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Support of this research was provided by National Science Foundation grant GV-42650.
Pliocene paleotemperatures and regional correlations, southern ocean FRED M. WEAVER and PAUL F. CIEsIELsKI
References Frkes, Lawrence A. 1973. USNS Eltanin sediment descripions, cruises 4 to 54. Sedimentology Research Laboratory, Department of Geology, Florida State University. Contriu tio n , 37. 259p. Grdon, Arnold L. 1971. Eltanin physical oceanography, ruises 44, 45, and 47. Antarctic Journal of the U.S., VI(5): 166-167. D., and N. D. Opdyke. 1967. Antarctic radiolaria, Hys, magnetic reversals, and climatic change. Science, 158:
J.
1001-1011.
MicCollum, D. W. In press. Antarctic Cenozoic diatoms: leg 28, Deep Sea Drilling Project. Initial Reports of the Deep :Sea Drilling Project (Frakes, L. A., et al), 28. Washington, D.C., U.S. Government Printing Office. Watkins, N. D., and J . P. Kennett. 1972. Regional sedimentary disconforrnites and Upper Cenozoic changes in bottom water velocities between Australasia and Antarctica. Antarctic Research Series, 19: 273-293.
September-October 1974
Antarctic Research Facility Department of Geology Florida State University Tallahassee, Florida 32306
Micropaleontological analyses have been completed on piston and drill cores of Middle to Early Pliocene age recovered from the southern ocean between 110°E. and 160°W. (fig. 1). All cores are dated by radiolarians, diatoms, and in part by paleomagnetic methods. Stratigraphic correlations are based on paleornagnetic data and recently developed southern ocean diatom and silicofiagellate zonations (McCollum, in press; Ciesielski, in press). From the silicoflagellate temperature curve constructed from the
generic ratios of Dictyocha/Distephanus (Ciesielski, 1974), we define seven temperature oscillations and suggest that a dramatic change in the thermal structure of the southern ocean occurred during the Gilbert
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Figure 1. Location map of Eltanin piston cores and Deep Sea Drilling Project drill cores utilized in silicoflagellate paleotemperature determinations.
magnetic epoch. Temperatures apparently fluctuated between those now found north of the present position of the Antarctic Convergence (Gilbert events II, IV ) V, and VII), to those restricted south of this oceanographic boundary (Gilbert I, III, and VI) (fig. 2). The highest inferred paleotemperatures are recorded in Lower Gilbert age sediments, where Dictyocha/Distephanus ratios are 1.0 or more at all sample intervals. Antarctic temperatures, similar to and possibly lower than those of the Holocene, are 24 S L CO z
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indicated for Gilbert events I and III (fig. 2). Within these events the Dictyocha/Distephanus ratios are less than 0.07, and in most sample intervals within Gilbert event I essentially no specimens of Dictyocha were found. The cooling events recorded in Gilbert events I and III may reflect the initial establishment of true antarctic climatic conditions within the southern ocean during the Pliocene (Ciesielski and Weaver, in press), although little paleoclimatic information is available for the interval between Gilbert magnetic event "c" and the epoch 5 boundary. Dictyocha/Distephanus ratios recorded at Gilbert events II, IV, and VI (fig. 2) are similar in that they reflect a temperature range indicative of subantalictic to northernmost antarctic conditions. These paleotemperatures are comparable to present day surface water temperatures between about 540 and 48°S. Silicoflagellate paleotemperatures delineate a major cooling trend between 4.30 and 3.70 million years ago (table). This Early Pliocene cooling records a major climatic deterioration in the southern ocean with surface water temperatures fluctuating from those commonly associated with waters north of the modern position of the Antarctic Convergence to those found associated with antarctic waters. Our silicoflagellate paleotemperature estimates for Lower Gilbert age cores average 8° to 10°C. higher than those found today in the southern ocean. Temperatures this severe would satisfy Mercer's (1968) requirements for partial or complete absence of the West Antarctic ice sheet during this time interval.
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MAJOR NORTHWARD DISPLACEMENT OF CIRCIJM-ANTARCTIC GLACIAL-MARINE DEPOSITIONAL BELT (WEAVER, 973) TAYLOR G & WRIGHT VALLEY GLACIATIONS ANTARCTICA 2.7 to 3.5-37 M.Y.
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Figure 2. Early Pliocene paleotemperatures and climatic events and regional correlation of continental glacial and interglacial evidence. Core correlations are based on close interval diatom, radiolarian, and siticoflagellate biostratigraphy, and on Eltanin core paleomagnetic stratigraphy.
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Paleomagnetic age determinations of Early Pliocene climatic events recorded between 69° and 57°S. Approximate Calculated paleomag- temperature Event netic age range Climatic (million years (seasonal regime before average, present) °C.)
