| Summary: | Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 1993 The Maestrichtian biogeography of calcareous nannoplankton is investigated in order to characterize paleoenvironmental conditions in the marine photic zone during the latest Cretaceous. Different theories explaining the biospheric turnover at the Cretaceous/Paleocene (KIP) boundary have alternatively suggested or denied substantial environmental perturbations during the last ~500 ky of the Cretaceous. The purpose of this study is to determine whether evidence from calcareous nannoplankton supports a gradual (or stepwise) decline of the photic zone environment presaging the K/P boundary. In order to achieve this goal a detailed quantitative study of the biogeography of calcareous nannoplankton was carried out in three time slices from early and late Maestrichtian. Well preserved material was investigated from five sections: Ocean Drilling Program Site 690 in the Atlantic sector of the Southern Ocean represents the Maestrichtian high southern nannoplankton province. Indian Ocean Sites 217 and 761, South Atlantic Site 528 and the land based, epicontinental section from Millers Ferry, Alabama, represent the Maestrichtian mid-/low latitudinal bioprovince. Quantitative counts were performed on settling slides under the light microscope. Occasionally scanning electron microscopy was employed to resolve taxonomic uncertainties. A pronounced turnover from early to late Maestrichtian occurred in the nannoplankton in high southern latitudes. Numerous taxa (Biscutum boletum, B. coronum, B. dissimilis, B. magnum, Misceomarginatus spp., Monomarginatus spp., Neocrepidolithus watkinsii, Nephrolithus corystus, Octocyclus magnus, Phanulithus obscurus, Psyktosphaera firthii, and Reinhardtites spp.) that are restricted to (or most abundant in) high southern latitudes became extinct in the latest early and earliest late Maestrichtian ...
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