Microfacies-Based Depositional Model for the Maastrichtian Upper Member of Thaqab Formation in Northern Oman: A Potential Outcrop Analog for Deep-Marine Slope Succession

Abstract

The Upper Member of the Upper Cretaceous Thaqab Formation, prominently exposed in Jabal Ruwaydah, Northern Oman, serves as a valuable analogue for subsurface hydrocarbon reservoirs in the Sohar Basin. This study conducts a comprehensive investigation into the lithofacies and microfacies of the Upper Member, integrating field-based sedimentological observations with laboratory-based petrographic analyses to elucidate its geological characteristics. The analysis identifies two distinct lithofacies: grain-dominated and mud-dominated facies. Microfacies analysis further delineates these lithofacies into five types, including polymictic breccia, bioclastic intraclastic grainstone interspersed with rudstone deposits containing rudist debris, quartzose bioclastic packstone transitioning to grainstone, and predominantly calcareous mudstone. Our study presents a novel depositional scenario for the Upper Member of the Thaqab Formation, based on unique lithofacies and microfacies characteristics, platform morphology, and the presence of biota. Our findings suggest a predominantly mud-dominated slope carbonate setting for this unit, with distinct grain-dominated microfacies indicating potential lateral continuity into a deep marine depositional environment to the east, specifically the Sohar Basin. These findings are significant as they provide insights into hydrocarbon-bearing deep marine slope strata within the subsurface Cretaceous succession of the Arabian Peninsula. Additionally, our study extends the application of these findings as an analog for similar facies in the Sohar Basin, thereby, contributing to the global understanding of comparable deep marine systems.