Sequencing events across the Permian-Triassic boundary, Guryul Ravine (Kashmir, India)

The Permian-Triassic boundary (PTB) section at Guryul Ravine (Kashmir, India) comprises a > 100-m-thick, apparently conformable succession of mixed siliciclastic-carbonate sediments deposited in a deep-shelf or ramp setting. This section, although long important in debates concerning placement of the PTB, has not previously been the focus of an integrated chemostratigraphic study. In the present study, samples from a 20-m-thick interval straddling the PTB were analyzed for major- and trace-element concentrations, TOC-TIC, REEs, and organic delta C-13-delta N-15 to investigate contemporaneous environmental changes. The Guryul Ravine section exhibits a sequence of discrete events that provide potentially important information about the character and cause(s) of the PTB. Two transient negative C-isotopic excursions within the upper changxingensis zone predate the Late Permian event horizon (LPEH, i.e., the global mass extinction event) by similar to 200-400 kyr and are associated with the onset of a major eustatic rise and with secondary extinction peaks. These excursions may record minor environmental disturbances prior to the main end-Permian crisis, supporting an intrinsic mechanism such as volcanism and climate change rather than an extrinsic mechanism such as a bolide impact. The onset of a large (similar to -4.0 to -4.5%), sustained negative C-isotope shift marks the LPEH, which is located at the Zewan-Khunamub formation contact similar to 260 cm below the biostratigraphically defined PTB, The Guryul Ravine section exhibits a stepwise extinction pattern, with the largest peak between the LPEH and PTB and a secondary peak just above the PTB, a pattern similar to that observed in the Meishan D GSSP. (C) 2007 Elsevier B.V. All rights reserved.