USING STABLE LIGHT ISOTOPES TO IDENTIFY ENVIRONMENTAL CHANGES IN NEO-TETHYS OCEAN DURING THE PERMIAN-TRIASSIC EXTINCTION

The Permian-Triassic (PT) extinction is regarded as the largest extinction in Earth’s history. During this time period, the Neo-Tethys a "young" ocean, with its opening driving a portion of the plate motion in the Paleo-Tethys. Unlike the Paleo-Tethys, little is known about the environmental conditions of the Neo-Tethys across the PT boundary. Spiti Valley, located in the Himalayan range of India, is one few areas where Neo-Tethys’ PT sediments are preserved. The lithostratigraphy of Spiti Valley PT sections consist of the upper Permian (Gungri Formation) black shale capped, unconformably, by a pebbly limonitic layer (ferruginous layer) regarded as the PT boundary. The lower Triassic (Mikin Formation) limestone interbedded with black shale unconformably overlies the ferruginous layer. In this study we evaluated the light stable (C, N, and S) isotopic record of Spiti Valley PT sections. Stable isotopes were measured using an Elemental Analyzer (EA) paired with an Isotopic Ratio Mass Spectrometer (IRMS). The C, N, and S data, in combination with other geochemical proxies, suggest that environmental conditions declined prior to the PT crisis. Spiti Valley records a series of negative δ¹³C excursions prior to the PT boundary, which are linked to changes in S isotopic composition and in major and trace element concentrations. The negative δ¹³C, and other geochemical, excursions are abrupt and some appear to record local/regional changes in the Neo-Tethys Ocean. Nonetheless, these δ¹³C excursions suggest a series of catastrophic environmental events well before the PT boundary that reveal clues about the cause(s) of the largest mass extinction in Earth's history.