Leg 208 Preliminary Report

This report was prepared from shipboard files by scientists who participated in the cruise. The report was assembled under time constraints and does not contain all works and findings that will appear in the DISCLAIMER Any opinions, findings, and conclusions or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the views of the National Science Foundation, the participating agencies, ABSTRACT During Ocean Drilling Program (ODP) Leg 208, six sites were drilled at water depths between 2500 and 4770 m to recover lower Cenozoic sediments on the northeastern flank of Walvis Ridge. Previous drilling in this region (Deep Sea Drilling Project [DSDP] Leg 74) recovered pelagic oozes and chalk spanning the Cretaceous/Paleogene (K/P), Paleocene/Eocene, and Eocene/Oligocene boundaries. The objective of Leg 208 was to recover intact composite sequences of these " critical " transitions from a wide range of depths. Multichannel seismic data (Meteor Cruise M49/1) along with information from DSDP Leg 74 sites were used to identify sites where continuous sequences of lower Cenozoic sediment should be present. Double to triple advanced hydraulic piston coring, occasional extended core barrel coring to deepen the holes, and high-resolution physical property measurements were employed to construct " composite sections. " The composite sections provide a detailed history of paleoceanographic variation associated with several prominent episodes of early Cenozoic climate change, including the K/P boundary, early Eocene Climatic Optimum, the Paleocene–Eocene Thermal Maximum (PETM), and the early Oligocene Glacial Maximum. The PETM interval, the main focus of Leg 208, was recovered at five sites along a depth transect of 2.2 km. The sediment sequence is marked by a red clay layer, which varies in thickness from 20 to 50 cm from site to site, within a thick and uniform sequence of upper Paleocene and lower Eocene foraminifer-bearing nannofossil ooze. The basal color contact is relatively sharp, although magnetic susceptibility data show a more gradual, steplike transition at the deeper Sites 1262 and 1267. The carbonate content drops to 0 wt% at all sites except for Site 1265. The upper contact is gradational in the shallow sites and relatively sharp at the deeper sites. Overlying the clay layer is a sequence of nannofossil ooze, which is slightly richer in carbonate than the unit immediately underlying the clay layer. The depth transect permits testing of the leading hypothesis for the cause of the PETM: the abrupt dissociation of as …