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

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.