Isotopic analysis of Permo-Carboniferous Talchir sediments from East-Central India: signature of glacial melt-water lakes

Presence of calcareous nodules in the upper part of the Talchir sedimentary sequence (Permo-Carboniferous) in Gondwana sediments of east-central India offers a chance to delineate the environment of deposition and the regional palaeo-climate. Carbon and oxygen isotopic compositions of the carbonate cement in these early diagenetic nodules indicate that this phase of Talchir sedimentation took place in lakes formed by glacial melt-water. The estimated mean δ18O of the meteoric water is about −22.5‰ , close to the expected composition at the 70°S palaeo-latitude of this area. Majority of the nodules have highly depleted carbon isotope ratios indicating significant contribution from biogenic carbon dioxide. Since the lower part of the Talchir Formation is characterized by glacier derived materials (conglomerates and diamictites), the presence of biotic signature in the upper part indicates a climatic change from the cold glacier regime to a warm period.