The biostratigraphy, microfacies and depositional environment of the Dammam formation in borehole no.1, south Samawa area, southern desert, Iraq

Abstract EN

This study deals with the biostratigraphy, microfacies and depositional environments of the rocks of the Dammam Formation (Eocene) encountered in Borehole No.1 in South Samawa, Southern Desert, Iraq.

Seventy four samples were studied and three formations were identified, they are from the oldest to the youngest: Rus Formation (Early Eocene), Dammam Formation (Middle – Late Eocene) and Euphrates Formation (Early Miocene).

Different species of the foraminifera were identified within the Dammam Formation, two biozones were recognized; they are from the older to the younger: - Nummulites gizehensis Zone of Middle Eocene (Late Lutetian) age - Miliolids – Peneroplid Assemblage Zone of Late Eocene (Bartonian) age The first biozone indicates Middle Eocene age for the Middle Member of the Dammam Formation and the second biozone indicates Late Eocene age for the Upper Member of the formation.

The Dammam Formation revealed three microfacies depending on the fossils content and lithological characters, these are from top to bottom: - Dolomitic Wackestone – Packstone Facies - Foraminiferal Dolomitic Packstone Facies - Nummulitic Dolomitic Packstone – Floatstone Facies The depositional environment of the Dammam Formation was determined by application of the environment triangle depending on the species of different groups of foraminiferal assemblages, which show that the depositional environment of the Dammam Formation extends from shelf sands area (winnowed edge sands FZ6) and the shoal to the open platform area (shelf lagoon open circulation FZ7) and its continuation to the restricted platform area (restricted circulation inner shelf and tidal flats FZ8).