T168 Extreme Environmental Conditions and Biotic Responses during the Permian-Triassic Boundary Crisis and Early Triassic Recovery I

Monday, 20 October 2014
1:00 PM - 5:00 PM
215/216

GEOCHEMICAL-SEDIMENTARY-PALEONTOLOGICAL CONSTRAINTS FOR PERMIAN-TRIASSIC TRANSITION IN THE NEO-TETHYS SEA: EVIDENCE FROM SPITI VALLEY, INDIA

Paper number: T168-2
Program: Technical Sessions
Time: 1:15 PM – 1:30 PM

Authors

Abstract

The 252 million year old Permian-Triassic (P-T) mass extinction event accompanied the strongest global environmental change in Earth’s geological history. The Spiti Valley in the Indian Himalaya represents a continental shelf section on the southern margin of the land-locked Neo-Tethys Sea and preserves this event in its rock record. We present new sedimentary-paleontological observations and high-resolution carbon and oxygen isotope data across the P-T boundary from two Spiti outcrops, Atargu and Guling. In these rock sections, brachiopod and crinoid-bearing Gungri shale layers with the presence of framboidal pyrites indicate an anoxic-dysaerobic environment during the Late Permian. Evidence of rapid transition to oxidizing conditions is clear from the iron-rich ferruginous layer, before the deposition of carbonates in the Early Triassic. Changes of 2.4‰ and 3.1‰ in δ13Corg of the two sections in Atargu and Guling respectively identify the Late Permian Event Horizon (LPEH) across the ferruginous layer and confirms a compositional change in the marine carbon pool and bio-productivity at this paleolatitude.

Unlike other global P-T sections, marine anoxia seems to have been restricted to the deeper waters of the Neo-Tethys and did not significantly affect the productivity of shallow waters in the Late Permian. Extinction occurred rapidly under oxic conditions in a regressing sea. Sharp fluctuations and highly depleted values in δ13Ccarb and δ18Ocarb in the Early Triassic Mikin Formation suggest a warmer arid climate with strong weathering fronts and rapid sea-level changes. We propose that the synchronicity of the Siberian Trap volcanism and the Araguainha impact in Brazil was the chief trigger for this catastrophe. Isotopically-depleted CO2 dominated the atmosphere-marine exchange, impacting the geochemical composition of the Neo-Tethys Sea. This study adds new perspectives to the possible mechanism of rapid environmental change at the P-T transition, especially in the Peri-Gondwanan realm. While the discovery of fossils in the ferruginous layer suggests the need for more biostratigraphic and chronological control, we believe a combination of factors including volcanism, meteorite impact, marine regression and anoxia were the drivers to this ecological bottleneck.