Pozycja geologiczna i główne cechy karbońskich zagłębi węglowych Polski

Adam Kotas, Józef Porzycki



The origin of Poland's Carboniferous coal basins has been closely related to the evolution of Variscan geosynclinal system and adjoining platform areas. The evolution resulted in formation of three types of basins: 1 - the intradeep molasse basin of the Lower Silesian Coal Basin (LSCB), 2 - the foredeep molasse basin of the Upper Silesian Coal Basin (USCB), and 3 - the epiplatform molasse basin of the Lublin Coal Basin (LCB, fig. 1).
There are three main types of coal - bearing formations (facies sequences) i.e. the marine - paralic coal - bearing formation, paralic coal - bearing formation and continental coal - bearing formation. They constitute major parts of variscan molasse sequences formed, in general, during the late - geosynclinal stage within the time - span Upper Visean - Upper Westphalian D (fig. 2).
The extension of Central European Variscan chain into the teritory of Poland, as well as its zonal arrangement and relation to the East European Platform (EEP) is due to the thick post - Variscan sedimentary cover (fig. 1) hypothetic and subjected to numerous speculations (see review in 10, 25, 26). The presented reconstruction is based on ideas of: 1 - an abrupt termination of the Variscan mountain belt at the Odra-Cracow lineament (5) which forms a part of the dextral shear - zone developed in Carboniferous time along the border of the EEP (1), 2 - northward motion of Brunnia, Upper Silesia (USM) and Małopolska Massifs (3,9), causing the development of the Upper Silesian foredeep basin in a marginal zone of the USM and the LCB in a marginal zone of the EEP (9).
In this context, the Fore-Sudetic zone, shaped as a shear-zone superposed on the Odra and Dolsk lineaments, is not a continuation of the Rheno-herzynian zone and one can not expect a classical Sub-Variscan foredeep: filled with coal - bearing molasse, along the EEP border marked by the Teisseyre-Tornquist line. The simple sequence of Variscan molasse basins, i.e. intradeep, foredeep and epiplatform basin, shows within the teritory of Poland rather specific spatal distribution, related to the very complex interaction of regional elements under consideration. This interaction reflects also the main features of coal basins.
The LSCB is situated within the Intra-Sudetic depression which forms the eastermost part of a W - E trending intramontane basin system of the Bohemian Massif. The depression is typified by a predominant continental molasse sequence reflecting the poliphase evolution of the basin from geosynclinal and late-geosynclinal intradeep into post-geosynclinal fault basin.
The coal - bearing formations of a maximum thickness ranging up to 1600 m were laid down in separate depocentres and show limited vertical and lateral extent. Up to 83 coal seams are known to occur, out of which 34 are of economic value. The rank of coal varies from coking coal to anthracite. The USCB, characterised by subtriangular shape (fig. 4), has been formed as e foredeep of the Moravo-Silesian fold zone; it is limited to NE by the Cracow Fold Belt. The entire basin fill (fig. 5) is represented by coal - bearing formations which rest concordantly on crypto-flysh and pseudo-molasse sequences. The about 8500 m thick succession displays two fold division. Its lower part is occupied by entirely siliciclastic paralic coal - bearing para-molasse; the upper part, separated by a sedimentary gap, consist of continental coal - bearing ortho-molasse originated in limno-fluvial and fluvial environments.
About 520 coal seams are known to occur throughout the basin, out of them 216 are of economic value. The rank of coal varies from subbituminous coal to anthracite. The basin displays complex tectonic zoning typified in its western part by SSW - NNE trending fold structures as well as by W - E arranged half-horst and half-grabens of the fault tectonic zone in the central and eastern parts of the basin.
The LCB is developed as a pericratonic depression within the EEP. Its basin infill (fig. 7) rests discordantly on the bedrock and consists of consecutive sequence of marine - paralic coal - bearing formation, paralic coal - bearing formation and continental coal - bearing formation. The total maximum thickness of coal - bearing formations range up to 2500 m. They are characterised by large extent, very slow thickness variations, excellent lithologic marker horizons, and limestone intercalations in the marine influenced parts of the succession. About 113 coal seams have been recorded; 32 are of economic value, most of them occur in the continental Lublin beds. The rank of coal varies from subbituminous coal to coking coal. The structure of the LCB is characterised by fault and fold - block tectonics as well as rather gentle dip of strata (3 - 5°).
The hard - coal resources of Poland, estimated up to the depth of 1800 m, amount to 200,6 billion ton. In detail (fig. 8) 61,5 bill. ton comprise A-C2 category reserves estimated up to 1000 m depth, 42,0 bill. ton D1 and 29,7 bill. ton D2 group perspective resources estimated up to the depth of 1250 m. The remaining 67,4 bill. ton belong to potential E group resources situated below 1250 m depth.

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