Early Triassic trace fossils from Gondwana Interior Sea: Implication for ecosystem recovery following the end-Permian mass extinction in south high-latitude region

Abstract

The Kockatea Shale Formation is one of few marine Early Triassic successions recorded in the Gondwana. This formation is exposed at the Northampton area of the northern Perth Basin, Western Australia and was deposited in the Gondwana interior sea during the Permian and Early Triassic. Trace fossils identified within the Kockatea Shale Formation are extremely abundant and contain 16 ichnogenera (including a problematic ichnogenus). The Gondwanan ichnoassemblage is constrained as late Smithian in age and is the most diverse among coeval ichnofaunas around the world. Several types of grazing traces are also reported for the first time in the Lower Triassic. Several proxies such as bioturbation level, ichnodiversity, burrow size, trace-fossil complexity, and tiring level suggest that tracemakers diversified in the Gondwana interior sea during the late Smithian. The Gondwanan ichnofauna-dominated ecosystem may have reached the ecologic recovery stage 3 of Twitchett's model in late Smithian. The rebound of ichnoassemblages in the aftermath of the end-Permian mass extinction was not controlled by particular environmental settings, all of which however were characterized by oxygenated substrata.