Friday, 31 August 2007
5.PS-120
Early Cenozoic glaciation: exploring the paradigm of an 'ice-free' Middle Eocene
Caroline F. Dawber and Aradhna K. Tripati. Earth Sciences, University of Cambridge, Downing Street, Cambridge, CB2 3EQ, United Kingdom
The onset of the Cenozoic ‘greenhouse-icehouse’ transition is poorly constrained, with most benthic foraminiferal oxygen isotope (δ18O) reconstructions assuming ‘ice-free’ conditions during this period. However, the occurrence of high-frequency sea-level change of tens of meters in the sequence stratigraphic record, is best explained by glacio-eustacy (e.g. Browning et al., 1996). To explore the paradigm of an ‘ice-free’ Middle Eocene, we discuss a high-resolution record of seawater δ18O from Ocean Drilling Project (ODP) Site 1209 in the northern tropical Pacific Ocean. The new seawater δ18O record for Site 1209 indicates two major glacial episodes occurred at ~44.8 and 42.7Ma. We also evaluate the seawater δ18O-sea-level calibration accounting for potential biases arising from carbonate ion concentration, Cenozoic ice δ18O composition and additional ice storage as a result of glacio-eustatic sea level fall.