Implications of Paleoweathering And Sediment Maturity in Geochemical Characterisation of Kalijhora Sandstones Exposed in The Extra-Peninsular Gondwana Basin, Darjeeling District, West Bengal, India

Abstract

This study examines specific geochemical attributes of extra-peninsular Kalijhora Gondwana sandstones from Darjeeling District, West Bengal, aiming to elucidate their weathering intensity, climatic conditions, and sediment maturity based on major oxide data. The Chemical Maturity Index (CMI) rises as quartz becomes more concentrated (60.57%-78.99%), replacing less resistant minerals through processes of weathering, transportation, and recycling. Elevated Al2O3 content (average 11.48%) results from finer particles and K-feldspar alteration, while K2O/Na2O ratios suggest K-feldspar transformation into Illite. Palaeo-weathering indices like high CIA (61.56%-77.55%), CIW (40.78%-92.80%), and PIA (32.59%-91.02%) values reveal intense weathering of source rocks. The Weathering Index of Parker (WIP) values (1275.37-3771.49), Vogel’s Index (V) values (1.05-6.24), and Silica-Titania Index (STI) values (72.94-93.01) indicate advanced weathering stages. The Index of Compositional Variability (ICV) values (0.62-6.95) suggest compositionally mature sediments. Hydraulic sorting effects indicate a recycled sedimentary source, with provenance discrimination diagrams highlighting deposition under active continental collision and compression. The findings align with the regional geological evolution of the Gondwana basin, indicating mature sediments from recycled sources deposited in a tectonically active setting influenced by post-collision uplift. Regionally, the Gondwana basin deepened northwards during the Gondwana period, with palaeo-current directions oriented towards north, suggesting a source in the Precambrian metamorphic terrain south of the basin. Significant detrital contributions likely came from the Eastern Ghats Supergroup and possibly the Transantarctic Mountains. This study highlights the complex interplay of weathering, transportation, and sediment recycling in shaping the geochemical characteristics of Kalijhora Gondwana sandstones.