Palynostratigraphy and palaeoecology of the Middle Jurassic strata, Tapal, west of Shahrood, eastern Alborz Subject Areas :

Palynological data are used for palynostratigraphy and reconstruction of some environmental parameters of the Middle Jurassic (Bajocian - Callovian) deposits at the Tapal stratigraphic section, west of Shahrood, eastern Alborz. The studied strata (Dalichai Formation) contain diverse, relatively well-preserved palynofloras, including miospores (spores and pollens), dinoflagellates cysts, fungal spores, foraminiferal test linings, acritarchs and Tasmanites. The palynofloras include 22 species of spores (belonging to 18 genera), 15 species of pollen (attributed to 9 genera) and 28 species of dinoflagellate cysts (assigned to 15 genera). Based on the stratigraphic distribution of miospores, the Klukisporites variegatus-Araucariacites australis-Cerebropollenites macroverrucosus Assemblage Zone is recognized in the sequence examined, Presence of some index dinoflagellate species led to the identification of three successive biozones including, in an ascending order, Cribroperidinium crispum Total Range Zone (late Bajocian), Dichadogonyaulax sellwoodii Interval Zone (Bathonian – early Callovian) and Ctenidodinum continuum Interval Biozone (early - middle Callovian). To reconstruct some parameters of the sedimentary environments of the studied strata, evidences such as frequency and diversity of spores attributable to ferns, relative abundance of drier/wetter and warmer/cooler elements in different plant communities, ratio of palynological elements and palynofacies, presence of index shallow water dinoflagellate cysts for instance Dichadogonyaulax sellwoodii, Ctenidodinium spp., Valensiella ovulum, Pareodinia spp., Nannoceratopsis gracilis, abundance of proximate dinocysts forms, presence of fungal spores and warm - temperate water dinoflagellate (Gonyaulacysta centriconnata, Nannoceratopsis pellucida, Gonyaulacysta jurassica, Pareodinia ceratophora) are utilized. Based on the above criteria, the material examined seems to have been deposited in a marine margin, low oxygen environment, with low rate sedimentation, under hot and humid climate conditions, where the surrounding terrestrial vegetation was dominated by ferns.