DIAGENEZA A ROZWÓJ PRZESTRZENI POROWEJ W PIASKOWCACH GÓRNEGO CZERWONEGO SPĄGOWCA POMORZA ZACHODNIEGO

Abstract

DIAGENESIS AND DEVELOPMENT OF THE PORE SPACE IN THE UPPER ROTLIEGEND SANDSTONES OF POMERANIA

Abstract. The paper presents the results of studies on Upper Rotliegend sandstones from 23 boreholes of Western Pomerania, acquired by applying different analytical methods (digital image analysis of thin sections, CL, SEM, EDS ISIS, XRD, stable isotope determinations, K/Ar age determination of crystallization of fibrous illite, organic matter studies) and the results of petrophysical analyses. These sandstones are represented mainly by sublithic and lithic arenites. Apart from detrital grains (quartz, feldspars, lithoclasts), authigenic minerals were identified in the sandstones’ cements. They correspond to iron oxides and hydroxides, clay minerals (kaolinite, chlorite, illite), carbonates (calcite, dolomite, ankerite), sulphates and quartz. The sandstones underwent a number of diagenetic processes. These are mechanical and chemical compaction, cementation and replacement, and dissolution and alteration of unstable components. The effects of these processes proceeded within the sediment with a different intensity being dependent on its mineral composition, degree of burial and temperature. In reference to that, two stages have been distinguished in the history of diagenesis: eo- and mesodiagenesis. The presumed maximum temperatures that affected the sediment could reach 160oC. It is suggested that the cementation, compaction and diagenetic dissolution had the main influence on the formation of the pore space in the sandstones. The closure of the pore space in the Permian sediments, preventing flow of formation fluids, occurred in the Early and Middle Jurassic.