Biometric study of late Oligocene larger benthic Foraminifera (Lepidocyclinidae and Nummulitidae) from the Qom Formation, Central Iran (Tajar-Kuh section)

Abstract

The Oligocene strata of the Qom Formation from the Tajar-Kuh section, Central Iran, are rich in various Larger Benthic Foraminifera (LBF). Morphometric studies of the internal features of the LBF tests were carried out based on matrix-free specimens from seven samples. The LBF assemblage studied in 24 populations mainly contains representatives of two nummulitid (the reticulate Nummulites bormidiensis Tellini, 1888, only in the lower three samples, and the radiate Nummulites kecskemetii Less, 1991 in all samples) and of two lepidocyclinid lineages. Of the latter, Nephrolepidina praemarginata (R. Douvillé, 1908) occurs in all the samples, whereas Eulepidina formosoides H. Douvillé, 1925 is present in the lower six samples. In the upper sample, the slightly more advanced Eulepidina ex. interc. formosoides H. Douvillé, 1925 et dilatata (Michelotti, 1861) is recorded. Due to the very similar taxonomic composition of the Tajar-Kuh section with their coeval faunas of the Mediterranean, the age was evaluated in the frame of the Western Tethyan Oligo-Miocene shallow benthic zonation (SBZ). Although the presence of E. formosoides suggests late Rupelian (SBZ 22A Zone) age, the occurrence of Heterostegina assilinoides, N. kecskemetii, N. bormidiensis, and Planolinderina sp. preferably represents the SBZ 22B Zone of the early Chattian. Based on the obtained results, at least the lower six samples can indicate the very basal part of the Chattian. More advanced Eulepidina from the uppermost sample suggests a slightly younger but still early Chattian age.

Biostratigraphy, microfacies and reservoir quality of the Oligocene Qom Formation (Kharzan section, Northwest of Ardestan, Central Iran)

“…Num mu lites and lepidocyclinid in dex spe cies are com mon in the Oligocene Qom For ma tion and its equiv a lent in the Zagros Ba sin, the Asmari For ma tion, and have been used for biozonation (Mohammadi and Ameri, 2015). In a few sec tions, Num mu lites spe cies have been found alone in Rupelian, or lower Rupelian, strata whereas lepidocyclinids alone have been found in Chattian strata or Aquitanian for ma tions (e.g., Bozorgnia and Kalantari, 1965;Kalantari, 1976;Amirshahkarami et al, 2007;Ehrenberg et al, 2007;Laursen et al, 2009;Amirshahkarami et al, 2010;Van Buchem et al, 2010;Yazdi-Moghadam, 2011;Mohammadi et al, 2013Karavan et al, 2014;Mohammadi and Ameri, 2015;Taheri et al, 2017;Basso et al, 2019;Akbar-Baskalayeh et al, 2020;Allahkarampour Dill et al, 2018;Mohammadi, 2022). In Iran, Biozone No.57, the Num mu lites intermedius-Num mu lites vascus as sem blage zone, was first pro posed as an in dex for the Oligocene by Wynd (1965), who de scribed the prop er ties and biostratigraphic fea tures of Oligocene-Mio cene strata in the Asmari For ma tion in the south-west of Iran.…”

Early Miocene larger benthic foraminifera from the northwestern Tethyan Seaway (NW Iran): new findings on Shallow Benthic Zone 25

“…Associated with the other shallow-marine biota (e.g., echinoderms, pelecypods, gastropods, coralline algae), LBF characterize widespread platform carbonates of the Oligo-Miocene age which are known under different formational names from central and southern Iran, e.g., Asmari, Mishan, and Gachsaran formations (Zagros Mountains), or Qom Formation (Central Iran). Attempts for detailed stratigraphy, and palaeoenvironmental studies of these platform carbonates in Iran, have been made by several authors and are still in progress (e.g., Ehrenberg et al 2007 ; Van Buchem et al 2010 ; Shabafrooz et al 2015 ; Allahkarampour Dill et al 2018 ; Yazdi-Moghadam et al 2018a , b ; Basso et al 2019 ; Akbar-Baskalayeh et al 2020 ). The present study makes an important contribution to this study process and reports the occurrence of hyaline and porcelaneous LBF recovered from three outcrop sections in the Hamedan–Miandoab area, NW Iran.…”