Biostratigraphy of the Bazehowz Formation at its Type section, South West Mashhad based on plant macrofossils

Jurassic deposits are well exposed in the Bazehowz area, South west of Mashhad city, East Alborz, Iran. It contains plant macrofossils belonging to eighteen species of eleven genera of various orders such as Equisetales, Filicales, Bennettitales, Cycadales, Corystospermales, Caytoniales, Ginkgoales and Pinales. Two biozones were recognized in the type section of Bazehowz Formation. Biozone I is an assemblage biozone with its lower and upper boundaries identified by first observed occurrence (FOO) and the last observed occurrence (LOO) of Nilssonia rigida, Nilsssonia sp. cf. N. bozorga and Nilssonia feriziensis. Since there are species from Liassic such as Nilssonia rigida and uppermost Liassic such as Nilssonia feriziensis and Nilssonia sp. cf. N. bozorga, a Toarcian age is suggested for this biozone. Biozone II is an interval zone with its lower and upper boundaries identified by FOO of Klukia exilis and Ptilophyllum vasekgahenses and Coniopteris hymenophylloides and Ctenozamites cycadea, respectively. According to occurrence of Klukia exilis, a lowermost Middle Jurassic age is suggested for the lower boundary and based on the occurrence of Coniopteris hymenophylloides Aalenian age is considered for upper boundary of Biozone II. On the basis of relative abundance of Filicales (%16.6), Bennettitales (%27.7) and Cycadales it is considered a humid sub-tropical climate for this period of time.