Microfacies and sedimentary environment of the Jahrum formation, south-central Zagros basin

The Jahrum formation in age Paleocene-Eocene is an important hydrocarbon reservoir rock in Zagros basin. Jahrum formation in wells number 11 and 13 of Golkhari oilfield located at the north of Bushehr port has been examined in this study. Petrography studies (to identify microfacies, sedimentary environment, and sedimentation model), biostratigraphy studies (to determine the age), the analysis and plotting charts (for better data analysis and interpretation of intervals without date), and section correlation with the five correlated sections were done to provide a better understanding of the sedimentary environment in Jahrum formation. Considering the biostratigraphy studies, the biological zone determined for both sections belongs to the Upper Eocene age (Priabonian) due to the presence of Baculogypsinoides (according to Wynd 53 biological zone) and Nummulites Fabiani (according to Nummulites Fabiani biological zone). Nine main microfacies and eight sub microfacies have been introduced based on the petrography studies. The sedimentary model of Jahrum formation in these sections, due to the lack of microfacies related to the shoal environment, the sudden emergence of shallow microfacies in the intervals of deep microfacies and vice-versa is of open-shelf type. Based on correlations between studied areas and five sections located in southwest and south of Iran, the Jahrum formation generally has been deposited in the shallow and semi-deep environment in the Eocene age.