Sedimentological and Petrographical Characterization of the Cambrian Abbottabad Formation in Kamsar Section, Muzaffarabad Area: Implications for Proto-Tethys Ocean Evolution

Abstract

The current sedimentological and petrographical research of the Abbottabad Formation has been carried out in order to understand the formation and evolution of the Proto-Tethys Ocean during the Cambrian on the northern margin of the Indian Plate. The Muzaffarabad region is located east of the Upper Indus Basin and the southern part of the Hazara Kashmir Syntaxis. The geological history of the region varies from the Precambrian to the recent period. The Cambrian Abbottabad Formation is well exposed along the Hazara Kashmir Syntaxis at the core of the 500-m-thick Muzaffarabad anticline. The Abbottabad Formation is an unconformity-bounded allo-stratigraphic unit. It has an unconformable lower contact with the Late Precambrian Dogra Formation and an unconformable upper contact with the Paleocene Hangu Formation. The Abbottabad Formation has been divided into four lithofacies, from bottom to top, namely, thinly interbedded dolomite and shale, cherty-stromatolitic dolomite, oxidized limonitic-brecciated zone, and quartzite, with significant lithological changes. Petrographic studies revealed four types of dolomites: fine crystalline dolomite (Dol. I), dolomitic cryptocrystalline chert (Dol. II), algal mat-stromatolitic dolomite (Dol. III), and intraclastic-dolo-grain stone (Dol. IV). The mineral composition of dolostone was analyzed using X-ray diffraction (XRD) and found to be consistent with previous petrographic studies. The dolomite mineral content decreased from base to top, while chert increased towards the top. Elemental weight percentages through energy dispersive X-ray (EDX) analysis show different elements constitute the minerals found in the dolostone, as confirmed by petrographic and XRD analysis. Using outcrop data, facies information, and geochemical data, a modified depositional model of the Abbottabad Formation was developed. During the Early Cambrian period, the formation was deposited in a shallow subtidal to supratidal setting of the Proto-Tethys Ocean. The top of this deposit marks the Cambrian–Paleocene boundary. Because of the progressively coarsening outcrop sequences, this formation seems to be at the very top of the Proto-Tethys Ocean’s shallow marine system.

Sedimentological, Diagenetic, and Sequence Stratigraphic Controls on the Shallow to Marginal Marine Carbonates of the Middle Jurassic Samana Suk Formation, North Pakistan

“…During this period, this region was a part of the Indian Plate's shelf edge, where thick depositions of platform sediments accumulated [33][34][35]. The thick shallow water carbonate platform deposits of the Samana Suk Formation, comprising oolitic, peloidal, fossiliferous, and micritic facies, were formed throughout the Toarcian to Callovian periods along the shelf margin of Neo-Tethys [34,[36][37][38][39]. This formation contains most of the examined dolomites, whereas the upper and lower formations are largely undolomitized.…”

Sedimentological Controls on the Reservoir Characteristics of the Mid-Triassic Tredian Formation in the Salt and Trans-Indus Surghar Ranges, Pakistan: Integration of Outcrop, Petrographic, and SEM Analyses

“…The Indo-Asia collision created the ~2500-kilometer-long seismically active Himalayan Mountain belt (55 Ma) [22]. The main frontal thrust (MFT) marks the southern boundary of this collisional zone and is represented by the Salt and Trans-Indus Ranges [23][24][25] (Figure 1). In comparison with the eastern and central Himalayas, MFT is a more than 100 km wide zone in the western Himalayas in Pakistan with a low degree of cross-sectional taper, resulting in the opening of wide basins, i.e., the Kohat and Potwar Basins [26,27].…”