Petrography and biostratigraphy of Eocene rocks in south Samawa area, southern Iraq

Abstract EN

The petrographic and biostratigraphic study of the Eocene rocks of South Samawa indicates the existence of the two Eocene formations: Rus and Dammam.

Detailed petrographic examination of the carbonate rocks of the Rus Formation has led to the distinction of one microfacies (gypsiferous bioclastic miliolidic dolowackestone) and one lithotype (fine crystalline dolostone).

In Dammam Formation, three main microfacies are recognized (mudstone, wackestone and floatstone), two lithotypes (crystalline dolostone and crystalline dedolostone) and one lithofacies (claystone).

Each of the microfacies is subdivided into several submicrofacies depending on the components of the rock.

The carbonate rocks of the Eocene are inferred to have undergone extensive diagenetic events including dolomitization that appear to have been widespread, dedolomitization, neomorphism, micritization, dissolution and porosity developments, cementation, physical compaction and silicification.

These microfacies are interpreted as having been deposited in different environments (platform margin sand shoals, open marine, shallow restricted and evaporitic platform interior).

Biostratigraphically, miliolids are the common fossils recognized within the Rus Formation and assigned to the Early Eocene age and restricted environment, while the Nummulites gizahensis – Nummulites discorbinus assemblage zone and other associated fossils represent the Middle Eocene age of the Middle Dammam Formation with Shoal environment.