COLLAPSE AND REBUILDING OF MARINE ECOSYSTEMS DURING PERMIAN-TRIASSIC TRANSITION IN THE GONDWANA INTERIOR SEA

The Permian-Triassic (P-Tr) mass extinction redirected dramatically the course of biotic evolution during the Mesozoic and Cenozoic. This event and its consequence have been globally studied. However, few data about this ecologic crisis and subsequent recovery are known from inland Gondwana. Here, we report the collapse and rebuilding of marine ecosystems in the P-Tr mass extinction and its aftermath recorded in the Perth Basin, which was part of the interior sea of the Gondwana during the Permian and Triassic times. The P-Tr boundary and Early Triassic successions are seen in borehole cores and outcrop sections in the northern Perth Basin (NPB). A complete P-Tr boundary sequence is revealed in the Well Hovea-3 of the basin where the Griesbachian (earliest Triassic) fossil assemblage comprises a high-abundance and low-diversity fauna dominated by Claraia spp. in contrast to the highly diverse fauna recorded in the uppermost Permian. Moreover, the Lower Triassic successions are also present in Wells Per-2, Cliff Head-3, 4, and Dongara-24. The published geochemical signature and framboid pyrite analysis indicate that the P-Tr boundary beds may reflect an anoxic setting. The Griesbachian-Dinerian succession is composed of black shales interbedded with Claraia-concretions and thin layers of stromatolites of the lower Kockatea Shale. The Smithian successions are widely distributed in boreholes and on the exposure in the Geraldton area. This unit is characterized by a distinct limestone layer or stromatolite layer at the base, microbial mats and shell beds in the lower, and abundant trace fossils in the upper. Accordingly, marine ecosystem in Gondwana interior sea collapsed in the P-Tr mass extinction. The post-extinction ecosystem has been degraded to a rather low level through the Griesbachian-Dinerian interval and started to rebuild in Smithian, which saw an increase in ichnodiversity