Comprehensive Facies Analysis and Depositional Environment Modeling of the Eocene Dammam Formation in Central to Southern Iraq

Abstract

The Dammam Formation holds immense geological significance, as it spans across a substantial portion of southern Iraq, encompassing a vast area. This formation stands out as the primary aquifer source in the region. To gain a comprehensive understanding of its sedimentology, a comprehensive study was conducted using 310 samples extracted from various boreholes. These boreholes, including Kr-1, Kr-c.q., Nj-20, Ns-13, Ns-24, R-742, and Ru-509. The lithology of the Dammam Formation is limestone, dolomitic limestone, and dolomite rocks, which are also used as raw materials in the manufacture of cement. The microfacies analysis was carried out on Lower-Upper Eocene carbonate rocks along a center-south transect in Iraq. This analysis establishing larger benthic foraminifera enables to reconstruction of the paleoenvironmental model and to show the evolution of a platform along the depth gradient. The analysis revealed the presence of five primary microfacies within the Dammam Formation, each offering unique insights into its composition. These microfacies include Lime-mudstone, Wackestone, Packstone, Floatstone, and Rudstone, all of which contribute to a comprehensive understanding of the formation’s sedimentary makeup. Moreover, this in-depth examination uncovered an additional eight submicrofacies. The benthic foraminiferal assemblages within the Dammam Formation provide valuable insights into the progressive shifts along an ecological gradient, indicating a gradual transition from shallower, more protected (inner) shelf environments to deeper, more open (outer) shelf settings. Within the inner shelf, one can observe the prevalence of orbitolitids, alveolinids, and, to some extent, small miliolids, indicative of this relatively shallow and sheltered environment. Moving towards the inner ramp or shoal region, the foraminiferal composition is characterized by robust nummulitids, signifying the distinctive conditions of this particular zone. From a paleoenvironmental perspective, the Dammam Formation reflects deposition in a diverse range of environments, including peritidal inner ramp areas, lagoons, shoals, restricted-marine platforms, and open marine interior platforms. This variability underscores the complexity of the formation’s geological history and the diverse conditions under which its sediments accumulated over time.