Anomalous dips of some Upper Carboniferous strata in the Mšeno-Roudnice Basin based on borehole data and reflection seismic measurements


Authors: Skopec J, Pešek J

Published in: Bulletin of Geosciences, volume 80, issue 1; pages: 85 - 92; Received 13 October 2004; Accepted in revised form 2 December 2004;

Keywords: Mšeno-Roudnice Basin, Stephanian B/C, seismic structural investigation, fold-like structure,

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Sediments of the Central Bohemian Carboniferous basins have long been considered as typical platform deposits with subhorizontal dips of strata and a predominance of normal faulting. Nevertheless, seismic measurements in the Mšeno-Roudnice Basin (MRB) have revealed that some Upper Carboniferous sediments dip at angles of 20° or more (Kadlečík et al. 1985, 1990). These strata are overlain by subhorizontally deposited Upper Carboniferous sediments. This situation was also confirmed by samples from several boreholes (Bosák 1989, Bosák in Žbánek et al. 1990). The dips were, however, explained by deltaic deposition in a lacustrine environment (Bosák 1991).
As suggested by the revision of seismic sections from theMRBarea performed during the past few years at the Faculty of Science of Charles University in Prague, the above mentioned dips of strata can be explained otherwise. Upper Carboniferous rocks usually dip at the same angle from the base of the Carboniferous up to a certain stratigraphic level (commonly to the lower part of the Hředle Member), while the overlying Upper Carboniferous sediments are subhorizontal. The length of the inclined structures often exceeds 1 km, and the respective dips of strata are generally observed even at intersecting seismic profiles.
A zone with the occurrence of mutually non-interlocking structures resembling monoclinal folds lies between Mělník and Benátky nad Jizerou, in an area about 20 km long and 3 km wide. This zone may represent the westernmost extension of folds documented in some Sudetic Permo-Carboniferous basins, e.g. in the southern part of the neighbouring Mnichovo Hradiště Basin, east of the MRB.