O dolomityzacji w jurze w zachodniej części przedgórza Karpat środkowych

Abstract

ON DOLOMITIZATION IN THE JURASSIC OF THE WESTERN PART OF THE MIDDLE CARPATHIAN FORELANDIn this paper the author discusses the phenomena of dolomitization occurring in the Jurassic of the western part of the Middle Carpathian Foreland (Fig. 1). As far as hitherto observed, the process occurs in the shape of minor, and major symptoms, and in the form of, total dolomitization.The symptoms of dolomitization in the Jurassic of the are discussed have mainly been recorded in the Kimmeridgian and Astartian sediments. The phenomena occur as fine-detrital and organodetrital, slightly marly limestones and strongly clayey marls. These symptoms were discovered by microscopic examinations. The partly dolomitized limestones and marls contain small rhombohedric dolomite crystals, either amply scattered or grouped in small concentrations.The total dolomitization, which, caused formation of typical dolomite rocks was ascertained by investigations within a series of rocky limestones and marls of the Rauracian and Oxfordian. The thickest banks of these rocks were encountered in three bore-holes (Fig. 2).For the most part, the dolomites under discussion are highly porous, cavernous and cracked, locally filled with anhytirite. Alongside, of strongly porous and caver-nous dolomites, also more compact dolomites and dolomitized marls occur. In their appearance, the latter resemble, in some degree, the arenaceous rocks.The investigations made show that the dolomitization occurring in the Jurassic of the western part of the Middle Carpathian Foreland may be referred to that of diagenetic and epigenetic type.The author considers diagenetic to be these minor symptoms of that process, which mostly were recorded amidst the Kimmeridgian and Astartian sediments. On the other hand, the dolomites occurring in the Rauracian and Oxfordian should be assigned to the epigenetic type, as indicated by various petrographical and geological features.Geological forms of the rock parts being dolomitized in some degree, i.e. these which show symptoms of dolomitization, most probably appear mainly in the form of lenticles and irregular nests. The typical dolomites form rather veins and' irregular lenticles, and are, presumably, connected with certain displacements occurring along the faults.In the author's opinion, the dolomitization processes both diagenetic and epi-genetic, must have taken place during, the Jurassic time.