Využití gamaspektrometrie při studiu spodnobadenských sedimentů ve vrtu 2241_B Brno-Černá Pole

Abstract

Lower Badenian deposits represent volumetrically significant part of the Carpathian Foredeep infill. New drilled borehole 2241_B Brno-Černá Pole recorded sedimentary profile of these deposits with an almost complete core data. Two different Lower Badenian facies were documented. The first facies of calcareous clays (Tegel) have been documented in depths 20–167 m. Calcareous clays cover underlying “Brno sands“, which represent the second lithofacies and were recorded in depths 167–236 m. Gamma-ray spectrometry was studied on 418 samples of both clays and sands. The results show signifi cant differences in both concentrations and source of signal for these two lithofacies. Lower Badenian clays reveal in general relatively higher concentrations of Th and K than was recognised for Lower Badenian sands. However, concentrations of U are higher in Lower Badenian sands. Remarkable is unusually high U content in selected samples from “Brno sands” (which was also confirmed by supplementary XRF analyses). Whereas Lower Badenian clays were deposited in mostly oxidic condition, deposition of “Brno sands” reveals more reducing conditions. The value Th /K points to varying mineralogy of clays, which is preliminary connected with alternation of more or less humid/arid climatic phases during Lower Badenian. Similar diff erences within the Lower Badenian sands are explained by source area variations.