Magnetostratigraphic chronology of a late Eocene to early Miocene glacimarine succession from the Victoria Land Basin, Ross Sea, Antarctica

Drilling offshore from Cape Roberts, Antarctica, has enabled recovery of a 1472-m cumulative record of late Eocene–early Miocene history of sedimentary basin development and climate change in the Western Ross Sea. In this paper, we synthesize the results of palaeomagnetic analyses carried out on the CRP-1, CRP-2 and CRP-3 sediment cores, and present a chronology for the recovered Eocene–Miocene succession. Stepwise demagnetization data demonstrate that secondary overprints have been successfully removed and that characteristic remanent magnetizations (ChRMs) have been clearly identified in most of the samples. A close sampling interval has allowed a detailed magnetic polarity stratigraphy to be established for the composite succession. Correlation with the geomagnetic polarity time scale (GPTS) has been constrained by a number of 40Ar/39Ar and 87Sr/86Sr ages, as well as by a recently developed Antarctic siliceous microfossil zonation, and by calcareous nannoplankton biostratigraphy. The basal sediments of the Eocene–Miocene succession rest unconformably on Devonian sandstones of the Beacon Supergroup. A basal sandstone breccia, which probably represents the onset of rifting in the Victoria Land Basin (VLB), is overlain by a succession of sandstones that are interbedded with thin conglomerate beds. These sediments give way to more clearly glacially influenced mudstones and diamictite facies in the mid Oligocene, and, by the Oligocene–Miocene boundary, coincident with the Mi-1 glaciation, a permanent glacial dominance was imprinted on the sedimentary record. Average sediment accumulation rates were initially rapid in the late Eocene–early Oligocene (up to 60 cm/k.y.), but reduced to only a few cm/k.y. in the early Miocene as basin subsidence slowed