TERRESTRIAL RECORD OF POST-EOCENE CLIMATE HISTORY IN MARIE BYRD LAND, WEST ANTARCTICA

ABSTRACT. Hydrovolcanic deposits, interbedded tills and recycled microfossils, together with erosion anomalies in the Marie Byrd Land (MBL) landscape, each provide a portion of the record of glaciation and deglaciation events from late Oligocene to the present. We have attempted to synthesize these data sources to provide a more complete record, and to reconcile them with climatic events recorded elsewhere in Antarctica and the deep sea. The MBL data suggest that the late Oligocene was marked by the development of an ice cap at Mount Petras, where the MBL dome was beginning to rise from a near-sea-level position. Furthermore, unusually advanced cirque development in the dome crest area is difficult to explain unless there was a period of effective cirque erosion in that area between c. 25 and 15 Ma BP. These inferences are consistent with evidence from the Ross Sea for an expansion of the West Antarctic Ice Sheet (WAIS) in mid-Miocene (15–17 Ma BP) time.
The deep sea oxygen isotope proxy record has been interpreted to show the inception of West Antarctic glaciation around 6 Ma BP. This can perhaps be reconciled with the terrestrial record if one considers (1) the observation that large volume changes in the WAIS cannot produce a ω¹⁸O signal that is significantly outside limits of error, and (2) that the landscape in West Antarctica has evolved from very low regional relief in the Oligocene, to more than 2 km of local relief in the present day, as a result of dome uplift since c. 27 Ma BP, and the growth of large volcanoes since c. 19 Ma BP.