Precambrian mixed clastic-carbonate systems of Saudi Arabia: Integrated sedimentological, micropaleontological and geochemical characterization

The Precambrian sedimentary successions in the northwestern part of the Arabian plate are found in various isolated basins, associated with the rifting phases of Precambrian Najd fault system. While some preliminary work focusing on the low-resolution geochemistry and radiometric age dating has been performed in some basins, it is considered insufficient in explaining the depositional system of these sediments. This absence of comprehensive sedimentological control has resulted in previously formulated conclusions which fail to clarify the extent and depositional environment of these sediments leading to debate and confusion, hampering research progress in the region. In this context, we focused on the Dhaiqa Basin of NW Saudi Arabia due to its exceptional and continuous exposures and perform integrated high resolution micropaleontological, geochemical and isotope analysis to unravel the origin and evolution of these deposits. Our sedimentological analysis revealed that contrary to common belief, the Ediacaran sequence in this basin contains a mixed clastic-carbonate system rather than a continuous carbonate succession lying conformably on sandstone layers. The deposited sediments include basal conglomerates, covered by shallow water mixed clastic-carbonates and microbialites facies of limestones. Overlying these carbonates are thinly laminated sandstones which also suggest a shallow-water origin, predominately lacustrine, overlain again by the mixed clastic carbonate deposits. The mineralogical data extracted using X-Ray diffraction and X-Ray florescence techniques aided with Axioscan and QEMScan analysis, also reveals a proximity to the source of sediments. Recovered Ediacaran microfossils from cherty carbonates, sandy microbialites as well as from siliceous mudstones also signify a shallow water environment. Stable isotope results are also found to consistent with these observations with δ13C values hardly reaching -2‰ VPDB, not consistent with Ediacaran isotopic values of global seas extracted from neighboring country of Oman where values go as negative as -12‰. This stratal pattern explicates the Dhaiqa basin to be a potentially fault-controlled basin, originating at the flak of a normal fault developed during some stage of the left-lateral transcurrent Najd Fault system with no evidence of connection with the global seas so far. These acquired results will not only contribute to the correlation of these sediments across the Arabian plate but will also facilitate comparisons with similar sediments worldwide.