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The AAPG/Datapages Combined Publications Database
GCAGS Transactions
Abstract
Cosmopolitan Biozonation for Late Cenozoic Radiolarians and Paleoceanography from Deep Sea Drilling Project Core 77B of LEG 9
Richard A. Reynolds (1)
ABSTRACT
A biozonation based on the stratigraphic ranges of cornutellid morphotypes, and paleoceanographic and geologic changes are interpreted for Deep Sea Drilling Project Core 77B of Leg 9, eastern equatorial Pacific. Development of the biozonation required definition of cornutellid morphotypes because of the confused taxonomy of these forms. Eleven morphotypes are defined as a basis for recognition of five zones in the late Cenozoic. Cornutellids are known to have a cosmopolitan distribution in modern oceans; thus, if the ancient forms had a similar distribution, then the proposed zonation also may be cosmopolitan.
Paleoceanographic and geologic events are recognized by changes in 1) paleo-productivity, 2) relative diversity and abundance of cornutellid morphotypes, 3) relative diversity and abundance of radiolarians, and 4) the thermal gradients. All these parameters correlate well. On these bases are recognized 1) separation of Australia from Antarctica (approximately 35 million years ago) and resulting changes in circulation patterns for the Southern Hemisphere, 2) initiation of Antarctic Miocene glaciation and formation of the first Neogene water masses (about 20-22 million years ago), 3) marked expansion of glaciation on the Antarctic continent in the late Miocene (approximately 5-6 million years ago), and 4) decline of Antarctic glaciation about 3-4 million years ago in the Pliocene.
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