Węglonośność górnego namuru A w Górnośląskim Zagłębiu Węglowym w świetle analizy rozwoju litologiczno-tektonicznego

Józef Ryszka

Abstrakt


SUMMATIVE THICKNESS OF NAMURIAN A COALS IN THE UPPER SILESIAN COAL BASIN IN THE LIGHT OF ANALYSIS OF LITHOLOGICAL-TECTONIC DEVELOPMENT

Summary
The studies showed a characteristic variability in both summative thickness of coals and thickness of individual coal layers in the Poręba Beds (Upper Namurian A) in northern part of the Upper Silesian Coal Basin. Results of surveys carried out in mining fields in that part of the basin indicate that the variability in summative thickness of coals is not related in any clear way with changes in thickness of the Poręba Beds but rather occurrence of a specific variety of rocks and presence of sedimentary discontinuities. The summative thickness has been found to be the lowest and frequency of changes in thickness of individual coal layers the highest in mining areas characterized by lithological columns displaying both numerous horizons of infraformational conglomerates (built of clay or peat intraclasts and sandy groundmass) and erosional gaps in sedimentary cyclothems and comprising montmorillonite deposits. It is concluded that the latter reflect tectonic quakes affecting sedimentary surface in these areas of the basin. Phenomena of redeposition of sandy sediment, related erosion of adjacent clay or phytogenic ones and subsequent redeposition of their clasts at some small distance were fairly common in epicentres of these quakes. It should be also noted that conditions predominating in these areas were not advantageous for development and preservation of coal-forming peat bogs. The process of intensified modification of surface, proceeding in these areas, was facilitating origin of depressions without outflow. In times of intense igneous intrusions and relatively less intense precipitations the depressions were characterized by conditions favourable for phase transitions leading to montmorillonization.
In mining areas characterized by low summative thickness of coals there were found large longitudinal faults with an opposite direction of downthrow, the oldest of those recorded in the Silesian rock massif, which seems to confirm activity of the above discussed geological processes. The faults and the characteristic structure of the Main Anticline indicate existence of a strike-slip fault, typical of Variscan lineament of northern Europe, beneath t]le anticline. The zone of maximum stresses related to strike-slip movements along that fault, was the site of tectonic quakes in the Namurian A and, subsequently, origin of the above mentioned major discontinuous dislocations.

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