Microfacies Analysis and Mechanical Properties of the Margalla Hill Limestone, Shah Alla Ditta Area, Islamabad

Abstract

A detailed geological investigation of Early Eocene Margalla Hill Limestone at Shah Alla Ditta area, Islamabad was carried out to describe its microfacies and engineering properties. The studied outcrop has total thickness of 60 meters from which sixteen samples were collected for petrographic analysis and four bulk samples to study their engineering properties. Four microfacies were identified i.e. bioclastic mudstone, bioclastic mud- wackestone, bioclastic wackestone and bioclastic wacke-packstone. A number of diagenetic overprints such as micritization, neomorphism, compaction (mechanical and chemical) and calcite filled fractures were recorded in the microfacies. These microfacies are interpreted to be deposited on inner ramp lagoon to middle ramp environment. Unconfined compression strength (UCS) was carried out and relation with micrite, bioclast and porosity also calculated. Linear relationship of UCS with micrite, bioclast and porosity are established through regression analysis, which showed that micrite have positive relation with higher regression coefficient values (R2=0.94) while bioclasts (R2=0.93) and porosity (R2=0.98) have negative trend with UCS. The physical properties showed that increase in micrite content caused increase in specific gravity and bulk density but consequently decrease in water absorption and porosity. On the other hand, bioclast content show negative relation with specific gravity and bulk density but positive relation with water absorption and porosity.