- GeoRef, Copyright 2004, American Geological Institute. Reference includes data supplied by American Association of Petroleum Geologists, Tulsa, OK, United States
A newly constructed composite oxygen isotope record is a proxy for eustasy that extends back to the Cretaceous-Tertiary boundary and provides an independent test of sequence stratigraphic-based eustatic curves. The isotope record shows several eustatic episodes that are consistent with the geological record of ice-sheet evolution. The first evidence for the existence of an ice sheet in East Antarctica occurs near the lower-middle Eocene boundary (base of the Lutetian stage). There is no evidence for a large ice sheet on Antarctica prior to this time; however, strata of this age are lacking over most of the continent. The isotope curve also indicates that the ice sheet experienced phases of growth during the late Eocene and middle Oligocene, followed by a decrease in volume in the early Miocene. The Ross Sea stratigraphic record indicates initial evolution of the West Antarctica ice sheet during the early Miocene. By the middle Miocene, the ice sheet spread across the Ross Sea, Weddell Sea, and Antarctic Peninsula continental shelves. The Pliocene-Pleistocene record of glaciation in Antarctica includes numerous glacial erosion surfaces on the continental shelf, indicating repeated advance and retreat of both East and West Antarctica ice sheets. These volume changes in the Antarctica ice sheet were in response to the rise and fall of sea level caused by expanding and contracting Northern Hemisphere ice sheets. There is a reasonable correlation between eustatic curves derived from sequence stratigraphic studies and the composite oxygen isotope record since the middle Eocene. This correlation indicates that glacial eustasy has been the principal factor regulating stratal stacking patterns on a global scale since the middle Eocene.