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Coal tonsteins and K- bentonite ( tuffs ) in Poruba Mbrs, Ostrava Formation in the Czech part of the Upper Silesian Basin ( Namur , Arnsberg )
Martinec, Petr ; Horák, J.
The Poruba Mbrs (Arnsbergian, Namurian A) constitute the topmost stratum of Ostrava Fm (Mississippian: Pendleian – Arnsbergian, Namurian A). The Poruba Mbrs incorporate sequences of terrigenous sediments (K-bentonites and coal tonsteins) where a total of 13 isochronous horizons were found: they extend over larger or smaller areas and exhibit a close spatial relationship to the other faunistic horizons or coal seams located there. The horizons, which are of volcanic origin, were formed by deep transformation of acidic volcanic ash under conditions of tropical climate, either in coal tonstein environments or in terrigenous environments (K-bentonites) in absence of humine substances. The petrographic type of the volcanic ash precursor can be interpreted within the context of the discrimination diagram of Zr/TiO2 vs. Nb/Y (FLOYD & WINCHESTER, 1977). The coal tonsteins and the K-bentonites correspond to the same type of volcanic material for which the points of projection of chemical analyses fall within the field bounded by rhyodacite to dacite, near the boundary with the andesite field.
Fulltext: content.csg -  DOC
Plný tet: UGN_0398207 - DOC
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Poruba Mbrs, Ostrava Formation ( Namurian A, Arnsberg ) in the Czech part of the Upper Silesian Basin
Horák, J. ; Martinec, Petr ; Hoch, I.
In the Czech part of the Upper Silesian basin, full preservation of the Poruba Mbrs of Ostrava Fm, i.e., retention of their full thickness, can be observed only in the eastern and southern zones of the basin, while no more than relics exposed by denudation remain in the western and central zones. The Poruba Mbrs (Namurian A, Arnsbergian, E2b) were deposited on the outskirts of Ostrava Fm (Namurian A, Pendleian-Arnsbergian) on a flat coastal plain, interspersed with infrequent but regularly spaced marine transgressions. Individual sedimentary sections—mezocycles—are well-defined (within the meaning of the concept put forward by ČEPEK & HAVLENA 1975). Their sedimentary development reflecting the climate changes during the Carboniferous period have been described. Five complete mezocycles were identified (named Koks, Konrad, Lotar, Otakar, and Gaebler after major marine horizons), plus an incomplete one (Filip, constituted by only the upper continental portion of the mezocycle), inasmuch as the marine part (a group of faunistic horizons of Barbora) is presently ascribed to Jaklovec Mbr.
Fulltext: content.csg - DOC
Plný tet: UGN_0398206 - DOC
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