Geology Seminar Series - Shakeel Ahmad (University of Regina) - Sedimentology and biostratigraphy of deep-shelf deposits of Paleocene-Eocene Patala Formation of the Hazara Sub-basin, Upper Indus Basin, Northern Pakistan

Title: Sedimentology and biostratigraphy of deep-shelf deposits of Paleocene-Eocene Patala Formation of the Hazara Sub-basin, Upper Indus Basin, Northern Pakistan

The Upper Indus Basin belongs to the eastern sector of the Neo-Tethys Ocean and it is subdivided in to discrete sub-basins, such as, Hazara, Potwar and Kohat sub basins. These sub-basins were sites of carbonate deposition with subordinate clastic influx during most of the Palecene and Eocene epochs. This study addresses the Patala Formation which straddles across the Paleocene-Eocene boundary. The formation is conformably underlain by Paleocene carbonates of the Lockhart Formation and conformably overlain by Eocene carbonates of the Margala Hill Limestone and Nammal formations. The Patala Formation was deposited in a range of environments, from subaerial coastal region with coal and sandstone deposits to deep shelf fine-grained siliciclastic and carbonate sediments. Most of the previous work dealt with the coal-bearing sections and less to the deep shelf deposits, particularly in the Hazara Sub-basin. The objective of this study is to examine the sedimentologic and biostratigraphic properties of the Patala Formation of the Hazara Sub-basin. In the study area, the Patala Formation can be stratigraphically divided into three units: lower and upper units of interbedded limestone and shale lithologies and middle unit which consists of organic-rich black shales. The field and petrographic studies of the formation recognize six lithofacies: Organic rich shale (Pf1), Planktonic-bearing mudstone (Pf2), Bioclastic wackestone (Pf3), Discocyclina-Ranikothalia wackestone (Pf4), mixed benthic foraminifera packstone (Pf5), and Mollusk-rich Rudstone (Pf6). These lithofacies can be grouped in to two lithofacies associations: LA1 consists of Pf1, Pf2 and Pf6 and represent distal middle to proximal outer ramp. Pf6 represents storm deposits within the deep shelf setting. LA2 consists of Pf3, Pf4 and Pf5; it is interpreted as low to moderate energy mid ramp accumulations. The larger benthic foraminifera in the formation consist of several important index fossils that are useful for age determination. The recognized age-diagnostic species include Lockhartia haimei, Miscellanea miscella, M. juliettae, Ranikothalia sindensis, R. sahni, and Nummulites mammillatus. These species indicate SBZ3/Early Thanetian of the late Paleocene to SBZ5/lower Ilredian stage 1 of the early Eocene Epochs. The Patala Formation of the study area (Hazara sub-basin) does not contain potential reservoirs. In the adjacent Potwar Sub-basin, the formation contains coal and organic-rich shales that constitute mature source rocks. The organic-rich black shales of the formation in the Hazara sub-basin are also deemed to be potential source rock that could charge the carbonate reservoirs of the Lockhart, Margala Hill and Nammal formations.