Larger foraminiferal biostratigraphy and microfacies analysis from the Ypresian (Ilerdian-Cuisian) limestones in the Sistan Suture Zone (eastern Iran)

Authors : Mehdi HADI, Mohammad VAHIDINIA, Juraj HRABOVSKY

Pages : 122-145

View : 8 | Download : 4

Publication Date : 0000-00-00

Article Type : Research Paper

Abstract :A high diversity of larger benthic foraminifera insert ignore into journalissuearticles values(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 insert ignore into journalissuearticles values(SBZ8 and SBZ10-12); have been designated in LBF horizons comprising index zonal markers such as Alveolina elliptica nuttalli insert ignore into journalissuearticles values(Davies);, A. decipiens insert ignore into journalissuearticles values(Schwager);, A. cf. oblonga, A. cf. minuta, A. cf. rugosa, A. cf. decastroi, A. aff. cremae, A. frumentiformis, A. aff. palermitana, N. cf. atacicus insert ignore into journalissuearticles values(Leymerie);, N. tauricus insert ignore into journalissuearticles values(De la Harpe);, N. pratti insert ignore into journalissuearticles values(d?Archia & Haime);, N. polygyratus insert ignore into journalissuearticles values(Deshayes);, N. cf. distans insert ignore into journalissuearticles values(Deshayes);, Assilina sublaminosa insert ignore into journalissuearticles values(Gill);, A. placentula insert ignore into journalissuearticles values(Deshayes);, Asterocyclina cf. schweighauseri insert ignore into journalissuearticles values(Less);, Discocyclina archiaci cf. staroseliensis insert ignore into journalissuearticles values(Less);, and D. cf. archiaci bartholomei insert ignore into journalissuearticles values(Schlumberger);. Five microfacies types including Alveolina-Opertorbitolites packstone insert ignore into journalissuearticles values(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.
Keywords : Eastern Iran, Ilerdian Cuisian, larger benthic foraminifera, microfacies, shallow benthic zone