Palynology and sequence stratigraphy of the Albian-Cenomanian strata from the Koppeh-Dagh Basin, northeastern Iran

The Albian-Cenomanian strata of the Koppeh-Dagh Basin were investigated for their marine palynomorphs and palynofacies contents and used for palaeoclimatic, palaeoenvironmental and sequence stratigraphical purposes. Various palynofacies criteria such as Palynological Marine Index (PMI), chorate/proximate, proximochorate and cavate ratio (C/PPC) and outer neritic/inner neritic index (ON/IN) were applied as alternative indicators to monitor the proximal-distal trends. Higher values of the former proxies versus low continental/marine ratio (CONT/MAR) were documented during periods of relative rise of sea-level. Increasing values of the marine palynological proxies such as the PMI, C/PPC and ON/IN were consistent with maximum flooding surfaces (MFS). A relatively diverse dinoflagellate cyst assemblage was reported at MFS, whereas, during the periods of relative sea-level fall, the dinocyst diversity decreased and coincided with those above-mentioned marine palynological ratios that reinforced terrestrial conditions. Palaeovegetation reconstruction showed the predominance of the pteridophyte spores. This palynoflora indicates a humid and warm climate during the Albian-Cenomanian time. Three deducted depositional sequences correspond with those suggested in previous studies based on surface and subsurface geological data. Sea-level changes correspond well with those reported from other parts of the Tethys.