USNS Eltanin piston cores E45-16, E45-19, Australia using calcareous nanofossils. Tallahassee, Florith E48-49, and E55-41. State University, Sedimentology Research Laboratory, Dc partment of Geology. Contribution, 41. Length Water Luyendyk, B. P., and T. A. Davies. 1974. Results of DSDP Ie Core Latitude Longitude (centi- depth 26 and the geologic history of the southern Indian ocean In: Initial Reports of the Deep Sea Drilling Project, 26: 909-943, meters) (meters) Washington, D.C., U.S. Government Printing Office. E45-16 3507.2S. 101 058.2E. 685 4,313 E45-19 37038.7S. 10306.2E. 1,000 4,507 E48-49 34028.9S. 10003.0E. 581 4,347 E55-41 330 1.0S. 110052.0E. 632 2,758 Regional deep-sea dynamic of Broken Ridge, show a distinct change from processes recorded in Eltanin Eocene carbonate rich sediment to "red" clay above. sedimentary cores from the In core E55-41, located on Naturaliste Plateau, a calcareous nanofossil ooze is overlain by a forami- southeast Indian Ocean niferal ooze. Calcareous nanofossils were examined below each lithologic change in each core. A late Eocene age was determined for the nanofossil ooze in E55- J. P. KENNETT and N. D. WATKINS 41 on the basis of the common occurrence of Dis- Graduate School of Oceanography coaster saipanensis and the presence of D. barbadien- University of Rhode Island sis in association with Chiasmolithus altus and C. Kingston, Rhode Island 02881 oamaruensis. The age of the sediment below the hiatus in cores E48-49, E45-16, and E45-19 is be- tween late Eocene and early Oligocene. The com- The USNS Eltanin deep-sea sedimentary cores mon occurrence of Isthmolithus recurvus and and bottom photographs from the southeast In- Cyclococcolithinaformosa suggests a late Eocene age dian Ocean, between 70°E. and 120E. and between (similar to DSDP leg 28, hole 267B). The absence Antarctica and 30°S., have been analyzed. Cores of Discoaster saipanensis and D. barbadiensis is from the crest and flanks of the midocean ridge probably due to paleolatitude rather than to the are mostly Late Quaternary in age with only rare extinction of both species. breaks in sedimentation. In greater contrast, flank- The unconformity in cores E45-16, E45-19, and ing this zone in deep basins immediately to the E48-49 is expressed as a dissolution facies. A rise south of the ridge in the South Indian Basin, and in calcium carbonate dissolution (CCD) resulted in in a broad zone in the western sector of South the deposition of red clay onto the underlying late Australian Basin, are areas where bottom currents Eocene calcareous sediment. A similar change in have systematically eroded or inhibited deposition CCD is suggested by Constans (in press) for the east- of sediments. These sediments range in age from ern Diamantina Fracture Zone. The red clay/cal- Quaternary to Pliocene, and occasionally are careous sediment contact contains a very etched Middle Tertiary (figure). This regional deep-basin assemblage of calcareous nannofossils and micro- erosion extends northward between Broken Ridge manganese nodules. No siliceous microfossils were and the Naturaliste Plateau to the Wharton Basin, noted, but an abundance of zeolitic crystals was ob- where sediments as old as Late Cretaceous are ex- served. posed. As indicated by discon form ities, ocean floor The calcareous nanofossil ooze/foraminiferal characteristics, and seismic profile data, much of ooze contact in core E55-41 samples includes both the shallower, north-south trending Kerguelen Pla- Neogene and late Eocene nanofossils. This floral teau has also undergone widespread erosion by mixing suggests that the lithologic change at this bottom currents. site is probably erosional in origin. The erosional disconformities in the deep basins This research was supported by National Science have been created by a general increase in veloci- Foundation grant opp 74-20109. ties of Antarctic Bottom Water during the last 2.5 million years, with apparently major separate pulses during the Brunhes epoch (t=0.69 million References years before present) and part of the Matuyama epoch (t=2.43 to 0.69). Extensive areas of manga- Constans, R. E. In press. A study of fluctuations in the car- nese nodules have developed in conjunction with bonate compensation depth in the southern ocean south of this bottom current activity, most spectacularly as 272 ANTARCTIC JOURNAL a vast pavement in the northwest sector of the square kilometers in area (Kennett and Watkins, South Australian Basin. This feature (figure), 1975; Kennett and Watkins, in press). which has been named the Southeast Indian Ocean Available evidence indicates long-term major

Map showing seafloor dynamic processes inferred for the southeast Indian Ocean. Bathymetric contours are for 2,000-, 3,000-, and 4,000-meter depths. Major physiographic features: NER, Ninetyeast Ridge; MIA, Mid-Indian Ocean Ridge; BR, Broken Ridge; WB, Wharton Basin; NP, Naturaliste Plateau; SAB, South Australian Basin; SEIR, Southeast Indian Ridge; KP, Kerguelen Plateau; SIB, South Indian Basin. Sites of interpreted observations based on bottom photographs or on sediment core analyses: 1, manganese nodule pavement to abundant manganese nodules; 2, common to scattered man- ganese nodules; 3, strong bottom current activity (including ripple marks, scour, and distinct lineations); 4, core or photo- graph showing minimal evidence of current activity; 5, Eltanin piston cores featuring disconformities; 6, site of Deep Sea Drilling Project core featuring major disconformity. The foot-shaped area shows the inferred limits of the Southeast Indian Ocean Manganese Pavement. Large arrows denote inferred paths and directions of major bottom water flow in the region. For detailed data, see Kennett and Watkins (in press). September/October 1975 273 rent across the central and southern parts of the Hays and Berggren (1971) show that the extinc- Kerguelen Plateau. In the deep basins, high- tion of Stylatractus universus (fltJ! boundary) for the velocity Antarctic Bottom Water flows eastward North Pacific and the southern ocean occurs at through the northern sector of the South Indian 400,000 years before present. Hays (personal corn. Basin, with important iorthward flow crossing the munication) suggests the same age for this extinc- midocean ridge at 1 1O°E. and 120°E. into the South tion datum in the equatorial Pacific Ocean. Australian Basin. This northward branch traverses The extinction datum age of Pseudoemiliana Ia- the western sector of the South Australian Basin cunosa is not as precisely known. In the subantarcti and the Southeast Indian Ocean Manganese Pave- southeast Indian Ocean the P. lacunosa datum ment, and then flows between Broken Ridge and occurs below the fl/I boundary at 400,000 year Naturaliste Plateau into the Wharton Basin. Major before present ±50,000 years (Miyajima, 1974, Cenozoic to Late Cretaceous hiatuses in the Whar- in press). Gartner (1973) indicates that in the equa- ton Basin revealed by deep-sea drilling suggest torial Pacific the P. lacunosa datum occurs below that northward-flowing bottom water through this the flII boundary and suggests an age of 350,000 conduit has been a very long-term feature. years before present. This age difference may be These results are presented in detail elsewhere the result of assuming constant sedimentation (Kennett and Watkins, 1975; Kennett and Watkins, rates. The discrepancy in age, however, can be in press). resolved by relating the extinction datum of P. La- This research was supported by National Science cunosa to the oxygen isotope curve of Emiliana and Foundation grants o pp 71-04027, opp 74-18529, Shackleton (1974). Gartner (1972) recorded the last and Gv-25400. occurrence of P. lacunosa between stage 12/13 of the oxygen isotope curve. Emiliana and Shackleton (1974) date this interval (stage 12/13) between References 400,000 and 450,000 years before present. An approximate age of 425,000 years before present is Kennett, J . P., and N. D. Watkins. 1975. Deep-sea erosion assigned to the extinction datum of P. lacunosa and and manganese nodule development in the southeast Indian suggests a concurrent datum in both the subantarc- Ocean. Science 188: 1011-1013. tic and equatorial latitudes. Kennett, J . P., and N. D. Watkins. In press. Regional deep sea dynamic processes recorded by Late Cenozoic sediments Such a concurrent extinction for both fauna and of the southeastern Indian Ocean. Geological Society ofAmerica flora would have been caused by a global change in Bulletin. the environment. One can only speculate on this problem due to a limited understanding of the ecology of these extinct microfossils as well as to the problems inherent to the dating techniques (i.e., the assumption of constant sedimentation rates). My observations of several high- and low- Synchronous late Pleistocene latitude site samples, however, indicate that the microfossil extinctions cause may be due to dramatic climatic deteriora- tion. Evidence of a climatic deterioration at 400,000 years before present in the equatorial latitudes is noted in the oxygen isotope curve at stage 12 and in the dissolution cycles (Event V) of Thompson MELVIN H. MIYAJIMA and Saito (1974). Climatic changes in high latitudes Antarctic Research Facility during this time (400,000 years before present) are Department of Geology noted by the following paleoceanographic studies: Florida State University Hays (1965, 1967) notes a break or gap in the Tallahassee, Florida 32306 ranges of the warm-water radiolarians at the f./I! boundary in southern ocean samples; Kennett (1970, figure 3, page 128) indicates deposition of Deep-sea biostratigraphic correlation of zonal an interval of clay essentially barren of foramini- boundaries between high- and low-latitude regions fera in subantarctic Pacific Ocean sediments; is complicated by time-transgressive first and last Miyajima (in press) notes intervals of marl with a occurrences of some key species. In the late Pleisto- coccolith assemblage of dissolution resistant spe- cene, however, extinction datums of the coccolith cies containing siliceous microfossils and micro- Pseudoemiliania lacunosa and the radiolarian Styla- manganese nodules in subantarctic southeast tractus universus are not coincident, but they do ap- Indian Ocean samples. pear to follow the same sequence in both high and The above evidence, although limited, suggests low latitudes. a change in the oceanic paleoenvironment to one 274 ANTARCTIC JOURNAL