Assel Layer

(named after the Assel’ River in the Southern Urals), the lower layer of the Permian system. It was distinguished by V. E. Ruzhentsev in 1954 and is characterized by a complex of Foraminifera (Schwagerina, Ps. krotowi schellw., Ps. uralica [Krot.]) and Ammonites (Shikhanites, Juresanites, Properrinites, and Proto-popanoceras). On the western slopes of the Urals the composition of the Assel’ layer is dominated by limestone, in which petroleum deposits occur in the massif varieties (Ishimbai). Layers corresponding to the Assel’ layer are also distinguished in the Don basin, Middle Asia, Pamir, and a number of foreign countries (Austria, the Chinese People’s Republic, Japan, and the USA).