Fluor w utworach węglanowych cechsztynu północnej części Niżu Polskiego

Abstract

FLUORINE IN THE ZECHSTEIN CARBONATE ROCKS OF THE NORTHERN PART OF THE POLISH LOWLANDS

Summary

Preliminary results of fluorine content examinations are presented and the conditions of fluorine concentration in the Polish Zechstein carbonate rocks are described. Twenty boreholes situated on the margin of the Polish part of the Zechstein basin provided data on fluorine distribution. The most abundant information was obtained from the Zechstein Limestone horizon and from the Main Dolomite horizon. It has been found that certain Zechstein carbonate horizons are particularly rich in fluorine. In the Koszalin - Chojnice fault zone the highest fluorine concentrations have been reported from the Main Dolomite horizon of the oncolite-free dolomite with sulphate and bitumen concentrations. A considerable differentiation of fluorine concentration in the Stassfurt dolomites may be related to recrystallization and anhydritization processes active in these sediments. An almost constant concentration level of this element on regional scale indicates that those processes had a wider range and were of similar intensity. In the Peri-Baltic syneclize the maximum fluorine concentrations occur in the Zechstein Limestone sediments formed in a shallow marine facies of highly saline waters. The biggest fluorine content differentiation is In the Podlasie depression in the Zechstein sequences that represent a variable facies of a very shallow sea. In all the sequences examined there is a striking recurrence of maximum fluorine concentrations invariably linked to the upper portion of the dolomites in each cycle. This increased concentration at the top of the sediments may be regarded as an original chemical sediment of a saline-water basin. Higher fluorine contents noted elsewhere in the sequences are probably related to fluorite occurrence in fissures and veins of the carbonate rocks and possibly due to remobilization and displacement of fluorine during the individual stages of the diagenetic processes. The comparison of the composition and trace elements contents of fluorites from the Peri-Baltic syneclize with hydrothermal fluorites confirmed the sedimentary origin of the former.