Brachiopods of the Imtachan Formation in the Upper Permian of the Southern Verkhoyanie, Northeast Russia

Abstract

An extensive collection of fossil brachiopods, all assigned to the Wuchiapingian Stage, was recovered from the lower part of the Imtachan Formation along the Ustupnyi Creek (right tributary of the Setorym River) in the Southern Verkhoyanie. It comprises strophalosiids (Strophalosia? aff. vollossovitschi (Fredericks), Strophalosia? sp., Subtaeniothaerus lungersgauzeni Solomina, Marginalosia? magna Abramov et Grigorjeva), spiriferids (Crassispirifer monumentalis Abramov et Grigorjeva, Crassispirifer cf. monumentalis Abramov et Grigorjeva, Crassispirifer sp.), athyridids (Cleiothyridina nikolaevi Grunt, Cleiothyridina sp. 1, Bajtugania sp.), and terebratulids (Marinurnula? aff. mantuanensis (Campbell), Marinurnula? sp.). The identified assemblage is associated with brachiopods from the lower part of the Khalpirki Formation of the Western Verkhoyanie, the appearance of which marks the boundary between the Dulgalakhian and Khalpirkian Regional Stages and also substantiates the lower boundary of the Crassispirifer monumentalis Zone. Single finds of Crassispirifer cf. monumentalis in the lower part of the Middle Imtachan Subformation indicate that the entire lower subformation and the lower part of the middle subformation belong to the C. monumentalis Zone. There are no reliable finds of brachiopods at higher levels of the Imtachan Formation.