Abstract

Fusulinaceans consisting of 56 species assignable to 30 genera are distinguished in the Surmaq Formation in the Abadeh region, central Iran. Based on the stratigraphic distribution of fusulinaceans, the Surmaq Formation is divisible into six biostratigraphic zones from lower to upper: Darvasites ordinatus, Pseudofusulina quasifusuliniformis, Eopolydiexodina percica, Afghanella schencki, Neoschwagerina occidentalis, and Chusenella abichi. Faunal composition and comparison between the Abadeh region, South West Asian, and Mediterranean Sea regions indicates that the first zone is Yahtashian in age, the second and third are definitely indeterminable, the fourth and fifth are Murgabian, and the last is Midian. Fusulinacean faunas of the Pseudofusulina quasifusuliniformis, Eopolydiexodina persica, and Chusenella abichi Zones are less diversified compared to the two intervening zones which have many neoschwagerinids and verbeekinids.

The Surmaq fusulinaceans, characterized by Eopolydiexodina and Afghanella, are one of the most widely represented Middle Permian faunas in the South West Asian and Mediterranean Sea regions, belonging to the western part of the Western Tethyan paleobiogeographic province. Murgabian and Midian faunas in this province differ from those of the eastern Tethyan Province in having only rare occurrences of Colania and Lepidolina, and from the Panthalassan Province in having Afghanella and Sumatrina. Permian carbonate deposition began in Yahtashian time throughout the Cimmerian terranes including the Abadeh region. Differences in fusulinacean faunal composition and species diversity in the Surmaq Formation are closely associated with differences in limestone lithologies. For example, the Chusenella abichi Zone is present mostly in lime-mudstone and wackestone that are partly dolomitized. These paleobiogeographic and lithologic chararacters have implications for the northward movement of this tectonic provenance, for the rift-drift-collision history of the western part of the Cimmerian Continent, and also for the evolution and extinction of fusulinaceans in Permian time.

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