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In contrast to the strongly cyclic isotopic record of late Pleistocene deep-sea cores, the isotopic record of earlier deep-sea sediment sections is much more uniform. The first pre-Pleistocene sediment sections analyzed isotopically for paleotemperatures include the lower section of Swedish core 234, previously assigned either a lower-middle Miocene age or an upper Miocene age on the basis of limited foraminiferal studies. Both the oxygen isotopic curve and calcium carbonate percentages reflect a sequence of three stratigraphically distinct units in the core section. Because of the significance of the isotopic results in terms of pre-Pleistocene climate and the paucity of paleontological data from the cursory foraminiferal examinations, a refined micropaleontologic investigation of the core section was carried out for more complete paleoclimatic information. The results confirm that: (1) the lower portion of the core is not as disturbed as previously thought; (2) clearly, three distinct biostratigraphic units are indicated, the bottommost being Pleistocene in age; (3) environment of deposition was tropical and deep-water; (4) the core penetrated through Pleistocene into only Pliocene sediments; (5) species in the fine fraction (<250 μm) are important to a complete faunal study and should not be eliminated from analyses; and (6) pelagic species often exhibit temperature-related trends in distribution, abundance and test morphology.

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