Petrography and geochemistry of the Murree formation, Kotli area, Kashmir basin, Pakistan (T-1430) (MFN 6234)

Abstract

The study area lies in Kashmir basin, eastern limb of the Hazara Kashmir syntaxis containing the molasse deposits of Miocene age known as the Murree Formation. The formation predominantly consists of shales, mudstone, siltstone and sandstone. Sandstone of the respective formation is medium to coarse grained and bears moderate to poor sorting. The frame work grains (quartz, feldspar and rock fragments) are angular to sub angular to sub rounded in shape. Petrographic study reflect that the Murree Formation is texturally and mineralogically immature. Sandstones of the Murree Formation is abundant in rock fragments and contains an average matrix of five volume percent and is hence classified as lithic arenite. X-ray Diffraction analysis shows that the shales of the Murree Formation contains authigenic, viz. palygorskite, halloysite and dickite minerals, and quartz, feldspar, phlogopite, biotite, muscovite, chlorite and opaque as inherited minerals. Calcite occurs as the cementing material. The ternary plot using major elements oxides define the sandstones of the Murree Formation as ferromagnesian and potassic. Major elements bivariant plots classify them into calcareous sandstones and non-sandstones. Chemical maturity of the sandstones is expressed in major elements bivariate plot of SiO2 verses Al2O3+K2O+Na2O, showing their deposition in semi-arid and semi-humid conditions. The plot of SiO2 versus K2O/Na2O shows oceanic island arc and active continental margin settings for the sandstones of the formation and the binary and ternary plots show non-marine deltaic sandstone characterization. The rocks of the Murree Formation seemed to have been formed due to rapid Himalayan uplift, high rate of erosion and speedy deposition.