چکيده

The Shemshak Group is well-exposed and spread in the Baladeh area (Central Alborz). 22 macrofossil species allocated into 14 genera of various orders such as Equisetales, Filicales, Bennettitales, Cycadales, Ginkgoales, Czekanowskiales and Coniferales are identified. Two asseblage biozones are recognized. Assemblage zone I is established based on Ptilophyllum minor and Klukia exilis, and assemblage zone II is recognized according to Coniopteris hymenophylloides and Ptilophyllum harrisianum. Furthermore, on the basis of presence of index fossils such as Equisetites columnaris, Coniopteris hymenophylloides, Klukia exilis, Nilssonia macrophylla and Ptilophyllum minor the Early to Middle Jurassic age (?Hettangian-Toarcian to Bajocian) is suggested for these sediments.