Charcoalified plant remains from the Lashly Formation of Allan Hills, Antarctica: Evidence of forest fire during the Triassic Period

Microscopic charcoal preserved in sediments of the Lashly Formation (Middle to Late Triassic) of South Victoria Land (SVL), Antarctica provides a proxy record of palaeofire. These charred fragments derived from wood and leaf pieces along with spores and pollen grains are part of the buried plant biomass preserved in the shale and carbonaceous shale of fluvial/lacustrine deposits. The evidence of paleofire in Antarctica during the Triassic Period is supported by the presence of a thin bed of silicic tuff interlayered with Dicroidiumbearing shale. The detailed morphology and comparative anatomy of least to high thermally altered plant fragments observed under the light, fluorescence and scanning electron microscope demonstrates the evidence of effect of fire on the vegetation during Middle to Late Triassic (240-200 million years). Most of the charred particles retain identifiable structures with well-preserved to distorted cellular details. Such plant fragments are dark brown, blackish brown, quadrangular-multiangular, equi-dimensional, opaque up to the edges and nonfluorescent. The pollen grains recorded from several sedimentary sequences (but the new data come from only one level i.e., member C of Lashly Formation) show distorted exinal sculptures and are light to dark brown in colour indicating intensive thermal effect. The detailed microscopic images of such fire-affected plant remains also explain their preservation biases in the sediments. The magnitude of the charred pieces and their abundance peaks from various locations in Allan Hills is related solely to the production and amount of burnt material embodied in the sediments. The high peaks indicate severity of fire and production of maximum charcoal of the standing vegetation in Allan Hills.