Middle Jurassic organic-walled dinoflagellate cysts and palynofacies from Telma-Dareh, south of Sari, northern Iran

Abstract

Analyses of organic-walled dinoflagellates and palynofacies from the marly Unit 3 of the Dalichai Formation in the Telma-Dareh section of the Central Alborz Mountains, northern Iran, have been carried out. Our palynological study has revealed diverse and well-preserved dinoflagellate cyst assemblages, comprising 49 taxa. Based on the first and last appearance datums of dinoflagellate index species, this marly part can be correlated with the northwest European Nannoceratopsis gracilis Biozone of Aalenian to early Bajocian age. Dinoflagellate cyst assemblage data allow the placement of the Aalenian/Bajocian boundary and correlation with the range of the belemnite Brevibelus breviformis. The Aalenian age of the Dalchai Formation at Telma-Dareh contrasts to the Bajocian age attribution by previous authors. Similarities of dinoflagellate cyst assemblages to those from northwest Europe and the northwest Tethys indicate marine connections between the two areas. The palynofacies predominance of land-derived phytoclasts reflects deposition on a proximal oxic shelf with high terrestrial and freshwater influx. Dinoflagellate cyst assemblages that are dominated by representatives of Nannoceratopsis presumably reflect brackish conditions.