This study focused on mineralogy, petrography andmicrofacies analysis of Twenty four samples of limestone, marl to marly limestone and shale-likelithofacies of Gulneriformation which exposed in Dokan, Azmir, Weller and Pushen in Sulaymaniyah area north-east Iraq in order to identify the mineralogical content and diagenetic processes that affect the formation aiming to detect the depositional environment of GulneriFormation. The X-Ray diffraction analysis shows that 67% of the samples are composed of calcite followed by 33% quartz, the insoluble residue indicated the presence of quartz and clay minerals represents by palygorskite and illite, palygorskite indicate that the formation was deposited in inner warm marine shelf to dray or semi dray environment, illite indicate the enrichment of Potassium in the environment. The presence of wacky limestone, bioclastic lime mudstone,andbioclastic lime packstonemicrofacies reflect the deposition of formation in shallow to deep open shelf environments. Cementation, recrystallization, silicification, pyritization and mechanical-chemical compaction are the main diagenetic processes that affect the rock formation.