Revision of the lower Viséan (MFZ11) calcareous algae and archaediscoid foraminifers of the Sari area (central Alborz, Iran)

Abstract

The microfloral and microfaunal assemblages of the MFZ11 foraminiferal biozone (late early SomervilleViséan; formerly V2a) are well developed in the Kiyasar section of the Sari area (central Alborz; northern Iran). Regionally, this biozone MFZ11 may be subdivided into three subzones. The lower subzone, MFZ11A, is characterized by the appearances of the algae Koninckopora tenuiramosa, coeloporellacean indet. Fourstonella fusiformis, and Nanopora anglica and, among the foraminifers, by the occurrence of Ammarchaediscus bozorgniai and the disappearance of Eoparastaffella simplex; the absence of Uralodiscus rotundus, U. spp., and primitive Glomodiscus spp. in this subzone is noticeable. The next subzone, MFZ11B1, is well characterized by the appearance of Glomodiscus spp. (G. oblongus and G. cf. miloni) and the local range zone of Pararchaediscus, a genus emended herein and interpreted as a junior synonym of Archaediscus at the involutus stage and Propermodiscus; only a few characteristic issinellacean and palaeoberesellacean algae are present in this subzone. Then, the last subzone, MFZ11B2, is characterized by Hemiarchaediscus (emended herein) and Glomodiscus miloni; the upper part of this latter subzone is only marked by the apparent absence of the archaediscids and the presence of two incertae sedis algae: Crassikamaena scabrosa and Epistacheoides bozorgniai nov. sp. These assemblages indicate that at that time, Alborz remained located on the Perigondwanan southern border of the Palaeotethys, and was probably connected with the Urals as well as the northwestern branch the Palaeotethys, from Belgium to the Donets Basin.