Extending the stratigraphic range of Nummulites bormidiensis Tellini in the Neo-Tethys (Zagros basin, SE Iran) through biometry and calcareous nannofossil biostratigraphy

Abstract

A biometrical study on four reticulate Nummulites populations from the lower part ofAsmari Formation of the Vazag section (Zagros zone) is carried out. The biostratigraphy obtained by studing the succession points to the Early Oligocene (Rupelian), indicating shallow benthic zones SBZ21 and SBZ22A by the occurrence of Operculina cf. complanata, Eulepidina formosoides, Nephrolepidina sp. The age assignment is calibrated with calcareous nannofossils biostratigraphy indicating the NP22-NP23 (=CNO2-CNO3) Zones.We have observed a stratigraphic trend related to Nummulites bormidiensis Tellini 1888 that results to be characterized by two populations composed of transitional Nummulites fichteli/bormidiensis with values of mean inner proloculus that exceeds by very little the boundary commonly established at 300 um. Such a populations, indicated as Nummulites ex interc. bormidiensis et fichteli, span through the lower Rupelianwhere classically just N. fichteli is reported so far. The stratigraphic distribution of Nummulites bormidiensisis and related transitional forms is here stretched to the Rupelian (SBZ21 and SBZ22A), encompassing older ages than previously recorded throughout the Neo-Tethys Ocean.