COMPARATIVE ANALYSIS OF SEDIMENTOLOGICAL CHARACTERISTICS OF THE LOCKHART LIMESTONE IN UPPER INDUS BASIN AND HAZARA BASIN, PAKISTAN

Abstract

The Late Paleocene (Thanetian) Lockhart Limestone, exposed in the Nammal Gorge, Salt Range and Harnoi section Abbottabad. It is composed of light to dark grey and thin to medium bedded limestone. In total 32 samples were taken from the Harnoi and Nammal Gorge section i-e 17 samples from Harnoi section and 15 samples from the Nammal Gorge. The samples were taken for the petroghraphy analysis.The Formation is rich in larger benthic foraminifera, four microfacies were established in the measured sections i.e. MLLN-1 Lockhartia Assilina Packstone Microfacies and MLLN-2 Foraminiferal Wackstone Microfacies representing microfacies of the Nammal Gorge and MLLH-1 Bioclastic Mud-Wackstone Microfacies and MLLH-2 Planktonic Mudstone Microfacies representing the microfacies of the Harnoi section. The depositional environment of both section microfacies were also different.The MLLN-1 Lockhartia Assilina Packstone Microfacies representing the inner ramp environmment, MLLN-2 Foraminiferal Wackstone Microfacies indicates the middle ramp environment of the Nammal Gorge and microfacies of the Harnoi section MLLH-1 Bioclastic Mud-Wackstone Microfacies represents the outer ramp environment and MLLH-2 Planktonic Mudstone microfacies representing open marine settings. The analysis further showed that various diagenetic modifications observed in the Lockhart Limestone include micritization, dissolution, compaction (chemical and mechanical), fractures and calcite veins. The micritization, dissolution and unfilled fractures in the studied rock unit enhance the porosity where as neomorphism and mechanical compaction lead to porosity occlusion and thus impacts on the reservoir potential.