Correlation of charophyte assemblages from the nonmarine Jurassic-Cretaceous transition of NW Germany

Abstract

Based upon the first detailed study of the charophytes from the complete Upper Jurassic-lowermost Cretaceous (partly nonmarine) sequence of NW Germany, we distinguish eight successive assemblages which can be used as a local biozonation for the Lower Saxonian basin. Though charophytes cannot yet contribute to refined biozonations from the Oxfordian Korallenoolith up to the Tithonian Unterer Münder Mergel (assemblages 1–3) and in the late Berriasian-early Valanginian Wealden (assemblage 8), if compared with traditional ostracod/foraminifer biozones or palynozones, they are as useful as ostracods at the Jurassic-Cretaceous boundary (assemblages 4–5) and even better for correlation of the early Berriasian Serpulit and Purbeck (assemblages 6–7). Among other useful clavatoraceans, taxa principally from the Globator lineage present both short stratigraphic ranges and a large geographic distribution allowing: (a) the correlation of at least parts of the British lower Purbeck with the German Oberer Münder Mergel, Serpulit and Purbeck; (b) confirmation of the position of the Jurassic-Cretaceous boundary near the base of the Oberer Münder Mergel, as already proposed by ostracod workers; and (c) presentation of a more refined correlation of the assemblages from the Oberer Münder Mergel and Serpulit (Boreal realm) with the Early Berriasian biozones of the French and Swiss Jura (Tethyan realm).