Diagenetic control on porosity types of carbonate rocks of Late Triassic Baluti Formation in Northern Thrust Zone, Iraqi Kurdistan region, Northern Iraq

Abstract

Abstract The carbonate rocks of Late Triassic Baluti Formation in Sararu outcrop, Northern Thrust Zone, Northern Iraqi Kurdistan region consist of brecciated marly limestone and sandy dolomitic limestone interbedded with shale that characterized by complex heterogeneity. The microscopic description of the porosity types and diagenetic processes controlled it were studied in current work. The petrographic study of 12 thin section of Baluti carbonate displayed that the main skeletal grains are shallow marine derivative fossils and non-skeletal grains are only monocrystalline quartz. The main matrix is micrite which sometimes changed to microspar and sparry calcite. Seven pore types were distinguished in the studied rocks of the formation from both primary and secondary stages. The primary porosity are interparticle and intraparticle pores. While, the secondary types were moldic, intercrystalline, fracture, vuggy and stylolitic porosities. The formation in studied outcrop was undergone in several diagenetic processes, that enhanced or reduced the porosity of the Baluti carbonates. Early micritization protect the primary pores from destroying by compaction. While, solution was assists in creating different secondary pores in different diagenetic stage of the formation particularly the dominant moldic porosity. Calcite cements aid in reducing all pore types in the studied formation. Late dolomitization contribute to formation intercrystalline and dolomoldic porosities. stylolites with dissolution helps to creating stylolitic porosity. Neomorphism, silicification and pyritization generally reduced porosity in the formation.