Middle Eocene Succession of Dammam Formation, Biostratigraphy and Microfacies Study, North Karbala Area, Western Iraq

Abstract

Stratigraphic and sedimentary study to Dammam Formation (Eocene age) at well Kr-1, Karbala Government, Western Desert of Iraq. Lithologically, Dammam Formation consists of Nummulitic limestone and dolomitic limestone. The contact between the upper and lower of Dammam Formation is unconformable, the lower contact is represented by Umm Er-Radhuma Formation by the unconformable surface in the Upper Paleocene age, while the upper is an unconformable surface with Euphrates Formation in the Early Miocene age. The rock section of the well Kr-1 is divided into several beds depending on Petrographical and paleontological contents, the results of the identified foraminifera are indicated to several groups and genera which are: Nummulites, Lindrina, Lockhartia, Rotaliid, Miliolid, also other groups of fossils like Ostracoda, Echinoderms, Bryozoa, Gastropod, Pelecypod, and different fragments. Based on the petrographic study and type of microfacies, the formation was divided into three main and secondary microfacies which are: Nummulitic packstone, Dolomitic and Bioclastic Packstone, and Floatstone. One main biozone was recognized in the studied section which is Nummulites gizehensis- Nummulites planulatus - Nummulites discorbinus Assemblage Zone with age Middle Eocene (Lutetian), this biozone is divided into two secondary biozones: Nummulites millecaput Rang zone Middle Eocene (Middle-Upper Lutetian) age and Nummulites elevate Rang zone Middle Eocene (Late Upper Lutetian) age. After collecting all the sedimentary and planetology data for the studied section, the Dammam Formation was deposited in shallow warm marine, tropical water, as well as, the absence of planktonic foraminifera crowds is another evidence that the environment is a shallow basin close to the coast. The basin is located at the Interior Platform represented by the evaporites basin, the restricted, and then the open sea environments.