Tikrit Journal of Pure Science Vol. 27 (5) 2022 57 Tikrit Journal of Pure Science ISSN: 1813 – 1662 (Print) --- E-ISSN: 2415 – 1726 (Online) Journal Homepage: http://tjps.tu.edu.iq/index.php/j Stratigraphy and Mineralogy of Balambo Formation (Aptian - Cenomanian) near Chomabrok village, Imbrication Zone, Iraqi Kurdistan Region Aheen O. Abdullah 1 , Sardar M. Balaky 2 1 Department of Earth Science and Petroleum, College of Science, Salahaddin University, Erbil, Kurdistan region, Iraq 2 Department of Petroleum Geosciences, faculty of Science, Soran University, Soran, Kurdistan region, Iraq DOI: http://dx.doi.org/10.25130/tjps.27.2022.068 A r t i c l e i n f o. Article history: -Received: 5 / 7 / 2022 -Accepted: 15 / 8 / 2022 -Available online: / / 2022 Keywords: Balambo, Stratigraphy, Lithostratigraphy, Mineralogy, Iraqi Kurdistan Corresponding Author: Name: Aheen O. Abdullah E-mail: aheen.abdullah@su.edu.krd Tel: ABSTRACT The stratigraphy and mineralogy of Balambo Formation (Aptian - Cenomanian) in exposed surface section near Chomabrok village in the Imbrication zone, northeastern Iraq is studied. The Formation is 450 meters thick and consists of thin to medium to thick bedded yellowish- brown, and black to dark gray limestones, marly limestones, with thin- medium bedded, grayish - black marl and shale, with thin bands of black cherts and abundant nodules and lenses. From the field observations and petrographic studies, the formation mainly made from two main lithofacies types; marly limestone-marl lithofacies and cherty limestone lithofacies. The petrographic study of carbonate rocks deepened on 79 thin sections and demonstrated that the carbonates of Balambo Formation composed of micrite ground mass with abundant skeletal grains; planktonic and some benthic foraminifera, radiolaria, calcisphere, ostracods, pelecypods, larva-ammonoids, small-brachiopods, sponge spicules, echinoid spines, and bioclasts. Non-skeletal grains include peloids only. Using extraction method and according to an assessment of foraminiferal assemblages and based on the defined planktonic foraminifera the assigned age of Balambo Formation in the studied section is Aptian to Cenomanian as upper Balambo age. The results of X-ray diffraction (XRD) analysis for bulk mineralogy of selected shale and marl samples suggested the presence of phyllosilicate with abundant calcite, common quartz, and moderate Fluorapatite with minor dolomite content. Illite is the dominant clay mineral in the Balambo Formation and indicates a hot, arid climate during most of the Cretaceous period in the Imbrication zone, Northeastern Iraq. 1. Introduction The Balambo Formation is one of the Cretaceous successions that have a considerable thickness and wide distribution throughout the northern Iraq (Kurdistan region) and corresponds to the Wasia Group that present throughout the whole country [1]. The formation represents deep-water sediments that deposited in the Imbrication zone of the northeastern Iraq during almost the whole Cretaceous, exactly from the Early Hauterivian up to the Turonian [2]. In the Imbrication Zone, the formation is carbonate- siliciclastic unit, composed of alternation between thin, yellowish- gray-black marly limestones and dolomitic limestones, with thin and medium-bedded gray-black shales. Thin to medium bedded, lenses and nodules of cherts are present all over parts of the formation. While in the subsurface sections, it defined in different tectonic zones from various wells, such as Chamchemal No. 1, Injana No. 5, Pulkhana No.5 and Jambur-18 in northeastern Iraq. In subsurface, the formation contains different lithological facies, and sediments of younger than Turonian age. A brief description of the formation was given in Iraq Geological Lexicon [3], were it was first described and recognized from the Sirwan valley near Halabja in NE Iraq. Due to its accessibility and widespread distribution in the western Zagros Folded belt, the Balambo Formation has been studied by several authors. These are including the studies of [4,