The Larger Foraminifera made a major contribution to Paleocene and Eocene biota. The microfacies and diagenetic setting of the Paleocene Lockhart Formation were analyzed in Shah Alla Ditta area, Islamabad. The Lockhart Formation is highly fossiliferous, comprising of thin nodular limestone with interbedded shale/ marl. The lower contact is unconformable with Jurassic Samansuk formation while the upper contact is conformable with Margalla Hill Limestone. Rock samples were collected from the field and thin sections were prepared and analyzed under the microscope and on the basis of detailed petrographic study three types of microfacies were identified and interpreted based on Dunham's textural classification, allochem type, fossil content and sedimentary structures. The microfacies include: LH-MF 1: Foraminiferal Wackestone/ Biomicrite Microfacies, LH-MF 2: Algal Foraminiferal Wackestone Microfacies, LH-MF 3: Mixed Bioclastic Mudstone Microfacies. A number of larger benthic foraminifera, and the lack of Planktonic foraminifera in the Lockhart Limestone, indicate 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 confirm the age of Lockhart Limestone as Paleocene. The main diagenetic fabric recognized in the limestone reveals mechanical and chemical compaction, deep burial water pressure, pressure solution and tectonics-related fracturing. The nodularity in the limestone is credited to pressure solution.
A research work was embarked in the area in order to understand the sedimentary geology, remote sensing, geomorphology and petrology of the district Sudhunhoti and Poonch, Azad Jammu and Kashmir, Pakistan. For this purpose the Khirik, Muttail Maira, Thandi Kassi, Kothian, Hill, Maidan, Rhera, Dar, Sairhan, Afsar Market, Gorah, Nakkar bazaar, Gui Nala, Bandia, Mang, Jassa Pir and Thorar areas were mapped and interpreted on Digital Elevtion Model (DEM) in the sub-Himalayas of Pakistan. The area has been mutilated by folding and faulting governed by orogenic forces. The clastic rocks exposed in the area are sandstone, siltstone, claystone and conglomerates. The sedimentary structures include planner bedding, ripple marks and pebble imbrications. The rip ups of siltstone and clay occur at the base of sandstone. The sandstone of Nagri Formation is well exposed in the area. The sandstone contains clasts of volcanics, quartzites, schist and chert. The sandstone of Dhok Pathan Formation is medium to coarse grained. It contains clasts of gneiss, schists, quartzites, granite, carbonate and marble. The sandstone is comprised of mineral quartz (23% to 45%), feldspar (3% to 13%) and the rock fragments of igneous, metamorphic and sedimentary rocks. The accessory minerals in the Nagri Formation sandstone are biotite (1% to 3%), muscovite (up to 2%), tourmaline (few traces) and zircon (1%). The cementing material in the rock is calcite (6% to 18%) and silica (2% to 3%). The modal mineralogical data of the sandstone shows that the sandstone is lithic arenite and lithic graywacke. The modal data reveal that the detritus was derived from the rising Himalayas in north of the area. The sedimentary structure and the conglomeration is the prima facie for the fluviatile origin of rocks.
In this study integrated approaches combining field study, petrographic analysis and petrophysical analysis has been used to infer the depositional and diagenetic effects on reservoir characteristics. The exposed stratigraphic section of Chorgali Formation at its type locality was logged, sampled and petrophysical analysis of well log data from Fimkassar-02 were carried out. Three microfacies recognized from petrographic studies are: Bioclastic Wackestone-Packstone Microfacies, Mixed Bioclastuc Wackestone-Packstone Microfacies and Larger Foraminiferal Wackestone-Packstone Microfacies. The depositional texture and faunal association suggested that the microfacies represents deposition in a low energy, distally steepened ramp type of setting. Due to the deposition in low energy environment the ratio of lime mud is more than bioclasts as a result the primary pore spaces in the formation are negligible. The analysis further showed that the carbonates of Chorgali Formation was also subjected to various diagenetic changes, mainly showing the compaction, stylolitization, aragonite to calcite transformation (neomorphism), tectonically induced fracturing and calcite veins passing from marine diagenesis to meteoric diagenesis through burial diagenesis. Fracturing due to later tectonic deformation have had a major influence on porosity generation and in some cases fracturing and stylolites together have had an important effect on permeability values. The petrophysical analysis shows that the Eocene Chorgali Formation is very good reservoir with average hydrocarbon saturation of 80 %.
The sedimentological study of the Lower Eocene Sakesar Limestone in Nammal gorge section, Western Salt Range, was carried out to elaborate the microfacies, diagenetic settings and reservoir potential. The Sakesar Limestone is widely distributed across the Salt and Surghar ranges. It mainly consists of massive and nodular fractured limestone with subordinate marls and chert in the upper part. The Eocene succession is only comprised of conformable Sakesar Limestone and Nammal Formation in Nammal gorge. The detailed study was conducted after measuring the vertical thickness of 18m section and the 6 six samples were obtained symmetrically. To give the detailed insight of sedimentological characteristics the well cuttings of Sakesar Limestone from well Pindori-01, were studied along with the un-stained thin sections to investigate the microfacies, diagenesis and reservoir potential. The well cuttings study revealed that the Sakesar Limestone is off white to dull grey calcite, moderately hard with cryptocrystalline to microcrystalline silica along with pyrite. Detailed field observations and laboratory investigations revealed that it contains Bioclastic wackstone microfacies. Neomorphism is present in various bioclasts. The presence of fractures filled with waxy leftover hydrocarbons makes it potential target for hydrocarbons. Petrophysical analysis shows an average hydrocarbon saturation of 85.5 percent in well Pindor-01 which confirms the huge reservoir potential of Sakesar Formation. Microfacies analysis indicates high lime mud and low faunal diversity which led towards the conclusion that the Eocene Sakesar Limestone was mainly deposited in semi restricted, low energy shallow marine shelf environment.
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