BIOSTRATIGRAPHIC ASSEMBLAGES OF AMMONOIDS AND RADIOLARIANS OF THE URALS

Ammonoids and radiolarians in the Lower Permian (Cisuralian) of the Western Urals permit the development of a regional biostratigraphic scale. The Permian families: Paragastrioceratidae, Metalegoceratidae, Popanoceratidae first appear in the Asselian ammonoid assemblage, and the key event is the occurrence of genus Svetlanoceras. Radiolarians of Asselian age can be differentiated into two assemblages: Latentifistula crux, Haplodiacanthus anfractus and beds with Copicyntra sp. The Asselian-Sakmarian boundary is not presently recognized by ammonoids in the Urals. According to radiolarians, the transition from the late Asselian beds with Copicyntra sp. to beds with early Sakmarian Tetragregnon vimineum - Copiellintra diploacantha can be recognized. Sakmarian ammonoids are characterized by the appearance of the genera: Synartinskia, Propopanoceras, Preshumardites, Medlicottia, Thalassoceras, Metalegoceras, Uraloceras, Crimites. Five biostratigraphically significant radiolarian assemblages can be recognized in the Sakmarian: Tetragregnon vimineum - Copiellintra diploacantha, Helioentactinia ikka - Haplodiacanthus perforatus, Entactinia pycnoclada - Tormentum circumfusum, Camptoalatus monopterygius and Rectotormentum fornicatum. Artinskian radiolarians are characterized by the assemblages: Entactinosphaera crassicalthrata – Quinqueremis arundinea, Tetracircinata reconda and Polyentactinia lautitia. The early Artinskian ammonoid assemblage in the Urals is the most representative and it differs from the Sakmarian one mainly on the specific level. The rich late Artinskian ammonoid assemblage includes representatives of the families Pronoritidae, Medlicottiidae, Daraelitidae, Thalassoceratidae, Agathiceratidae, Popanoceratidae, Paragastrioceratidae, Eothinitidae, Adrianitidae, Marathonitidae. Metalegoceratidae, Somoholitidae, Vidrioceratidae. The Artinskian-Kungurian boundary can be recognized by the presence of an ammonoid assemblage containing both Artinskian and Kungurian species. The most typical species that marks the lower boundary of the Kungurian is Uraloceras tchuvaschovi, accompanied with the Kungurian conodont Neostreptognatodus pnevi. Kungurian radiolarians are represented by the Ruzhencevispongus uralicus assemblage.