T337 Permian and Triassic Terrestrial Biotic Responses to Global Perturbations

Thursday, 9 October 2008
8:00 AM - 12:00 PM

An Assessment of Terrestrial Ecosystem Response to the End Permian Crisis, Karoo Basin, South Africa

Paper number: T337-10
Program: Technical Sessions
Time: 10:30 AM – 10:45 AM

Authors

Abstract

The presently accepted model for biotic response to the global perturbation at the end of the Phanerozoic is a coincidence of marine and terrestrial ecosystem collapse. The principal extinction pulse in the marine realm has been dated previously at ~252 Ma, with no apparent difference in the age of the boundary between marine and non-marine sections in China. In South Africa, the abrupt extinction of vertebrates, correlated to the Meishan section using d13C chemostratigraphic trends, is considered to be slightly older than the formal stratigraphic boundary. The rarity of paleobotanical evidence is due, in large part, to taphonomic processes associated with changes in regional watertable in Late Permian and Early Triassic aggradational and degradational landscapes. But, in rare instances, parautochthonous and autochthonous megafloras are preserved.

The present study reports on an autochthonous forest-floor litter preserved by volcanic tuff, now devitrified, above a rooted, poorly developed paleosol at Wapadsberg Pass, in the Graaff-Reinet area, Eastern Cape Province. The gleyed protosol contains subvertical Vertebraria roots and is -70 m below the purported P/Tr boundary as defined by vertebrate biostratigraphy. The horizon is traceable over 1 km in lateral extent, occurring in both New and Old Wapadsberg Passes. The litter (O) horizon preserves not only leaves of aerial shrubs (Glossopteris) but also rhizomatous sphenopsid ground cover (Phyllotheca, Trizygia). To date, only Glossopteris leaves and stem debris have been recovered from -5 m below the reported boundary at Old Wapadsberg Pass.

A suite of zircons recovered from the tuffaceous horizon comprises grains that range in age from Neoproterozoic to the mid-Phanerozoic. Evidence indicates that the terrestrial response to the main marine pulse may not have been coincident.