Organic Geochemistry and Petrography of the Shemshak Formation in the eastern Alborz,

Category Sedimentology
Group GSI.IR
Location The 24 Symposium of Geosciences
Author Ali Shekarifard, Kazem Seyed-Emami and Francois Baudin
Holding Date 18 August 2007


Organic geochemistry and petrography investigations for determination of organic matter quality, type and thermal maturity were carried out on shaly sediments of the Shemshak Formation (Upper Triassic to Lower-Middle Jurassic) from twelve sites in eastern Alborz basin. So far 165 fresh surface samples have been studied. The total organic carbon) TOC( content of samples is between 0.2 and 6.7 wt %, indicating a poor to very good organic content. Organic geochemical analyses (Rock-Eval Pyrolysis) performed on thirteen kerogen concentrates reveal the dominance of organic matter with low hydrogen content of terrestrial or degraded marine origin. The location of studied samples on the modified Van-Krevelen diagram (Tmax-HI) shows the presence of mixture of kerogens type III and type IV. Tmax values obtained from Rock-Eval Pyrolysis ranges from 390 ºC to 587 ºC, indicating immature, mature and over-mature organic matter. Organic Petrography by using transmitted light microscopy suggests that organic matter of the studied samples, include continental (manily) and marine fraction. The continental fraction contains opaque phytoclasts, semi-opaque phytoclasts, translucent phytoclasts and terrestrial sporomorphs. The marine fraction is composed of algal debris, acritarch and dinoflagellate cysts ?. Amorphous organic matter dominates in all samples and it could be derived from the degradation of both terrestrial and marine constituents. Organic Petrography in the studied samples indicates also the presence of kerogen type II. The sedimentary organic matter of the Shemshak Formation, in the studied samples corresponds to inertinite, vitrinite, cutinite, spornite and exinite macerals .

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