Geochemistry of the Permian shales in the Chintalpudi sub-Basin, Pranhita-Godavari Basin, India: Implications for Provenance, weathering, and tectonic setting

The elemental (major, trace, and rare-earth elements - REEs) distribution in sedimentary rocks provides an essential tool for basin-scale investigations, enabling the interpretation of geochemical characteristics within stratigraphic successions and thereby providing regional provenance and insights into the tectonic evolution of the basin. Here, numerous discrimination diagrams based on the major, trace, and rare earth element (REE) geochemistry were used to infer the sediment provenance, degree of weathering, and tectonic setting of the Permian Pranhita-Godavari (PG) Basin in South-Eastern India. Permian extensional basins are widely documented across the Gondwana basin in India, and the Chintalpudi sub-basin of the PG preserves a thick (~3000 m) and complete Gondwana sequence, spanning from the Permian Talchir diamictites to the Cretaceous Gangapur Formation. This research presents new geochemical results from the Barakar and Kamthi Formations within the Chintalpudi sub-basin, aiming to understand the sediment provenance, tectonic evolution, and weathering phenomena during the Late Permian. The distributions of major, trace, and rare-earth elements indicate that the clastic sediments are compositionally mature and derived predominantly from intensely weathered continental sources. The Post-Archean Average-Australian-Shale (PASS) normalized REE data shows enrichment of light rare earth elements (LREE) with relatively flat heavy rare earth elements (HREE), and a negative Europium (Eu) anomaly implies that the majority of contributing source rocks were felsic, with minor input from rocks of andesitic composition. Furthermore, multi-parameter discrimination plots using major (K2O/Na2O vs. SiO2/Al2O3), log (K2O/Na2O)/SiO2, and trace elements (La/Y vs. Sc/Cr) compositions reveal that the majority of the samples in the Chintalpudi sub-basin are part of a passive continental geotectonic setting. The ratio of Zr/Sc and Th/Sc is higher, corroborating the felsic origin without sediment recycling. Major oxide ratios indicate that the samples are highly mature and have a high chemical index of alteration (CIA), with a low index of compositional variability (ICV), suggesting that they were deposited in warm and humid climatic conditions, with intensive weathering during deposition.

Keywords: Permian Shale, Provenance, Weathering, tectonic setting, Chintalpudi sub-basin