Geochemical and petrographic interpretation of Sandhan Formation: An insight into provenance, tectonics and paleoclimatic conditions

Abstract

The relative sea-level fall in terminal Cenozoic exposed continental shelf of Kutch provided opportunity to develop a fluvial system of braided nature. The terminal Cenozoic formation of Kutch, the Sandhan Formation provides a rare opportunity where a clear transition from a marine to fluvial succession can be identified in the field. The occurrence of fluvial deposits in the rock record suggest an abrupt and considerable fall in the base level. The ~157 m thick upper part of the Sandhan Formation is deposited in the fluvial environment. The fluvial succession of the Sandhan Formation has not been studied for their sediment geochemistry. Provenance, tectonic setting, paleo-weathering, and paleoclimate of the upper part of the Sandhan Formation is interpreted on the basis of extensive geochemical and petrographic analysis of sandstone samples by using XRF, the bivariate diagram Log (SiO2/Al2O3) versus Log (Na2O/K2O) diagram, QFL diagram, Provenance Discrimination Plot, SiO2/Al2O3 ratio with K2O/Na2O ratio, Chemical Index of Alteration (CIA) weathering indices, Plagioclase Index of Alteration (PIA), Chemical index of Weathering (CIW), A-CN-K Diagram, SiO2/Al2O3 ratio and binary SiO2 wt.% versus (Al2O3 + K2O + Na2O) wt.% diagram. These provided the detailed geological origin of the upper part of the Sandhan Formation as, it originated from a mixed provenance (quartzose sedimentary and mafic igneous), with arkose to subarkose nature. The upper part of Sandhan Formation is formed in an arid paleoclimate, both Active Continental Margin (ACM) and Passive Margin (PM) tectonic setting and moderate to intense paleo-weathering conditions.