Geochemical and organic carbon isotope studies across the continental Permo-Triassic boundary of Raniganj Basin, Eastern India

Abstract

Organic carbon isotope and geochemical changes across a continental interior Permo-Triassic boundary section from the Raniganj Basin, India, indicate a ~9‰ drop in organic carbon δ¹³C in the Early Triassic and synchroneity of this event throughout the Pangea. The study demands a common causative mechanism for the perturbation of the global carbon reservoir and not a combination of multiple causes. A global sea-level fall and oxidation of marine gas hydrates possibly increased the ¹²CO₂ input in the ocean-atmosphere system which caused a climatic shift from humid to warm semi-arid type and consequent extinction of land plants. Simultaneous increase in erosion from near-barren lands, change in the erosional base level and provenance deposited the boundary sandstone with positive europium anomaly and debris flow type matrix rich conglomerate. No extraterrestrial source, therefore, is needed to explain this Eu anomaly. The response of the terrestrial plant community to this perturbation of the carbon reservoir was, however, sluggish and the d13C drop took place slowly, being maximal in the Early Triassic only.