عنوان مقاله [English]
نویسندگان [English]چکیده [English]
The present study has focused on the lithology and mineralogy of the Bangestan reservoir shale unit, 5 meters thick at the 45 m below the upper boundary of Sarvak formation, located in the Lali oil field, to clear the existing lithostratigraphic ambiguities which refer it as a tongue of the Surgah Formation. After examining the petrophysical logs to determine the exact location of these deposits and core descriptions, the petrography was performed, and XRD analyses to recognize the mineralogy of the total sample as well as clay minerals. Core studying indicates that the unit is pyrite bearing gray shales. Moreover, based on petrography, the studied samples are argillaceous and fossil-free mudstone. The results of the XRD analysis show that the mineralogy of these deposits is mainly clay minerals, calcite, quartz, and pyrite. The samples' average abundance of clay minerals is 56%, and the most frequent ones are the mixed-layered clays (illite/smectite), illite, and kaolinite, respectively. The SEM images often exhibit clay minerals of detrital origin. Due to the lack of fossils, the age of this unit was determined based on its stratigraphic position, which is surrounded by the Sarvak Formation deposits of the Cenomanian age and is distinguished from the Sorgah Formation (Turonian- Santonian age). Due to the absence of deep-marine organisms in this unit and the identification of lagoon and shoal carbonate microfacies in its surrounding layers, a calm and reducing lagoon environment is attributed to these sediments, which is against the deep marine of the Surgah Formation.