Cenozoic cornutellid biostratigraphy and paleoceanography from Deep Sea Drilling Project core 77B of Leg 9 (eastern equatorial Pacific)
Reynolds, Richard Alan
Casey, Richard E.
Master of Arts
Samples from Deep Sea Drilling Project core 77B of Leg 9 taken in the eastern equatorial Pacific were used to develop a biostratigraphic zonation based on the ranges of cornutellid morphotypes and to observe any paleoceanographic and geologic changes in the study region. Before the biostratigraphic zonation could be developed, definition of cornutellid morphotypes was required due to the poor state of the taxonomy of such forms. Two separate sets of cornutellid morphotypes were defined in the study: one set based on a subjective classification method (yielded 11 morphotypes), and one set based on an objective classification method (yielded 17 morphotypes). Using the ranges of the morphotypes defined by the classification methods two zonations were developed. The morphotypes defined by the objective classification method yielded four zones, and five zones were developed using the morphotypes defined by the other classification method. Casey (1971) has shown that recent cornutellids have a cosmopolitan oceanographic extent. If the ones used in this study had a similar distribution, then the zonations developed in this study might be cosmopolitan zonations. Paleoceanographic and geologic events were recognized by examining changes in the following parameters: (1) paleo-productivity, (2) relative radiolarian diversity and abundance, (3) relative cornutellid morphotype "diversity" and abundance, (4) nannophytoplankton abundance (from Hays et al, 1972), and (5) vertical thermal gradient (from Savin et al, 1975). All of the parameters are positively correlated except for the nannophytoplankton abundance. The paleoceanographic and geologic events recognized using these parameters are as follows: (1) separation of Australia from Antarctica (approximately 35 million years ago) and the associated changes in the circulation patterns in the Southern hemisphere, (2) initiation of Antarctic Miocene glaciation and the formation of the first Neogene water masses (about 2-22 million years ago), (3) intense glacial surge on the Antarctic continent in the late Miocene (approximately 5-6 million years ago), and (4) drop in intensity of Antarctic glaciation (about 3-4 million years ago).