Articles written in Journal of Earth System Science

    • Petrographic and geochemical attributes of Oligocene Barail sandstones in parts of Cachar Fold Belt, northeast India


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      The Oligocene Barail sandstones in parts of Cachar Fold Belt, northeast India have been studied to understand their tectonic provenance, paleoweathering and the depositional settings employing petrographic and geochemical attributes. Predominantly, arenaceous Barail succession is mainly composed of very fine (3.53 ${\oslash}$) to medium (1.50 ${\oslash}$) grained sandstone, silty-shale and carbonaceous shale with minor coal seams. Petrographically, Barail sandstones may be grouped into two categories, i.e., sub-litharenite and lithic greywacke possessing an average recalculated modal composition Q$_{67}$F$_{13}$R$_{20}$. Among framework constituents, majority of quartz grains belong to monocrystalline non-undulatory variety, the feldspars and rock fragments being dominantly plagioclase and metamorphic types, respectively. Geochemically, Barail sandstones possess high SiO$_{2}$, more Na$_{2}$O than K$_{2}$O and relatively low Fe$_{2}$O$_{3}$ and thus conforming to the modal composition. The weathering indices like CIA, CIW, PIA and ICV suggest derivation from a moderately weathered source terrain possibly Tonalite and Granodiorite having plagioclase feldspars in the range of An$_{10}$–An$_{50}$, i.e., Oligoclase (Og) to Andesine (Ad). Barail sandstones seem to have been derived predominantly from a recycled orogenic provenance with minor contribution from mixed-transitional continental sources and deposited in an arc active continental margin setup.

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