The Induan-Olenekian boundary in Western Australia: Conodont biostratigraphy, carbon isotopes and constraints on post mass extinction anoxia

Abstract

Ocean anoxia was widespread in the latest Permian and continued episodically into the Early Triassic. These episodes of anoxia have been interpreted to be due to the upward rise(s) of the chemocline, oceanic overturn(s) and/or major climatic perturbations. A significant anoxic event is recorded in the Kockatea Shale of the lower part of the Senecio-1 borehole core from the northern Perth Basin, Australia. We here present new biostratigraphic and chemostratigraphic data constraining the age of this anoxic event. The Early Triassic Induan-Olenkian Stage boundary (Dienerian-Smithian Sub-Stage boundary) has been identified in the Senecio-1 Well. This is the first international Triassic stage boundary to be unequivocally placed in Australia. Relatively abundant conodont faunas (1,000+ elements) represent three conodont zones in ascending order, the 'Clarkina carinata' - 'Neospathodus dieneri' Zone, the 'Neospathodus waageni eowaageni' Zone and the 'Neospathodus waageni waageni' Zone. In addition, a 'Neospathodus waageni' subsp. nov. subzone is recognised in the upper part of the 'Neospathodus waageni waageni' Zone.