Contribution to the geology of the northern part of the Plzeň Basin and the southern part of the Carboniferous Žihle Basin


Authors: Prouza V

Published in: Bulletin of Geosciences, volume 80, issue 1; pages: 79 - 84; Received 1 October 2004; Accepted in revised form 6 December 2004;

Keywords: Kladno and Týnec formations, lithology, stratigraphy, tectonics,

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The Žihle Basin is a structure trending approximately in a N-S direction. While Carboniferous deposits overlap the Upper Proterozoic basement on the eastern side of the basin, the western boundary is comprised of the prominent Maloměřice-Chrášťovice Fault. This dislocation has probably existed since before the Carboniferous sediments were deposited, and continues further to the south and north. Tectonic movements have been repeated here throughout geological history. Structurally, the basin is an asymmetric one-sided graben. Among other faults in the system, those trending WNW-ESE and NW-SE are the most frequent.
The Carboniferous deposition started in Westphalian D (Nýřany Member of the Kladno Formation). Older sediments (Radnice Member) were also deposited only locally (mostly in the south). The deposition continued during the Stephanian (Týnec Formation). As the lithology of the Nýřany Member and Týnec Formation are similar (mostly arkoses, feldspathic sandstones, and conglomerates of fluvial origin, with lesser interbeds of mudstone and fine sandstone), and comparative markers are rare and unreliable, the units mentioned above cannot be differentiated. The situation is different south of the Střela River (especially in the surroundings of Kaznějov), where the Týnec and Kladno formations can be distinguished (also based on data from several boreholes). The Střela River is the conventional approximate boundary between the Žihle and Plzeň basins. Thin coal seams and their claystone or mudstone equivalents found at the western margin of the basin at Chrášťovice, and at the eastern one NE of Mladotice, belong to the Chotíkov Group of Seams of the Nýřany Member, while seams from Žebnice and the Richardka hunting lodge ENE of Nebřeziny belong to the Radnice Group of Seams.