Plant macrofossils and Biostratigraphy of the Calshaneh section, NW Tabas and its palaeoclimate analysis

Jurassic deposits are well exposed in the Calshaneh area, north western of the Tabas city, Central-East Iran. It contains plant macrofossils belonging to seventeen species allocated to eleven genera of various orders such as of Equisetales, Filicales, Bennettitales, Cycadales, Caytoniales, Ginkgoales and Pinales. One biozone was recognized in the Hojedk Formation at Calshaneh section. According to occurrence of Klukia exilis and Coniopteris hymenophylloides a Middle Jurassic age is suggested for this biozones. One Assemblage zone, Nilssnonia sp. cf. N. bozorga-Klukia exilis Assemblage zone, and three subzones were recognized in this section. Subzones are from base to up 1- Ptilophyllum harrisianum Taxon range zone 2- Elatides thomasii-Sphenobaiera longifolia concurrent range zone and 3- Ginkgoites sp. cf. G. parasingularis - Coniopteris hymenophylloides concurrent range zone. This Assemblage biozone is comparable to other biozones of the same age in Iran. Furthermore, relative abundances of taxa was studied and relative abundances of order Nilssoniales, Ginkgoales, Filicales, and Equisetales were 44.44%, 20.64%, 15.87, and 7.94% respectively. It is noteworthy that variety and relative abundance of the species of Genus Nilssonia (six species and 42.27%) and species of Order Ginkgoales (two taxa and 17.46%), as a macrophyllous cycadophyte, was high within the Calshaneh area. Therefore, a humid subtropical to temperate climate is considered for this period of time in this area.