Facies Analysis and Depositional Environment of the Euphrates Formation in Selected Sections, Southwestern Iraq

Abstract

The current study aims to investigate the microfacies, diagenetic processes, and depositional environments of the twenty-three rock samples from the Lower Miocene Euphrates Formation of two outcrops collected at Bahar-Najaf in Najaf governorate and Al-Shinafiya in Diwaniyah governorate, southern Iraq. Thin sections of these samples were prepared; hence, the nature of microfacies and related depositional environments was established. The formation contains abundant benthonic foraminifers and other fossils like miliolids, echinoderm, coral, gastropods, and pelecypods. Seven distinct microfacies were identified: lime mudstone, miliolid packstone, Pelletal Grainstone, Lime Wackestone, Peloidal Grainstone, Oolitic grainstone Microfacies, and fossiliferous packstone packed with bioclasts. Diagenetic processes evidenced in this study are dissolution, neomorphism, cementation, micritization, and dolomitization. The Euphrates Formation was deposited in a shallow marine setting with fluctuating energy levels, ranging from low-energy lagoons to moderate and high-energy shoals and fore-reef environments. Various microfacies indicate a complex depositional environment on a carbonate platform influenced by biota and sedimentary processes. These observations support the inference that the Euphrates Formation accumulated in shallow open marine, inner barrier, and shoal settings, providing a detailed interpretation of its para-depositional and diagenetic development.