Florian Wobbe

Preglacial to glacial sediment thickness grids for the Southern Pacific Margin of West Antarctica

Circum-Antarctic sediment thickness grids provide constraints for basin evolution and paleotopographic reconstructions, which are important for paleo-ice sheet formation histories. By compiling old and new seismic data, we identify sequences representing pre-glacial, transitional and full glacial deposition processes along the Pacific margin of West Antarctica. The pre-glacial sediment grid depicts 1.3 to 4.0 km thick depocenters, relatively evenly distributed along the margin. The depocenters change markedly in the transitional phase at, or after, the Eocene/Oligocene boundary, when the first major ice sheets reached the shelf. Full glacial sequences, starting in the middle Miocene, indicate new depocenter formation North of the Amundsen Sea Embayment and localized eastward shifts in the Bellingshausen Sea and Antarctic Peninsula basins. Using present-day drainage paths and source areas on the continent, our calculations indicate an estimated observed total sedimentary volume of ∼10 x 106 km3 was eroded from West Antarctica since the separation of New Zealand in the Late Cretaceous. Of this 4.9 x 106 km3 predates the onset of glaciation and need to be considered for a paleotopography reconstruction of 34 Ma. Whereas 5.1 x 106 km3 postdate the onset of glaciation, of which 2.5 x 106 km3 were deposited in post mid-Miocene full glacial conditions. This article is protected by copyright. All rights reserved.

Continental deformation of Antarctica during Gondwana’s breakup

Geophysical data acquired along the Antarctic passive margins constrain the structure and geometry of the deformed continental crust. Crustal thickness estimates range between 7 and 50 km and the Antarctic continent–ocean transition zone (COTZ) extends up to 100–670 km towards the ocean. Continental deformation prior to rifting over a c. 100 million years long time span resulted in crustal stretching factors varying between 1.8 and 5.9. The time span of deformation was sufficiently large and the rifting velocity low enough to extend the margin by up to 300–400 km. Crustal thinning generates a significant subsidence and shallow water passages might already have developed during the rifting phase along the margin. Accounting for accurate continental margin deformation has also consequences for plate-tectonic reconstructions.