A high diversity of larger benthic foraminifera (LBF) fauna is recognized from the Ilerdian-Cuisian sedimentary succession for
the first time of the Birjand region, Sistan Suture Zone of eastern Iran. These foraminifera are described in accordance with the standard
shallow benthic zonation, placing considerable emphasis on biostratigraphic and microfacies analysis implications. Four shallow benthic
zones (SBZ8 and SBZ10-12) have been designated in LBF horizons comprising index zonal markers such as Alveolina elliptica nuttalli
(Davies), A. decipiens (Schwager), A. cf. oblonga, A. cf. minuta, A. cf. rugosa, A. cf. decastroi, A. aff. cremae, A. frumentiformis, A.
aff. palermitana, N. cf. atacicus (Leymerie), N. tauricus (De la Harpe), N. pratti (d?Archia & Haime), N. polygyratus (Deshayes), N. cf.
distans (Deshayes), Assilina sublaminosa (Gill), A. placentula (Deshayes), Asterocyclina cf. schweighauseri (Less), Discocyclina archiaci
cf. staroseliensis (Less), and D. cf. archiaci bartholomei (Schlumberger). Five microfacies types including Alveolina-Opertorbitolites
packstone (locally grainstone), nummulitids-Alveolina rudstone, Nummulites rudstone, Assilina-Nummulites rudstone, and
orthophragminid-nummulitid pack-rudstone have been defined in the current study. Microfacies type 1 is finely characterized by high
abundance of Alveolina with the predominance of A-form and globular to slightly elongate forms. Microfacies type 2 is dominated by
small nummulitids in association with the abundance of the most diverse Alveolina species. Microfacies type 3 is composed of a diverse
community of nummulitids, principally Nummulites A-forms along with Assilina. Microfacies type 4 is distinguished by a high diversity
of not only A- and B-forms of Nummulites, but also Assilina specimens. Eventually, orthophragminids and nummulitids are common
in microfacies type 5. Analysis of the Ilerdian-Cuisian deposits on the basis of the distribution of both biotic and abiotic components
suggests depositions in a shallow ramp environment with deepening upward from the middle Ilerdian to the late Cuisian.
Eastern Iran, Ilerdian-Cuisian, larger benthic foraminifera, microfacies, shallow benthic zone