Guadalupian (Permian) brachiopods from the Ruteh Limestone, North Iran

Thirty-three brachiopod species from the Guadalupian Ruteh Limestone of North Iran have been systematically described and illustrated. Brachiopods have been bed-by-bed collected along five stratigraphic sections and in one fossiliferous locality in the region between Dorud and Shirinibad in the Alborz Mountains. Quantitative biostratigraphic analysis of the brachiopod data based on the Unitary Association method (Guex, 1991) has lead to the construction of a local sequence of three discrete biozones: the Squamularia sp. B-M. bassa Biozone at the base of the formation, the H. kiangsiensis-N. (N.) asseretoi Biozone in its middle part and the R. exile-R. gemmellaroi Biozone at its top. The latter however has been recognized only in the Shirinabad section. The Ruteh brachiopod assemblages show a peri-Gondwanan biotic affinity which is related to the palaeogeographic position of the Iranian microplate, still close to the Gondwanan margin in the Guadalupian due to the incipient opening of the Neotethys Ocean in this sector. As already envisaged for the Carboniferous and Lower Permian brachiopod faunas from North Iran, also the Guadalupian fauna comprises cosmopolitan taxa, confirming the role of the Iranian microplate as a staging-post for most of the late Palaeozoic. When compared to the younger Lopingian faunas collected in the same regions of North Iran, the Ruteh brachiopods appear significantly different, indicating a marked biotic change in the brachiopod communities across the end- Guadalupian biotic crisis.