Lithostratigarphy and Biostratigaraphy of the Dalichai Formation in Absharaf Section, Northwest of Damghan on the base of Ammonites (East Alborz)

The Middle and Upper Jurassic sedimentary well successions is located in the northwestern Damghan, (eastern Alborz range). The Dalichai Formation with a thickness of 618 meters in the studied section consists of marl, limestone and marly limestone. The lower boundary with the siliciclastic of the underlying Shemshak Formation is unconformable and in the upper boundary is gradually covered by the Lar Formation. From studied section, altogether 371 fossile sample were collected of which 15 sample were related to other taxon (Bellemnite, Bivalve, Coral and Sponge). Altogether, 51 species of ammonites from the Dalichai Formations belonging to 25 genera and 9 families and 14 zones are described. The following families are reported: Phylloceratidae, Lytoceratidae, Haploceratidae, Oppeliidae, Parkinsoniidae, Morphoceratidae, Reineckeiidae, Perisphinctidae and Aspidoceratidae. Based on ammonites, the Dalichai Formation ranges from the Upper Bajocian to Lower Kimmeridgin and can be subdivided, from bottom to top, into six informal members. Palaeobiogeographically the ammonite fauna is closely related to that of the sub-Mediterranean Province of the northwestern Tethys.