Integrated Biostratigraphy, Depositional Setting and Geochemical Analyses for Petroleum Potential Evaluation of the Lower Cretaceous (Barremian - Albian) Strata of the Koppeh-Dagh Basin, Northeastern Iran

The lower Cretaceous rock units of the Koppeh-Dagh Basin of northeastern Iran were investigated here in terms of biostratigraphy, depositional setting and geochemical analyses to find out if they, alike other parts of the world, are rich in petroleum. For this purpose, a stratigraphic framework is established using calcareous nannofossil and palynological elements. A nannoplankton zonation based on which subzones of the zones CC7 - CC8 of Sissingh (1977) and their equivalent NC6 - NC8 of Roth (1978) was established indicating a Late Barremian-Albian age. Palynological assemblages led us to establish the local palynozone of Odontochitina operculata. A dominantly marginal basin to a transitional zone between shelf and basin under a dysoxic-anoxic condition with low to moderate sedimentation rates coincided with a gradual sea level rise was introduced as the environment of deposition for the strata via interpretation of the palynological parameters and quantitative palynology. The obtained data from Rock-Eval pyrolysis in compilation with palynofacies analysis reveals that the studied succession contains mainly gas-prone type III kerogen. The Spore Coloration Index (SCI) alongside with the Rock-Eval pyrolysis results (low values of HI and TOC) proves that these rock units locally produced natural gas during the time under consideration.