Review of the petroleum systems of the Iranian Zagros and Persian Gulf regions

This study provides a comprehensive review of the petroleum systems in the Iranian Zagros and Persian Gulf regions, spanning the Phanerozoic, with the objective of synthesizing geological, geochemical and basin-modelling data to enhance exploration strategies. Three primary petroleum systems are identified: Paleozoic–Triassic, Jurassic–Cretaceous and Cenozoic, each characterized by distinct source rocks, reservoirs and seals. The methodology integrates extensive literature reviews and original geochemical analyses, including Rock-Eval pyrolysis, vitrinite reflectance, biomarker studies, carbon isotope and kinetic modelling, to assess source-rock maturity, kerogen type and oil-source correlations. The main results highlight the Paleozoic–Triassic system, driven by Silurian Sarchahan ‘hot shales’, feeding gas-rich Permian–Triassic Dalan and Kangan reservoirs, sealed by Triassic Dashtak evaporites, but challenged by deep burial and high non-hydrocarbon content. The Jurassic–Cretaceous system, which contributes more than 50% of Iran's oil, features the oil-prone Sargelu, Garau and Kazhdumi source rocks, with reservoirs in the Khami and Bangestan groups, sealed by the Hith/Gotnia and Gurpi formations. The Cenozoic system, centred in the Dezful Embayment, relies on the Pabdeh source rock, Asmari reservoir and Gachsaran seal, with significant vertical migration from underlying Mesozoic systems. Chemometric classification of 21 oil samples revealed three distinct oil families that are genetically linked to these petroleum systems. Family A oils are attributed to Upper Jurassic–Miocene source rocks, characterized by a high C 28 /C 29 regular sterane ratio. Family B oils correlate to Jurassic or older source rocks, and are classified as high-maturity oils. Family C oils sourced from the Aptian–Albian Kazhdumi Formation and display biomarker parameters indicative of anoxic marine conditions.