The primary objective of Ocean Drilling Program (ODP) Leg 198 was to obtain high-quality and high-resolution records of the Cretaceous and Paleogene greenhouse climates. A key aspect during the cruise was locating sites along depth and latitudinal transects to provide additional dimensions to reconstruct the paleoenvironment through time. Sites 1209–1214 were drilled on the Southern High of Shatsky Rise in a 500-m range of water depths (2387–2907 m) (Fig. F1). A prominent 5- to 25-cm-thick clay-rich calcareous nannofossil ooze layer was found at all of these sites in early late Paleocene sediments (Bralower et al., 2002; Bralower, Premoli Silva, Malone, et al., 2002). An age of ~58.4 Ma (timescale of Berggren et al., 1995) was assigned to this layer based on the first occurrence (FO) of the nannofossil Heliolithus kleinpellii, a marker for the base of nannofossil Zone CP5, which lies a few centimeters below the clay-rich layer (Bralower et al., 2002; Bralower, Premoli Silva, Malone, et al., 2002). This age is in agreement with the planktonic foraminiferal zonation, which belongs to the P4 Globanomalina pseudomenardii planktonic foraminiferal Zone (Bralower et al., 2002; Bralower, Premoli Silva, Malone, et al., 2002).
Detailed analysis was performed on samples from selected Leg 198 holes (1209A, 1210A, 1211B, and 1212B; water depths = 2387, 2573, 2907, and 2681 m, respectively) (Table T1). The clay-rich ooze shows changes in thickness and color. In Holes 1209A, 1210A, and 1211B, the clay-rich layer is located between 124.80 and 211.70 meters below seafloor (mbsf) and is characterized by a dark brown color. In Hole 1212B, the clay-rich layer is located at 88.30 mbsf and the sediments are considerably lighter in color (tan to light brown) than in Holes 1209A, 1210A, and 1211B. The thickness of the clay-rich layer decreases with increasing water depth; it is 23 cm thick in Hole 1209A compared to 11 cm thick in Hole 1211B (Table T1).
The clay-rich layer contains common crystals of phillipsite, fish teeth, and phosphatic micronodules and corresponds to a prominent peak in magnetic susceptibility, which probably reflects the higher amount of terrigenous material as Fe-Mn coating of grains (Bralower et al., 2002; Bralower, Premoli Silva, Malone, et al., 2002). There is a direct relationship between magnetic susceptibility and the amount of phillipsite; phillipsite can be found throughout the interval characterized by high magnetic susceptibility values. The top of the event is marked by the disappearance of phillipsite and a corresponding decrease in magnetic susceptibility (Fig. F2). The aim of this paper is to document changes in the planktonic foraminiferal assemblages associated with the clay-rich layer interval and to determine the oceanographic conditions that gave rise to this early late Paleocene event.