Biostratigraphy and depositional history of Coniacian-Santonian succession in East of Ramhormoz area (Tange-Bulfaris section)

This study is focused on the biostratigraphy, sedimentary environments, facies distribution, and sequence stratigraphy of the Coniacian–Santonian sediments of Tange-Bulfaris section. Five assemblage zones have been recognized by distribution of the foraminifera in the study area. Assemblage zone 1(Chara Ostracods zone) is Coniacian in age and occurs in the lower part of the succession. Assemblage zone 2 (Valvulammina – Dicyclina zone) and Assemblage zone 3 (Rotalia cf. skourensis- Algae zone) are Coniacian – Santonian in age. Dicarinella concavata interval zone suggests a Coniacian to earliest Santonian age. Dicarinella asymetrica total range zone is Santonian in age. These sediments are subdivided into eight microfacies types belonging to various sedimentary environments, ranging from continental lacustrine to very shallow and relatively deep-water (hemipelagic to pelagic) marine environments. The observed facies patterns indicate a carbonate open shelf depositional environment. The inner shelf facies is characterized by wackestone–packstone, dominated by various taxa including miliolids, Rotalia, bryozoa, mollusca, ostracods and green algae. The middle shelf is represented by wackestone-packstone with a diverse assemblage of echinoid, corallinacean and bryozoans. Basinwards is dominated by argillaceous packstone characterized by planktonic foraminifera. Based on field observations, microfacies analysis and sequence stratigraphic concept, one-third-order sequence in the study section was identified. Shallow brackish to fresh-water ponds or lakes (MF 1) were deposited during short periods of very low sea level. The establishment of an open shelf carbonate platform took place during the transgressive system tract. MF (2,3,4,5,6,7) are deposited during the transgressive system tract. Appearance of deeper fauna and glauconite are interpreted as a maximum flooding surface (MF. 8).