petroleum source rock potential of ordovician-silurian sediments in n-e bandar abbas, sw iran

the petroleum potential of the seyahou (ordovician) and sarchahan (lower silurian) formations in northern bandar abbas has not been investigated sufficiently. these sediments crop out as thinly laminated shales and are about 100 meters thick. a number of thirty-five selected samples were subjected to rock-eval pyrolysis followed by transmitted, reflected and uv light microscopy together with clay mineralogical studies. the rock-eval pyrolysis indicates that the samples from seyahou formation are poor in organic matter  ( toc <0.30% )  and  are  thermally over mature (tmax>470; tai>4) and microscopically have no fluorescing liptinite macerals. in comparison, the sarchahan formation is evaluated as a good and effective hydrocarbon source rock (toc>1%; ro%=1.15-1.20; tai=3+). the organic matter is chiefly composed of liptinite group of macerals including lamalginite and telalginite (type ii kerogen) which are brown under white light and weakly fluoresces under uv excitation. in addition, the other maturity indicators such as clay minerals and crystallinity of illite are in agreement with organic petrography suggesting that sarchahan formationn  is  thermally  mature  and  is at catagenetic stage of hydrcarbon generation (end of oil generation window and the beginning of gas generation zone). the seyahou and sarchahan formations formerly referred as gahkum fm. by previous workers (1978) were reported to be overmature and have reached graphitic stage. the lower silurian shales (sarchahan fm.) is correlated stratigraphically with silurian hot shales from saudi arabia, where their petroleum source potential have already been approved. this paper supported by new experimental data elucidates and emphasis the importance of petroleum potential of paleozoic strata for future hydrocarbon exploration in iran.