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Characterization of organic matter in the fine-grained siliciclastic sediments of the Shemshak Group (Upper Triassic–Middle Jurassic) in the Alborz Range, Northern Iran

By
Ali Shekarifard
Ali Shekarifard
University College of Engineering, School of Mining Engineering, University of Tehran, Tehran, IranUPMC UniversitéParis 06, UMR Tectonique, case 117, 4, place Jussieu, F-75005 Paris, FranceCNRS, UMR Tectonique, F-75005 Paris, France
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François Baudin
François Baudin
UPMC UniversitéParis 06, UMR Tectonique, case 117, 4, place Jussieu, F-75005 Paris, FranceCNRS, UMR Tectonique, F-75005 Paris, France
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Johann Schnyder
Johann Schnyder
UPMC UniversitéParis 06, UMR Tectonique, case 117, 4, place Jussieu, F-75005 Paris, FranceCNRS, UMR Tectonique, F-75005 Paris, France
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Kazem Seyed-Emami
Kazem Seyed-Emami
University College of Engineering, School of Mining Engineering, University of Tehran, Tehran, Iran
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Published:
January 01, 2009

Abstract

Bulk organic geochemical and microscopic studies (Rock-Eval pyrolysis, light transmitted–uv microscope) were carried out on the shales of the Upper Triassic–Middle Jurassic Shemshak Group in the northern, central and southern Alborz Range of northern Iran. Total organic carbon (TOC) values range from 0 to 29.4 wt% (1.2 wt% on average) indicating a generally poor–moderate organic carbon content. Upper Triassic shales in the lower part of the Shemshak Group have been mainly deposited in marine/lake settings under dysoxic–anoxic conditions, with TOC=0.7 wt% on average. Toarcian–Aalenian shales in the upper part of the Shemshak Group were deposited under comparatively deeper marine oxic–dysoxic conditions with the lowest TOC contents recorded (0.3 wt% on average). Carbonaceous shales at different stratigraphic levels of the Shemshak Group show the highest TOC contents (14.2 wt% on average). Tmax values range from 439 to 599 °C (average 500 °C), indicating that the organic matter has experienced high temperatures during deep burial and active post-sedimentary tectonics. The hydrogen index (HI)–Tmax diagram shows the presence of Type IV kerogen of altered organic matter with a very low mean HI value. The palynofacies is characterized by the dominance of amorphous organic matter probably predominately derived from degradation of marine–non-marine phytoplankton. The Upper Shemshak Group has low potential to produce petroleum, whereas the Lower Shemshak Group is an important effective petroleum source rock in the Alborz Range. The latter may have generated a considerable amount of petroleum at some localities (e.g. Tazareh and Paland) in the geological past.

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Geological Society, London, Special Publications

South Caspian to Central Iran Basins

M.-F. Brunet
M.-F. Brunet
CNRS-INSU and Université Pierre et Marie Curie, France
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M. Wilmsen
M. Wilmsen
Senckenberg Naturhistorische Sammlungen Dresden, Museum für Mineralogie und Geologie, Germany
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J. W. Granath
J. W. Granath
Granath & Associates Consulting Geology, USA
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Geological Society of London
Volume
312
ISBN electronic:
9781862395602
Publication date:
January 01, 2009

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