Organic geochemical characteristics and mineralogy of the Asmari basal shale unit in the central Dezful Embayment


1 Department of Petroleum Geology and Sedimentary Basins, Faculty of Earth Sciences, Shahid Chamran University of Ahvaz

2 Department of Geology, National Iranian South Oil Company (NISOC), Ahvaz, Iran


Asmari Formation, comprises mixed carbonate-siliciclastic lithologies in the central Dezful Embayment, with thick shale intervals at the base. In this study mineralogy, organic petrography, thermal maturity and generation potential of the basal shale sediments of the Asmari Formation is investigated in Ahwaz, Marun and Kupal oilfields. Clay mineralogy including kaolinite and mixed layer illite-smectite are the most abundant minerals. Secondary important minerals are calcite and quartz. Microscopic examinations indicate that the organic matter in this unit have mostly originated from continental settings and comprises vitrinite, inertinite, pollen, woody phytoclasts with minor marine liptinite macerals and amorphous materials. TOC contents range from 0.2 to 1.25 wt.% (avg. 0.75 wt%), indicating poor to fair oil generation potential. HI values ranging between 141 to 244 (mg HC/g TOC), is consistent with type III and II/III kerogen. The dominance of terrestrial organic matter (kerogen type III), with relatively high oxygen index indicates that the organic matter was most likely deposited under oxic/suboxic conditions when the relative sea level was low. Vitrinite reflectance (0.45-0.7 %Ro) and Tmax values (417-444 ℃, avg. 432 ℃) suggest that the Asmari basal shale is thermally immature to early mature in the study area.


Alavi, M., 2007. Structures of the Zagros fold-thrust belt in Iran. American Journal of Science 307, 1064-1095.
Alavi, M., Mahdavi, M.A., 1994. Stratigraphy and structures of the Nahavand region in western Iran, and their implications for the Zagros tectonics. Geological Magazine 131, 43-47.
Alizadeh, B., Sarafdokht, H., Rajabi, M., Opera, A., Janbaz, M., 2012. Organic geochemistry and petrography of Kazhdumi (Albian-Cenomanian) and Pabdeh (Paleogene) potential source rocks in southern part of the Dezful Embayment, Iran. Organic Geochemistry 49, 36-46.
Amini, A., Ranjbaran, M., Sajadi, F., Lankarani, M., Honarmand, J., Mahdipor, Z., Tavakoli, V., Daraei, M., Ansari, M., Mohammadpor, H., Ramazani, F., 2010. Facies analysis and sequence stratigraphy of Asmari, Ilam, and Sarvak formations in the Danan Block. National Iranian Oil Company, Internal Report (unpublished).
Barker, C., 1996. Thermal modeling of petroleum generation: theory and applications, Developments in Petroleum Science, P. 600.
Behar, F., Beaumont, V., De B. Penteado, H.L., 2001. Rock-Eval 6 Technology: Performances and Developments. Oil and Gas Science and Technology 56, 111-134.
Berberian, M., King, G.C.P., 1981. Towards a paleogeography and tectonic evolution of Iran. Canadian Journal of Earth Science 18, 210-265.
Bergmann, J., Friedel, P., Kleeberg, R., 1998. BGMN - a new fundamental parameters based Rietveld program for laboratory X-ray sources, it’s use in quantitative analysis and structure investigations, in: IUCr Commission on Powder Diffraction Newsletter.
Beydoun, Z.R., Clarke, M.H., Stoneley, R., 1992. Petroleum in the Zagros Basin; a late Tertiary foreland basin overprinted onto the outer edge of a vast hydrocarbon-rich Paleozoic–Mesozoic passive-margin shelf, in: Foreland Basins and Foldbelts. AAPG Memoir 55, 309-339.
Bordenave, M.L., 2014. Petroleum Systems and Distribution of the Oil and Gas Fields in the Iranian Part of the Tethyan Region. AAPG Memoir 106, 505-540.
Bordenave, M.L., Hegre, J., 2010. Current distribution of oil and gas fields in the Zagros Fold Belt of Iran and contiguous offshore as the result of the petroleum systems. Geological Society of London, Special Publication 330, 291-353.
Dow, W.G., 1977. Kerogen studies and geological interpretations. Journal of Geochemical Exploration 7, 79–9.
Ehrenberg, S.N., Pickard, N.A.H., Laursen, G.V., Monibi, S.Z., Mossadegh, K.T. Svana, A.A., Aqrawi, A.M., McArthur, J.M., Thirlwall M.F., 2007. Strontium isotope stratigraphy of the Asmari Formation (Oligocene– Lower Miocene), SW Iran. Journal of Petroleum Geology 30, 107–128.
Hessami, K., Koyi, H.A., Talbot, C.J., Tabasi, H., Shabanian, E., 2001. Progressive unconformities within an evolving foreland fold-thrust belt, Zagros Mountains. Journal Geological Society of London 158, 969–981.
Hower, J., Eslinger, E.V., Hower, M.E., Perry, E.A., 1976. Mechanism of burial metamorphism of argillaceous sediment: 1. Mineralogical and chemical evidence. AAPG Bulltin 87, 725-737.
Hunt, J.M., 1996. Petroleum Geochemistry and Geology. 2nd edition. W.H. Freeman and Company, New York, P. 743.
Jacob, H., 1989. Classification, structure, genesis and practical importance of natural solid oil bitumen (“migrabitumen”), International Journal of Coal Geology 11, 65-79.
James G.A., Wynd J.G., 1965. Stratigraphic Nomenclature of Iranian Oil Consortium Agreement Area.  AAPG Bulltin 49, 2182-2245.
Kalani, M., Jahren, J., Mondol, N.H., Faleide, J.I., 2015. Compaction processes and rock properties in uplifted clay dominated units- the Egersund Basin, Norwegian North Sea. Marine and Petroleum Geology 68, 596-613.
Lüning, S., Kolonic, S., 2003. Uranium spectralmgamma-ray response as a proxy for organic richness in black shales: applicability and limitations. Journal of Petroleum Geology 26, 153-174.
Opera, A., Alizadeh, B., Sarafdokht, H., Janbaz, M., Fouladvand, R., Heidarifard, M.H., 2013. Burial history reconstruction and thermal maturity modeling for the Middle Cretaceous-Early Miocene Petroleum System, southern Dezful Embayment, SW Iran. International Journal of Coal Geology 120, 1-14.
Paxton, S.T., Aufill, M., Kamann, P., Krystyniak, A., 2008. Spectral gamma-ray response of Oklahoma shales in outcrop: Gas Shales Workshop, Oklahoma Geological Survey, University of Oklahoma, Norman, Oklahoma, October 22, 2008.
Peters, K.E., 1986. Guidelines for Evaluating Petroleum Source Rock Using Programmed Pyrolysis. AAPG Bulletin 70, 318-329.
Peters, K.E., Casa, M.R., 1994. Applied source rock geochemistry, in Magoon, L.B., and Dow, W.G., eds., The petroleum system-from source to trap. AAPG Memoir 60, Chapter 5.
Peters, K.E., Walters, C.C., Moldowan, J.M., 2005. The Biomarker Guide, 2nd Edition. Cambridge University Press, p. 680.
Poppe, L.J., Paskevich, V.F., Hathaway, J.C., Blackwood, D.S., 2001. A laboratory manual for X-ray powder diffraction, US Geological Survey Open-File Report.
Sepehr, M., Cosgrove, J.W., 2004. Structural framework of the Zagros Fold-Thrust Belt, Iran. Marine and Petroleum Geology 21, 829-843.
Serra, O., 1989. Sedimentary environments from wire line logs, Schlumberger Publications, p. 243.
Shabafrooz, R., Mahboubi, A., Vaziri-Moghaddam, H., Ghabeishavi, A., Moussavi-Harami, R., 2015. Depositional architecture and sequence stratigraphy of the Oligo-Miocene Asmari platform; Southeastern Izeh Zone, Zagros Basin, Iran. Facies 61, 1-32.
Sharland, P.R., Archer, R., Casey, D.M., Davies, R.B., Hall, S.H., Heward, A. P., Horbury, A.D., Simmons, M.D., 2001. Arabian Plate sequence stratigraphy. GeoArabia Special Publication No 2, Gulf PetroLink, Bahrain, p. 371.
Sherkati, S., Molinaro, M., Frizon de Lamotte, D., Letouzey, J., 2005. Detachment folding in the Central and Eastern Zagros fold-belt (Iran): Salt mobility, multiple detachments and late basement control. Journal Structural Geology 27, 1680-1696.
Siddique, A.N., EL-Ghali, A.M., Bin Abd Rahman, H.A., Mijinyawa, A., Ben-Awuah, J., 2013. Depositional Environment of Shallow- Marine Sandstones from Outcrop Gamma- Ray Logs, Belait Formation, Meragang Beach, Brunei Darussalam. Research Journal of Environmental and Earth Sciences 5, 305-324.
Stach, E., Mackowsky, M.T., Teichmüller, M., Taylor, G.H., Chandra, D., Teichmüller, R., 1982. Stach's Textbook of Coal Petrology, third Revised and Enlarged Edition. Ber- lin-Stuttgart, Gebrüder Borntraeger, P. 535.
Taylor, G.H., Teichmüller, M., Davis, A., Diessel, C.F.K., Littke, R., Robert, P., 1998. Organic Petrology. Schweizerbart Science Publishers, Stuttgart, Germany, p. 704.
Thyberg, B., Jahren, J., Winje, T., Bjørlykke, K., Faleide, J.I., Marcussen, Ø., 2010. Quartz cementation in Late Cretaceous mudstones, northern North Sea: Changes in rock properties due to dissolution of smectite and precipitation of micro-quartz crystals. Marine and Petroleum Geology 27, 1752–1764.
Tissot, B.P., Welte, D.H., 1984. Petroleum Formation and Occurrence. 2nd Edition. Springer - Verlag, Berlin P. 699.
Van Buchem, F.S.P., Allan, T.L., Laursen, G. V., Lotfpour, M., Moallemi, A., Monibi, S., Motiei, H., Pickard, N.A.H., Tahmasbi, A.R., Vedrenne, V., Vincent, B., 2010. Regional stratigraphic architecture and reservoir types of the Oligo-Miocene deposits in the Dezful Embayment (Asmari and Pabdeh Formations) SW Iran, Geological Society, London, Special Publications. Vol. 329(1), 219-263.
Vaziri-Moghaddam, H., Kimiagari, M., Taheri, A., 2006. Depositional environment and sequence stratigraphy of the Oligo – Miocene Asmari Formation in SW Iran. Facies 52, 41-51.
Wilkin, R.T., Barnes, H.L., 1997. Formation processes of framboidal pyrite. Geochimca et Cosmochimica Acta 61, 323-339.