The Paleoenvironment of the Meyer Desert Formation, Transantarctic Mountains

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OPP 9615252 Ashworth Abstract The Meyer Desert Formation crops out in the Oliver Bluffs region of the Dominion Range in the central Transantarctic Mountains, latitude 85 degrees South, about 500 km from the South Pole. The site is on the Beardmore Glacier near the margin of the Polar Plateau. The polar desert climate is too cold and too dry to support higher forms of life. This award support studies of fossils that will be extracted from siltstones containing wood, and from peat and marl deposits discovered in 1995. Fossils discovered in earlier studies include: pollen, wood, and leaves of Nothofagus (southern beech), seeds of 4 species of vascular plants, stems and leaves of mosses, leg parts of a flightless beetle, valves of ostracodes, shells of gastropods and bivalves, and a fish tooth. A cushion of a woody vascular plant in its original growth position demonstrates that the fossil assemblage is in situ and not transported to the site. The diverse organisms represented by the fossils lived at latitude 85 degrees South during a time when the Antarctic ice sheets were smaller. Stratigraphic evidence suggests an environment that included a lake with vegetation-covered moraines, near a glacier margin. There is a question of how warm temperatures were at the site. Studies of the Nothofagus fossils suggest a harsh climate at the limits of plant growth. That interpretation, however, does not agree with the diversity of organisms represented by fossils. Also, the occurrence of fish in the lake indicates that it did not freeze to the bottom. The Magellanic Moorland of southern South America, with a mean annual temperature of at least 23 degrees Celsius higher than the Oliver Bluffs location today, is a possible analog for the paleoenvironment. Biogeographically, the organisms also seem to have closer evolutionary links with southern South America. Based on 250 kg of sediments collected at the site in 1995, a series of paleontological and geochemical s tudies will be undertaken to determine how warm the climate was. The question of when these organisms inhabited the Beardmore Valley is very important to answer because of the question of stability of the ice sheets. The best estimate for the age of the sediments is Pliocene based on transported marine diatoms. This implies that the existing configuration of the Antarctic ice sheets is a relatively recent feature, developing during the Quaternary. Other evidence from Antarctica and the Southern Ocean suggests that the polar ice sheets are much older and that the landscapes of the Dry Valleys region have not changed much since the Miocene. The Pliocene is known for its globally high sea levels and warmer climates in the Arctic. Did this warming cause a major disintegration of the Antarctic ice sheets during the Pliocene or did they remain stable? This question is especially important to answer in regard to our present concerns about global warming. The Pliocene age that has been assigned to the Meyer Desert Formation, with its in situ fossils of terrestrial organisms indicating much warmer conditions, is critical to this question. The age needs to be confirmed and a series of exploratory projects will be undertaken to attempt to date the deposits using the biostratigraphy of the fossils of terrestrial organisms, amino acid analysis of the gastropod and bivalve shells, and argon/argon analysis of crystals growing inside the seeds. The fossils are very important to test hypotheses about Southern Hemisphere biogeography. These hypotheses have attempted to explain the distribution of related organisms between South America, Australasia, the Subantarctic Islands, and Antarctica but until now they have been untestable because of an absence of Neogene terrestrial fossil data.