Characterization of organic matter in the fine-grained siliciclastic sediments of the Shemshak Group (Upper Triassic–Middle Jurassic) in the Alborz Range, Northern Iran
Ali Shekarifard, François Baudin, Johann Schnyder, Kazem Seyed-Emami, 2009. "Characterization of organic matter in the fine-grained siliciclastic sediments of the Shemshak Group (Upper Triassic–Middle Jurassic) in the Alborz Range, Northern Iran", South Caspian to Central Iran Basins, M.-F. Brunet, M. Wilmsen, J. W. Granath
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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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This book combines interdisciplinary research results using structural geology, geophysics, sedimentology, stratigraphy, palaeontology, palaeomagnetism and subsidence modelling obtained through the MEBE (Middle East Basins Evolution) Programme and other groups in the South Caspian and Northern and Central Iran.
A great part of the volume is devoted to Northern Iran (Alborz, Binalud and Koppeh Dagh belts), dealing mainly with the Late Palaeozoic and the Mesozoic Eras. Two papers present subsidence models of the South Caspian Basin since the Jurassic and three papers focus on Central Iran.
The data and models in this compilation of papers present a detailed picture and a very comprehensive understanding of the Late Palaeozoic to Cenozoic evolution of the South Caspian and North Iran to Central Iran basins. Geodynamic evolution and sedimentation are mainly controlled by the closure of the Palaeo–Tethys due to collision of Eocimmerian blocks with south Laurasia, opening of the South Caspian Basin, and Neo–Tethys ocean closure associated with Arabia–Eurasia collision.