--> Abstract: Determining the Permian/Triassic Boundary in Australia through C-Isotope Chemostratigraphy, by R. Morante, A. S. Andrew, J. Veevers, and P. J. Hamilton; #90987 (1993).

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MORANTE, R., and A. S. ANDREW, School of Earth Sciences, Macquarie Univ., North Ryde, NSW, Australia; J. VEEVERS, and * P. JOE HAMILTON, CSIRO Division of Exploration Geosciences, North Ryde, NSW, Australia

ABSTRACT: Determining the Permian/Triassic Boundary in Australia through C-Isotope Chemostratigraphy

Determination of the Permian/Triassic (P/Tr) boundary in Gondwanaland, including Australia, by paleontological means is imprecise because the Gondwana facies is almost wholly non-marine. The distinctive shape of the (isotope)C{13} profile at the P/Tr boundary in marine sediments elsewhere provides a means of defining the P/Tr boundary in Australia by C-isotope chemostratigraphy. The P/Tr boundary in marine sediments in the Chinese stratotype is characterized by a negative step in the (isotope)C{13} values in carbonate from about +3 permil (PDB) in the Permian to +1 permil in the Triassic.

Known marine transitions across the P/Tr boundary in Australia are restricted to the northwest. In the Paradise Station region of the northern Canning basin, core-holes penetrate the Blina Shale and the Hardman and Condren Formations, which straddle the P/Tr boundary. The (isotope)C{13} profile for organic matter in the Paradise section shows a marked shift of 9 per mil from about -32 to -23 permil within an interval of 35 m. The (isotope)C{13} shift occurs between samples from the Western Australian palynomorph zones of Upper Stage 5 and Protohaploxypinus reticulatus and is within the lower third of the Hardman Formation. We suggest this correlates with the P/Tr boundary. Thus the overlying Blina Shale, which has been dated by fossils as earliest Triassic is now placed 150 m above th P/Tr.

The P/Tr boundary determined by the organic (isotope)C{13} profile is correlated with Eastern Australian sections by palynomorphs to the boundary of Upper Stage 5 and P. microcorpus zones, assuming these are not diachronous, thus placing the boundary between the coal measures below, and the Rewan and Narrabeen Groups above. This contradicts intercontinental palynomorph correlation, which places the P/Tr boundary about 200 m above the base of the Rewan and Narrabeen Groups.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.