Middle Jurassic palynology of the southwest Tabas Block, Central-East Iran

Abstract

Diverse and moderately to poorly preserved palynofloras occur in the lower Middle Jurassic strata of the Hojedk Formation in the Chahrekhneh, southwest of Tabas, east central Iran. The palynofloras comprise 56 species including spores (15 species allocated to seven genera), various types of pollen (30 species designated to 16 genera), dinoflagellate cysts (five representatives of three genera), and one acritarch. The vertical distribution of miospores allows the erection within the Hojedk Formation of one biozone, the Klukisporites variegatus—Callialasporites trilobatus Assemblage zone, based on the first observed occurrence and the last observed occurrence of selected taxa. Moreover, the vertical distribution of dinoflagellate cysts allows the erection within this formation of one biozone, the Nannoceratopsis sp. cf. N. gracilis Interval zone. These biozones are compared with palynozones from approximately coeval strata in Iran and elsewhere. Abundance of ferns and cycadophytes in the parent floras implies that the host strata accumulated under a moist warm climate during the early Middle Jurassic in this locality. Based on various data of ecogroups in Chahrekhneh, it is considered that there were several environments of upland, warmer lowland, wetter lowland, rivers and delta. Furthermore, based on the occurrence of dinoflagellate cysts it can be concluded that Chahrekhneh is located at the south coastal boundary of the Iran Plate, along the Tethys Ocean.