The Biostratigraphy of Lower Triassic Strata in Ruteh Section (Central Alborz) at North of Tehran

The studied section (Ruteh) is situated in central alborz، 31km north of Tehran. The thikness of measured section is 312m. The Elika Fm in Ruteh section is located 1 km far from the north of Ruteh village and 3 km far from the north of Fasham city. Lowermost strata seems to be parallel to rocks of the units which attribiuted to the Nessen Formation. and the upper boundary with Shemshak Fm. is obviously indicate disconformity. The Elika Fm. is subdivided to 9 lithological subunits. the lower part is consisting of thin-medium-bedded limestone. The upper part is mainly consisting of thick-bedded dolomite with intercalations of thin-bedded limestones. The Nessen Fm in this section subdivided to 2 lithological subunits. The lower part is consisting of 8 m bauxite-laterite and the upper part is mainly consisting of thin-medium-bedded limestones. Base of micropaleontology studies، 26 genus، 47 species and 1 subspecies of Foraminifers and conodont element have been recognized illustrating 1 Foraminifer biozone and 4 Conodont biozones. This Conodont biozones in Elika Fm consist of: Hindeodus parvus zone Pachycladina – Hadrodontina zone، Neospathodus cristagalli zone، Parachirognathus – Furnishius zone. According to Conodont data، carboniferous sequences in Ruteh Section were deposited from lower Griesbachian to Anisian-Ladinian in age. Also 8 genus and 14 species of Foraminifers have been described for the first time in uppermost of the bauxite – laterite، so 1 Assemblage zones have been reported: Paraglobivalvulina mira – Pachyphloia iranica Assemblage zone. Comparision of color index Alteration (CAI) or postmortal facies Conodont elements with standard table presented by Epstein et al. (1977)، show that CAI is 4 that indicate temporal interval of 190 – 300 with notation to this degree of temperature absence Oil and Gas in area.