Sedimentology, Geochemistry, and Sequence Stratigraphy of the Kharaib and Shuaiba Formations in Wadi Rahabah, Ras Al Khaimah, UAE

Abstract

This study provides sedimentological, geochemical, and sequence stratigraphic analyses of a Lower Cretaceous sedimentary section in Wadi Rahabah, Ras Al-Khaimah. Outcrop analogues for the Kharaib and Shuaiba formations in Wadi Rahabah assist in studying reservoir continuity and distribution in Abu Dhabi subsurface as well as improving and revising sequence stratigraphic and facies models. New data were acquired from geochemical methods (x-ray fluorescence, stable carbon and oxygen isotope analysis) to understand the formation, evolution, and chronostratigraphy of reservoir facies in the context of fundamental Earth system science. The outcrops in Wadi Rahabah expose a carbonate platform setting, which was situated in the northern side of the Bab Basin, opposite of the well-studied southern and southwestern margin of the Bab Basin, and close to the Early Cretaceous shelf margin. According to the obtained results, the depositional environment ranges from brackish lagoon to middle ramp. The carbon isotope values fall in the Barremian-Aptian range and show a strong correlation with the Cismon core (northern Italy), a well-studied global reference section. Based on global and regional correlations, the studied section extends from the uppermost Lekhwair to the Lower Shuaiba formations (Lower Barremian – Lower Aptian). The Lekhwair-Kharaib boundary is a sequence boundary that is evident from a subaerial exposure surface and karstification. The Barremian-Aptian boundary is another sequence boundary that is evident from the presence of rootlets and shrinkage pores. The occurrence of characean gyrogonites suggests freshwater influx into lagoonal settings causing a negative CIE. The obtained data also reveal that the Hawar lithostratigraphical unit is not developed in Wadi Rahabah and its time-equivalent is a very thin (around 1.7 m), high energy grainstone unit. The negative CIE is weak due to diagenetic overprint and possibly reworking in a high energy environment. The top Hawar-equivalent is not a sequence boundary as there is no evidence of subaerial exposure and no abrupt change in depositional facies. The Kharaib facies range from skeletal wackestone to Bacinella-dominated orbitolinid floatstone with Salpingoporella. dinarica. The de-dolomite marker is not correlative to Abu Dhabi, where in Abu Dhabi the dolomite marker is older. The abundancy of discoidal orbitolinids and Bacinella in slightly argillaceous limestone in the Early Aptian indicates deposition in relatively high trophic conditions. This marks the transition from arid-warm (Barremian) to humid-warm (Early Aptian) climate.

Date of Award	May 2021
Original language	American English