Study and comparison of biomarker and isotopic characteristics of Garau source rock in southwestern Iran and adjacent areas

Document Type : Research Article

Authors

Dept. of Mining and Metallurgical Engineering, Yazd University, Yazd, Iran

10.22034/anm.2026.23980.1712

Abstract

The Zagros Basin ranks among the world’s most prolific hydrocarbon provinces, featuring multiple active petroleum systems and a dense concentration of oil and gas fields. The Cretaceous Garau Formation represents a regionally extensive, organic-rich source rock that spans southwestern Iran, Iraq, and Kuwait. This study presents a regional investigation of the biomarker and isotopic characteristics of the Garau source rock from southwestern Iran and the northeastern and southeastern sectors of Iraq. The dataset includes biomarker indices and isotopic measurements from 33 fields and outcrops located within the Lorestan Basin, Dezful Embayment, Abadan Plain, and northern and southern Iraq. Biomarker patterns and isotopic signatures are indicative of deposition under normal-salinity, carbonate-dominated marine conditions. Organic geochemical evidence points to the dominance of Type II kerogen, highlighting a strong hydrocarbon generation potential. Thermal maturity assessment reveals that the Garau Formation in the eastern Lorestan sub-basin remains immature, whereas in other studied areas it has entered the peak to late oil window, generating substantial hydrocarbons over geological timescales. These findings underscore the major role of the Garau Formation in regional petroleum systems and offer valuable insights for exploration-risk assessment and development strategies in the Zagros Basin and contiguous areas.

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[1]                 Hosseiny, E., & Barati Boldaji, S. (2020). Evaluation of hydrocarbon generation potential of Sargelu source rock in southwestern Iran and the northwestern Persian Gulf. Journal of Analytical and Numerical Methods in Mining Engineering, 10(23), 79–89. (In Persian)
[2]                 Hosseiny, E., Beirami, A., & Amini Mostafaabadi, A. (2024). Geochemical assessment of the Pabdeh Formation from the perspective of conventional and unconventional hydrocarbon resources, southwest of Iran. Journal of Stratigraphy and Sedimentology Researches, 40(1), 45–58.
[3]                 Kobraei, M., Rabbani, A. R., & Taati, F. (2017). Source rock characteristics of the Early Cretaceous Garau and Gadvan formations in the western Zagros Basin–southwest Iran. Journal of Petroleum Exploration and Production Technology, 7(4), 1051–1070.
[4]                 Hosseiny, E., & Mohseni, A. (2023). Garau Formation as an unconventional hydrocarbon resource in southwestern Iran: A geochemical investigation. Journal of Petroleum Exploration and Production Technology, 13(7), 1535–1549.
[5]                 Shekarifard, A., Daryabandeh, M., Rashidi, M., Hajian, M., & Röth, J. (2019). Petroleum geochemical properties of the oil shales from the Early Cretaceous Garau Formation, Qalikuh locality, Zagros Mountains, Iran. International Journal of Coal Geology, 206, 1–18.
[6]                 Kobraei, M., Rabbani, A., & Taati, F. (2019). Upper Jurassic–Lower Cretaceous source-rock evaluation and oil–source rock correlation in the Abadan plain, Southwest Iran. Geochemistry International, 57, 790–804.
[7]                 Mahbobipour, H., Kamali, M. R., & Solgi, A. (2016). Organic geochemistry and petroleum potential of Early Cretaceous Garau Formation in central part of Lurestan zone, northwest of Zagros, Iran. Marine and Petroleum Geology, 77, 991–1009.
[8]                 Asadi Mehmandousti, E., Adabi, M. H., Bowden, S. A., & Alizadeh, B. (2015). Geochemical investigation, oil–oil and oil–source rock correlation in the Dezful Embayment, Marun Oilfield, Zagros, Iran. *Marine and Petroleum Geology, 68*, 648–663
[9]                 Zeinalzadeh, A., Moussavi-Harami, R., Mahboubi, A., & Sajjadian, V. A. (2018). Source rock potential of the Early Cretaceous intervals in the Darquain field, Abadan Plain, Zagros Basin, SW Iran. Geosciences Journal, 22, 569–580.
[10]             Zohrevand, M., Shekarifard, A., & Tavakoli, V. (2020). Petroleum geochemistry of the Albian–Turonian Sarvak reservoir in one of the oil fields of southwest Iran. Journal of Petroleum Science and Technology, 10(3), 39.
[11]             Hemmati, M., Ahmadi, Y., Vaferi, B., Alibak, A. H., & Wood, D. A. (2025). Surveying organic matter, thermal maturity level, and paleo-environmental conditions by considering biomarker and stable carbon isotopic analysis. Journal of Earth Science, 36(2), 428–440.
[12]             Ghorbani, B., Tavakoli, V., Rahimpour–Bonab, H., & Vahidimotlagh, N. (2025). Oil–oil and oil–source correlations in the Abadan Plain, SW Iran: Updated insights into Middle Jurassic–Lower Cretaceous petroleum systems through biomarker analysis and chemometrics. Journal of African Earth Sciences, 223, 105525.
[13]             Jalil, S., & Ahmadreza, R. (2018). Characteristics of the first occurrence of Jurassic petroleum in the Zagros Basin, Iran. Acta Geologica Sinica‐English Edition, 92(6), 2280–2296.
[14]             Khadivi, S. (2010). Tectonic evolution and growth of the Zagros Mountain Belt (Fars, Iran): Constraints from magnetostratigraphy, sedimentology and low-temperature thermochronometry [Master's thesis, Université Pierre et Marie Curie - Paris VI]. HAL Open Science.
[15]             Motiei, H. (1993). Stratigraphy of Zagros. In A. Hushmandzadeh (Ed.), Treatise on the Geology of Iran (No. 1). Geological Survey of Iran, Tehran, 536 p. (In Persian)
[16]             Ammari, A., & Alipour, M. (2024). Organic geochemistry and petrography of the early Cretaceous Garau Formation in the Kabir-Kuh Anticline, Ilam. *Journal of Stratigraphy and Sedimentology Researches, 40*(3), 29–46
[17]             Aqrawi, A. A., & Badics, B. (2015). Geochemical characterisation, volumetric assessment and shale-oil/gas potential of the Middle Jurassic–Lower Cretaceous source rocks of NE Arabian Plate. *GeoArabia, 20*(3), 99–140.
[18]             Al-Ameri, T. K., & Al-Musawi, F. A. A. (2011). Hydrocarbon generation potential of the uppermost Jurassic—basal Cretaceous Sulaiy formation, South Iraq. Arabian Journal of Geosciences, 4(1), 53–58.
[19]             Mohialdeen, I. M., Hakimi, M. H., & Al-Beyati, F. M. (2013). Geochemical and petrographic characterization of Late Jurassic–Early Cretaceous Chia Gara Formation in Northern Iraq: Palaeoenvironment and oil-generation potential. Marine and Petroleum Geology, 43, 166–177.
[20]             Edilbi, A. N., & Sherwani, G. H. (2019). Petrography and source rock potential of Chia Gara formation (late jurassic–early cretaceous) in Northern Iraq and Kurdistan Region. Journal of Petroleum Exploration and Production Technology, 9(3), 1801-1818.
[21]             Asadi Mehmandoosti, E., Adabi, M. H., & Alizadeh, M. (2010). Dadeh-haye biomarkeri nemuneh-haye naft-e kham va bitumen estekhraj shodeh az sang-haye mansha' vaqe' dar meydan-e nafti-ye Marun [Biomarker data of crude oil and bitumen samples extracted from source rocks in the Marun oil field]. Pajoohesh-haye Chineh Negari va Rasub Shenasi, 26(1), 69–88. (In Persian)
[22]             Kobraei, M., Rabbani, A., & Taati, F. (2019). Upper Jurassic-lower cretaceous source-rock evaluation and oil—source rock correlation in the Abadan plain, Southwest Iran. Geochemistry International, 57(7), 790-804.
[23]             Mehmandosti, E. A., Adabi, M. H., Bowden, S. A., & Alizadeh, B. (2015). Geochemical investigation, oil–oil and oil–source rock correlation in the Dezful Embayment, Marun Oilfield, Zagros, Iran. Marine and Petroleum Geology, 68, 648-663.
[24]             Zeinalzadeh, A., Moussavi-Harami, R., Mahboubi, A., & Sajjadian, V. A. (2018). Source rock potential of the early cretaceous intervals in the Darquain field, Abadan Plain, Zagros Basin, SW Iran. Geosciences Journal, 22(4), 569-580.
[25]             Mohialdeen, I. M., Hakimi, M. H., & Al-Beyati, F. M. (2015). Biomarker characteristics of certain crude oils and the oil–source rock correlation for the Kurdistan oilfields, Northern Iraq. Arabian Journal of Geosciences, 8(1), 507–523.
[26]             El Diasty, W. S., El Beialy, S., Mahdi, A., & Peters, K. (2016). Geochemical characterization of source rocks and oils from northern Iraq: Insights from biomarker and stable carbon isotope investigations. Marine and Petroleum Geology, 77, 1140–1162.
[27]             Rastegar Kalateh, O., & Ghavami Riyabi, S. R. (2015). Arzyabi-ye shimiayi-ye sazand-e Gur (Kretaseh Pishin) be onvan-e sang-e madar dar nahieh-ye Lorestan [Geochemical evaluation of the Garau Formation (Lower Cretaceous) as a source rock in the Lorestan region]. In 2nd International Congress on Applied Geology (Conference paper). (In Persian)
[28]             Mahboobi Pour, H., Kamali, M. R., & Salgi, A. (2016). Arzyabi-ye geoshimiayi-ye sazandeh-ye Gur dar taghdis-haye Anjir va Kabirkuh dar jonub-e gharb-e nahieh-ye Lorestan [Geochemical evaluation of the Garau Formation in the Anjir and Kabirkuh anticlines in the southwest of the Lorestan region]. (In Persian).
[29]             Nae'mati, M., Ghavami Riyabi, S. R., & Tavangarranjbar, M. (2014). Arzyabi-ye potential-e shale gas dar do sazand-e Gur va Sargalu bar asas-e etela'at-e geoshimi-ye ali [Evaluation of shale gas potential in the Garau and Sargalu formations based on organic geochemistry data]. Ministry of Science, Research, and Technology – Shahrood University of Technology, Faculty of Mining Engineering. (In Persian).
[30]             Abeed, Q., Alkhafaji, A., & Littke, R. (2011). Source rock potential of the Upper Jurassic–Lower Cretaceous succession in the southern Mesopotamian Basin, southern Iraq. Journal of Petroleum Geology, 34(2), 117–134.
[31]             Abdula, R. A. (2020). Crude oil classification based on age and provenance from the Southern Iraq: A review. Bulletin of the Geological Society of Malaysia, 70, 87–102
[32]             Ten Haven, H., De Leeuw, J., Rullkötter, J., & Damsté, J. S. (1987). Restricted utility of the pristane/phytane ratio as a palaeoenvironmental indicator. Nature, 330(6149), 641–643.
[33]             Moldowan, J. M., Seifert, W. K., & Gallegos, E. J. (1985). Relationship between petroleum composition and depositional environment of petroleum source rocks. AAPG Bulletin, 69(8), 1255–1268.
[34]             Peters, K. E, and J. M. Moldowan. 1993. The biomarker guide: Interpreting molecular fossils in petroleum and ancient sediments. Englewood Cliffs, NJ: Prentice-Hall.
[35]             Hill, R. J., Jarvie, D. M., Zumberge, J., Henry, M., & Pollastro, R. M. (2007). Oil and gas geochemistry and petroleum systems of the Fort Worth Basin. AAPG Bulletin, 91(4), 445–473.
[36]             Hosseiny, E. (2024). Geochemical variability of oils from Jurassic petroleum system in the east of Persian Gulf. Petroleum Science and Technology, 42(1), 102–121.
[37]             Peters, K. E., K. E. Peters, C. C. Walters, and J. Moldowan. 2005. The biomarker guide, vol. 1. New York: Cambridge University Press
[38]             Hosseiny, E., Rabbani, A. R., & Moallemi, S. A. (2017). Oil families and migration paths by biological markers in the eastern Iranian sector of Persian Gulf. Journal of Petroleum Science and Engineering, 150, 54–68.
[39]             Zumberge, J. E., & Ramos, S. (1996). Classification of crude oils based on genetic origin using multivariate modeling techniques. In Proceedings, 13th Australian Geological Convention, Canberra: Australian Geological Survey Organisation, Abstracts (Vol. 492).
[40]             Zumberge, J. E. 1984. Source rocks of the La Luna Formation (Upper Cretaceous) in the Middle Magdalena Valley, Colombia, Palacas. In: Palacas, J.G. (Ed.), Geochemistry and Source Rock Potential of Carbonate Rocks. American Association of Petroleum Geologists, pp. 127–133.
[41]             Hughes, W. B., Holba, A. G., & Dzou, L. I. (1995). The ratios of dibenzothiophene to phenanthrene and pristane to phytane as indicators of depositional environment and lithology of petroleum source rocks. Geochimica et Cosmochimica Acta, 59(17), 3581–3598.
[42]             Liu, B., Bechtel, A., Sachsenhofer, R. F., Gross, D., Gratzer, R., & Chen, X. (2017). Depositional environment of oil shale within the second member of Permian Lucaogou Formation in the Santanghu Basin, Northwest China. International Journal of Coal Geology, 175, 10–25.
[43]             Sofer, Z. (1984). Stable carbon isotope compositions of crude oils: Application to source depositional environments and petroleum alteration. AAPG Bulletin, 68(1), 31–49.
[44]             Seifert, W., & Moldowan, J. (1986). Use of biological markers in petroleum exploration. Methods in Geochemistry and Geophysics, 24, 261–290.