Biostratigraphy and microfacies analysis of the Jahrum Formation in the interior Fars Province, folded Zagros Region, SW Iran

This study presents a comprehensive biostratigraphic analysis of the Jahrum Formation in the interior Fars Province, SW Iran. The formation dates from the Late Paleocene to the Middle Eocene, and is characterized by four biozones and seven depositional environment groups. A thorough methodology combining biostratigraphy and microfacies analysis was employed to examine 495 thin sections and identify biozones. The results indicate that the sedimentary basin of the Jahrum Formation is of an internal ramp type, conforming to the Sachun Formation at its lower boundary and exhibiting an erosional unconformity with the Asmari Formation at its upper frontier. This study concentrates on understanding the geological history of this region and its hydrocarbon potential. The depositional environment of the Jahrum Formation is a combination of shallow marine and continental facies documented by biozones and fossils. Geochemical analyses, including cathodoluminescence and electron probe microanalysis, reveal high calcite content (up to 50 wt %) and dolomite content (up to 12 wt %), respectively, indicating favorable conditions for hydrocarbon reservoir potential. This research is built upon detailed biostratigraphic analysis and clarification of the Jahrum Formation's depositional setting and geological age. The insights provided into the geological history and potential resources of this region are crucial for understanding the hydrocarbon prospects of the Zagros Region. Our innovative approach integrates biostratigraphy and microfacies analysis, utilizing satellite data and geological maps to select suitable sections and optical microscopy for samples analysis. The biostratigraphic analysis enhances understanding of the region's hydrocarbon potential by providing a framework for correlating the geological formations and identifying critical depositional environments. This study interrogates the paleoenvironments conducive to hydrocarbon accumulation, such as shallow marine and lagoonal settings within the Jahrum Formation, through the detailed documentation of biozones and microfacies. (c) 2025 Guangzhou Institute of Geochemistry, CAS. Published by Elsevier BV. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).