Geochemical characteristics of the tura formation in parts of the upper Assam basin: An implication on provenance, tectonic setting and source – area weathering Sahariah N.*, Bhattacharyya P. Department of Applied Geology, Dibrugarh University, Dibrugarh *E-mail: nishantasahariahns21@gmail.com
Online published on 13 February, 2019. Abstract Geochemical analysis of a few borehole samples of Tura Formation belonging to both North and South Assam Shelf of Upper Assam Basin have been undertaken to interpret their provenance, tectonic setting, palaeo- weathering and climatic conditions. Geochemically, the sandstone samples are classified as wacke type. Provenance discrimination plots of sediments based on major oxides depict that the sandstone of Tura Formation was derived from a quartzose sedimentary rock source. The tectonic discrimination diagrams suggest a passive continental margin setting for the sandstone. Chemical Index of Alteration (CIA), Chemical Index of Weathering (CIW), Plagioclase Index of Alteration (PIA) and A – CN – K plot suggest moderate weathering of the source rocks under arid climatic conditions. The Mg – Na (Wt%) diagram suggests a shallow marine environment for the sandstones of Tura Formation. The chondrite normalized REE pattern of the samples is equivalent to the upper continental crust, which reflects enriched LREE and depleted HREE with negative Eu anomaly. The Eu/Eu* (∼ 0.69), La/Sc (∼ 5.69), Th/Sc (∼ 2.84), La/Co (∼ 10.89), Th/Co (∼ 5.26) and Cr/Th (∼ 5.22) ratios indicate derivation of the Tura Sandstones from a felsic rock source. Furthermore, La-Th-Sc ternary plot, Th/Sc-Zr/Sc and La/Sc-Th/Co binary plots also suggest felsic igneous source rock for the sandstone. Top Keywords Tura Formation, Upper Assam Basin, Geochemistry, Provenance, Tectonic setting, Source – Area Weathering. Top |