Dolomitization and paleoenvironment of deposition of the Lower and Middle Rus Formation (Early Eocene, Dammam Dome, Eastern Saudi Arabia)

Dammam Dome Formation (Eastern Saudi Arabia) consists of carbonate rocks ranging in age from Paleocene to Eocene. The Rus Formation (Early Eocene) comprises almost 56 m of mixed carbonate-evaporite succession and is exposed in the Dammam Dome area. The present study integrates detailed field, outcrop spectral gamma-ray logging, petrographic microscope, X-ray diffraction (XRD), scanning electron microscope (SEM), and advanced geochemical studies to decipher the facies of Rus Formation, the boundary between its Lower and Middle parts, and its possible reservoir potential. Heterogeneity is present from the megascopic to microscopic scale in both the Lower and Middle Rus Formation. This heterogeneity in the formation in terms of facies distribution patterns mainly reflects both dynamic and static controls on it. The Rus Formation is exposed in the Dammam Dome area, this allows us the opportunity to map and build a framework in terms of lithology, elemental chemistry, mineralogy, and spectral gamma-ray response, to check the facies variation and heterogeneity. The shallow burial of the Rus Formation and post-deposition changes made the carbonate succession highly dolomitized. The dolomitization in the Lower and Middle Rus is dissimilar and should have been formed by various diagenetic fluids. The geochemical elemental signatures of Ca, Mg, Mn, Ti, P, Fe, Sr, Ba, S, Y, and Zr show a peak at the boundary of Middle to Lower Rus. The Spectral Gamma Ray [SGR (U, Th, and K)] and illustrates eight different flooding surfaces. Macro-vuggs to micropores exist in relatively tight considered Rus Formation. The Rus Formation is characterized by a high percentage of dolomitic limestone, dolomitized marl, shale, and dolomite intercalations and calcarenite. There is a robust distinction in stratigraphy, lithology, sedimentary structures, petrography, mineralogy, elemental composition between the Lower and Middle Rus. The Rus Formation is characterized by the high dominance of dolomite-dominated structures in the lagoonal to sabkha environment for this mixed carbonate-evaporitic unit. The six lithofacies were deposited in a lagoonal, shoal to a tidal flat depositional environment with the minor clastic influx. Finally, the study has also pointed to understand the cyclicity and paleoenvironmental conditions that can aid in equivalent stratigraphic sections in the region.