Facies Association and Depositional Environment of the Sarmord Formation (Valanginian-Aptian), Kurdistan Region, Northeastern Iraq

Abstract

The facies analysis, mineralogy and depositional environment of the Cretaceous Sarmord Formation are studied in two outcrops in the Imbrication and High Folded Zones of Northeastern Kurdistan region of Iraq. The formation comprises of rhythmic alternation of medium to thick-bedded marly limestone with marls. Petrographic investigation of marly limestones is on 60 thin sections and showed a variety of pelagic (open sea) faunas such as; ammonites, planktonic forams (Globigerina), radiolarians, calcispheres, ostracods, bioclasts, echinoderm plates and rare calpionellids. Peloids are the only non-skeletal grains components. Depending on detailed microfacies analysis of limestones, three main microfacies types and nine sub-microfacies are identified in the studied sections of the Sarmord Formation, these facies were incorporated into one facies association type relating to their environmental interpretation, that is basinal facies association. X-ray diffraction analysis of selected marl samples, displayed that the main clay minerals in the Sarmord Formation are illite, kaolinite, chlorite and mixed-layers of illite – chlorite. The high abundance of illite indicates that hot-arid climatic conditions prevailed during the deposition of the Sarmord Formation in the study area. From all of the petrographic, facies, textural and mineralogical analyses, it is concluded that the Sarmord Formation in the northeastern Iraq, was deposited in deep water, basinal (outer ramp) environment.