Leg 208 Synthesis: Cenozoic Climate Cycles and Excursions

During Ocean Drilling Program Leg 208, six sites were drilled at water depths between 2500 and 4770 m to recover 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/Pg), Paleocene/Eocene, and Eocene/Oligocene boundaries. The composite sections, recovered via double and triple coring, provide a detailed history of paleoceano-graphic variation associated with several prominent episodes of early Cenozoic climate change, including the K/Pg boundary, Paleocene/ Eocene Thermal Maximum (PETM), early Eocene Climatic Optimum, and early Oligocene Glacial Maximum. The PETM interval, the main target of Leg 208, was recovered at five sites along a depth transect of 2.2 km. A prominent red clay layer marks the boundary sequence at all sites. Additionally, two as-yet undocumented early Eocene hyperther-mal events were recovered: Elmo and X, dated at ~53.5 and ~52 Ma, respectively. A number of postcruise investigations were undertaken on these critical intervals, principally to improve stratigraphic control and the resolution of proxy records of climate and ocean chemistry, and to better understand the regional impacts of these events on biota. The major contributions of Leg 208 include (1) development of new orbitally tuned chronologies for the Paleocene and lower Eocene, (2) high-resolution characterization of Paleocene/Eocene boundary carbonate dissolution horizons and correlation to the carbon isotope excursion and PETM, (3) development of the first marine-based carbon isotope record of terrestrial n-alkanes for the PETM, (4) documentation of the ecological impacts of the PETM on calcareous algae, (5) resolving the full magnitude of the carbonate compensation depth shift as well as its timing relative to the onset of Antarctic glaciation in the earliest Oligocene, (6) coupling the middle Miocene high abundances of biserial planktonic foraminifers to changes in regional ocean circulation, (7) constraining the timing of initiation and intensification of North Atlantic Deep Water formation in the Oligocene, (8) increasing the resolution of the Li isotope record for the Neogene, and (9) increasing the resolution of the seawater Sr isotope record for the upper Paleocene and lower Eocene.