Climatic fluctuations during a mass extinction: Rapid carbon and oxygen isotope variations across the Permian-Triassic (PTr) boundary at Guryul Ravine, Kashmir, India

Abstract

In one of the most extended Permo-Triassic (PTr) boundary sections at Guryul Ravine (Kashmir), both carbon and oxygen isotopes show no marked trend across the boundary, but do show zigzag variations at a scale not seen above and below. These are interpreted as major short-term variations in biological storage of carbon (δ13Ccarb), temperature (δ18Ocarb), and land/ocean carbon mixing (δ13Corg) which also occur in other sections with the required detail of analysis. Oxygen isotopes, though probably altered show that relative sea surface temperatures fluctuated greatly at Guryul Ravine; if unaltered they fluctuated between 22 °C and 42 °C, using a salinity-stratified model for the partially enclosed PTr Neotethys Ocean, about the same range as at Meishan and Shangsi in China at lower equatorial latitudes. Together with the carbonate isotopes, this suggests large fluctuations in climate and terrestrial biomass from the latest Permian event horizons to the fossil-defined base of the Triassic which lasted, on current estimates about 60 ± 48 ka, and, by analogy with Quaternary studies, fit a 100kyr eccentricity cycle, with the main end Permian extinction occurring within the cycle. The lack of consistent element geochemical changes across the boundary accompanied by significant carbon, sulphur, and other isotopic changes, here and elsewhere, suggests that atmospheric and oceanic chemistry rather than physical changes, such as provenance and sea‐level changes, drove the PTr environmental changes and extinctions at least on the mid‐latitude Tethyan shelf of northern India.