Middle Triassic Paleosols and paleoclimate of Antarctica

Abstract

ABSTRACT The Lashly Formation in the Allan Hills of southern Victoria Land, Antarctica, is now at a latitude of 76°S and during the Middle Triassic was at least 70°S. The combined evidence of fossil roots and soils indicates a paleoclimate unusual for such a high latitude. Temperate paleotemperature is indicated by roots, logs, and leaves of woody plants and the degree of chemical weathering and clay formation within the paleosols. Paleosols of the Lashly Formation are more like soils of southern Sweden than those of either Finland or southern Europe. Silt infiltration structures around root traces and in cracks within the paleosols are evidence for a seasonally snowy climate, but there is no evidence of ice wedges or other permafrost features in the paleosols. Other evidence of climatic seasonality includes well-defined growth rings in fossil wood, and abscission scars at the base of fossil leaves. Diverse broadleaf plants, and noncalcareous paleosols, indicate a humid climate with mean annual precipitation of about 1200 mm. Such a wet climate is anomalous for the interior of the supercontinent of Pangea, and such a warm and mildly seasonal climate is anomalous for such high latitudes. This paleoclimatic anomaly may be a lingering effect of global greenhouse initiated at the Permian-Triassic boundary. Paleoclimatic variables calculated here may be useful for recalibrating global paleoclimatic models for the middle Triassic.