PERMIAN TO TRIASSIC TRANSITION IN THE CENTRAL TRANSANTARCTIC MOUNTAINS, ANTARCTICA

The Permian-Triassic boundary occurs within a relatively complete terrestrial sequence in the central Transantarctic Mountains. In the best-documented section at Graphite Peak in the Beardmore Glacier area, the boundary may be below the uppermost coal of the Buckley Formation, 1.2 m below the contact with the Fremouw Formation. Here the base of the Protohaploxypinus microcorpus Zone, which has been assigned a mainly Triassic age (Morante, 1996), coincides with a previously reported major negative d¹³C excursion (Krull and Retallack, 2000). The P. microcorpus Zone could also be uppermost Permian, in which case the boundary is at the contact with the Fremouw Formation or higher. In the Shackleton Glacier area, the boundary is within a 7- to 10-m-thick interval between the Permian Glossopteris flora and the Lower Triassic Lystrosaurus fauna. The Glossopteris flora, including fossil wood and leaves, occurs within the lowermost part of the Fremouw Formation. The occurrence of a possible Permian vertebrate, Lystrosaurus maccaigi, at the base of the vertebrate-bearing sequence, may narrow the boundary even further. The unfossiliferous interval, perhaps representing 140,000 to 200,000 years, includes the transition from Permian into Triassic.

During the Permian-Triassic transition, coal and gray carbonaceous fine-grained beds were replaced by greenish-gray and red beds in an otherwise similar cyclical sandstone sequence. This change marked warmer climatic conditions that permitted reptiles and amphibians to migrate into polar latitudes. The Antarctic Lystrosaurus fauna has several species in common with the South African fauna that lived 20° to 35° closer to the equator, suggesting a uniform climate over a wide latitudinal range.