Microfacies Analysis and Stratigraphic Development of the Shiranish Formation Late Cretaceous (Maastrichtian) in Mergasur Area, Northern Iraq

A petrographic and microfacies analysis was conducted to understand better the sequence development of Shiranish Formation in Mergasur area within Erbil governorate (Lailuk section), Northern Iraq. These analyses interpreted the depositional environment, an essential aspect of stratigraphic analysis. Shiranish Formation is overlying Bekhme Formation in Lailuk region, with an unconformable contact. Shiranish series consists of four main microfacies: lime mudstone, wackestone, packstone, and grainstone. These microfacies are further divided into seven sub-microfacies: planktonic foraminiferal lime mudstone, planktonic foraminiferal lime mudstone to wackestone, planktonic foraminiferal wackestone, bioclastic planktonic foraminiferal wackestone, bioclastic planktonic foraminiferal wackestone to packstone, planktonic foraminiferal packstone, and planktonic foraminiferal packstone to grainstone. The sub-facies are associated with four discrete depositional settings: profound shelf, abyssal or cratonic deep basin, incline, and the inclined base. The studied region, Shiranish Formation, contains three asymmetrical depositional sequences (A, B, and C). The sequence disparity suggests a correlation between sea level and carbonate production variation. Asymmetrical cycles represent a phase of increasing sea level after a calm period. Shiranish sequence was formed over a discontinuous surface, creating a clear distinction from the underlying Bekhme Formation. The surface is represented using a type two-sequence boundary (SB-2). the Shiranish succession in the research region is created in an area of high subsidence. A significant transgression caused by a series of sea level occurrences resulted in the formation of the Shiranish Formation on a carbonate platform with significant subsidence. A significant transgression that caused several periods of sea level rise and stillstand is responsible for the formation of the Shiranish Formation on a carbonate platform that has seen significant subsidence. The depositional sequence stratigraphy, Shiranish sequences A to C, is distinguished by three maximum flooding surfaces (MFS-165, MFS-170, and MFS-175). These sequences have a notable correlation with comparable stratigraphic patterns reported in Iraq and other regions of the Arabian plate.