Publisher © Czech Geological Survey, ISSN: 2336-5757 (online), 0514-8057 (print)

Geology of hydrogeological district 2242 (Kuřim Basin) and concept of the Svratka River flow changes in the Cenozic

 

Jan Vít, Pavla Tomanová Petrová, Zuzana Skácelová, Milan Hrutka

Geoscience Research Reports 50, 2017, pages 173–180
Map sheets: Brno (24-32)

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Published online: 31 October 2017

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Abstract

Hydrogeological district 2242 - the Kuřim Basin (HGD 2242) lies NNW of the Brno city. The project “Groundwater balance in the selected areas of the Czech Republic” implemented by the Czech Geological Survey provided an opportunity to process and interpret data from many earlier drilled boreholes, geological maps and other records from this HGD. Several new boreholes enabled new recordings of groundwater behaviour and also provided data on lithology. The well logging also allowed to upgrade the position of individual beds and their lithology. The character of NW termination of hydrogeological district was verified by geophysical methods on P1 and P2 profiles, where vertical electrical sounding (VES) and electrical profiling (DOP) in dipole-dipole array were used. Electrical resistivity tomography (ERT), dipole electromagnetic profiling (DEMP) and shallow seismic refraction survey (MRS) were employed only in selected sections of the profiles.
The Tišnov Fault (NW-SE trending zone) in particular demarcates areas with different development which is reflected in distribution of sediments of various stratigraphic levels. While the central part represents tectonically the most affected, and simultaneously the most sunken area with relatively large thickness of Badenian sediments (more than 100 m), the marginal parts in the NE (Šebrov, Milonice) and in the SW (Vohančice, Čebín-Chudčice and Jinačovice) represent remodelled relics of Lower Miocene valleys filled with Ottnangian sediments the thickness of which only rarely exceeds 50 meters. Moreover, the lithology of both the above-mentioned types of sediments is also different. Ottnangian sediments consist of a sequence of alternating sands, gravels and clays with coal seams. Lower Badenian sediments are represented by marine calcareous clays that form most of their thickness, whereas coarse-grained clastics occur only on their basis.
One of the project objectives was also to create a contour model of the base of Miocene sediments. Consequently, a border line defining the extent of Miocene sediments was established. It should become a new boundary of the hydrogeological district enabling balancing the groundwater supply and demand in the future. This contour model was derived from data obtained from the newly drilled boreholes and from the results of geophysical methods that allowed to create a concept of changing paleoflow of the Svratka River during the Neogene and Quaternary. The Pre-Ottnangian course of the Paleo-Svratka River is not clear. It later sinks along the Tišnov Fault forming a pre-Badenian valley trending approximately in the direction of Štěpánovice-Drásov-Kuřim-Brno. The valley was later filled with marine sediments markedly exceeding the current relief level. Both the tectonic vertical movements and blocks inclines continued in the Badenian and post-Badenian times so that the Svratka River course changed to its recent position that could have been partly similar to that during the pre-Ottnangian times.