Palynostratigraphy and Foraminiferal Stratigraphy of the Early Miocene Qom Formation in the Northeastern Margin of the Tethyan Seaway

Abstract

Lower Miocene strata are exposed in the northwest of Ashtian, in the Central Iran Zone. Biostratigraphy of the Qom Formation was investigated using dinoflagellate cyst and benthic foraminifera. The stratigraphic distribution of the dinocysts lead to the identification of two distinctive stratigraphically non-continuous palynozones viz., Caligodinium amiculum (late Aquitanian) and Cordosphaeridium cantharellus (early Burdigalian) zones. This biozonation is equivalent to that recognized in Northwest Europe. Moreover, the presence of such stratigraphically distinctive taxa as Borelis melo curdica, Meandropsina iranica, Elphidium sp. 14, and Miogypsina sp. enabled the identification of the two consecutive biozones: the Elphidium sp. 14—Miogypsina Assemblage Subzone and the Borelis melo group Meandropsina iranica Assemblage Zone. The late Aquitanian–Burdigalian age is collectively attributed, therefore, to the studied section. This age assignment is based on the dinocysts and foraminifer species compared with other stratigraphic sections. The close resemblance of the dinoflagellate cyst assemblages of the Qom Basin with Northwest Europe and the northwestern Tethys during the Oligocene-early Miocene indicates a marine connection and faunal exchange between the two regions.