Biostratigraphy, depositional environment and sequence stratigraphy of clastic-carbonate deposits of Lower Cretaceous, East of central Iran, Dehuk

The Lower Cretaceous deposits in Dehuk section from Southeast of Tabas attain a thickness of 72/5 meters and consist of conglomerate, sandstone, Orbitolinids limestone, ooid limestone, marl and sandy limestone. The lower boundary of these deposits with Esfandiar Formation is a faulty contact and upwards they are followed by Kerman Conglomerate with disconformity. In this study by an analysis of 53 samples and based on paleontological studies, 4 genera and 3 species of Orbitolinids consist of Palorbitolina lenticularis, Preaorbitolina cormyi, Mesorbitolina texana and Orbitolina sp. and three biozones consist of Palorbitolina lenticularis Interval Zone, Preaorbitolina cormyi Total range Zone and Mesorbitolina texata Interval Zone have been distinguished. The relative age of carbonate part is Late Barremian to Late Aptian according to determined genera, species and Orbitolinids biozones. In these deposits have been identificated two clastic lithofacies belong to oxygenated coastal belt consist of Gcm lithofacies belongs to beach channel fill and sandstone lithofacies with interbeddeds of mud belongs to offshore transition; And twelve carbonate facies from marine to shore consist of two Orbitolinids facies and five Orbitolinids subfacies belong to restricted to open marine, nine grainstone to packstone facies and two subfacies belong to shoal and one marl with no fossils facies belongs to tidalflat. These deposits formed in four depositional sequences of III category and each systems tract contains several progression and regression parasequences. The boundaries of between of sequences are SB1? Due to the frequency of iron oxides around the Orbitolinids and the other allochems. The lower of sequence boundary is unknown due to the faulty contact and the upper of sequence boundary is SB1 and RSME for disconformity. Due to the presence of index fossils in these sequences, the first sequence (carbonate part) deposited in the Late Barremian-Early Aptian, the second and the third sequences deposited in the Early Aptian and the fourth sequence deposited in the Late Aptian. The interpretation of sea level fluctuation at the time of deposition corresponded to global eustatic curve and differences can be result from progressions and regressions for the structure of the region.