Abstract

The Lower Carboniferous Culm Basin of the Czech Republic represents the most easterly and southerly part of the European Variscan foreland basin system. The NNE–SSW-trending basin is exposed along the eastern flank of the Bohemian 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 Viséan, sediment was sourced from a predominantly low-grade metamorphic terrane and Viséan limestones. In the latest Viséan, a progressive change in source material is recorded by an increase in high-grade metamorphic detritus. Studies of Variscan nappe pile emplacement along the eastern flank of the Bohemian Massif allow an assessment of the relationship between basin development and nappe emplacement. Basin initiation coincided with underthrusting of high grade metamorphic (Moldanubian) nappes at 340 Ma. Sedimentation was synchronous with nappe emplacement throughout the Viséan which resulted in uplift and erosion of a low grade metamorphic terrane. Moldanubian nappes were exhumed at approximately 330 Ma when high grade metamorphic detritus entered the basin. Two phases of northward-directed sediment progradation are recognized. Sediment progradation is considered to be related to changes in drainage basin size and/or climatic fluctuations within the Variscan Orogen, since sediment is inferred to have been supplied to the basin axially rather than laterally and subsidence curves show no significant change in subsidence rates. In contrast to many models of foreland basin sediment distribution, filling of the Culm Basin was largely independent of tectonic activity adjacent to the basin margin and/or of subsidence rate changes. Sedimentation in the Culm Basin commenced 10–15 Ma earlier than the rest of the Variscan foreland, and records the first impact of the northwardly propagating Variscan Orogen in northern Europe.

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