Texas A&M University, United States

Planktonic foraminiferal results indicate that Paleogene sediments recovered at Sites 1126, 1130, 1132, and 1134 in the Great Australian Bight are of middle Eocene-late Oligocene age, in intervals equivalent to (sub)tropical Zones P12-P22. The southern temperate assemblage hosted several subtropical species in the middle-late Eocene and late Oligocene as immigrants probably transported by a warm-water system similar to the present-day Leeuwin Current. The four major hiatuses recognized or inferred fall (1) between Zones P12-13 and P15 in the middle Eocene, (2) within Zone P15, (3) between Zones P16 and P18 across the Eocene/Oligocene boundary, and (4) between Zones P19 and P20 and Subzone P21b in the mid-Oligocene. These unconformities represent region-wide events across the southern Australian margin, corresponding to global sequence boundaries Part-1 (39.1 Ma), Pr1 + Pr2 (37.1-36.0 Ma), Pr4/Ru1 (33.7 Ma), and Ru4/Ch1 (28.5 Ma), respectively. Unconformities at Site 1130 had a longer duration as lower Oligocene ooze with Zone P18-P19 species overlying a middle Eocene sandy limestone of Zone P12 age and the whole Oligocene were condensed to only half as thick as the coeval sediments from up- and downslope, indicating stronger erosion at this upper slope locality during the late Eocene. The biostratigraphic results confirm previous studies of the neritic record, reporting that carbonate deposition began in the middle Eocene probably as a response to global warming and marginal subsidence because of the accelerated seafloor spreading between Australia and Antarctica at approximately 43 Ma.