Petrography of Sandstone

تاریخ : فروری ۲۰۱٦ - نومبر ۲۰۱٦

The project area lies in eastern limb of Hazara Kashmir Syntaxis (HKS) in Sub Himalayas. The sub Himalayas are bounded by the Main Boundary Thrust (MBT) in the north and Himalayan Frontal Thrust (HFT) in the south. The study deals with the geology and petrography of the sandstone in the Tain, Paniwala and Rawalakot area. The Neogene molasse deposits are deformed into folds and faults due to tectonic activities. The rocks of Murree and Kamlial Formations of Rawalpindi Group are exposed in the area. The area was mapped on a scale of 1:50,000. Eighteen representative rock samples were thin sectioned and studied under microscope. The lithology of Murree Formation is dark red and purple clay, siltstone and purple grey and greenish grey sandstone with subordinate intraformational conglomerate in the area. The sandstone of Murree Formation is fine to medium grained in texture and thin to medium bedded. Primary sedimentary structures such as ripple marks, mud crakes, worm barrows, load cast and flute casts were observed. The sandstone is fractured. Fractures are filled by calcite and quartz veins. Sandstone of Murree Formation is mainly comprised of angular to sub-angular and rounded to sub-rounded quartz grains. The quartz is of igneous and metamorphic origin. The feldspar is plagioclase and microcline- perthite in the sandstone. The Kamlial Formation consists of purple-grey to greenish-grey sandstone which is medium to coarse grained and contains interbeds of brownish, grayish, calcareous to yellowish shale. The sandstone has Intraformational conglomerate of yellowish to brownish shale. The sandstone is distinguished from the underlying Murree Formation by its usually spheroidal weathering. Hematite concretion in mud rocks is common in Kamlial Formation. The alteration of hematite into limonite is found in sandstone of Kamlial Formation which shows different levels of oxidizing and reducing conditions.