Baghamshah Formation was previously attributed to Jurassic age in Iran, based on stratigraphic distribution of ammonite. But, recent studies of calcareous nannofossils in Lut Block show that the age of this formation was attributed to Early Cretaceous (Early Berriasian to Early Barremian). This study analyzed stratigraphic distribution of calcareous nannofossils of Baghmashah Formation in Esfandiar section located in the southeast of Tabas Block (close to type section). Examining collected samples resulted in identifying 39 calcareous nannofossil and 6 didemnid ascidian spicules species belonging to 19 genera, corresponding from CC1 to CC5 biozones with the age of early Berriasian to early Barremian. Index nannofossil species in studying succession indicate that sedimentary basin of Baghamshah Formation in Esfandiar section was located in low latitudes of Tethyan realm with warm surface water with rising depth toward the top of section. Also, the oceanic basin was oligotrophic type with low-fertility, which its nutrient supply had dropped toward the top of section. The oligotrophic paleoenvironment during the late Berriasian to early Valanginian in the studied area in Eastern Iran may have corresponded to the global low sea-level.

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