PERMIAN HIGH-LATITUDE GONDWANAN CLIMATE AND ENVIRONMENT CONSTRAINED BY PLANT TAPHONOMY

Analysis of abundant plant material preserved in diverse forms ranging from in situ stumps to macerated debris elucidates Late Permian paleoclimatic and paleoenvironmental conditions during deposition of the upper Buckley Formation, Beardmore Glacier area, Central Transantarctic Mountains (CTM). Then, as now, the CTM were located at very high latitude (~75°S). Fossil forests preserved at three stratigraphic levels are comprised of 87 in situ stumps. Tree density was a maximum of 2345 trees per hectare, with trees ~18 m tall. Such healthy forests imply conditions sufficiently warm and wet to promote growth during the growing season, in spite of a strongly seasonal light regime. Of 87 stumps, all are upright with roots extending outward from the stump; none had been uprooted. Fossil leaf mats are comprised of densely packed impressions of Glossopteris leaves that encircle the stumps. The leaves were flattened into mats, as are modern leaf mats that accumulate in very wet conditions. The roots are very shallow, which is consistent with a high water table or boggy conditions. The stumps are rooted in very poorly developed paleosols as would occur if plants colonized ephemeral habitats such as emergent bars in a braided stream system. Abundant large logs preserved as impressions occur on a few bedding planes. They lack branches and roots that presumably were lost during transport. Scaled stream table experiments with logs and braided channels demonstrate that transported logs are deposited in a bimodal pattern of preferred orientations that resembles that of the Permian logs. Plant material becomes increasingly abundant upward in the Buckley Formation; in situ forests and coal do not occur near the base of the formation. This distribution reflects climate amelioration and increase in vegetation following Gondwanan glaciation.