Biostratigraphy, facies and sequence stratigraphy of the Kalat Formation in the West of Kopet Dagh Basin

In order to determine biostratigraphy, facies and sequence stratigraphy of the Kalat Formation in the West of Kopet Dagh Basin, two Jozak and Chakhmaghlu stratigraphic sections were selected and sampled. The thickness of the Kalat Formation in the Jozak and Chakhmaghlu stratigraphic sections are 158 and 139m respectively, and its lithology consists mainly of gray to brown limestones and few marl. Biostratigraphic studies led to recognition of 32 genera and 15 species of benthic foraminifera and 11 genera and 6 species of planktonic foraminifera and then, Siderolites calcitrapoides-Sirtina orbitoidiformis Assemblage Zone was identified. Based on the indicated biozone and fossil contents, the age of the Kalat Formation is Maestrichtian. Petrographic analysis led to recognition of one silliciclastic and ten carbonate facies belonging to four depositional environments including tidal flat, restricted and semi-restricted lagoon, shoal and open marine. The identified facies were deposited on a homoclinal ramp setting. On the basis of facies distribution and depositional environments, two depositional sequences were proposed for the Kalat Formation. Depositional sequence 1 consists mainly of proximal open marine and shoal facies. Maximum flooding surface of this sequence is characterized by open marine facies containing echinoid and planktonic foraminifera. Depositional sequence 2 consists mainly of shoal facies rich in bioclast, intraclast, benthic foraminifera and rudist. MFS of depositional sequence 2 is represented by bioclast echinoid packstone facies. Comparison between sea level changes in the study area with eustatic sea level and Arabian Plate sea level curves show that sedimentation of the Kalat Formation was influenced by eustatic sea level change.