Writers : Kord ghadimi,Barat mohammad;supervisor: A.Ashouri
Refference : M.Sc.Thesis-Ferdowsi University, Mashhad
Publishing Year : 1383

Abstract :

The Late Devonian strata in west and northwest of Esfarayen (NE of Iran) are one of fossiliferous units, which are outcropped in two different areas:
1- Chahar-borj (30 km west of Esfarayen) and 2- Shiroyeh (25 km northwest of Esfarayen). The study of rich and good preserved coral fossils of the unit is the aim of the present research.
The studied strata composed of limestone, marly limestone, sandy limestone and shale which have a conforme graduate contact with Padeha Formation, the lower, and disconform contact with the Shemshak Formation, the upper.
Stratigraphically, this unit is part of the Khoshyeilagh Formation in the eastem Alborz.
In this study 12 genera and 18 species have been identified and introduced. All identified species here in, introduced for the first time from the studied areas; 5 of them for the first time in Iran.
Baswd on the identified coral fossils, Frasnian-Famennian age has been suggested for the unit.
Some identified index Frasnisn species herein have been reported from the other part of Iran: Alborz Mountains and Central Iran (Tabas, Esfahan and Kerman areas). These evidence display all this areas have been covered by the same sea. In the large scale, similar situation have been reported from Afghanistan, Australia and South of China. This mains similar latitude position for these areas.
Lithological facies and morphology configuration study reveals 2 ecological zones:
1- Shallow and highly energetic environment contains large corals with dissepiments, Frasnian in age.
2- Low energetic environment contains shallow and medium solitary corals with auloses, Famennian in age.
The presence of corals with dissepiments, less abundance and variety in Frasnian time which has been displaced with corals containing auloses, less variety and high abundance shows the effect of the Late Frasnian mass extinction.
Lithological facies study shows four facies (open marian, barrier, lagoon and tidal flat), which indicate the studied strata, have been deposited in a shallow to shore environment.