Petrographic and heavy mineral evidence for a transcontinental drainage system in the Permo-Triassic Raniganj Basin: implications for paleoclimate and paleogeographic reconstruction of East Gondwana

This study establishes the provenance evolution of the Raniganj Basin and paleoclimatic conditions during Permo-Triassic sedimentation through an integrated analysis of framework mineralogy and heavy minerals. The QFL modal composition indicates transitional continent and cratonic interior provenance for the sediments. Garnet, tourmaline, and rutile are the most common heavy mineral assemblages. ZTR values decrease from the Barakar (74%) and Barren Measures (69%) formations to the Raniganj (54%) and Panchet (47%) formations. The high abundance of garnets in the heavy mineral assemblage, along with a high garnet–zircon and rutile–zircon indices, indicates the predominance of metamorphic source terrains. Detrital tourmalines (dravite and schorl) are sourced primarily from the proximal Chhotanagpur Granite Gneiss Complex and secondarily from the Singbhum Craton. Detrital garnets are primarily almandine-rich, with high XFe populations, indicating amphibolite-grade metapelites of the Assam–Meghalaya Gneissic Complex, whereas moderate XMg (~ 25%) compositions link to granulite-facies rocks of the Eastern Ghats Metamorphic Belt and East Antarctica. The detrital almandines with the highest XMg (~ 42%) from ultrahigh-pressure eclogite rocks are similar to those from East Antarctica, whereas those bearing signatures of blueschist/greenschist facies indicate a source in southwestern Australia. The preservation of distal signatures suggests a mature, transcontinental-scale fluvial network that facilitated the mixing of local and distal sediments across the East Gondwanan supercontinent. The transition from quartzose to feldspar-rich arkosic sandstones, along with a decrease in kaolinite cement and an increase in apatite–tourmaline indices, documents a shift from humid early Permian to semi-humid early Triassic conditions.