Environmental Magnetic Record of the Eocene-Oligocene Transition in CRP-3 Drillcore, Victoria Land Basin, Antarctica

A 1500-m-thick Cenozoic sequence was recovered in a series of 3 drill holes from the Victoria Land Basin, Antarctica, in association with the Cape Roberts Project. The CRP-3 drill hole penetrated the oldest Palaeogene strata in the Granite Harbour region and terminated in strata from the Devonian Beacon Supergroup. The upper 823-m of the CRP-3 drill-core is an expanded sequence that may span the Eocene-Oligocene boundary. Lithostratigraphic analysis indicates a transition from rapidly deposited deltaic strata below 480 metres below sea floor (mbsf) to distinctly glaciomarine strata above 307 mbsf. A variety of rock magnetic parameters indicate that magnetite is the main magnetic mineral in the CRP-3 Eocene-Oligocene sequence. Magnetite concentration varies in a distinct pattern, which allows subdivision of the CRP-3 sequence into four main rock magnetic intervals that do not correspond to the lithostratigraphic units or to the sequence stratigraphic subdivisions identified in the core. Intervals I (0-243 mbsf) and IV (627-790 mbsf) have high concentrations of magnetite, with moderate variations. Intervals II (243-440 mbsf) and III (440-627 mbsf) have low background magnetite concentrations, but contain thin zones with higher magnetite concentrations. Rock magnetic interval III coincides with the part of the core that is dominated by clean sands. The transition upward from high to low magnetite concentration at 627 mbsf coincides with the chron C13r-C13n transition and is correlated with a major oxygen isotope shift in deep-sea records (Oi-1) across the Eocene-Oligocene boundary. Comparison with other Eocene and Oligocene environmental magnetic records from the southern Victoria Land Basin indicates that transition observed in the environmental magnetic record of the CRP-3 core may mark the most prominent cooling event in Antarctica during a stepwise deterioration of climate that extended across the (~5 m.y.) Eocene-Oligocene transition.