PALEOENVIRONMENTAL CHANGES DURING THE EARLY EOCENE ON THE SOUTH TASMAN RISE: OCEAN DRILLING PROGRAM ODP SITE 1171

Paleoenvironmental changes were determined by developing an integrated sequence stratigraphic framework in Early Eocene sediments obtained from ODP (Ocean Drilling Program) Leg 189 Site 1171 (located on the South Tasman Rise). This was accomplished by using grain size analysis, foraminiferal biofacies and planktonic/benthic foraminiferal ratios. Grain size analysis was used to determine changes in the water depth, foraminiferal biofacies provided information on paleoenvironmental changes (e.g., water depths, bottom water oxygen levels, etc.) and planktonic/benthic foraminiferal ratios were used to estimate water depths. The South Tasman Rise is an ideal location to investigate paleooceanographic and climatic changes around Antarctica, as it was near Antarctica during the Early Eocene. Additionally, this foraminiferal study represents among the most southerly Early Eocene sites with well-preserved calcareous microfossils.

Grain size analysis shows that the percentage of muds ranged from 90 to 95%, indicating low energy environments, with water depths being generally below storm wave base. In the samples examined, foraminiferal taxa alternated between agglutinates and calcareous forms. Dominant benthic calcareous genera include: Lenticulina, Bolivina, Guttulina, Elphidium and Fissurina. Planktonic/benthic foraminiferal ratios ranged from 0 to 12%, which suggest shallow waters on the shelf, although dissolution recognized in some samples may have biased these ratios. Taking together the lithofacies and biofacies data, two sequence boundaries were identified at 51.0 Ma and 52.5 Ma. A possible third sequence boundary occurs at 51.5 Ma. Records from other shallow-water margins and deep-sea oxygen records correlates well with these three sequence boundaries suggesting a global mechanism.