Late Triassic dinoflagellate cysts from the base of the Shemshak Group in north of Alborz Mountains, Iran

Ghasemi-Nejad, Ebrahim; Aghanabati, Ali; Dabiri, O

doi:10.1016/j.revpalbo.2004.07.001

Cited by 20 publications

(13 citation statements)

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“…Here the Ekrasar Formation follows apparently conformably the middle Triassic carbonates and is composed of homogeneous black shales, sometimes rich in pyrite, especially in the basal part of the formation. Some dinoflagellate cysts have been observed at some levels of the black shales indicating marine conditions (Ghasemi-Nejad et al 2004). …”

Section: A Upper Triassic Shales (Uts)mentioning

confidence: 99%

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Thermal maturity of the Upper Triassic–Middle Jurassic Shemshak Group (Alborz Range, Northern Iran) based on organic petrography, geochemistry and basin modelling: implications for source rock evaluation and petroleum exploration

Shekarifard

Baudin²,

Seyed–Emami

et al. 2011

Geol. Mag.

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Organic petrography and geochemical analyses have been carried out on shales, carbonaceous shales and coals of the Shemshak Group (Upper Triassic–Middle Jurassic) from 15 localities along the Alborz Range of Northern Iran. Thermal maturity of organic matter (OM) has been investigated using vitrinite reflectance, Rock-Eval pyrolysis and elemental analysis of kerogen. Reflectance of autochthonous vitrinite varies from 0.6 to 2.2% indicating thermally early-mature to over-mature OM in the Shemshak Group, in agreement with other maturity parameters used. The shales of the Shemshak Group are characterized by poor to high residual organic carbon contents (0.13 to 5.84%) and the presence of hydrogen-depleted OM, predominantly as a consequence of oxidation of OM at the time of deposition and the hydrogen loss during petroleum generation. According to light-reflected microscopy results, vitrinite/vitrinite-like macerals are dominant in the kerogen concentrates from the shaly facies. The coals and carbonaceous shales of the Shemshak Group show a wide range in organic carbon concentration (3.5 to 88.6%) and composition (inertinite- and vitrinite-rich types), and thereby different petroleum potentials. Thermal modelling results suggest that low to moderate palaeo-heat flow, ranging from 47 to 79 mW m−2 (57 mW m−2 on average), affected the Central-Eastern Alborz basin during Tertiary time, the time of maximum burial of the Shemshak Group. The maximum temperature that induced OM maturation of the Shemshak Group seems to be related to its deep burial rather than to a very strong heat flow related to an uppermost Triassic–Liassic rifting. The interval of petroleum generation in the most deeply buried part of the Shemshak Group (i.e. Tazareh section) corresponds to Middle Jurassic–Early Cretaceous times. Exhumation of the Alborz Range during Late Neogene time, especially along the axis of the Central-Eastern Alborz, where maximum vitrinite reflectance values are recorded, probably destroyed possible petroleum accumulations. However, on the northern flank of the Central-Eastern Alborz, preservation of petroleum accumulations may be expected. The northern part of the basin therefore seems the best target for petroleum exploration.

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Section: A Upper Triassic Shales (Uts)mentioning

confidence: 99%

“…According to sedimentological and palynological evidence, the Ekrasar Formation was deposited in a marine basin (Ghasemi-Nejad et al, 2004;Fürsich et al 2009) under suboxic to anoxic conditions. The black shales are locally enriched in organic carbon and are thermally over-mature ).…”

Section: A Upper Triassic Shales (Uts)mentioning

confidence: 99%

Thermal maturity of the Upper Triassic–Middle Jurassic Shemshak Group (Alborz Range, Northern Iran) based on organic petrography, geochemistry and basin modelling: implications for source rock evaluation and petroleum exploration

Shekarifard

Baudin²,

Seyed–Emami

et al. 2011

Geol. Mag.

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“…2004); SW: Switzerland (Hochuli & Frank 2000); UK: England (Morbey 1975;Morbey & Dunay 1978;Gaunt et al . 1992; this study); I: Alborz Mountains, Iran (Ghasemi-Nejad et al . 2004).…”

Section: Discussionmentioning

confidence: 62%

“…Rhaetogonyaulax and Heibergella have also been recovered in early Norian successions from the Alborz Mountains, Iran (Ghasemi-Nejad et al . 2004).…”

mentioning

confidence: 99%

High diversity dinoflagellate cyst assemblages from the Late Triassic of southern England: new information on early dinoflagellate evolution and palaeogeography

Palliani

Buratti

2006

LET

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“…at Sharif-Abad). Palynological observations of the basal shales of the Shemshak Group (Ekrasar Formation) at the Galanderud section showed a relatively rich assemblage of dinoflagellate (Ghasemi-Nejad et al 2004). These palynomorphs indicate the occurrence, at least in some levels, of restricted marine conditions during deposition of the TAS and the Ekrasar Formation.…”

Section: Palynofaciesmentioning

confidence: 90%

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

Shekarifard

Baudin²,

Schnyder³

et al. 2009

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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 ¼ 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).T max values range from 439 to 599 8C (average 500 8C), indicating that the organic matter has experienced high temperatures during deep burial and active post-sedimentary tectonics. The hydrogen index (HI)-T max 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-nonmarine 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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Late Triassic dinoflagellate cysts from the base of the Shemshak Group in north of Alborz Mountains, Iran

Cited by 20 publications

References 3 publications

Thermal maturity of the Upper Triassic–Middle Jurassic Shemshak Group (Alborz Range, Northern Iran) based on organic petrography, geochemistry and basin modelling: implications for source rock evaluation and petroleum exploration

Thermal maturity of the Upper Triassic–Middle Jurassic Shemshak Group (Alborz Range, Northern Iran) based on organic petrography, geochemistry and basin modelling: implications for source rock evaluation and petroleum exploration

High diversity dinoflagellate cyst assemblages from the Late Triassic of southern England: new information on early dinoflagellate evolution and palaeogeography

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

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