Detrital composition of Ordovician sandstones from the Rügen boreholes: implications for the evolution of the Tornquist Ocean

The Lower Palaeozoic sequences of the Rügen boreholes are composed of pelitic-clastic sediments which range in age from the Cambro-Ordovician boundary to the Late Ordovician. Provenance studies have been carried out on Cambro-Ordovician sandstones from the Loissin borehole and on Middle-Upper Ordovician greywackes of the Rugen 5 borehole.The Loissin sandstones were deposited as turbidites and debris flows in an unstable sedimentary basin. They form immature arkoses and subarkoses with high matrix contents. Their debris derived from a polycyclic, sedimentary cratonic provenance and from a monocyclic magmatic provenance. This is reflected in the heavy mineral spectrum, which is dominated by an anhedral, coloured zircon fraction and a euhedral, transparent zircon fraction.The Middle-Upper Ordovician Rügen greywackes derived from proximal, high energy turbidites which were transported into a deep marine basin. They form homogeneous lithic arkoses and arkosic litharenites. Their debris derived from a composite provenance with an ultramafic-mafic, ophiolitic source, an acidic magmatic source and a heterogeneous sedimentary cratonic source.Although the Loissin sandstones probably originated in an intracratonic, rift-related sedimentary basin, the debris of the Rugen greywackes is regarded as derived from a heterogeneous active continental margin. Results and interpretations of the provenance study are discussed in the light of proposed Lower Palaeozoic palaeogeographic reconstructions.