Abstract:
The most prominent cooling event of the Cenozoic Earth surface during the long-term transition from an unglaciated planet, or "greenhouse world", to a polar glaciated planet, or "ice-house world", is the earliest Oligocene glacial maximum (EOGM), which immediately followed the Eocene-Oligocene (E/O) boundary at about 33.7 Ma. This study analyzes benthic foraminiferal oxygen and carbon isotopes, carbonate content, the coarse fraction, planktonic foraminiferal fragmentation, benthic foraminiferal percentage, and carbonate ooze grain size in samples from Deep Water Site 1265, Ocean Drilling Program (ODP) Leg 208, on the Walvis Ridge, South Atlantic. The results show that the earliest Oligocene delta (super 18) O values represent the magnitude of continental ice sheets on East Antarctica and indicate a large decrease in both surface and deep water marine temperatures worldwide during the Eocene-Oligocene transition. Carbonate content, coarse fraction, planktonic foraminiferal fragmentation, benthic foraminiferal percentage and grain size at ODP Site 1265 indicate that carbonate content increased rapidly across the E/O boundary, reflecting increased marine paleo-productivity, the abrupt deepening in carbonate compensation depth (CCD), and their impacts on fauna and carbonate deposition.