Geochemical subdivision and correlation of clay-rich beds in Turonian sediments of northern Germany

Thin, clay-rich beds form a key component of the lithostratigraphic scheme established for Middle and Upper Turonian sediments in northern Germany. Previously, using limited petrographic evidence, clay-rich beds across much of this region have been classified as either containing altered volcanic ash (bentonites) or detrital clays. This paper demonstrates that the use of rare-earth element (REE) data enables a rapid and reliable subdivision of clay-rich beds into those composed of bentonitic clays and those composed of detrital clays. Application of this method to the Lower Saxony region of northern Germany demonstrates that four bentonites (TC Tdi, Te and Tf) and a number of detrital beds can be reliably identified and correlated. Three beds previously proposed to be bentonites are reinterpreted as being composed of detrital clays (To, TD2 and TG) and a revision of the stratigraphic nomenclature is proposed. Analysis of clay-rich beds from the Munster Basin demonstrates that it is possible to correlate individual bentonites and detrital beds between Lower Saxony and the Miinster Basin, and between shallow and deep water facies.