Geology Seminar Series: Shakeel Ahmad: Preliminary study on the sedimentologic properties of Paleocene-Eocene Patala Formation of the Hazara Sub-basin, Upper Indus Basin, Northern Pakistan

Wed., Mar. 31, 2021 4:00 p.m.

Location: https://uregina-ca.zoom.us/j/92337163072?pwd=b2xnMFpVYXRUQnlRYnZaWEF2WDlnUT09

Title: Preliminary study on the sedimentologic properties of Paleocene-Eocene Patala Formation of the Hazara Sub-basin, Upper Indus Baisn, Northern Pakistan

Speaker: Shakeel Ahmad, MSc student, Department of Geology, University of Regina

Abstract:

The late Paleocene-early Eocene Patala Formation is a lithologically heterogeneous unit that occurs in the upper Indus Basin of Northern Pakistan. During the Paleocene and Eocene epochs, the basin was a broad depositional site that belonged to the Neo-Tethys Ocean. Compressional tectonics related to the Indian-Eurasian collision fragmented the Indus Basin into discrete sub-basins that include salt range, Kohat, Potwar, Kala-Chitta range, and Hazara. The Patala Formation occurs in all of these sub-basins. However, due to differential paleobathymetric conditions, from coastal/backshore to deep shelf, different lithologic units represent the formation. Such lithologic units include coal, sandstone, shales, marls and limestone lithofacies. Most of the previous studies addressed the coal-bearing and associated sandstone units of the formation due to the coal’s potential as hydrocarbon source rocks. Sedimentologic and biostratigraphic attributes of the basinward shale and carbonate facies of the Patala Formation are relatively less understood, particularly in the Hazara Sub-basin. This study intends to explore these relatively deep shelf sediments of the Patala Formation in the Hazara Sub-basin. The formation conformably overlies middle Paleocene Lockhart Limestone and is conformably overlain by Eocene Margalla Hill Limestone. In the study area, the formation varies from 60m to 180m thick that can be divided in to three units: lower unit of shale-limestone interbeds, middle shale unit and upper unit of shale-limestone interbeds. Five outcrop sections were studied in the field, samples collected and studied petrographically. Six lithofacies (PF1 to PF6) were recognized and include: Organic-rich Shale (PF1): dark gray to black, medium to thickly bedded shale that forms the most abundant lithologic facies of the formation; Planktonic Foraminifera Mudstone (PF2): dark gray, thin to thickly bedded mudstone associated with PF1; Bioclastic Wackestone (PF3): light to dark gray limestone with different planktonic and benthic foraminifera species, thin-walled ostracodes and crinoids; Discocyclina-Ranikothalia wackestone (PF4): dark gray, medium to thickly bedded limestone with larger benthic foraminifera; Mixed Benthic Foraminifera Packstone (PF5): light to dark gray, medium to thickly bedded limestone with different types of benthic foraminifera tests; and Mollusk Rudstone (PF6): light to dark gray, thin to medium bedded, normally-grading limestone with gastropod and bivalve shells. PF6 has basal erosional surfaces and associated with PF1 and PF2. Recognized trace fossils include Planolites and Zoophycos. The six lithofacies can be arranged under two lithofacies associations (LA1 and LA2). LA1 consists of interbedded PF1 and PF2 with subordinate occurrence of PF6, and LA2 consists of PF3, PF4 and PF5 interbeds. LA1 represents distal middle to proximal outer ramp where fine-grained planktonic and organic rich PF1 and PF2 accumulated with rare storm deposits of PF6. LA2 is envisaged as mid ramp deposits of low to moderate energy setting. Absence of any intertidal and supratidal signatures and presence of the planktonic organisms, thin-walled ostracods, trace fossils and the overall dominance of the fine-grained texture suggest that deposition of the formation in the study area took place mainly in a quiet subtidal setting. Correlations with the shallower coal-bearing and sandstone lithofacies in the southern Salt Range Sub-basin (i.e., landward) are in progress. The accomplishment of this work is expected to document a depositional model for the Patala Formation along the depositional dip of the Neo-Tethys shelf relevant to the study area.