GEOCHEMISTRY AND PETROGRAPHY OF THERMALLY METAMORPHOSED ANTARCTIC COAL: IMPLICATIONS FOR 13C –DEPLETED METHANE RELEASE

Several studies have focused on the cause of the mass extinction at the Permian-Triassic boundary. Large δ¹³C excursions are present at this boundary, indicating a considerable release of isotopically light carbon into the atmosphere; these excursions are evident worldwide in the carbon isotopic values of carbonate, bone, and organic matter. The largest of these excursions are measured in Antarctica, specifically Graphite Peak (up to -22.2‰) (Retallack and Jahren, 2008).

Since Antarctic coal is heavily intruded, the apparent excursions in δ¹³C values of the coal may have been influenced by later alteration, and may not accurately reflect the δ¹³C values of the Permian atmosphere. Such alteration must be considered in paleoenvironmental studies on the cause(s) of global climate change at the Permian-Triassic boundary. In order to evaluate the influence of rank and maceral content on isotopic composition, a total of 335 samples described as "coal" were obtained primarily from the U.S. Polar Rock Repository at Ohio State University. All of the samples are Permian in age and are from exposed seams along the Transantarctic Mountains: South Victoria Land, the central Transantarctic Mountains, and the Queen Maud-Horlick Mountains.

Preliminary vitrinite reflectance measurements on the high-carbon samples range from 1.9 to 7.5% for the Graphite Peak samples. Most of the samples are either natural anisotropic cokes or meta-anthracites with very high reflectances. Volatile matter contents for the Graphite Peak and Allan Hills samples vary widely (from 3% to over 70%, dry basis). The extremely low VM contents are expected due to the high rank of the coals; the high values may be influenced, in part, by the ash contents (24% to 96%, dry basis). δ¹³C values range from -26.7‰ at Graphite Peak to -20.9‰ at Mount Ropar. Geochemical and petrographic data will be presented to evaluate to what extent thermal alteration of the coal, weathering, variations in maceral composition, or even the presence of condensed volatiles (pyrolitic carbon) in the coal may contribute to the isotopic variability of the coal.