PALEOGENE PALEOENVIRONMENTS OF THE WEST ANTARCTIC INTERIOR

Paleogene development of West Antarctic basins and environments is poorly known. Wilson et al. (2012) used regional tectonics, sediment volume from continental erosion, and climate history to model Eocene paleotopography and tectonic development of West Antarctica. We report micropaleontologic evidence of Paleogene sediments recovered from subglacial tills from the West Antarctic interior by the recent WISSARD (Whillans Ice Stream Subglacial Access Research Drilling) project and samples collected by Caltech glaciologists from past drilling expeditions (80’s and 90’s) and infer Paleogene paleoenvironments to evaluate the Wilson reconstruction.

All analyzed sediments recovered by hot water drilling through the West Antarctic Ice Sheet include some fraction of Paleogene siliceous and organic-walled microfossils. Evidence of Paleogene terrestrial lowland habitats that include lakes, woodlands, and bogs, are inferred from pollen and diatoms. Paleogene marine microfossils including diatoms, silicoflagellates, ebridians, dinoflagellates and rare calcareous nannofossils and foraminifera represent West Antarctic seaways. The distribution and concentration of these displaced fossils among recovered sediments indicate variable degrees of glacial erosion and transport and inferences regarding relative uplift rates.

Paleogene diatom assemblages are divided into three events from total age ranges of marine diatoms in Ross Embayment sediments. An early Eocene event (~58-48 Ma) is defined by the co-occurrence of Trinacria simulacrum, Pterotheca aculeifera, and Triceratium crenulatum. The Eocene-Oligocene boundary (~34 Ma) is defined by the co-occurrence of Pseudotriceratium radiosoreticulatum, Pyxilla reticulata, and Triceratium crenulatum. A Late Oligocene to Early Miocene assemblage is defined by the occurrence of Rocella spp., Asteromphalus symmetricus, and Aulacodiscus cf. brownei. The rare calcareous microfossils indicate a Late Eocene to Early Oligocene age.

Our results corroborate published paleotopography models and contribute to a better understanding of West Antarctic rift system development, which contributed to climatic and ice sheet evolution.