Postapocalyptic greenhouse paleoclimate revealed by earliest Triassic paleosols in the Sydney Basin, Australia

Abstract

The Permian-Triassic boundary in the Sydney Basin of Australia is coincident with a pronounced decrease in δ 13 C isotopic values of organic carbon, the last coals anywhere in the world for all of the Early Triassic (ca. 6 m.y.) time, and extirpation of the Glossopteris flora at the top of the Illawarra and Newcastle Coal Measures. Coal-bearing paleosols of the latest Permian represent extensive swamplands of the seasonally deciduous Glossopteris flora in a humid cold temperate lowland southwest of an Andean-style volcanic arc. Stone-rolls (large ribs of floor rock up into the coal) within some of the uppermost coals of the Permian coal measures can be interpreted as string bogs of a kind now found in cold climates at latitudes of 68°–70°, which is compatible with a paleomagnetically estimated paleolatitude of 65°–85°S for the Sydney Basin. Paleolatitude was not much different for earliest Triassic time, but paleosols of that age include Inceptisols and Entisols showing substantial chemical and textural weathering, more like soils now forming at latitudes of 40°–58° than those within polar circles. This anomalous high-latitude warmth set in at the Permian-Triassic boundary. Sedimentation rates increased at the boundary marked by geochemically unusual acidification of clay and a dramatic carbon isotopic excursion. These changes in environments and ecosystems can be explained by soil erosion following deforestation implied by the plant extinctions and abundant fungal remains at the Permian-Triassic boundary. Evidence from paleosols can now be added to that from paleontological and isotopic studies showing that disruption of the carbon cycle at the Permian-Triassic boundary resulted in a CO 2 or CH 4 post-apocalyptic greenhouse paleoclimate.