Marine microplankton biostratigraphy of the Volgian-Ryazanian boundary strata, western Barents Shelf

Abstract

Dinoflagellate cyst assemblages from Volgian-Ryazanian boundary strata of the western Barents Shelf are generally of low species diversity and moderate to low abundance. The assemblages can be correlated with the Paragonyaulacysta?boeralis assemblage Zone as defined in Arctic Canada and Northwest Siberia. The age of this zone is Late Volgian to Ryazanian, covering the Chetaites chetae, Heteroceras kochi and Surites analogus ammonite zones. Most of the dinoflagellate cyst biostratigraphic key species used for zonations in the sub-Boreal realm appear to be aabsent in the Barents Sea region, hampering the possibilities for long-distance correlations with successions in the North Sea and northern Tethys areas. There are no dinoflagellate cyst extinctions or first appearances which can be directly used to determine the Volgian-Ryazanian stage boundary in the region. However, a prolific bloom of Leiospaeridia (prasinophytes), probably induced by the Mjølnir meteroite impact, is an excellent marker horizon for the Volgian-Ryazanian boundary (142.2+\/-2.6 Ma) deposits of the shelf areas adjacent to the impact site.