Sedimentological Study of the Chia Gara Formation Successions in Selected Outcrop Sections of Northern Iraq,

Abstract

The current study deals with the rock successions of the Chia Gara Formation (Late Jurassic- Early Cretaceous) in two outcrop sections (Rania and Barsarin) from the northern part of Iraq. The successions are composed of hard limestone and dark grey fissile shale containing bituminous materials, with phaciod structures in its lower part, and Ammonite fossils in its upper part. The Chia Gara Formation in the study sections conformably underlies the Barsarin Formation. However, it conformably overlies the Balambo Formation in the Rania section, while it is conformably overlain by the Sarmord Formation in the Barsarin section.Petrographic examinations have revealed that the most abundant skeletal grains are ammonite, radiolaria and, calcispheres. However, siliceous sponge spicules and ostracode are locally present and occur in a minor amount in the micritic groundmass. The detailed facies analysis of the rock successions of the Chia Gara Formation reveals that they are composed of three main microfacies and two lithofacies. The microfacies include lime mudstone, lime wackestone, and lime packstone, these microfacies are subdivided into seven submicroficias. On the other hand, the lithofacies comprise limestone and shale lithofacies. Based on the evidence from microfacies, lithofacies, the Chia Gara Formation was inferred to be deposited in a deep marine environment. Thus, the lower, middle and, upper part of the successions was deposited in the upper bathyal, middle bathyal and, outer shelf setting respectively.