Provenance, tectonic setting, paleoweathering and paleoclimatic conditions of early to mid-Eocene sandstones of the Dalbuing Formation, Arunachal Pradesh, NE India: Inferences from petrography and geochemistry

Abstract

Petrography and geochemistry of sandstones of the Dalbuing Formation of Eastern Himalaya have been investigated to unveil their provenance, tectonic setting, paleoclimate and source rock weathering. This study suggests that the sandstones are wacke type and their provenance is quartzose recycled to transitional recycled orogenic provenance. The chondrite-normalized Rare Earth Element (REE) patterns of the sandstones show an enrichment of LREE, flat HREE patterns and negative Eu anomalies similar to those exhibited by Upper Continental Crust (UCC) and Post Archean Australian Shale (PAAS). This is an indicative of felsic igneous source for the sandstones and A–CN–K plot suggest their intermediate source. The study of paleoweathering conditions based on as Chemical Index of Alteration (CIA), Plagioclase Index of Alteration (PIA), Chemical Index of Weathering (CIW) and A–CN–K (A = Al2O3, CNCaO + Na2O and KK2O) plot indicate moderate to intense chemical weathering in the source area. Tectonic setting discrimination study based on geochemical data of these sandstones suggests both the passive margin (PM) and the active continental margin (ACM) tectonic settings of depositional condition. Paleoclimatic condition of the basin as suggested by the quartz-feldspar-lithic fragment (QFL) plot of petrographic study was arid to humid and by the bivariant log/log plot of (Qp/F + RF) versus (Qt/F + RF) was semi-arid to semi-humid. However, the bivariant SiO2 versus Al2O3 + K2O + Na2O plot suggest arid paleoclimatic condition with increasing trend of chemical maturity during the entire process of sedimentation. The C-value plots as well as Sr/Cu ratio suggests humid climatic condition specifically during the time of deposition of the sediments.