Publisher © Czech Geological Survey, ISSN: 2336-5757 (online), 0514-8057 (print)
Ground gamma-ray spectrometrical measurement of natural radioactivity of rocks in the Moravian-Silesian Culm area in the Nízký Jeseník Mts.
Abstract
The Upper Devonian-Lower Carboniferous siliciclastic flysch formations called the Moravian-Silesian Culm are widespread on the northeastern margin of the Bohemian Massif. The Moravian-Silesian Culm belongs to the Rhenohercynian belt of the Central European Variscides, it forms an accretion wedge developed as a result of a collision of two blocks of Continental crust - the inner parts of the Bohemian Massif and the Bruno-Vistulicum. The Culm sequences in the Nízký Jeseník Mts. are formed by various types of psammites (mainly graywackes), conglomerates and clayey shales to siltstones (and locally also by carbonate rocks), epizonally metamorphosed in the westernmost part (in the Andělská Hora Formation). The studied siliciclastic sediments usually contain 1.5 to 6.5 wt per cent of K (avg. 3.5 wt per cent) but graywackes and gravellites of the northern part of the Hradec-Kyjovice Formation are characterized by relatively higher concentrations of K (avg. 5.0 wt per cent) which corresponds to increased content of K-feldspars in these rocks. Uranium and thorium contents in the studied siliciclastic sediments are usually 0.7 to 11.6 ppm (avg. 5.6 ppm) and 7. l to 32.6 ppm (avg. 17.2 ppm), respectivelly; vety high contents of both elements were found in the graywackes and siltstones of the northern part of the Moravice Formation (up to 23 ppm U and 43 ppm Th).
