Original Mineralogy and Recognition of Upper Boundary of the Sarvak Formation Based on Geochemistry and Isotope Studies

Carbonate sequence of upper cretaceous (Cenomanian) of Sarvak Formation is a part of Bangestan Group with the thickness of 760 m in Ahvaz oil field (well no. 63). This formation is overlain by the Kazhdumi Formation and is uncomfortably underlain by the Ilam Formation. In this study major and minor elements and carbon and oxygen isotope values and bivariate plot of them indicate that aragonite was the original carbonate mineralogy of the Sarvak Formation. Variations of Sr/Ca and δ¹⁸O values versus Mn also illustrate that they were affected by nonmarine diagenesis in a nearly closed system. Recognition of the exact boundary between the Sarvak and Ilam Formations is difficult, due to similar lithologies. So in this study, elemental and oxygen and carbon isotope analysis were used to determine the exact boundary between these Formations. Geochemical data clearly indicate a sub aerial exposure surface, below which meteoric diagenesis effected the sediments.