Paleoclimatology of Australia During the Pangaean Interval

Marita T. Bradshaw, Albert T. Brakel, Judith T. Parrish, Jennifer M. Totterdell, Anthony N. Yeates

The supercontinent Pangea stretched nearly from pole to pole, creating a continuous barrier to zonal atmospheric and oceanic circulation. Climatic models predict that monsoonal circulation would have prevailed during the Permian through to the Middle Jurassic, reaching its greatest intensity in the Triassic, and with its impact felt most strongly in low latitudes. During the Pangaean interval, Australia provided a sensitive record of the impact of the monsoon as it was consistently located in high latitudes on the margin of the supercontinent.

The database to test this model has been assembled by the Palaeogeographic Map Project carried out by the Australian Geological Survey Organisation. In this project, data and interpretative environment maps were compiled for 70 time slice intervals for the Phanerozoic. Paleoclimatic indicators including red beds, carbonates, coal, dropstones and glendonite, were mapped for 23 time slices from the Permian through to the Jurassic. Climatic changes shown in this series of maps are largely in response to changes in the global circulation and sea level, rather than shifts in paleolatitude.

In the earliest Permian, Australia was dominated by ice which left an extensive record of glacial deposits. Following retreat of the ice and the resulting rise in sea level, there was widespread deposition of coals and lake deposits, consistent with a humid and cool climate. In the Late Permian a strong thermal gradient developed across the continent with carbonates being deposited on the western margin under the influence of warm Tethyan currents. The Early Triassic was characterised by red bed deposition and the cessation of peat accumulation, indicating seasonality of rainfall. Late Triassic coral reefs on the western margin are clear evidence of warm conditions. The impact of the Pangaean monsoon continued into the Early Jurassic as evidenced by red beds deposition and the abundan e of Classopollis, consistent with a warm and seasonally dry climate. By the Middle Jurassic the climate was cooler and/or wetter, pointing to the decay of monsoonal circulation with the breakup of the supercontinent.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995