The lower Upper Cretaceous of the south-eastern Münsterland Cretaceous Basin, Germany: facies, integrated stratigraphy and inter-basinal correlation

Abstract

Integrated stratigraphic (litho-, bio-, event, chemo-, gamma ray, and sequence stratigraphy) and sedimentologic analyses of two new core sections greatly improved the understanding of facies development, sea-level changes and correlation of the lower Upper Cretaceous in the south-eastern Münsterland Cretaceous Basin, Germany. A large-scale second-order sea-level cycle is mirrored by the increasing importance of offshore facies and thicknesses of depositional sequences, reflecting the rise of accommodation during the Cenomanian to Early Turonian. In the Middle Turonian, this trend started to become reversed and the cycle ends with a major unconformity at the base of the Soest Grünsand Member in the mid-Upper Turonian. Condensation of the mid- and uppermost Turonian reflects the lack of accommodation during a phase of second-order lowstand, followed by a retrogradational trend during the Early Coniacian that marks the transgressive part of a new second-order cycle. Sedimentary unconformities in the Cenomanian–Turonian successions provide evidence for third-order sea-level changes superimposed onto the first early Late Cretaceous second-order cycle. They correspond to sequence boundaries SB Ce 1–5 and SB Tu 1–4 that have been identified in Central European basins and elsewhere, supporting their eustatic origin. The sea-level fall expressed by Upper Turonian unconformity SB Tu 4 is of major magnitude. The overlying Soest Grünsand Member is the only level of greensands in the Upper Turonian of the south-eastern Münsterland: the Alme Grünsand, introduced for another, allegedly uppermost Turonian greensand level, does not exist. Carbon stable isotopes from the mid-Upper Cenomanian to Lower Coniacian allowed calibrating the successions on intra- and interbasinal scales. A conspicuous mid-Middle Turonian positive isotope event has been newly named, i.e., the Niederntudorf Event. Sequence boundaries, marker beds (marl layers) and bentonites turned out to be isochronous within the chemostratigraphic framework. The identification of Turonian bentonites greatly improved the understanding of the stratigraphic relationships, especially in the Upper Turonian while natural gamma radiation logs turned out as a valuable method for intrabasinal correlation. In conclusion, the new sections provide a high-quality standard succession for the lower Upper Cretaceous in the south-eastern Münsterland Cretaceous Basin.