BENTHIC FORAMINIFERAL BIOSTRATIGRAPHY, MICROFACIES ANALYSIS AND DEPOSITIONAL ENVIRONMENT OF CHORGALI FORMATION YAADGAR SECTION, MUZAFFARABAD, PAKISTAN
Journal: Pakistan Journa l of Geology (PJG)
Author: Muhammad Shahid Khawaj , Muhammad Faisal , Qasim Ur Rehman , Tofeeq Ahmad , Salman Ahmad Khattak , Ahsaan Saeed , Muhammad Toseef Adnan , Irfan , Saif Ur Rehman , Iqtidar Ahmed , Muhammad Ishfaque
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Present study deals with microfacies analysis, interpretation of depositional environment and foraminiferal biostratigraphy of Early Eocene Chorgali Formation in Yadgar section, Muzaffarabad, Azad Jammu and Kashmir, Pakistan. Study area lies on apex of western limb of the Hazara-Kashmir Syntaxis, which is the part of North-West Himalayan Fold and Thrust Belt. The stratigraphic succession of the area is consisted of sedimentary sequences, ranging in age from Precambrian to Miocene excluding Ordovician to Cretaceous and Oligocene successions, those are marked by unconformity. Early Eocene Chorgali formation in this area is consisted of dark to reddish grey limestone, light grey dolomite, greenish grey shale intercalations, marl and argillaceous limestone. Nodulations is also present in few limestone beds. Formation was measured and described in the field. Thickness in this area is 52 meters. Detailed petrographic analysis of 15 thin sections was carried out. On the basis of fauna and lithology, four microfacies are identified, they are as followed:
1. Dolomitic Grainstone Microfacies,
2. Benthic Foraminiferal Packstone Microfacies,
3. Mixed Bioclastic Wackstone Microfacies,
4. Planktonic Mud-Wackstone Microfacies.
Allochemical constituents present in the formation include pelloids, intraclasts, extraclasts and bioclasts (Gastropods, Bivalves, Ostracods and brachiopods). Orthochemical material is mostly micrite. Spar is also present but in less amount. Foraminifera are the major fossil contents present in the Chorgali Formation and have good age diagnostic fossils. Faunal assemblages include following Genera: Assilina, Nummulites, Lockhartia, Miscellanea, Discocyclina, Operculina, Brachiopoda and Mollusks. Early Eocene age is assigned to Chorgali formation on the basis of these Larger Benthic Foraminifera i.e. Assilina, Nummulites and Lockhartia. Planktonic foraminifera are also present including Milliolids, Nodosaria and Echinoderms. But these are not studied in detail as they are not index fossil. Depositional environment is interpreted on the basis of microfacies and foraminiferal assemblages. Most part of the formation is deposited in inner shelf, while some part is deposited in middle to outer shelf. Lagoonal to tidal flat deposition is also found. Overall the formation represents the deposition in inner shelf, more specifically middle shelf to inner shelf environment.