Sedimentology and Facies Analysis of the Early Miocene Succession in the Zurbatiya Area, Eastern Iraq

Abstract

The present study is focused upon the sedimentology and basin development of the Serikagni and Dhiban Formations by using the field observations and microfacies analysis. The area of study situated in the Zurbatiyah area to the south of the Shur sharin valley about 21 km northeast of Badrah city to the southeast of Baghdad. This area lies within the Zagros foreland basin and located between the Zagros Mountains at the northeastern and the Arabian shield at the southeastern. The studied succession which including the Serikagni and Dhiban Formations were deposited within four associated facies for the Serikagni Formation and three for the Dhiban Formation, as shown below:

Serikagni Formation includes planktic foraminiferal packstone microfacies, planktic foraminiferal wackestone / packstone, algal-foraminiferal lime mudstone microfacies, and bioclastic packstone, which represent the deposition in the deep open sea, deep shelf, outer shelf and the slope/toe slope.

Dhiban Formation includes Dolomitic mudstone and dolomitic wackstone, Miliolid mud to wackstone, Stromatolite boundstone, and Massive gypsum. Which representing the deposition in the lagoon, restricted and semi-restricted environments. The facies analysis for the studied succession showing three stages of deposition:

The First stage was started during the sea level rise after the regression stage which marked by the unconformity between the studied succession and the Oligocene succession. The Sea level continued to rise and to settle at the deposition of the deep shelf margin during the transgression stage. The sea level was settled with the deposition was continued to fill the basin by the sediments causing the shallowing upward. Second stage was represented the deposition during the transgressive stage as a deepening upward. This stage is represented by the alternative of the basinal shale sediments and deep shelf margin. Near the contact with Dhiban Formation the environment was changed to shallow open marine to record the sea level fall and end this stage. At last, the sea level was falled and deposition the dolostone in the restricted environment to refer upon the end the Serikagni deposition. Then the lagoon environment was deposited the massive gypsum overlying the dolomite unit for the Dhiban Formation.