Nowy horyzont tonsteinowy w warstwach porębskich (namur A) Górnośląkiego Zagłębia Węglowego

Abstract

Nowo stwierdzony tonstein występuje nieco poniżej poziomu fauny morskiej Koks IV w pokładzie 626. Jest to tonstein ziarnisty, pseudomorfozowy. Dominującym rezystatem jest biotyt o różnym stopniu przemiany. Tonstein ten stanowi obecnie horyzont litostratygraficzny o znaczeniu lokalnym, lecz jego znaczenie będzie rosło w miarę coraz lepszego rozpoznania warstw brzeżnych górnośląskiej formacji węglonośnej. NEW TONSTEINHORIZON IN THE PORĘ,BA BEDS (NAMURIAN A) FROM THE UPPER SILESIAN COALBASINSummary Hitherto in the Poręba Beds of Namurian age from the Upper Silesian Carboniferous was known only one, widely expanded tonstein horizon, occuring within 610 seam. Results of studies on mining area of coal mine Julian (Fig. 1) documented a new tonstein horizon within the Poręba Beds, under horizon Koks IV with marine fauna within 626 seam (Fig. 2). Tnus tonstein is about 4-5 cm thick and with naked eye it seams a fractionally graded sandstone. Macroscopically it is grained, pseudomorphic tonstein. Prevailing resistate is biotite in various stages of transformation (Tab. I, Fig. 3). First changes in biotite are indicated with spotted microareas of lowered pleochroism and birefringence. More advanced changes cause growth of these areas and “bulging” of plates, resulted due to more loose structure of new origined minerals: kaolinite or illite or clay minerals of mixed-layer structure (Tab. 2). Mostly changed biotites have no pleochroism. Quartz, quantitatively second component of resistates, distinguishing with splinder-like and needle-shaped sections of its sharp-edged crystals, has origined due to thermic autoclase of rapidly cooled in air quartz fenocrystals during volcanic eruption. Important clay components of this tonstein are worm-shaped and platty aggregates of kaolinite (Fig. 3), effects of koalinitization of biotite and sanidine; it is indicated by occurrence of relicts of these minerals. Microcristalline kaolinite matrix, infilling voids between resistates and aggregates of coarse-grained kaolinite, is intensively saturated with fine dispersive coal matter, assuming a honey-yellow colour. The component, especially distinguishable, are large (0.5-0.8 mm), “granular” concentrations of microcrystalline kaolinite. They could be kaolinitized globules of volcanic glass. The chemical analyses of tonstein from 626 seam indicate (Tab. 3) that it characterizes with varied koalinization stage in individual occurrences. It is documented by comparison of value of molar ratio SiO2/Al2O3 and of K2O content. It could have relation with physical-chemical conditions of sedimentary and diagenetic environments. In boreholes B 242 and B 243 the pyroclastic material has consisted intercalation within coal seam but in borehole B 245 it located within siltstones and sandstones. It is commonly known that physical-chemical conditions of coal-fonning marshes favour more kaolinitization process than conditions, existing in sedimentary environment of clastic rocks.