The Turonian-Coniacian stage boundary in an expanded siliciclastic succession: Integrated stratigraphy in deltaic through offshore facies, Bohemian Cretaceous Basin

Abstract

During the latest Turonian – early Coniacian time, a succession of sand-rich, Gilbert-type deltas was deposited along the faulted margin of the Bohemian Cretaceous Basin (BCB, Central Europe), fining along depositional dip into prodeltaic heterolithic facies and offshore mudstones to marlstones. The active tectonic setting with accelerated subsidence and supply rates contributed to deposition and preservation of an expanded record showing otherwise insufficiently known parts of the Turonian-Coniacian (T–C) boundary interval. In this study a combination of detailed biostratigraphy, genetic sequence stratigraphy, and carbon isotope chemostratigraphy is employed to characterize the T–C boundary in the northern part of the BCB, in both nearshore and offshore facies. The basis of the biostratigraphic framework was the establishment of the same succession of inoceramid bivalves and other molluscan marker taxa and bioevents as that in Salzgitter-Salder (Germany) and Słupia Nadbrzeżna (Poland). All the faunal markers from the Mytiloides scupini through Cremnoceramus crassus crassus inoceramid zones were found both in the nearshore and offshore facies. The linkage of biostratigraphic and carbon isotope-stratigraphic data to a regional stratigraphic picture, as well as to individual outcrop and core sections, provides an important new database for further study of the boundary interval, with a direct link to the transgressive-regressive history of the nearshore depositional systems. Therefore it is proposed here that the T–C interval in the BCB complements the Salzgitter-Salder and Słupia Nadbrzeżna sections and together with them constitutes a broader type region for definition of the T–C boundary.