We requested approval to deepen Site 1146 beyond the originally approved 520 m penetration to extend the paleoenvironmental record in time, after the sediment age turned out to be younger than expected and after we had confirmed that no significant hydrocarbon concentrations occurred in the entire interval recovered. The core-logging data enabled construction of a continuous mcd scale and a continuous spliced record from 0 to 266.7 mcd. We expect that postcruise correlation with downhole logging data will allow construction of a complete, continuous section to 640 mcd. The Pleistocene-age sediments are composed of greenish gray nannofossil clay that is relatively enriched with quartz, plagioclase, chlorite, and illite relative to lower sections. This unit grades downhole into clayey nannofossil ooze within the Pliocene section.
Planktonic foraminifers are abundant and have good preservation for the site's entire interval.
Depletion of methanogenesis products such as alkalinity, phosphate, and ammonium with depth suggests that methanogenesis is active only in the upper sediments. This agrees with the interpretation of higher methane levels and higher order hydrocarbons in headspace gas samples below 200 mcd as gases that have migrated into this site, either laterally or from depth. Dissolved silica and strontium correlate with the amount of biogenic silica and carbonate in the sediments, respectively. A transition from reverse declinations to normal occurs between 160.5 and 165.8 mcd, possibly marking the Olduvai Event. This corresponds to a general downhole decrease in accumulation rate at that depth.