Constraining the amplitude of late Oligocene bathymetric changes in Western Ross Sea during orbitally-induced oscillations in the East Antarctic Ice Sheet: (1) Implications for glacimarine sequence stratigraphic models

Late Oligocene shallow glacimarine sequences recovered from western Ross Sea, Antarctica by the Cape Roberts (drilling) Project display orbitally-influenced cycles of advance and retreat of a laterally-extensive ice sheet across the continental shelf, in concert with changes in contemporary water-depth. During interglacial periods, when the glacier terminated on land, the coastline was largely ice-free and wave-influenced, and sediments accumulated in hydrodynamic equilibrium with the contemporary wave-climate. Here, we present estimates of paleobathymetry from intervals of three Milankovitch-duration glacimarine sequences (9, 10 and 11) that accumulated in open ocean conditions. We utilise an approach where the percentage of mud (< 63 µm fraction) in bulk sediment is related to the wave-induced bed shear stress, and for a given wave climate, water depth (e.g. [Dunbar, G.B. and Barrett, P.J., 2005. Estimating palaeobathymetry of wave-graded continental shelves from sediment texture. Sedimentology 52, 253–269.]). Particle size-derived changes in paleobathymetry for the three late Oligocene sequences were between 20–40 and 60–90 m. These water depth changes are consistent with the magnitude of contemporary global eustatic sea-level changes of 30–40 m estimated from far-field continental margin and deep-marine ocean proxy records. On the basis of our bathymetric constraints we contribute to a conceptual stratigraphic model for shallow glacimarine sequences, whose depositional architecture is controlled by a combination glacier advance and retreat and changes in relative sea-level.