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Islamic Azad University , Behbahan , Iran
Islamic Azad University , Ahvaz , Iran
This study investigates the geochemistry of oil shales from the Ab Kaseh section in western Kohrang, Chaharmahal and Bakhtiari Province, Iran. Ten shale samples were collected for geochemical analyses, including Rock-Eval pyrolysis and XRF/ICP analyses. Ten thin sections were also prepared for petrographic analysis. A stratigraphic column and depositional model were constructed based on microfacies characteristics. Results indicate that the oil shales formed in a marine, reducing environment within the Tethys Ocean. However, due to discontinuous sedimentation and insufficient heat supply, the shales never reached the necessary thermal maturity for hydrocarbon generation. Hydrocarbon generation is only achievable through artificial heating (pyrolysis). Rock-Eval pyrolysis data revealed high hydrocarbon potential, with TOC values exceeding 2%, indicating excellent source rock quality. The kerogen type is classified as Type II, suggesting a predominantly oil-prone nature with good to excellent petroleum potential. The samples are situated at the early stage of the oil window (late diagenesis/early catagenesis) and show no potential for gas generation. XRF and ICP analyses showed elevated concentrations of heavy metals (Ni, Pb, Rb, Sr, V, W, Zr, Zn) and rare earth elements (Ba, Ce, Co, Cr, Cu, Th, Nb, Mo, U) within the oil shales. Potential sources of these elements include organic matter, detrital material, seawater, submarine volcanism, and biogenic sources. In the Ab Kaseh section (Saraglu Formation), elements such as Sr and P may have biogenic origins. Ti, Al, and Si, constituents of oxide and clay minerals, have a detrital origin. The origin of Ni, U, W, and Cr is likely linked to organic matter and adsorption onto clay minerals. Positive correlation between P and TOC supports a biogenic origin for P in the Ab Kaseh section. Conversely, the negative correlation between Sr and TOC suggests a non-biogenic source for Sr. A positive correlation between Ni and TOC was also observed. The negative correlation between U and both SiO2 and Al2O3 indicates an uncertain origin for U, but organic matter and clay minerals likely contributed to its enrichment.
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