Advanced Applied Geology

Advanced Applied Geology

Integrated source rock evaluation of the Dalichai Formation based on Organic Geochemistry and Palynofacies analysis: A case study from the Vana stratigraphic section (Central Alborz)

Authors
Afsaneh Dehbozorgi 1
Bijan Beiranvand 2
1 Faculty of Science, Imam Khomeini International University, Qazvin 34149–16818, Iran
2 Research Institute of Petroleum Industry (RIPI), Tehran, Iran
10.22055/aag.2026.53101.2589
Abstract
This study provides the first evaluation of the source rock potential of the Dalichai Formation at the Vana stratigraphic section (Central Alborz) by integrating palynofacies analysis and organic geochemical data. Based on the identified biozones and key dinocyst species, the age of the Dalichai Formation in this section is determined as late Bajocian to late Callovian. Source rock potential was evaluated using Rock-Eval pyrolysis data and organic geochemical indices, including Total Organic Carbon (TOC), S1, S2, S3, Hydrogen Index (HI), and Oxygen Index (OI). Due to the low TOC and S2 values, this formation is classified as significantly poor in organic matter content. The distribution of samples on the relevant diagrams indicates that the organic matter predominantly consists of Type IV kerogen, with no effective potential for hydrocarbon generation. Although some intervals of the studied succession show a relative decrease in terrestrial organic input, a relative increase in AOM abundance, and an increase in marine components based on palynofacies analysis, indicating a relative improvement in preservation conditions, this state was likely the result of a combination of low sedimentation rates and prolonged oxygen exposure. Under slow sedimentation conditions, organic matter remains in contact with oxygen for an extended period, facilitating gradual oxidation and the loss of hydrocarbon-generating components. Consequently, even in intervals of this formation characterized by slower deposition, the sedimentary environment was unsuitable for preserving organic matter and converting it into productive kerogen. From an applied perspective, these findings conclusively rule out the hydrocarbon-generating potential of the Dalichai Formation and, consequently, its possible role as a source rock in the Alborz Basin. They further indicate that additional investigations into its source rock potential are not warranted. Accordingly, the Dalichai Formation may be excluded from subsequent regional source rock assessments.
Keywords
Dalichai Formation
Organic Geochemistry
Rock-Eval pyrolysis
Source rock potential
Palynofacies
Aggarwal, N., 2022. Sedimentary organic matter as a proficient tool for the palaeoenvironmental and palaeodepositional settings on Gondwana coal deposits. Journal of Petroleum Exploration and Production Technology 12, 257-278. https://doi.org/10.1007/s13202-021-01331-x.
Batten, D.J., 1996. Upper Jurassic and Cretaceous miospores. Chapter 26A, Palynofacies and palaeoenvironmental interpretation. In: Jansonius, J., McGregor, D.C., (Eds.). Palynology: Principles and Application. American Association Stratigraphic Palynologists Foundation 3, pp. 1011-1064.
Behar, F., Beaumont, V., Penteado, H.D.B., 2001. Rock-Eval 6 technology: performances and developments. Oil and Gas Science and Technology 56, 111-134. https://doi.org/10.2516/ogst:2001013.
Bombardiere, L., Gorin, G.E., 2000. Stratigraphical and lateral distribution of sedimentary organic matter in Upper Jurassic carbonates of SE France. Sedimentary Geology 132, 177-203. https://doi.org/10.1016/S0037-0738(00)00006-3.
Borges, M.E.N., Riding, J.B., Fernandes, P., Pereira, Z., 2011. The Jurassic (Pliensbachian to Kimmeridgian) palynology of the Algarve Basin and the Carrapateira outlier, southern Portugal. Review of Palaeobotany and Palynology 163(3-4), 190-204. https://doi.org/10.1016/j.revpalbo.2010.09.006.
Carvalho, M.A., Bengtson, P., Lana, C.C., 2016. Late Aptian (Cretaceous) paleoceanography of the South Atlantic Ocean inferred from dinocyst communities of the Sergipe Basin, Brazil. Paleoceanography 31, 2-26. https://doi.org/10.1002/2014PA002772.
Carvalho M.A., Sucerquia, P.A., Krahl, G., Fauth, G., 2026. Sedimentary organic matter changes across the Cretaceous – Paleogene boundary in northeastern Brazil. Journal of South American Earth Sciences 178, 106096. https://doi.org/10.1016/j.jsames.2026.106096.
Dehbozorgi, A., Sajjadi, F., Hashemi, H., 2013. Middle Jurassic palynomorphs of the Dalichai Formation, central Alborz Ranges, northeastern Iran: Paleoecological inferences. Science China Earth Sciences 56, 2107-2115. https://doi.org/10.1007/s11430-013-4697-z.
Dehbozorgi, A., 2014. Palynology and Palaeoecology of the Middle Jurassic (Dalichai and Baghamshah formations) east of Semnan (Jam area). PhD thesis, Faculty of Geology, College of Science, University of Tehran (In Persian).
Dehbozorgi, A., Hashemi Yazdi, F., Sajjadi, F., 2018. Palynostratigraphy and paleoenvironmental interpretation of the Dalichai Formation, at the Pol Dokhtar stratigraphic section, central Alborz. Applied Sedimentology 6, 35-48. https://doi.org/10.22084/psj.2018.13434.1143.
Dehbozorgi, A., Senemari, S., 2020. Palynostratigraphy, paleoclimate, and paleoenvironment of the Dalichai Formation in the Bashm stratigraphic section (Eastern Alborz). Scientific Semiannual Journal of Sedimentary Facies 13(1), 1-21. https://doi.org/10.22067/sed.facies.v13i1.87380.
Dehbozorgi, A., Hashemi Yazdi, F., Sajjadi, F., Hashemi, H., 2024. The importance of Sporomorph EcoGroups and palynofacies in recognition of paleoenvironments and paleoecology of the Middle Jurassic strata of the central and eastern Alborz. Advanced Applied Geology 14(1), 23-43. https://doi.org/10.22055/AAG.2023.44363.2389.
Eskandari, M., Khosravi, M., Jahangard, A.A., Salehi, M.A., Tabaei, M., 2026. Hydrocarbon generation potential of the Upper Triassic – Middle Jurassic coal-bearing strata in the Parvadeh mine, Tabas, east-central Iran. Advanced Applied Geology 16(1), 38-56. https://doi.org/10.22055/aag.2026.51483.2555.
Espitalié, J., Madec, M., Tissot, B., Mennig, J.J., Leplat, P., 1977. Source rock characterization method for petroleum exploration. In: Proceedings of the 9th Annual Offshore Technology Conference 3, 439-448. https://doi.org/10.4043/2935-ms.
Gedl, P., Ziaja, J., 2012. Palynofacies from Bathonian (Middle Jurassic) ore-bearing clays at Gnaszyn, Kraków-Silesia Homocline, Poland, with special emphasis on sporomorph eco-groups. Acta Geologica Polonica 62(3), 325-349. https://doi.org/10.2478/v10263-012-0018-7.
Ghasemi-Nejad, E., Sabbaghiyan, H., Mosaddegh, H., 2012. Paleobiogeographic implications of late Bajocian-late Callovian (Middle Jurassic) dinoflagellate cysts from the Central Alborz Mountain, northern Iran. Journal of Asian Earth Sciences 43, 1–10. https://doi.org/10.1016/j.jseaes.2011.08.006.
Gorin, G.E., Steffen, D., 1991. Organic facies as a tool for recording eustatic variations in marine fine-grained carbonates-example of the Berriasian stratotype at Berrias (Ardéche, SE France). Palaeogeography, Palaeoclimatology, Palaeoecology 85, 303-320. https://doi.org/10.1016/0031-0182(91)90164-M.
Hamidi, Z., Fardoust, F., Jafarzadeh, M., Rabbani, A.R., 2018. Organic geochemistry of the Upper Triassic–Middle Jurassic Shemshak Group (Alborz Mountains, NE Iran). Petroleum Science and Technology 36(21), 1764–1770. https://doi.org/10.1080/10916466.2018.1511587.
Hashemi Yazdi, F., 2015. Palynology and Palaeoecology of the Dalichai Formation in central-eastern Alborz basin and the Hojedk Formation at the east-central Iran. PhD thesis, Faculty of Geology, College of Science, University of Tehran (In Persian).
Hashemi Yazdi, F., Bashiri, N., Sajjadi, F., 2020. Palynofacies and Sporomorph EcoGroups-based paleoecology implications for the Dalichai Formation, Andariyeh, central Alborz. Journal of Stratigraphy and Sedimentology Researches 36(1), 39-60. https://doi.org/10.22108/jssr.2020.118759.1116.
Hunt, J.M., 1996. Petroleum Geochemistry and Geology. W. H. Freeman, New York. p. 743.
Kalanat, B., Raoufian, A., 2023. Palynological evidence for the Middle Jurassic environmental evolution in the eastern part of the Alborz Mountains (northern Iran). Review of Palaeobotany and Palynology 312. 104874. https://doi.org/10.1016/j.revpalbo.2023.104874.
Mohammad Khani, Kh., Zarei, E., 2019. Palynostratigraphy of the Dalichai Formation in Darjazin section, North of Semnan. Journal of Stratigraphy and Sedimentology Researches 34, 21-38. https://doi.org/10.22108/jssr.2019.112088.1062.
Mueller, S., Veld, H., Nagy, J., Kǖrschner, W.M., 2014. Depositional history of the Upper Triassic Kapp Toscana Group on Svalbard, Norway, inferred from palynofacies analysis and organic geochemistry.     Sedimentary Geology 310, 16-29. https://10.1016/j.sedgeo.2014.06.003.
Mukhopadhyay, P.K., 1994. Vitrinite reflectance as maturity parameter: petrographic and molecular characterization and its applications to basin modeling. ACS Symposium Series 570. https://doi.org/10.1021/bk-1994-0570.ch001.
Peters, K.E., 1986. Guidelines for evaluating petroleum source rock using programmed pyrolysis. American Association of Petroleum Geologists Bulletin 70(3), 318-329. 10.1306/94885688-1704-11D7-8645000102C1865D.
Peters, K.E., Cassa, M.R., 1994. Applied source rock geochemistry. In: Magoon, L.B., Dow, W.G. (Eds.), The Petroleum System-From Source to Trap. American Association of Petroleum Geologists 60, pp. 93-120.
Phipps, D., Playford, G., 1984. Laboratory techniques for extraction of palynomorphs from sediments. Department of Geology, University of Queensland, Papers 11(1), 1-23.
Poulsen, N.E., Riding, J.B., 2003. The Jurassic dinoflagellate cyst zonation of Subboreal Northwest Europe. In: Ineson, J.R., Surlyk, F., (Eds.), The Jurassic of Denmark and Greenland. Geological Survey of Denmark and Greenland Bulletin 1, 115-144.
Riding, J.B., Thomas, J.E., 1992. Dinoflagellate cysts of the Jurassic System. In: Powell, A.J. (Ed.), A stratigraphic index of dinoflagellate cysts. British Micropalaeontological Society Publications Series. Chapman and Hall, London, pp. 7-97.
Sajjadi, F., Dermanaki Farahani, S., Hashemi Yazdi, F., 2018. Palynology of the Dalichai Formation in the Guydagh section, southeastern Maragheh, according to dinoflagellate. Journal of Stratigraphy and Sedimentology Researches 70, 91–108. https://doi.org/10.22108/JSSR.2018.84036.0.
Sajjadi, F., Hashemi Yazdi, F., Hashemi, H., 2023. Palynostratigraphy and palaeoecology of the Dalichai Formation at the Yonjehzar stratigraphic section, northeastern Tehran, central Alborz. Scientific Quarterly Journal of Geosciences 33(2), 128, 259-282. https://doi.10.22071/gsj.2023.350092.2013.
Shekarifard, A., Baudin, F., Seyed-Emami, K., Schnyder, J., Rahimpour-Bonab, H., 2012. Organic Matter Characterization and Thermal Modeling of the Basal Black Shale from the Shemshak Group (Upper Triassic- Middle Jurassic) in the Tazareh Section, Eastern Alborz, Northern Iran. Scientific Quarterly Journal of Geosciences 21(83), 219-228. https://doi.org/10.22071/gsj.2012.54549.
Skupien, P., Pavluš, J., Falahatgar, M., Javidan, M., 2015. Middle Jurassic organic-walled dinoflagellate cysts and palynofacies from Telma-Dareh, south of Sari, northern Iran. Review of Palaeobotany and Palynology 223, 128-137. https://doi.org/10.1016/j.revpalbo.2015.09.009.
Taylor, G.H., Teichmüller, M., Davis, A.C.F.K., Diessel, C.F.K., Littke, R., Robert, P., 1998. Organic petrology: Berlin. Gebrüder Borntraeger. p. 704.
Tyson, R.V., 1993. Palynofacies analysis. In: Jenkins D.G. (Ed.), Applied Micropaleontology. Dordrecht. pp. 153-172.
Tyson, R.V., 1995. Sedimentary organic matter; organic facies and palynofacies. Chapman and Hall, London, p. 615. https://doi.org/10.1007/978-94-011-0739-6.
Tyson, R.V., Follows, B., 2000. Palynofacies prediction of distance from sediment source: a case study from the Upper Cretaceous of the Pyrenees. Geology 28, 569-571. https:// doi. org/ 10. 1130/ 0091-7613(2000) 28% 3c569: PPODFS% 3e2.0. CO;2.
Vallejo, J.D., Gusmão, R.B., Andrade Lima, L.M., Piovesan, E.K., 2026. Sedimentary organic matter and paleoenvironmental reconstruction of the Santana Group (Lower Cretaceous), Araripe Basin, Northeast Brazil. Cretaceous Research 185, 106397. https://doi.org/10.1016/j.cretres.2026.106397.
Van der Zwan, C.J., 1990. Palynostratigraphy and Palynofacies reconstruction of the Upper Jurassic to lowermost Cretaceous of the Draugen Field, offshore Mid Norway. Review of Palaeobotany and Palynology 62, 157-186. https:// doi. org/ 10.1016/0034-6667(90)90021-A.
Ward, J.H., 1963. Hierarchical Grouping to Optimize an Objective Function. Journal of the American Statistical Association 58, 236-244. https://doi.org/10.1080/01621459.1963.10500845.
Waveren, I., Visscher, H., 1994. Analysis of the composition and selective preservation of organic matter in surficial deep-sea sediment from a high-productivity area (Banda Sea, Indonesia). Palaeogeography, Palaeoclimatology, Palaeocology 112, 85-111. https:// doi. org/10.1016/0031-0182(94)90135-X.
Welte, D.H., Tissot, P.B., 1984. Petroleum formation and occurrence. Springer-verlag. p. 702.
Wiggan, N.J., Riding, J.B., Franz, M., 2017. Resolving the Middle Jurassic dinoflagellate radiation: the palynology of the Bajocian of Swabia, southwest Germany. Review of Palaeobotany and Palynology 238, 55-87. https:// doi. org/10.1016/j.revpalbo.2016.11.010.
Woollam, R., 1980. Jurassic dinocysts from shallow marine deposits of the East Midlands, England. Journal of the University of Sheffield. Geological Society 7(5), 243-261.
Woollam, R., Riding, J.B., 1983. Dinoflagellate cyst zonation of the English Jurassic. Institute of Geological Sciences. Report No. 83/2, 42 p.
Zhang, M., Ji, L., Wu, Y., He, C., 2015. Palynofacies and geochemical analysis of the Triassic Yanchang Formation, Ordos Basin: Implications for hydrocarbon generation potential and the paleoenvironment of continental source rocks. International Journal of Coal Geology 152, 159-176. https:// doi. org/ 10. 1016/j. coal. 2015. 11. 005.
Zobaa, M.K., Oboh-Ikuenobe, F.E., Ibrahim, M.I., 2011. The Cenomanian/Turonian oceanic anoxic event in the Razzak Field, north Western Desert, Egypt: source rock potential and paleoenvironmental association. Marine and Petroleum Geology 28, 1475-1482. https:// doi. org/ 10.1016/j. marpe tgeo. 2011. 05. 005.
Zonneveld, K.A.F., Versteegh, G.J.M., Lange, G.J., 1997. Preservation of organic-walled dinoflagellate cysts in different oxygen regimes: a 10000 year natural experiment. Marine Micropaleontology 29, 393-405. https://doi.org/10.1016/j.marmicro.2008.01.015.
Advanced Applied Geology
Volume 16, Issue 2
Summer 2026
Pages 55-80