Marine palynology and environmental interpretation of the Lower Cretaceous (Barremian?-Aptian) rock units in the Koppeh-Dagh Basin, NE Iran

The Sarcheshmeh and Sanganeh formations are the Lower Cretaceous deep marine sequences of the Koppeh-Dagh sedimentary basin, which revealed a diverse assemblage of dinoflagellates. The paper discusses palynostratigraphy, palynofacies and palaeoenvironment of these rock units in a borehole drilled in the eastern part of this basin. Ninety-five ditch-cutting samples were prepared and studied palynologically, which resulted in recognition of 76 species of dinoflagellate cysts belonging to 29 genera. The recorded assemblages are in accordance with the Odontochitina operculata Zone suggesting a Barremian?-Aptian age for the formations. Palynological data extracted led to identification of five palynofacies types based on the categories of Tyson (1995). These indicate a marginal, proximal and distal shelf environment of deposition. The obtained data from calculated palaeoecological factors revealed a gradual sea level rise during the deposition of these rock units, resulting in replacement of the oxic/dysoxic Sarcheshmeh Formation by the dysoxic/anoxic Sanganeh Formation.