Bashkirian foraminifera in the Sanandaj-Sirjan Zone (Iran): Their importance in taxonomy, biostratigraphy, and palaeobiogeographic reconstruction of the southern margin of Western Palaeotethys

Abstract

A noteworthy Lower Pennsylvanian fusulinid fauna is, for the first time, reported from the Sanandaj-Sirjan Zone in Iran. From the main outcrop, eighty five species of thirty genera belonging to two classes, five orders, five suborders, seven superfamilies, sixteen families, and seven subfamilies are examined. The present fusulinids are assigned to the early–late Bashkirian (Syuranian, Akavassian, and Askynbashian substages). The characteristic taxa include Semistaffella spp., Plectostaffella varvariensis, Millerella marblensis, Pseudostaffella spp., Profusulinella cf. parva, and Ozawainella spp. Three successive assemblages spanning the early–late Bashkirian are proposed: (1) Assemblage with Semistaffella variabilis-S. minuscilaria-Plectostaffella seslavica (Syuranian age); (2) Assemblage with Pseudostaffella antiqua-P. compressa (Akavassian age); and (3) Assemblage with Ozawainella mosquensis-Profusulinella cf. parva (Askynbashian age). The new found fusulinid assemblages of the Sanandaj-Sirjan Zone have close resemblance and are well correlative with the Bashkirian standard and reference sections of the Russian Platform, Donets Basin, Urals, Southern Turkey, and Central Asia. The Iranian Bashkirian foraminiferal faunas, furthermore, exhibit very similar compositions to their counterparts in other areas of the Western Palaeotethys Region; many foraminifers, both smaller foraminifers and fusulinids, are in common between them. The new findings, in addition to clarifying the biostratigraphic correlation with the well-known type sections of the same age, are also important for reconstructing the palaeoposition of the Sanandaj-Sirjan Zone as a southern margin of Western Palaeotethys.