ALBERT

Description: Five sites were drilled in the Celebes Sea and Sulu Sea During ODP Leg 124. Sites 767 and 771 in the Celebes Sea are below the regional carbonate compensation depth (CCD) and all calcareous nannofossils recovered in post-Oligocene sediments were recovered from turbidites. From the late middle Eocene to the late Oligocene, Site 771 was above the CCD and accumulated pelagic nannofossil clay. The highest occurrence of Chiasmolithus grandis is just above basement and indicates a late middle Eocene age for the Celebes Basin. In the southeast Sulu Basin, calcareous nannofossils are preserved only in post early middle Miocene sediments and are not useful for estimating the age of the basin. A late Pliocene change in calcareous nannofossil preservation and lithology at Sites 768 and 769 indicate deepening of the CCD. This corresponds to the progressive isolation of the southeast Sulu Basin, which is a consequence of global lowering of sea level and local tectonic adjustment of sill depth. The calcareous nannofossils at all five sites provide a good biostratigraphic framework for the sedimentary histories of the two basins even though some of the fossils were deposited by turbidity currents below the regional CCD, or have been mixed with redeposited specimens. The biostratigraphy record of Sites 767, 768, and 769 show that the lowest occurrence of Gephyrocapsa oceanica s.l. is consistently the nearest datum to the top of the Olduvai paleomagnetic event and, therefore, is the most suitable biohorizon for approximating the Pliocene/Pleistocene Boundary in the Celebes and Sulu Seas.