Abstract:
The microfacies analysis and diagenetic fabric of the Lockhart Limestone (Paleocene age) are studied along the Grand Trunk Road, near Nicholson Monument, Taxila, punjab in the western part of the Margala Hill Ranges. In this study, 80m thick stratigraphic section is measured and sampled with a total of 25 samples. Lithologically, the rock unit is composed predominantly of nodular limestone with marl/shale intercalations.
Four microfacies have been recognized based on field and petrographic studies and include: 1) Packstone Microfacies, 2) Wackestone Microfacies, 3) WackePackstone Microfacies and 4) Mud-Wackestone Microfacies. These microfacies contain further twelve sub-microfacies. Larger Benthic foraminifera and Dasycladacean green algae are the two major fossil contents present in the Lockhart Limestone. The foraminiferal assemblage includes; Genera Miscellanea, Lockhartia, Ranikothalia and Miliolids. The algal-foraminiferal assemblages and presence of family Miscellaneidae confirm that the deposition of Lockahrt limestone occurred in Shallow Benthic Zone (SBZ3-4) of late Paleocene age. The depositional texture and faunal association suggested that the microfacies represents deposition on an inner ramp lagoon carbonate shelf. The analysis further showed that the Lockhart Limestone was also subjected to various diagenetic changes, mainly showing the compaction, aragonite to calcite transformation, pressure dissolution (microstylolites), development of microspar, micritization, tectonically induced fracturing and calcite veins passing from marine diagenesis to meteoric diagenesis through burial diagenesis.
