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Sedimentology, biostratigraphy and depositional setting of the Early Eocene Chorgali Formation, Potwar Basin, northern Pakistan.

Wed., Oct. 7, 2020 4:00 p.m. - Wed., Oct. 7, 2020 5:00 p.m.

Speaker: Mr. Muhammad Khan, Masters Student in the Dept. of Geology, University of Regina


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Abstract: The Chorgali Formation is a carbonate-dominated Early Eocene stratigraphic unit that occurs in several basins of northern Pakistan, such as, Potwar, Hazara, and Kohat. The formation is part of a thick, mainly carbonate succession deposited in the Neo-Tethys Sea shelf. The formation occupies an important position of pre-collision Cenozoic tectono-stratigraphic evolution of the then southern Indo-Pakistani plate shelf. The formation conformably overlies shallow marine, Early Eocene Sakesar / Margala Hills Limestone and is overlain by either mixed shallow marine-continental strata of Middle Eocene Kuldana Formation, with apparently conformable contact, or unconformably continentally-deposited Miocene molasses (the Siwaliks) related to the uplifting of the Himalayan Mountains. The sedimentologic and biostratigraphic properties of the Chorgali Formation and their significance in relation to the closure of the Tethys Ocean are poorly constrained. This study intends to explore the spatial and temporal evolution of the Chorgali Formation of the Potwar Basin and analyze it within the regional tectono-eustatic context. Although extensively tectonically dislocated, the formation is well exposed in the study area. The project is in its early stage, and only five sections are currently studied in the field and in the lab, as well. The collection of more data is in progress. The preliminary results of the few sections studied so far are summarized below. The formation has an average thickness of 30 m in the study area. The field observation and petrographic studies led to the identification of six lithofacies (LF1-LF6). These lithofacies units include: Algal-miliolid Mudstone (LF1), Coralline Red Algae (LF2), Assilina Packstone (LF3), Floatstone to rudstone (LF4), Planktonic-bearing Mudstone (MF5), and shale ((Lf6). The sedimentary features, textures, and fossil associations of these lithofacies suggest that deposition took place in a homoclinal carbonate ramp setting. It is envisaged that the formation accumulated in low to moderate energy normal marine realm where LF1, LF2, and LF3 represent inner ramp, and LF4, LF5, and LF6 represent mid ramp accumulations. The absence of intertidal and supratidal signatures suggests a subtidal depositional environment. Larger benthic foraminifera that are useful for age determination include: Nummulites globulus, N. atacicus, N. mammillatus, Assilina spinose, A. subspinosa and Lockartia conditi. By considering the age ranges of these fossils along with its stratigraphic position, the Chorgali Formation can be considered as latest Ypersian (latest early Eocene) to possibly early Lutetian (earliest middle Eocene) in age.



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Department of Geology


Topic: Ian Coulson's Personal Meeting Room

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