Microfacies analysis and depositional environments of the Upper Cretaceous Fort Munro Formation in the Rakhi Nala Sectio
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ORIGINAL ARTICLE
Microfacies analysis and depositional environments of the Upper Cretaceous Fort Munro Formation in the Rakhi Nala Section, Sulaiman range, Pakistan Muhammad Rizwan1 · Muhammad Hanif1 · Nowrad Ali1,2 · Maqsood Ur Rehman1,3 Accepted: 12 September 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract The Fort Munro Formation is 200-m-thick mixed carbonate–siliciclastic succession of Late Cretaceous (Campanian) age exposed at the Rakhi Nala Section, Sulaiman Range, Lower Indus Basin, Pakistan. The Fort Munro Formation is representing thin- to thick-bedded limestone with interbedded marls, shale and sandstone. Detailed microfacies analysis revealed the recognition of 15 microfacies types (11 carbonate and 4 sandstone). These facies were deposited on both inner and middle ramp platform. The inner ramp sediments are more widespread than the corresponding middle ramp including open-marine, skeletal shoals, semi-restricted, carbonate sand shoals and banks and lagoon depositional environments. The uppermost part of the Fort Munro Formation has received sufficient amount of siliciclasts, thereby producing a sandstone texture. These siliciclasts indicate the tectonic uplift, which thereby increases the source area rejuvenation. Therefore, a mixed carbonate–siliciclastic, moderately storm-dominated homoclinal ramp depositional environment is suggested for the Fort Munro Formation. Keywords Microfacies · Depositional environments · Carbonate ramp · Fort Munro formation · Sulaiman range · Pakistan
Introduction The Upper Cretaceous Fort Munro Formation is exposed at the Rakhi Nala Section, Lower Indus Basin (Sulaiman range), Pakistan (Fig. 1). The Rakhi Nala section is located about 60 km West of Dera Ghazi Khan City of the Punjab District along the Sakhi Sarwar–Quetta–Fort Munro Road (Highway N70). The term “Fort Munro Limestone Member” of Williams (1959) was elevated to the status of a formation by Shah (1977, 2009) because of its distinct lithological character and wide geographical distribution. The western flank of the Fort Munro anticline, along the Fort Munro–Dera Ghazi Khan Road (Lat. 2 9° 57′ 14″ N: Long. * Muhammad Rizwan [email protected] 1
National Centre of Excellence in Geology, University of Peshawar, Peshawar, Pakistan
2
Department of Geology, University of Peshawar, Peshawar, Pakistan
3
Hubei Key Laboratory of Marine Geological Resources, China University of Geosciences, Wuhan 430074, China
70 10′ 30″ E) is designated as the type section by Williams (1959). Most of the previous work on Fort Munro Formation is related to biostratigraphy. Eames (1952) and Nagappa (1959) assigned Campanian to Maastrichtian age to the formation based on larger foraminifera, while Williams (1959) and Hunting Survey Corporation (1961) assigned a Maastrichtian age to the formation on the basis of larger foraminifera, such as Orbitoides spp. Marks (1962) assigned Early to Middle Campanian age to the formation on the basis of larger benthic foraminifera (LBF), such as Orbito
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