RADIOLARIANS FROM UPPER CRETACEOUS DEPOSITS, THE NOVODEVICH'E SECTIOON (SAMARA OBLAST, VOLGA RIVER MIDDLE COURSES)

Abstract

Radiolarians from the Novodevich'e section, Samara oblast, are described. Two subdivisions of the section correspond to the 6.5-m-thick member of clay and chalk with Turonian-Coniacian benthic foraminifers and to the other member of intercalated opoka and clay beds, which are 6.8 m thick in total a6d yield benthic foraminifers of the upper Coniacian-Santonian in association with radiolarians. Of 41 radiolarian species, which have been identified, the most typical are Cromyodruppa concentrica Lipman, Crucella aster (Lipman), C. cachensis Pessagno, C latum (Lipman), Orbiculiforma monticelloensis Pessagno, O. quadrata Pessagno, Paronaella santonica (Lipman), P. tumida (Lipman), Patulibracchium ingens (Lipman), Pentinastrum subbotinae Lipman, Praeconocaryomma lipmanae Pessagno, P. universa Pessagno, Pseudoaulophacus lenticulatus (White), Triactoma compressa (Squinabol), Amphipyndax stocki (Campbell et Clark), Dictyomitra multicostata Zittel, and Xitus asymbatos (Foreman). The late Coniacian-Santonian age of radiolarian assemblage is inferred based on coexisting radiolarians and on correlation with radiolarians characteristic of the Zagorsk Formation of the Moscow syneclise. As compared to radiolarian assemblages of the Moscow syneclise, which are taxonomically diverse and include many taxa known from California and bottom sediments of tropical oceanic regions, and to concurrent assemblages of the Urals and West Siberia, which are depleted in thermophilic species, the Late Cretaceous radiolarians from the Volga River middle courses are of a transitional taxonomic composition. It is plausible to conclude therefore that thermophilic taxa migrated into the East European sea from the west, whereas cryophilic forms characteristic of the West Siberian basin arrived from the east and northeast. Species originally identified by Lipman (1952) are revised and described anew.