High-Resolution Carbon Isotopic Records from the Ediacaran Sequence in Saudi Arabia: Implications to Shuram Anomaly and Petroleum Prospectivity

Abstract The southern regions of the Arabian plate in Oman feature remarkable exposures of Ediacaran strata, which hold significance not only for their association with subsurface hydrocarbon reserves but also for hosting evidence of the world's largest negative marine Carbon excursion "The Shuram-Wanoka Anomaly". In contrast, analogous Ediacaran sequences present in the northern sections of the plate within the Kingdom of Saudi Arabia, have yet to reveal their hydrocarbon potential or indication of the Shuram anomaly and this disparity has fueled geological inquires. Our study focused on two well-exposed Ediacaran successions, the "Dhaiqa Basin" being the most northern Ediacaran basin in the Kingdom, and the "Antaq Basin" being the southernmost basin. We have conducted a comprehensive multiproxy characterization including sedimentological, micropaleontological, mineralogical and isotopic measurements. The findings unveiled some distinct depositional characteristics and diagenetic histories in these sediments despite their similar age. In the kingdom of Saudi Arabia, the northern most Ediacaran basin, the Dhaiqa basin exhibit carbonate facies with some microfossils suggesting a shallow-water environment, whereas the southernmost basin in the Kingdom, the Antaq basin is predominantly siliciclastic indicating a terrestrial origin. Stable isotopic results of Carbon and Oxygen further advocate on the isolated nature of these deposits with values diverging significantly from the global sea values as well as values recovered from Oman. The dissimilarity is attributed to the presence of the Najd Fault system in northern portions of the Arabian plate. Although the deposition in Oman is identified as a shallow open marine environment, the sediments in Saudi Arabia indicate deposition mainly in isolated basins influenced by the movements associated with the Najd Fault system. Although certain carbonate lithofacies in northern Dhaiqa Basin contain carbonaceous organic matter, resulting in a fetid odor in freshly broken rock samples, the Total Organic Carbon (TOC) results indicate an overall organic content ranging below 0.2%, classified as type IV. However, akin to their Omani counterparts, the proximity of these sediments to subsurface evaporites in the southern parts of the kingdom suggest a potential prospect for future hydrocarbon exploration.