Biostratigraphy,depositional environment and sequence stratigraphy of late cretaceous clastic-evaporite-carbonate deposits,east of central Iran,Bajestan

Late cretaceous deposits in chahchool section from bajestan (ne iran) attain a thickness of 352 m. four lithostratigraphic units composed of conglomerates,sandstones,siltstones,shales,marls,gypsum,bioclastic and hippuritic limestones are recognized. upwards they are followed by quaternary alluviums and transgressively overlain by quaternary sediments. in this study,nineteen genera and twelve species of benthic foraminifera,one genus of planktic foraminifera,three genera and four species of calcareous algae and lingulogavelinella arnagerensis assemblage zone were identified. the middle coniacian age of the carbonate deposits is based on determined benthic foraminifera genera,species and biozones. the carbonate deposits conformably overlie clastic-evaporitic sediments which contain no fossils. this succession likely belongs to progression of early late cretaceous(?). twenty four facies have been identified including six siliciclastic lithofacies belong to oxygenated coastal belt-tidal flat consists of 1-gcm lithofacies as beach channel fill 2-3-two sandstone lithofacies belongs to shoreface and offshore transition 4-siltstone lithofacies belongs to offshore and supratidal 5-6-two shale lithofacies consist of shale devoid of fossils belongs to supratidal and shale with foraminifera belongs to shallow open marine,one evaporative lithofacies belongs to saline,seventeen carbonate faciesfrom sea toward land consist of nine facies most of them micritic belong to open marine,two grain stone facies belong to barrier,five miliolid,ostracoda and peloid facies belong to lagoon and one marl with no fossils facies belongs to supratidal. these sediments deposited in one depositional sequence of iii category according to the test composition of foraminifera and facies. this depositional sequence deposited in lst,tst and hst systems tracts. the lower boundary of this sequence is sb1? according to the cover and conglomerate layer in this boundary and the upper boundary of this sequence is sb1 due to erosional evidences or disconformity. the interpretation of sea level fluctuation at the time of deposition corresponded to global eustatic curve and differences are attributed to the regional tectonic. © 2017,national centre of excellence in geology. all rights reserved.