MINERALOGICAL AND GEOTECHNICAL CHARACTERISTICS OF SANDSTONE OF THE MUREE FORMATION, ISLAMABAD SECTION, ISLAMABAD, PAKISTAN

Abstract

The Murree Formation is a part of the Miocene molasses deposits of the Rawalpindi Group that crops out in Islamabad, Pakistan. The rock sequence of the formation consists of a series of alternating beds of sandstone, siltstone and shale with subordinate marls and conglomerates. The sporadic exposures of the formation occur south of the Main Boundary Thrust (MBT) at Shah Allah Ditta, Barakahu, around Rawal Dam, G and H Sectors of Islamabad and along the Srinagar Highway. The sandstone of the Murree Formation is predominantly fine - to medium- grained and moderate to poorly sorted. The rock contains angular to sub-angular quartz (30-55 vol.%) and feldspar (2-3.5 vol.%) with abundant rock fragments (20-51 vol.%). The cementing material is calcite which constitutes (14-28 vol.%). The relative abundances of quartz, feldspar and rockfragments suggest the sandstone of the formation as sub-mature whereas the presence of calcite matrix and angular grains of quartz place it texturally as immature. The observed accessory minerals include epidote, monazite and tourmaline. The sandstone, on the basis of quartz, feldspar and rock fragments classify as litharenite and recycled orogenic in the (Q-F-LF) ternary plots, which might have formed due to rapid deposition in the tectonically deformed areas. For knowing the potential of the sandstone of the Muree Formation for utilization as the geotechnical properties obtained include uniaxial compressive strength (50.9-16.1), uniaxial tensile strength (8.19-2.31), specific gravity (2.67-2.636) and water absorption (0.59-0.25). Based on the research study, sandstone of the Murree Formation is considered suitable for dimension stones and construction material.