چینه نگاری زیستی و سکانسی سازند تیرگان در شرق حوضه کپه داغ (دره خور، شمال شرق مشهد)

Abstract

Barremian-Aptian Tirgan Formation has an exellent northwest- southeast trending exposure in eastern part of the Kopet-Dagh Basin. This formation consists mainly of oolitic and Orbitolina limestone and shale interbeds. It is conformably overlain and underlain by the Sarcheshmeh and Shurijeh Formations respectively. In order to recognize the sedimentary facies and study the bio and sequence stratigraphy, two stratigraphic sections were measured and sampled in northestern and southwesterern flanks of Khore syncline. The results of this study revealed that these sediments are deposited in shallow carbonate ramp and in 4 facies belt including open marine, bar, lagoon and tidal flat. Based on sequence stratigraphic analysis, 2 depositional sequences have been identified that are bounded by type 2 sequence boundries. Paleontological studies in this area show the present of two fossil associations from bentonic foraminifers and calcareous green algae. For the first time, Juraella bifurcata is reported from the eastern Kopet-Dagh basin. Based of recognition of 8 genuses and 11 species of bentonic foraminifers and 3 genuses and species of calcareous green algae in Khore syncline, we suggest Barremian- Aptian age for these sediments.