Abstract
An attempt is made in the present study to unravel the provenance, paleoweathering and paleoclimatic conditions of the Jurassic (Spiti Formation) black shales and sandstones from the Spiti region, Tethys Himalaya, using multi proxy approach. The sandstones are subarkose in composition and texturally poorly sorted, subrounded to subangular in shape with moderate spheriocity. The range of the chemical index of alteration (CIA) is 55–90, recorded in the black shales strongly suggests moderate to strong chemical weathering conditions in the source area, which in turn reflect fluctuating climatic conditions prevailing during the deposition of these sediments in Jurassic period in the Spiti region. Geochemical studies reveal that shales are enriched in felsic elements (high SiO2, Al2O3, K2O) and depleted in mafic components (Fe2O3 and MgO).The various geochemical discriminant plots and elemental ratios (SiO2/Al2O3, K2O/Al2O3, Al2O3/TiO2, K2O/Na2O, etc.) indicate the rocks to be the product of weathering of felsic rocks. The paleoclimate in the source area seems to be mostly semi-humid. The plot of the samples on the A-CN-K ternary diagram indicates a granitic weathering trend. The X-ray Diffraction studies show that the prominent clay minerals in the Spiti shales are illite, smectite, chlorite, kaolinite and vermiculite along with quartz, muscovite, alkali feldspar, calcite and phosphatic phase.When plotted on the tectonic discrimination diagram, the samples indicate passive margin tectonic setting.
Published Version
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