Zagadnienie zlepieńców śródformacyjnych typu puddingstone w formacjach sylezu Górnośląskiego Zagłębia Węglowego

Józef Ryszka



Attention is paid to occurrence of a number of petro-geological phenomena such as infraformational conglomerate horizons of specific type, the thickest bentonite deposit, exceptionally frequent changes in thickness of coal seams and others in profiles of Namurian A formations in the Chorzów region. On the basis of these phenomena, at attempt is made to reconstruct natural mechanisms responsible for origin of that conglomerate and deposits of the bentonite horizon in the Upper Silesian Coal Basin.
The recorded variety of infraformational conglomerate, built of clay-muddy intraclasts and sandy groundmass, was covered by mineralogical-petrological studies and its stratigraphic-lithological setting and location in relation to tectonic units of the Basin were analysed. There were also compared lithofacies profiles (in the sense of sedimentary environments) as revealed by three borehole columns penetrating formations of the whole Namurian A in this region. In that comparison, attention was mainly paid to quantitative interrelations of occurrences of the horizons with conglomerates and coal resources, breaks in sedimentation and facies changes in isochroneous sediments. The conglomerates of this variety were found to occur in transitional zone between areas characterized by the maximum and minimum rates of subsidence, i.e. between Bytom Basis and the Main Anticline. Quantitative increase in share of horizons of this conglomerate variety in the column of Namurian A formations was found to be proportional to a number of sedimentary breaks and inversely proportional to number of coal seams. It was also noted that isochroneous sediments from the three drillings situated relatively close to one another, markedly differ in facies. The conglomerates are shown to originate due to erosion of clay-muddy deposits by water-saturated sandy medium and their subsequent deposition at parent bedrock or in its close neighbourhood in the form of mixed undiageneses clay-muddy intraclasts with sandy groundmass. The mineralogical and chemical studies showed that processes of sedimentation of parent rocks and the conglomerates were taking place in saline lagoon-like environments in times of intense volcanic extrusions.
The results of the studies and observations suggest that the Chorzów region belonged to tectonically epicentral zones within the frame of the Coal Basin. In such region, origin of morphological forms impermeable for free water flow, especially in times of less intense precipitation, is more probable under continental conditions. Geochemical conditions prevailing in such water reservoirs without outlet, especially those connected with deposition and redeposition of peats, were appropriate for phase transformations towards montmorillonization and origin of bentonite deposits.

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