Sediment provenance and dispersal in a deep marine foreland basin: the Lower Carboniferous Culm Basin, Czech Republic

The Lower Carboniferous Culm Basin of the Czech Republic represents the mos t easterly and southerly part of the European Variscan foreland basin syste m. The NNE-SSW-trending basin is exposed along the eastern Rank of the Bohe mian Massif. It contains up to 7.5 km of deep marine sediment deposited as an axial turbidite system sourced from south/southwest of the basin. Heavy mineral data and clast types indicate that for much of the Visean, sediment was sourced from a predominantly low-grade metamorphic terrane and Visean limestones. In the latest Visean, a progressive change in source material i s recorded by an increase in high-grade metamorphic detritus. Studies of Va riscan nappe pile emplacement along the eastern Rank of the Bohemian Massif allow an assessment of the relationship between basin development and napp e emplacement. Basin initiation coincided with underthrusting of high grade metamorphic (Moldanubian) nappes at 340 Ma. Sedimentation was synchronous with nappe emplacement throughout the Visean which resulted in uplift and e rosion of a low grade metamorphic terrane. Moldanubian nappes were exhumed at approximately 330 Ma when high grade metamorphic detritus entered the ba sin. Two phases of northward-directed sediment progradation are recognized. Sediment progradation is considered to be related to changes in drainage b asin size and/or climatic fluctuations within the Variscan Orogen, since se diment is inferred to have been supplied to the basin axially rather than l aterally and subsidence curves show no significant change in subsidence rat es. In contrast to many models of foreland basin sediment distribution, fil ling of the Culm Basin was largely independent of tectonic activity adjacen t to the basin margin and/or of subsidence rate changes. Sedimentation in t he Culm Basin commenced 10 15 Ma earlier than the rest of the Variscan fore land, and records the first impact of the northwardly propagating Variscan Orogen in northern Europe.