Comprehensive Facies Analysis and Depositional Environment of the Lower Cretaceous Yamama Formation in the Nasiriyah Oilfield, Southern Iraq

The carbonate ramp facies and depositional environments of the Early Cretaceous Epoch Yamama Formation in the Nasiriyah Oilfield, Dhi Qar Governorate, southern Iraq (Ns2- (45° 51' 59.3" E and 31° 22' 06" N) and Ns-5 (45° 22' 25.2" E and 31° 23' 47.4" N)), have been determined through a comprehensive petrographic evaluation. The Yamama Formation is composed of shallow marine-derived skeletal grains, including large and small benthic foraminifera, red and green algae, bryozoans, molluscs, rudists, and echinoderms, as well as non-skeletal grains like lithoclasts, peloids, and ooids. Petrographic observations revealed five distinct facies associations in the Yamama Formation, representing a variety of depositional settings. These associations comprise: a peritidal facies association, characterized by fossiliferous lime mudstone and unfossiliferous mudstone submicrofacies; a lagoonal facies association, including algal wackestone, bioclastic wackestone, algal packstone, and peloidal packstone submicrofacies; a shoal facies association, represented by oolitic grainstone, peloidal grainstone, and bioclastic grainstone submicrofacies; a restricted marine facies association, which consists of miliolid-rich bioclastic wackestone; and a shallow open marine facies association, created up of benthic foraminiferal packstone, echinoderm packstone, and bioclastic packstone submicrofacies. This study provides a carbonate ramp depositional system for the Yamama Formation in the spatial distribution of facies demonstrating variances in water depth and energy. These results shed light on the stratigraphic architecture of the Yamama Formation in the Nasiriyah Oilfield, leading to a better comprehension of hydrocarbon reservoir heterogeneity in this regionally important carbonate system.