Sandstone Geochemistry of Dalbuing Formation of Yinkiong Group, Arunachal Pradesh, NE India: Implications for Provenance, Paleoweathering and Tectonic Settings

Abstract

This study presents the results of geochemical investigations of early to middle Eocene sandstones belonging to the Dalbuing Formation of Yinkiong Group, occurring in and around Yamne valley of Arunachal Pradesh. Geochemically, these sandstones are wacke and lithic arenite, with the former being dominant than the other. The various indices of weathering (CIA, CIW, PIA) suggest intense chemical weathering of the source rock. Moreover, the average Th/U ratio (mean = 6.97) also indicates intense chemical weathering in the source areas and derivation of the sediments from the upper continental crust. However, the plot of chemical index of alteration (CIA) vs. index of compositional variability (ICV) shows that most of the sandstones are geochemically mature and were derived from intensively weathered source rock. The sandstones were deposited dominantly in semi-arid condition. Tectonically, these sandstones are found to have affinities towards both the passive margin (PM) and the active continental margin (ACM) settings, which further implies existence of multiple tectonic activities during their deposition. Moreover, the elemental ratios of Eu/Eu*, La/Sc, Th/Sc, La/Co, Th/Co, Th/Cr and chondrite normalized REE distribution pattern suggest their derivation from sources of felsic composition. The high ratio of Zr/Sc indicates the enrichment of heavy mineral zircon supplemented by sediment recycling.