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Sedimentology and Regional Significance of a Polar Permian Icehouse Record: Lower Parmeener Supergroup, Tasmania, Australia

Frank, Tracy D.1; Fielding, Christopher 1; Isbell, John 2
1 Geosciences, University of Nebraska-Lincoln, Lincoln, NE.
2 Geosciences, University of Wisconsin-Milwaukee, Milwaukee, WI.

Despite a long history of sedimentological research on the Permian System of Tasmania, there is little consensus as to the timing, duration, and character of glacial events preserved therein. Recent work on the eastern Australian mainland has documented four discrete glacial intervals (P1-P4) separated by warmer epochs, which together span Asselian through Capitanian time. The present study evaluates whether the same pattern is also evident in Tasmania, which lay further south at polar latitudes. To establish the timing, character, and duration of potential glacial intervals, key outcrops and drillcores through the Lower Parmeener Supergroup were examined. The most proximal glacial facies, including interpreted sub- and pro-glacial diamictites and outwash conglomerates containing faceted and striated cobbles, occur at the base of the succession in the Late Pennsylvanian - earliest Permian Wynyard, Truro, and equivalent formations. Glacigenic facies in younger parts of the succession tend to be more distal in character, typified by outsized lonestones and occasional glendonites in fine-grained, offshore marine facies. Lonestones are commonly striated, indicating glacial reworking. Such deposits occur in the Asselian Woody Island Siltstone, the Sakmarian Bundella Formation, the lower part of the Artinskian Cascades Group, the Kungurian-Roadian Malbina Formation, and the lower part of the Capitanian Abels Bay Formation. These units are separated by strata that lack evidence for glacial activity, including alluvial, lacustrine, and shallow marine deposits of the latest Sakmarian-early Artinskian Liffey Group and shallow marine strata of the upper Cascades Group. Results reveal a pattern of alternating glacial and non-glacial conditions similar to that documented in regions to the north. However, available biostratigraphic constraints suggest that glacial epochs in Tasmania are temporally offset from those on the mainland. Given that the chronostratigraphic framework relies on fauna that are largely endemic to Tasmania, whether the apparent offsets are real or the products of biostratigraphic complications is under debate. Whatever the answer, results contribute to an emerging picture of the late Paleozoic Ice Age as a series of discrete glacial epochs separated by intervals of warmer climate.

 

AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009