Sandstone Composition and Provenance of the Nari Formation, Central Kirthar Fold belt, Pakistan

Abstract

Abstract The Oligocene-Early Miocene Nari Formation is widely distributed in the Kirthar thrust-fold belt. The formation in the study area is mainly consist of sandstone and shale. Field observations and detailed petrographic study reveal that these sandstones are mostly fine to medium grained, subangular to subrounded and poorly to moderately sorted. Detrital grains are dominantly quartz ranging in proportion 36-76%, feldspar 7-17% and lithic grains 1-13%, reflecting that these sandstones are compositionally submature. Quartz is mostly monocrystalline with some polycrystalline grains. Feldspar is dominantly plagioclase (albite) with some alkali feldspar (orthoclase and microcline). Lithic fragments are siltstone, mudstone and chert. Biotite and muscovite are present as accessory minerals. Heavy minerals such as apatite, tourmaline, and zircon are present in trace amount. The QFL diagrams show that the sandstones of the Nari formation are subarkose and lithic subarkose. The QtFL, QmFLt ternary diagrams and paleocurrent direction suggest that the sediments were transported from the Indian shield exposed to the northeast of the Nari Basin.