Lithostratigraphy and Microfacies Analysis of the Govanda Formation (Early–Middle Miocene) in the Sherwan Mazin Area, Kurdistan Region, NE Iraq

Abstract

The Govanda Formation was deposited during the Miocene in the intermontane areas between the Zagros suture and imbricate zones. The Govanda Formation was studied in the Sherwan Mazin area within Mergasor district, Erbil Governorate to identify the lithostratigraphy and microfacies analysis in order to determine the depositional environment of the formation. The formation in the studied section is 116 m thick and mainly consists of reddish-brown, hard, thick-bedded, chert-bearing conglomerate, pinkish shale and yellowish-grey, thick-bedded, detrital, fossiliferous limestone. The formation is unconformably underlain by the Upper Cretaceous Tanjero Formation and conformably overlain by the Merga Red Beds series. Four different lithostratigraphic units were identified, based on field observation and petrographic analysis, including a basal conglomerate unit (A), a shale unit (B), a well-bedded limestone unit (C) and a thick and massively-bedded limestone unit (D). The presence of a thick conglomerate bed at the base of the formation indicates a large unconformity that lasted nearly 40 million years. Based on detailed microfacies analysis of carbonate rocks, five main microfacies and 15 submicrofacies are recognized. The main microfacies types include mudstone, wackestone, packstone, grainstone and boundstone microfacies. Based on the microfacies types the depositional environment are defined as open lagoon, reef, fore-reef and back-reef environments of normal to saline, nutrient rich water.