Eight sites were drilled on Shatsky Rise during Ocean Drilling Program Leg 198. All sites (1207-1214) recovered Cretaceous sediments ranging in age from Maastrichtian to Berriasian. In the Upper Cretaceous, Maastrichtian-Campanian nannofossil oozes were recovered at Sites 1207-1212. At Sites 1207 and 1212 Santonian-Cenomanian oozes were also recovered from chert-dominated sequences, but this interval contains multiple hiatuses. Sites 1209-1211 terminated in chert. Calcareous nannofossil assemblages are abundant, diverse, and relatively well preserved throughout, but biostratigraphy is problematic in places due to missing or rare and sporadically distributed marker species. In the upper Maastrichtian, the first occurrences (FOs) of Micula murus and Lithraphidites quadratus appear to be reversed in most sections, and in the Campanian, Reinhardtites levis, Misceomarginatus pleniporus, and Eiffellithus parallelus are absent or virtually absent, probably due to biogeographic limitations. However, a number of previously unused bioevents were recognized that may prove to be useful Pacific-wide, including the FO of Ceratolithoides ultimus (in Subzone UC20dTP) and the last occurrence (LO) of Tegumentum stradneri (in Subzone UC20bTP) in the upper Maastrichtian; the FOs of Micula praemurus and consistent Cribrocorona gallica, the LOs of Zeugrhabdotus bicrescenticus and Cribrocorona echinus, and the FO of C. echinus lower in the Maastrichtian; and the LO of Rucinolithus? magnus (in Zone UC16), FO of R.? magnus (in Subzone UC15bTP), FO of Perchnielsenella stradneri (in Subzone UC15a/bTP), and FO of Ceratolithoides indiensis (Subzone UC14d-UC15dTP) in the Campanian.
The assemblages are distinctly different in composition from those of the Atlantic Ocean and its marginal basins but show similarities with some Indian Ocean nannofloras, and so these sections will provide important insights into the paleobiogeography and paleoecology of Late Cretaceous nannoplankton. The assemblages are broadly dominated by cosmopolitan taxa such as Prediscosphaera, Watznaueria, and Retecapsa, but abundance data together with key occurrences and absences reveal a distinct paleobiogeographic character. High-latitude species such as Seribiscutum primitivum, Repagulum parvidentatum, and Nephrolithus frequens are completely absent from the Shatsky sites. The common presence of Ceratolithoides, Uniplanarius, Micula, and Cylindralithus/Perchnielsenella are indicative of tropical to subtropical paleolatitudes and reflect an open-ocean setting
