Sequence stratigraphy of Upper Jurassic deposits in the North German Basin (Lower Saxony, Süntel Mountains)

A core recovered in the North German Basin at the locality of Eulenflucht in the Süntel Mountains, 30 km SE of Hannover, Germany, is interpreted in terms of Oxfordian to Kimmeridgian sequence stratigraphy of this basin. Thirteen different facies are recognized which record the evolution of an outer ramp into a restricted hypersaline lagoon. Changes in grain size, variations in the amount of components, fluctuations of the matrix content and of the microscopic texture, as well as vertical lithofacies stacking patterns, were integrated to define small-scale sequences. Medium-scale sequences were identified by changes in facies combinations of the constituent small-scale sequences. Large-scale sequences were differentiated by facies proportion statistics in the distinct medium-scale sequences. This allows the complete sequence stratigraphic subdivision of the Oxfordian and Kimmeridgian succession to be interpreted. The stable carbon isotopic composition of bulk samples enables a correlation with chemostratigraphic records found elsewhere. This result is supported by an ostracod biostratigraphy that allows a chronostratigraphic assignment of the succession. The large-scale sequences were controlled by climate and local tectonic movements. It is proposed that a long-term shallowing trend during the Kimmeridgian time was induced by regional uplift.