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During Ocean Drilling Program (ODP) Leg 208, we will drill a depth transect of five sites between 2500 and 4800 m water depth targeting early Cenozoic sediments on the northeastern flank of the Walvis Ridge. Previous drilling in this region (Deep Sea Drilling Project [DSDP] Leg 74) recovered pelagic oozes and chalk spanning both the Paleocene/Eocene and Eocene/Oligocene boundaries. Our drilling objective is to recover fully intact sequences spanning both of these "critical" intervals as well as the Cretaceous/ Tertiary (K/T) boundary at the deep end-member sites. New multichannel seismic data (Meteor cruise M49/ 1) along with existing information from DSDP Leg 74 sites were used to identify site locations where continuous sequences of early Cenozoic sediment should be present. Double/triple advanced hydraulic piston coring and double extended core barrel coring, high-resolution physical property measurements, and construction of composite sections will be employed at each site to ensure 100% recovery of the sedimentary section. These composite sections will provide a detailed history of paleoceanographic variations associated with several prominent episodes of early Cenozoic climate change including the early Eocene Climate Optimum (EECO), the Paleocene-Eocene Thermal Maximum (PETM, also known as LPTM), and the Early Oligocene Glacial Maximum (EOGM). In particular, the transect will enable characterization of depth-dependent changes in deepwater chemistry and circulation associated with these extreme climatic states. This will facilitate testing of the leading hypothesis for the cause of the PETM and carbon isotope excursion, the abrupt dissociation of as much as 2000 gigatons of marine methane hydrate. Numerical modeling demonstrates that the injection of such a large mass of carbon to the ocean/atmosphere should have triggered an abrupt (<10 k.y.) shoaling of the carbonate compensation depth and lysocline, followed by a gradual recovery. Sediment cores recovered during this leg will be used to constrain both the rate and scale of recovery, as well changes in other aspects of deep-sea chemistry. The Leg 208 transect will complement a transect drilled on the southern Shatsky Rise during ODP Leg 198. L EG 208 S CIENTIFIC P ROSPECTUS 92 *Staffing is incomplete and subject to change.

Sixteen holes were drilled at five sites on the northeastern flank of Ontong Java Plateau during Leg 130 (Sites 803 through 807). All of these sites are near the equator, but are at different depths (803: 02°26.0'N, 3410 m; 804: 01°00.3'N, 3861 m; 805: 01°13.7'N, 3188 m; 806: 00°19.1'N, 2520 m; and 807: 03°36.4'N, 2805 m). One of our goals was to obtain a depth transect of Neogene carbonate deposition for reconstructing the history of ocean climate, chemistry, and productivity, and for understanding the origin of acoustic reflectors. Another goal was to achieve considerable penetration into basement for elucidating the origin of the plateau.All sites yielded multiple Neogene sequences, which were cored using the advanced hydraulic piston corer (APC) to the ooze-chalk transition (10-14 Ma) and with the extended core barrel (XCB) below that. Sites 803 and 807 were drilled to basement and yielded incomplete Paleogene and Cretaceous sections. Penetration into basement was 25 m at Site 803 and 149 m at Site 807; 98 m of basalt was recovered. In all, we cored 5889 m, taking 639 cores. Of the record 4822 m recovered, 55% was taken with the APC, 39% with the XCB, and 6% with the rotary core barrel (RCB). All sites except Site 804 were logged.Neogene sedimentation rates were found to vary by more than a factor of 2, with a striking maximum in the latest Miocene to early Pliocene and a strong minimum in the Pleistocene. Fluctuations in carbonate content on the millionyear scale are highly coherent among depths over the last 12 m.y., perhaps less so before that. Many acoustic reflectors appear synchronous with carbonate reduction events (CREs) and other paleoceanographic events. Other reflectors are tied to diagenesis (e.g., the ooze-chalk transformation, which is diachronous).Recovery of the Cretaceous/Tertiary (K/T) boundary at Sites 803 and 807 demonstrates the presence of a deep carbonate-compensation depth (CCD) across the transition: one sequence is calcareous, the other is not. Because the K/T sections occur below and above major hiatuses, we postulate that special conditions for preservation existed during the transition. In addition, there is evidence of volcanic activity at that time.The basalts cored at Sites 803 and 807 are predominantly olivine-bearing and were erupted during the mid-Cretaceous. At Site 807, pillow lavas buried sediments. One thick flow (at about 28 m) was penetrated here, apparently a flood basalt. Magnetic paleolatitudes suggest that the Ontong Java Plateau has moved coherently with the Pacific Plate since the Early Cretaceous.

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