Bulk carbonate isotope stratigraphy from CRP-3 core (Victoria Land Basin, Antartica): evidence for Eocene-Oligocene palaeoclimatic evolution.

Bulk carbonate isotope compositions and carbonate petrography from Early Oligocene and Late Eocene sand-grained sediments of the Cape Roberts Project core CRP-3 (Victoria Land Basin, Antarctica) were investigated in the aim of reconstructing the palaeoclimatic evolution through the Cenozoic in Antarctica. Most of the carbonate is calcite cement occurring as patches, nodules and horizons consisting of equant and/or drusy sparry calcite, pervasive blocky calcite and more rare poikilotopic calcite spar. 18O-depleted values (from –17 to –8 d ) of the CRP-3 carbonates suggest that the precipitating fluids were a mixing between marine and meteoric waters from melting glaciers. The d18O record exhibits a number of steps in a downward decreasing trend that reflects the evolution of ice-sheet decay over the Early Oligocene and Late Eocene in response to a global warming trend. The carbonate 13C-depletion in the CRP-3 drillcore is consistent with this interpretation. Some anomalously light carbon compositions (between –25 and –18 d ) are interpreted as a record of addition to the system of methane-derived CO2.