Sedimentary Environments and Age Determination of the Chia Gara Formation, Northern Iraq

Abstract

The rock successions of the Chia Gara Formation were studied at two surface sections (Barsarin and Rania) from North-Eastern Iraq. The detailed sedimentological study reveals that the formation consists basically of thin-bedded black limestone, dolomitic limestone, marly limestone, bituminous shales, and Ammonitic limestone. The petrography results showed that the formation consists of various petrographic components as Ammonites, calcispheres, radiolarian, and silicate sponges in addition to the groundmass of micrite. Ammonite taxa are examined in the upper part of the Chia Gara Formation to find Ammonite species, of which seven species have been identified. One biozone is postulated based on the above assemblages, in order of age: Berriasella Jacobi, from a regional perspective, this biozone was connected with other Ammonite assemblages, leading to the conclusion that the Formation age is Early Cretaceous in age. The facies analysis demonstrates that the rock succession consists mainly of three microfacies. The main microfacies include lime mudstone, wackestone, and packstone. At the same time, the lithofacies comprise limestones and shales. The overall characteristics of these facies show that the Chia Gara Formation was deposited in three different environments; (1) the Lower part of the Upper bathyal (2) the Middle part of the bathyal, and (3) the Upper part of the outer shelf environment.