HR: 15:10h
AN: PP53C-07    [Abstracts]
TI: The Neogene Environment of the Beardmore Glacier, Transantarctic Mountains
AU: * Ashworth, A C
EM: allan.ashworth@ndsu.nodak.edu
AF: Department of Geosciences, North Dakota State University, Fargo, ND 58105-5517 United States
AU: Cantrill, D J
AF: Department of Palaeobotany, Swedish Museum of Natural History, Stockholm, SE-104 05 Sweden
AU: Francis, J E
AF: School of Earth Sciences, University of Leeds, Leeds, LS2 9JT United Kingdom
AU: Roof, S R
AF: School of Natural Science, Hampshire College, Amherst, MA 01002 United States
AB: Discontinuous sequences of Neogene marine and non-marine glacigenic sequences, including the Meyer Desert Formation (MDF), occur throughout the Transantarctic Mountains. The upper 85m of the MDF, consisting of interbedded diamictites, conglomerates, sandstones and siltstones, outcrops in the Oliver Bluffs on the Beardmore Glacier at $85\deg$07'S, $166\deg$35'E. The location is about 170 km south of the confluence of the Beardmore Glacier with the Ross Ice Shelf and about 500 km north of the South Pole The glacial, fluvioglacial and glaciolacustrine facies of the MDF represent a dynamic glacial margin which advanced and retreated on at least four occasions. On at least one occasion, the retreat was sufficiently long for plants and animals to colonize the head of a major fjord which existed in the place of the existing Beardmore Glacier. From the fossils we have identified at least 18 species of plants, 3 species of insects, 2 species of freshwater mollusks, and a species of fish. The plant fossils consist of pollen, seeds, fruits, flowers, leaves, wood, and in situ plants. The plants include a cryptogamic flora of mosses and liverworts, conifers, and angiosperms in the families Gramineae, Cyperaceae, Nothofagaceae, Ranunculaceae, Hippuridaceae, ?Caryophyllaceae, and ?Chenopodiaceae or ?Myrtaceae. The plants grew in a weakly developed soil developed on a complex periglacial environment that included moraines, glacial outwash streams, well-drained gravel ridges, and poorly drained depressions in which peat and marl were being deposited. The fossil assemblage represents a mosaic tundra environment of well- and poorly-drained micro-sites, in which nutrient availability would have been patchily distributed. Antarctica has been essentially in a polar position since the Early Cretaceous and at $85\deg$S receives no sunlight from the middle of March until the end of September. Today, the annual radiation received is about 42% that of Tierra del Fuego at $55\deg$S. During the Neogene, the absence of solar heating for about 5.5 months, even though there would have been additional heat from open water in the fjord, would have resulted in a low mean annual temperature. Mean summer temperatures, based on the minimal thermal requirements for Nothofagus, listroderine weevils, and freshwater molluscs, are estimated to have been between 4 and 5øC for at least two summer months. The research is supported by NSF grant OPP-0230696
DE: 9310 Antarctica
DE: 9604 Cenozoic
DE: 4815 Ecosystems, structure and dynamics
DE: 3344 Paleoclimatology
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting