Microfacies and Diagenetic Analysis of Lockhart Limestone, Shah Alla Ditta Area, Islamabad, Pakistan (T-1408) (MFN 5641)

Abstract

Paleocene and Eocene is very important and provide a major contribution of the Larger Foraminifera. The microfacies and diagenetic setting of Paleocene Lockhart Formation were analyzed in Shah Alla ditta area, Islamabad. The Lockhart Formation is highly fossilerous, comprising of thin nodular limestone with interbeded shale/marl. The Lower contact is unconformable with Jurrasic Samansuk while the upper contact is conformable with Margalla hill Limestone. The rock samples were collected from field and then thin section were prepared, measured thin sections were analyzed under microscope and on the basis of detailed petrographic study three type of microfacies were identified and interpreted based on Dunham’s textural classification, allochem type, and fossil content and sedimentary structures. The microfacies include, LH-MF 1: Foraminiferal Wackstone/Biomicrite, Microfacies LH-MF 2: Algal Foraminiferal Wackstone Microfacies, LH-MF 3: Mixed Bioclastic Mudstone Microfacies. A number of larger benthic foraminifera and lack of Planktonic foraminifera in the Lockhart Limestone indicates shallow to deep water of restricted, inner to middle shelf environment of deposition. Larger foraminifera and dasycladacena algae are the two major fossil contents present in the Lockhart Formation. Larger foraminiferal species like Lockhartia hameii and Lockhartia conditi present in the formation confirms the age of Lockhart Limestone as Paleocene. The main digenetic fabric recognized in the Limestone reveals mechanical and chemical compaction, deep burial water pressure, pressure dissolution and tectonics related fracturing. The nodularity in the Limestone is credited to pressure dissolution.