Conodonts Biostratigraphy of Mila Formation, Shahmirzad Section, Central Alborz, Iran

The studied section is located in the southern flank of the Central Alborz, 5 kilometers north of Shahmirzad City in the Semnan province. This section is situated at 35° 48′ 40″ N latitude and 53° 16′ 59″ E longitude. The Mila Formation has 5 measurable members in Type Section (Mila Kuh, Damghan City) and only in this studied section. This formation overlies conformably the Early Cambrian Lalun Sandstone Formation and underlies disconformably the Early Devonian red conglomerates. Studied Conodonts of this formation are of Proconodontus type belonging to Coniform Groups. 14 species and 6 genera of these conodonts were acquired indicating an age of Mid-Late Cambrian and Early Ordovician. These Conodonts are listed as below: Proconodontus serratus, Proconodontus muelleri, Proconodontus rotundatus, Prooneotodus sp?, Prooneotudus tenuis, Furnishina furnishi, Furnishina asymmetrica, Furnishina sp., Furnishina obliqus-Hirsutodontus?, Westergardodina cf. mossbergensis, Westergardodina fossa, Cordylodus, Cordylodus intermedius, Cordylodus lindstromi, Cordylodus proavus, Oneotodus nakamurai & Problematoconites sp. A remarkable point is the discovery of species Prooneotodus tenuis in the second member of Mila Formation because no conodont has already been reported this member.
Other microfossils such as Trilobites, Brachiopoda, Hyolithes, Eocrinoidae, Rusophycus, Cruziana, Paleoscoleidae and Sponges were also obtained indicating the deposition of Mila Formation in a shallow marine environment. These fossils assemblage are comparable with those other parts of Iran and neighbor countries.