Late Permian upper-Khuff equivalent sediments (thickness up to 200 m) crop out over large parts of the Alborz Mountains, northern Iran, and are represented both by continental and marine facies. The continental facies is represented by the Gheshlagh Formation cropping out mostly to the south and east, consisting of fluvial quartzarenites and lateritic horizons with occasional dark shales (with plant fragments) inter-bedded. This unit inter-fingers with the marine Nesen Formation, which in places is very organic rich. In the Central Alborz, the Nesen Sequence thins out rapidly and in the south, it is usually less than 20 m thick. Preliminary analyses on the vitrinite reflectance of the Nesen Formation suggests that Ro falls in the lower part of the oil-window.The organic matter appears to be mostly of land plant origin. The Nesen Formation is rich in fossils including brachiopods (which form very diversified assemblages), palynomorphs, rugose corals, small foraminifers and fusulinids. Five brachiopod biozones have been erected allowing detailed correlation between five widely separated sections between Elikah (in the west), Dashnt-Nadir Bear, Mangol and Abrendan (in the east). The brachiopods suggest a Late Permian (Wuchiapingian-Changhsingian) age for the biozones. Independent evidence supports this assignment including the presence of the Wuchiapingian-Lower Changhsingian conodont Hindeodus julfensis and the Changhsingian palynomorph Triquitrites proratus. Trends in δ13C from carbonates indicate the presence of the Permian-Triassic boundary close the base of the overlying Elikah Formation and biotic trends, including proportional extinction rates, there can be related to mass extinction.


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