Inter-regional correlation of Jurassic/Cretaceous boundary strata based on the Tithonian-Valanginian dinoflagellate cyst biostratigraphy of the Volga Basin, western Russia

摘要

Correlation of Jurassic/Cretaceous boundary successions in the Boreal Realm based on ammonite biostratigraphy is problematical due to faunal provincialism. This paper investigates the marine palynology of the Tithonian to Valanginian strata at Gorodishche and Kashpir in western Russia, documenting the ranges of > 100 dinoflagellate cyst species used to compile a detailed Tithonian-Valanginian palynostratigraphy for the Volga Basin. Datums of key taxa are used to define ages for unreliably dated strata in the Russian successions by comparison with ranges calibrated to ammonite zones in Boreal northwest Europe. The appearance of Gochteodinia villosa indicates a correlation between the bases of the Late Tithonian Epivirgatites nikitini (ammonite) Zone of the Volga Basin and the Galbanites kerberus Zone of northwest Europe. A dinoflagellate cyst interval zonation, comprising five zones and seven subzones is defined for the Volga Basin. There are notable differences between Tithonian and Berriasian dinoflagellate cyst floras in the Volga Basin and northwest Europe, but Valanginian dinoflagellate cyst assemblages throughout the Northern Hemisphere demonstrate a much more cosmopolitan composition.\ud\ud