PETROLOGY OF LOWER CRETACEOUS LUMSHIWAL FORMATION, MAROBA SECTION, WESTERN KALA CHITTA RANGE, PAKISTAN

Abstract

This study deals with petrology of the Lumshiwal Formation, Maroba section, Kala Chitta Range. In the study area, lower contact of the Lumshiwal Formation is conformable with the Chichali Formation and upper contact is conformable with the Kawagarh Formation. The formation mainly consists of sandstone and carbonate beds. 12 fresh rock samples were processed for petrographic analysis to interpret petrofacies, environment of deposition, tectono provenance, source rock composition, paleoclimate and diagenesis. The sandstone unit is interpreted as quartz arenite facies using QFL ternary plot consisting of quartz as dominant essential mineral by volume with range of 90 vol. % to 96 vol. % having sutured, planar and concavo-convex contact, feldspars 1% to 2% by volume and lithic grains 1% to 2% by volume. Sandstone of the Lumshiwal Formation is marked as compositionally mature and texturally submature. The quartz arenite facies have total thickness of 15m. Quartz is dominantly monocrystalline with very few grains of polycrystalline quartz. The iron oxides and silica overgrowth act as major cementing material in the sandstone unit of the formation. Major accessory minerals identified include glauconite, muscovite, biotite and heavy mineral suite of zircon, tourmaline, monazite and rutile. Heavy minerals are present as inclusion in quartz grains. The carbonate beds consist of quartz, glauconite and bioclast as major grains with iron oxides and calcite as matrix. Grains are dominantly floating. Carbonate beds are interpreted as glauconitic siliciclastic wackestone-packstone with total thickness of ~4m. Ternary plots and bivarient logs suggest Craton Interior as tectono provenance for the sediments of the formation. Source rock composition for sandstone unit of the formation is interpreted as acidic igneous rocks. The paleoclimatic conditions under which sediments were eroded, transported and deposited are interpreted as humid conditions. Indian Craton, present in the east of the study area, is interpreted as source for the sandstone unit of the formation. The environment of deposition for Lumshiwal Formation is concluded as middle shelf and inner shelf on the basis of lithological characters. The presence of fractures, coarse calcite grains very less abundance of feldspars reveal deep burial diagenetic modification in the formation.