Abstract
Abstract Global environments changed greatly during the Late Jurassic and Early Cretaceous, Particularly during the Jurassic Cretaceous boundary interval. Separation of the world into Tethyan, Boreal and other biogeographic realms complicates international correlation, and even the pelaagic ammonites cannot play their characteristic role of principle correlation criteria. In the Boreal and North Pacific realms, the Late Jurassic and Cretaceous buchiid bivalve zones have very good calibration to Boreal ammonite zones, which, in turn, have approximate correlation to Tethyan ammonite zones. Therefore, buchiid bivalves provide a means to identify Upper Jurassic-Lower Cretaceous stages and the Jurassic Cretaceous boundary interval. The base of the Buchia unschensis Zone is roughly coincident with the Boreal ammonite Craspedites exoticus subzone, Upper Volgian Craspedites okensis Zone, which in turn closely corresponds to the base of the Tethyan ammonite basal Berriasian Berriasella jacobi Zone. The top of the ...
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