region of Antarctica. The oldest sediments recovered were latest
Eocene olive grey, sparsely chertified silty claystone (Site 274, Fig.3), and a thin bed of Late Eocene nanno chalk (Site 267B, Fig.l). Spreading of Australia away from Antarctica began during Late Paleocene--Early Eocene time, and euxinic claystone of Eocene age should occur at sites close to Wilkes Land (viz. Sites 268, 269), as it does close to Australia (Sites 280, 282). It is presumed that if drilling had penetrated to basement at Sites 268 and 269 (Fig. 1), euxinic claystone facies would have been recovered. Drilling was abandoned in Late Oligocene chertified silty clay and clayey silt at Site 268, and in Early Miocene/?Late Oligocene clay, silty clay and silt at Site 269. Nowhere in the circum-Antarctic regions covered by Fig.1 is the oldest oceanic crust known to be overlain by facies other than the euxinic claystone facies. ENVIRONMENT OF DEPOSITION
It is widely agreed that the euxinic claystone facies accumulated under either restricted circulation conditions or stagnant conditions (Barker et al., 1974; Girdley et al., 1974; Andrews and Ovenshine, 1975; Melguen et al., 1975; Ciesielski and Wise, 1976). Certainly, in the South Atlantic area (Cape Basin and its extension the Argentine Basin) and the southwest Indian Ocean (Mozambique Plateau and Mozambique Basin area), where organic carbon values are high, there is negligible evidence of a benthic fauna. Burrowing is largely absent, and the sparse faunal elements present consist almost wholly of planktonic forms. These features are consistent with stagnant bottom waters and oxygenated surface waters of open marine character. In the Bellingshausen Sea, Campbell Plateau area, and in the vicinity ef the South Tasman Rise, burrowing is quite widespread, and despite high organic carbon values, bottom waters were probably oxygenated. However, the absence of primary stratification and the fineness of the sediments suggest that bottom-water circulation was sluggish. The restricted character of the micro-faunas and floras suggests that the bottom conditions were limiting in some respect, perhaps depth. Similarly, the relatively high sedimentation rates (Table II) may have exerted a limiting influence, although their effect is difficult to assess. Webb (1975) concluded from a review of the literature that the arenaceous foram fauna indicates an abyssal environment of deposition. The presence of diverse dinoflagellate palynofloras in the vicinity of the South Tasman Rise suggests that oceanic waters periodically penetrated the depositional basins (Haskell and Wilson, 1975). However, the depth of deposition is difficult to determine. The rarity of calcareous planktonic microfaunas and microfloras suggests deposition below the carbonate compensation depth of the time, yet the few calcareous elements preserved show few signs of dissolution. Barker et al. (1974) concluded that accumulation of the euxinic claystone facies on the Falkland Plateau began when the plateau was quite shallow (perhaps only hundreds of metres deep), and that only when most of the facies had accumulated did the plateau subside (rapidly) to its present depth of 2500 m.
10
Successive studies have demonstrated a direct relationship between age and depth of oceanic crust. The empirical relationship summarized by Le Pichon et al. (1973) showed that oceanic crust generated at spreading ridges forms at a depth of about 2500 m. In their study of depositional environments and the southern Australian continental margin, Deighton et al. (1976, p.29), showed that spreading "ridges as shallow as 1000 m may be typical in y o u n g . . , and n a r r o w . . , spreading ocean basins", for example the Gulf of Aden. Taken together the above considerations show that the euxinic claystone facies accumulated on continental crust during the rifting stage of basin development, at depths measured in hundreds rather than thousands of metres. It also accumulated on oceanic crust formed during the early spreading phase of basin development, at depths that probably ranged from 1000 to 2500 m. S O U T H E R N H E M I S P H E R E D I S T R I B U T I O N O F THE F A C I E S
Although this paper is primarily concerned with circum-Antarctic basins, DSDP results show that the euxinic claystone facies is widespread throughout the Southern Hemisphere as an index of the early phase of an ocean basin's development (Andrews and Ovenshine, 1975). Veevers and Johnstone (1974) viewed the facies as a product of restricted circulation during the early history of the Wharton Basin, northwest of Australia. Similarly, Melguen et al. (1975) regarded the facies as an index of stagnant bottom conditions during the early history of Angola Basin, west of Africa. L A T E R E V E N T S IN BASIN E V O L U T I O N - - E V I D E N C E F R O M B I O G E N I C S E D I M E N T S
At all sites discussed herein, the euxinic claystone facies is succeeded stratigraphically by biogenic sediments. A similar succession is characteristic of the additional sites listed by Andrews and Ovenshine (1975), with the exception that at a few very deep sites (viz., 256, 257), the facies persists unchanged. Further, biogenic sediment, and not euxinic claystone, accumulates on young oceanic crust (middle and later stages in a basin's evolution), as is shown by the sequence of drillholes (265--267) across the southeast Indian Ocean (Hayes and Frakes, 1975), The timing of the change from claystone to persistent biogenic sediments is different in each of the developing basins, occurring earliest in the oldest basins, and latest in the youngest basins, regardless of whether the succeeding biogenic sediment is siliceous or calcareous (Table I). The time interval between first deposition of claystone and first deposition of biogenic sediments anywhere in a basin is approximately 50 m.y. for older basins (Jurassic--Early Cretaceous origin) and 25 m.y. for younger basins (Late Cretaceous--Early Tertiary origin). It is concluded that this systematic succession of claystone by biogenic sediments was closely linked to the gradual increase in size of the ocean
11
basins by sea-floor spreading, and to the related development of the oceanic circulation patterns as they now exist. During the early phase of sea-floor spreading the basins were relatively small and circulation was restricted; fine-grained land-derived detritus was deposited. Only when the continental fragments had drifted far apart did a thermohaline circulation of oceanic waters develop. Organic nutrients increased, an abundant and diverse plankton developed, and biogenic sediments began to accumulate (Veevers and Johnstone, 1974; Andrews and Ovenshine, 1975). In detail, different thermohaline circulation systems developed in the different basins, the older systems becoming modified and some becoming integrated as younger ocean basins developed (cf. Kennett et al., 1974; Drewry, 1976). Although the detail varies from one basin to another, the above generalized sequence of events is characteristic of the Southern Hemisphere basins. ACKNOWLEDGEMENTS
Preparation of this paper has benefited substantially from discussions with several participants at the 25th International Geological Congress, Sydney, 1976. I am particularly indebted to Dr. A.D. Partridge, Esso Australia Ltd.; Dr. D. Falvey, University of Sydney; and Dr. S.W. Wise, Florida State University. I also acknowledge the sterling work of Ms. Lee Leonard, University of Canterbury, who drafted the figures. Mr. G. Warren, New Zealand Geological Survey, kindly reviewed the manuscript.
REFERENCES Andrews, P.B. and Ovenshine, A.T., 1975. Terrigenous silt and clay facies: deposits of the early phase of ocean basin evolution. Initial Reports of the Deep Sea Drilling Project, 29. U.S. Govt. Printing Office, Washington, D.C., pp.1049--1063. Barker, P.F., Dalziel, I.W.D., Elliott, D.H., Von der Borch, C.C., Thompson, R.W., Plafker, G., Tjalsma, R.C., Wise, S.W., Dinkelman, M.G., Gombos, A.M., Lonardi, A. and Tarney, J., 1974. Southwestern Atlantic Leg 36. Geotimes, 19 (11): 16--18. Christoffel, D.A. and Falconer, R.K.H., 197~2. Marine magnetic measurements in the southwest Pacific Ocean and the identification of new tectonic features. In: D.E. Hayes (Editor), Antarctic Oceanology, II: The Australian--New Zealand Sector. Antarct. Res. Ser., 19: 197--209. Ciesielski, P.F. and Wise, S.W., 1976. South Atlantic sector of the Southern Ocean: Mesozoic/Cenozoic paleoenvironments of deposition recorded in sediments of the Falkland Plateau and adjacent basins (abstract). Abstr. 25th Int. Geol. Congr., Sydney, 3: 882--883. Cook, H.E., Zemmels, I. and Matti, J.C., 1974. X-ray mineralogy data, Southern Indian Ocean Leg 26 Deep Sea Drilling Project. Initial Reports of the Deep Sea Drilling Project, 26. U.S. Govt. Printing Office, Washington, D.C., pp.573--592. Davies, T.A., Luyendyk, B., Rodolfo, K.S., Kempe, D.R.C., McKelvey, B.C., Leidy, R.D., Horvath, G.J., Hyndman, R.D., Thierstein, H.R., Herb, R.C., Boltovskoy, E. and Doyle, P., 1974. Initial Reports of the Deep Sea Drilling Project, 26. U.S. Govt. Printing Office, Washington, D.C., 1129 pp. Deighton, I., Falvey, D.A. and Taylor, D.J., 1976. Depositional environments and geotectonic framework: Southern Australian continental margin. J. Aust. Pet. Explor. Assoc., 16: 25--36. -
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~'2 Drewry, D.J., 1976. Deep-sea drilling from Glomar Challenger in the Southern Ocean. The results and geophysical and geological implications. Polar Rec., 18 (112): 47--77. Goodell, H.G., Houtz, R., Ewing, M., Hayes, D., Naini, B., Echols, R.J., Kennett, J.P. and Donahue, J.G., 1973. Marine sediments of the southern oceans. Am. Geogr. Soc., Antarct. Map Folio Set., Folio 17. Girdley, W.A., Leclaire, L., Moore, C., Vallier, T.L. and White, S.M., 1974. Lithologic summary, Leg 25, Deep Sea Drilling Project. Initial Reports of the Deep Sea Drilling Project, 25. U.S. Govt. Printing Office, Washington, D.C., pp.725--741. Haskell, T.R. and Wilson, G.J., 1 975. Palynology of sites 280--284, DSDP Leg 29, off southeastern Australia and western New Zealand. Initial Reports of the Deep Sea Drilling Project, 29. U.S. Govt. Printing Office, Washington, D.C., pp. 723--741. Hayes, D.E. and Frakes, L.A., 1975. General synthesis, Deep Sea Drilling Project, Leg 28. Initial Reports of the Deep Sea Drilling Project, 28. U.S. Govt. Printing Office. Washington, D.C., pp.919--942. Hayes, D.E. and Ringis, a., 1973. Seafloor spreading in the Tasman S~a. Nature, 243: 454--458. Herron, E.M., 1971. Crustal plates and seafloor spreading in the southeastern Pacific. In: J.L. Reid (Editor), Antarctic Oceanology, I. Antarct. Res. Ser., 15: 229--237. Hollister, C.D., Craddock, C., Bogdanov, J.A., Edgar, N.T., Gieskes, J., Haq, B.U., Lawrence, J., RSgl, F., Schrader, H.J., Tucholke, B.E., Vennum, W., Weaver, F.M. and Zhivago, V.N., 1974. Deep drilling in the Southeast Pacific Basin. Geotimes, 19 (8): 16--19. Hunt, J.M., 1975. Hydrocarbon studies. Initial Reports of the Deep Sea Drilling Project, 31. U,S. Govt. Printing Office, Washington, D.C., pp.901--903. Kennett, J.P., Houtz, R.E., Andrews, P.B., Edwards, A.R., Gostin, V.A., Hajos, M., Hampton, M.A., Jenkins, D.G., Margolis, S.V., Ovenshine, A.T. and Perch-Nielsen, K., 1974. Development of the Circum-Antarctic Current. Science, 186: 144--147. Larson, R.L. and Ladd, J.W., 1973. Evidence for the opening of the South Atlantic in the Early Cretaceous. Nature, 246: 210--212. Le Pichon, X., Francheteau, J. and Bonin, J., 1973. Plate Tectonics, Elsevier, Amsterdam, 300 pp. Luyendyk, B.P., 1974. Gondwanaland dispersal and the early formation of the Indian Ocean. Initial Reports of the Deep Sea Drilling Project, 26. U.S. Govt. Printing Office, Washington, D.C., pp.945--952. Matti, J.C., Zemmels, I. and Cook, H.E., 1974. X-ray mineralogy data, western Indian Ocean -- Leg 25, Deep Sea Drilling Project. Initial Reports of the Deep Sea Drilling Project, 25. U.S. Govt. Printing Office, Washington, D.C., pp.843--861. Melguen, M., Bolli, H.M., Ryan, W.B.F., Foresman, J.B., Hottman, W.E., Kagami, H., Longoria, J.F., McKnight, B.K., Natland, J., Protodecima, F. and Siesser, W.G., 1975. Facies evolution and carbonate dissolution cycles in sediments from basins and continental margins of the eastern South Atlantic since early Cretaceous. Int. Cong. Sedimentol., 9th, Nice, 8: 43--50. Pitman, W.C., Herron, E.M. and Heirtzler, J.R., 1968. Magnetic anomalies in the Pacific and sea floor spreading. J. Geophys. Res., 73 (6): 2069--2085. Simpson, E.S.W., Schlich, R,, Gieskes, J.M., Girdley, W.A., Leclaire, L., Marshall, B.V., Moore, C., Muller, C., Sigal, J., Vallier, T.L., White, S.M. and Zobel, B., 1974. Initial Reports of the Deep Sea Drilling Project, 25. U.S. Govt. Printing Office, Washington, D.C., 884 pp. Summerhayes, C., 1969. Marine geology of the New Zealand sub-antarctic seafloor. N.Z. Oceanogr. Inst. Mere., 5 0 : 9 2 pp. Veevers, J.J. and Johnstone, M.H., 1974. Comparative stratigraphy and structure of the western Australian margin and the adjacent deep ocean floor. Initial Reports of the Deep Sea Drilling Project, 27. U.S. Govt. Printing Office, Washington, D,C., pp.571-585.
13 Webb, P.N., 1975. Paleocene foraminifera from DSDP site 283, South Tasman Basin. Initial Reports of the Deep Sea Drilling Project, 29. U.S. Govt. Printing Office, Washington, D.C., pp.833--843. Weissel, J.K. and Hayes, D.E., 1972. Magnetic anomalies in the southeast Indian Ocean. In: D.E. Hayes (Editor), Antarctic Oceanology, II: The Australian--New Zealand Sector. Antarct. Res. Ser., 19: 165--196.