Geology Seminar Series - Muhammad Khan

Wed., Mar. 10, 2021 4:00 p.m. - Wed., Mar. 10, 2021 5:00 p.m.

Location: https://uregina-ca.zoom.us/j/6741541667

Title: Lithofacies attributes, biostratigraphic dating and interpretation of depositional setting of the Chorgali Formation, Potwar and Hazara Basins, Northern Pakistan

Speaker: Muhammad T. Khan, MSc student, Department of Geology, University of Regina

Abstract:

The Chorgali Formation is a hydrocarbon-producing rock that occurs in the Kala Chitta, Hazara, Kohat, and Potwar basins of northern Pakistan. The formation is part of a very thick carbonate succession deposited in the Neo-Tethys Sea shelf. It conformably overlies the early Eocene Sakesar Formation and Margala Hills Limestone. This research project addresses the Chorgali Formation of the Potwar and Hazara basins. In the southern part of the Potwar Basin, the upper contact of the formation is marked by an unconformable contact followed by continental Miocene strata, known as Siwaliks of the Himalayan molass deposits. In the northern part of the Potwar Basin and the Hazara Basin, the upper contact of the Chorgali Formation appears conformable with the with mixed clastic-carbonate strata of the middle Eocene Kuldana Formation. This study intends to explore the spatial and temporal evolution of the Chorgali Formation of the Hazara and Potwar Basin and analyze it within the regional tectono-eustatic context. The Chorgali Formation is well exposed in the study area where 8 sections that offer an average thickness of 30 m are studied.

The field observation and petrographic analysis recognized 9 lithofacies units (LF1-LF9) for the Chorgali Formation. These lithofacies include: Silty Mudstone (LF1), Dolomitic Mudstone (LF2), Algal-miliolid Mudstone (LF3), Coralline algae Mudstone (LF4), Assilina-Nummulites Wacke-Packstone (LF5), Mixed benthic-planktonic froraminfera wackestone (LF6), benthic foraminfera rudstone (LF7), shale lithofacies ((LF8), and Planktonic Mudstone (LF9). The sedimentary features and fossil associations of the formation suggest that deposition of the formation took place in a homoclinal carbonate ramp characterized by low to moderate energy hydrodynamic conditions. The LF1 to LF6 represent inner ramp whereas LF7 to LF9 represent mid ramp accumulations.

The Chorgali Formation contains a number of larger benthic foraminifera that are deemed to be useful for age determination. Such index fossils include Nummulites globulus, N. atacicus, N. Mammillatus, Assilina granulosa, A. laminose, A. spinose, and Lockartia conditi. They indicate an age range of late Paleocene to middle Eocene. By considering the age ranges of these index fossils and formation’s stratigraphic position (i.e., between early Ypresian Sakaser/Margala Hills formations and Lutetian Kuldana Formation), the Chorgali Formation can be regarded as early Eocene (late Ypresian, ~ 49 Ma) to possibly the lowest part of the middle Eocene (early Lutetian, ~ 46 Ma) in age.

The stratigraphic position and age of the Chorgali Formation indicate that it evolved in a time in which the Neo-Tethys Sea was getting more restricted as the Indo-Pakistan plate moved farther north and got closer to collide with the Euroasian plate. The collision event was diachronous (~ 52 Ma to 41 Ma, from east to west). Thus, deposition of the Chorgali Formation took place at stage of initial collision, basin closure and withdrawal of the marine conditions. Sedimentologic properties that potentially indicate signatures of basin closure are present in the upper part of the formation. This data collection and interpretation are in their infant stage and will be discussed in the presentation.