Bivalve zones and assemblages of the circum-Pacific region

DAMBORENEA, S.E.; POLUBOTKO, I.V.; SEY, I.I.; PARAKETSOV,K.V.

The Jurassic of the Circum-Pacific

Cambridge University Press

Lugar: Cambridge; Año: 1992; p. 300 - 307

The use of Late Jurassic bivalves (Buchiids) in bioestratigraphy has been successful in the northern circum-Pacific for a long time. In recent years the increase of detailed studies on other bivalve faunas has extended the potential biostratigraphic usefulness of bivalves to cover also the Early and Middle Jurassic of other circum-Pacific regions. Only some bivalve groups have proved useful, notably monotaceans and pectinaceans for the Lower Jurassic, inoceramids (s.l.) for the Middle Jurassic, and buchiids for the Upper Jurassic. As knowledge of systematic and vertical ranges of bivalve species is still very uneven, many more studies are needed to obtain a comprehensive picture. A correlation chart for several circum-Pacific regions has been compiled showing approximate equivalences. Many of the biostratigraphic units recognized thus far are based on and named after local species belonging to mainly circum-Pacific general, such as Otapiria, Radulonectites, Parainoceramus, Retroceramus (or Mytiloceramus), and Buchia. Although this is only a consequence of the fact that correlation tables are commonly based on offshore species, it makes comparison between circum-Pacific regions easier. This analysis should not overlook the progressive displacement of local vertical ranges of some of these bivalve taxa along their geographic ranges. Bivalve biostratigraphic units have only local or, at best, regional value, and up to now correlation between them has been done by independent reference of the local zonations to the European standard zonation, thus introducing a certain degree of ambiguity and inaccuracy. A zonation for the whole Jurassic based on bivalves is available only for northern Russia, but data from South America and New Zealand ace sufficiently complete to merit further comments.