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Abstract

A detailed study of facies, microfacies, diagenesis and environment of deposition of Lumshiwal Formation of Early Cretaceous age from Thub Top near Ayubia has been carried out for the first time. The objective was to study the facies, microfacies, provenance, environment of deposition and diagenesis of the formation in the northwestern part of the oil and gas producinq Indus Basin. The formation is producing gas at Nandpur and Panjpir located near Sargodha high in the northern part of Punjab platform.This section of Lumshiwal Formation is divisible into 5 facies and 20 microfacies. Compositionally all the sandstone horizons are mature. Texturally only one microfacies is immature and one microfacies is super mature, rest of the microfacies are mature to sub-mature. The sandstone is predominantly fine to very fine grained, only one microfacies is medium grained, and two microfacies are coarse grained.Quartz and glauconite are the common cements while iron oxides, clay and flint occurs as subordinate cements.Accessory to trace amounts of tourmaline, zircon, epidote and sphene which may occurs either as discrete grains or as inclusions within quartz grains suggest an ultimate derivation from sialic metamorphic-igneous basement with minor contribution from basic sources. The source granitoids were mainly S-type. However, overall mineralogy and texture strongly suggest recycling.The Lumshiwal Formation was deposited in low energy conditions in the subtidal zone. The formation of glauconite itself suggests slow rates of sedimentation and mildly reducing conditions. Diagenetic history indicates the formation of glauconite followed by flint and kaolinite. This was followed by ferroan calcite and dolomite at a later stage. Suturing of quartz grains occurred during deep burial. Fracturing of quartz grains occurred during tectonic deformation in a brittle regime. Microcrystalline quartz developed along fracture cleavage. The last stage involved the formation of ferroan dolomite during final uplift with parts converting into dedolomite.