Sedimentology and Geochemistry of the Upper Jurassic to Lowermost Cretaceous carbonate succession at Wadi Hagil (Ras Al Khaimah, United Arab Emirates)

Abstract

Outcropping carbonates in Wadi Hagil, northern Emirate of Ras Al Khaimah, include the upper portion of the Jurassic Musandam Group and extend into the lower Cretaceous Thamama Group. These outcrops have a high potential for paleoenvironmental studies during key Mesozoic intervals such as the Jurassic–Cretaceous (J-K) transition as they offer a continuously marine sedimentological record, which contrasts time-equivalent carbonateevaporite sequences from the Emirate of Abu Dhabi. This study provides new field-scale paleoenvironmental data and a depositional model from an UAE's Upper Jurassic Musandam Formation shallow marine succession, to understand the temporal evolution of the local sedimentary system and the changes in the conditions of deposition from a paleoequatorial perspective. The methodology included facies analysis based on fieldwork, coupled sedimentological-petrographical analysis, x-ray fluorescence elemental analysis, and stable isotope analysis for correlation with time equivalent sections in other regions. The analyzed data allowed the recognition of 6 lithofacies across the section, and a change in the local depositional environments across the studied interval. These shifts are represented by a transition from shallow marine settings to outer ramp and hemipelagic environments. The transgression in the uppermost Jurassic was linked to a rise in the sea level that has been reported in sections regionally and globally, and it is here associated with a lithological change from platform carbonates to marlstones. The paleoenvironmental interpretation is supported by the elemental analysis of the succession, with high carbonate productivity and low siliciclastic input across the lower portion of the section and a decrease in the carbonate productivity in deeper facies. The marlstones in the top portion are interrupted by coarse flows linked to short duration regressive episodes that produced the failure of the carbonate ramp, within a global transgressive period. Carbon isotope stratigraphy allowed the correlation with a time equivalent section in Oman based on a negative excursion that has also been reported in other regions outside the Arabian Peninsula during the J-K transition, and calpionellid biostratigraphy. The position of the J-K boundary at Wadi Hagil is placed stratigraphically below the transgressive event and is based on the correlation of the carbon isotope curve and in line with existing biostratigraphy.

Date of Award	Aug 2021
Original language	American English