Contourite erosional and depositional features of the Maastrichtian chalk on Jasmund peninsula (Rügen island, NE Germany)

ABSTRACT

Seismic‐scale features such as deeply incised submarine valleys and mounded drifts together with ichnological features indicative of discontinuous sedimentation and erosional episodes have recently been documented from the Upper Cretaceous chalk in the southern Baltic Sea area. These features are interpreted to result from a contourite system with intermittent high‐energy peak‐flow conditions. South‐east‐directed bottom currents are believed to have controlled the accumulation and reworking of calcareous plankton in the epicontinental Chalk Sea from the Late Coniacian to the Maastrichtian. A 90 m section of lower Maastrichtian chalk, exposed at the sea cliffs of the Jasmund peninsula on Rügen island, provides a rare possibility to compare seismic‐scale features with bed‐scale characteristics and microfacies. Based on facies analysis, the chalk deposits on Rügen are composed of three facies associations, namely bioturbated, nodular and conglomeratic chalk. These chalk deposits are interpreted as calcareous pelagites, muddy and silty contourites, which drape omission surfaces and fill cavities of excavated burrows, intraclastic gravel‐lag contourites, reflecting initial stages of current‐induced hardground delamination and debrites. The calcareous contourites documented herein provide diagnostic criteria for the identification of bottom current‐induced winnowing and bedload traction of fines related to temporal changes in flow characteristics. Winnowed calcareous plankton and lag deposits are identified as integral parts of bi‐gradational contourite sequences and are suggested to have been deposited in a sediment‐starved or sediment‐transfer carbonate environment. This interpretation is consistent with seismic, palaeontological and ichnological data and demonstrates the presence of erosional and depositional features in a contourite depositional system, which formed under control of deep‐marine bottom currents in the central European Chalk Sea.