Reconstructions of Antarctic topography since the Eocene–Oligocene boundary

Paleogene Marine and Terrestrial Development of the West Antarctic Rift System

“…Updated ice sheet and tectonic reconstructions should utilize parameters established by analysis of subglacial sediments because they provide a wealth of proximal paleoenvironmental information about the Cenozoic development of the West Antarctic basin. Our data provide clear biostratigraphic and paleoenvironmental evidence favoring the “minimum” paleotopographic reconstruction hypotheses (Paxman et al, ; Wilson et al, ) , indicating more extensive marine incursion than the “maximum” reconstructions, which are dominated by subaerial exposure with elevations up to 1,000 m at the Eocene‐Oligocene transition. Basin history, including the recognition of deeper glacial erosion into older strata, can be inferred by differences in microfossil assemblages observed in till overlying eroding strata.…”

“…Marine deposits accumulated across the broad basin during times lacking grounded ice or ice shelves, but subsequent glacial activity led to significant erosion and transport of these deposits (Paxman et al, ; Wilson et al, ). Reworked Upper and Middle Miocene diatoms occur at Site 6 (Harwood et al, ) , but Lower Miocene diatoms dominate, including abundant soft sediment clasts of Lower Miocene diatomite, suggesting that in situ Lower Miocene strata unconformably lie beneath the glacial sediments at the seafloor (Harwood et al, ).…”

“…Our analyses show that these tills contain terrestrial and marine microfossils and biomarkers, which document Paleogene woodlands and coastal wetlands and also extensive neritic and pelagic marine habitats across the basin. Though stratigraphically mixed, they provide clear evidence of a range of past West Antarctic interior depositional systems, providing a direct test of inferred late Paleogene environments, and can be used to test published model-based paleotopographic reconstructions (Paxman et al, 2019;Wilson et al, 2012) (Figures 1c and 1d).…”

“…West Antarctica is characterized by high heat flow and a low‐viscosity mantle (Whitehouse et al, ) that developed prior to Cretaceous/early Paleogene initiation of the WARS. Based on thermal subsidence estimates, plate movement and glacial erosion inferred from seismically defined offshore sedimentary bodies (Paxman et al, ; Wilson et al, , ), models reconstructing the Antarctic landmass suggest that extensive uplands and coastal lowlands existed in the Ross Embayment sector of West Antarctica during Late Eocene time. Evaluating Late Paleogene paleotopographic conditions is important because one of two alternate published paleolandscape models (Wilson et al, ) has been widely applied in paleoglaciological (Levy et al, ) and paleotectonic (Whitehouse et al, ) studies.…”

“…Ice sheet models suggest that glaciers coalesced over highlands, spreading to lowlands as the Antarctic cooled, leading to the growth of ephemeral continental scale ice sheets, including marine‐based ice sheets in the Oligocene (DeConto & Pollard , ). The model results are highly dependent on the topographic inputs (Colleoni et al, ; Galeotti et al, ; Gasson et al, , ; Paxman et al, ; Wilson et al, ), which have not been constrained by proximal geologic data in the Ross Embayment (Figure b). New geological constraints on the paleolandscape (presented in this study) are crucial for improving paleotopographic reconstructions and, therefore, ice sheet models.…”