Palaeoecological evolution of a spring-fed fen in Pawłów (eastern Poland)

A continuous record of sedimentation in spring-fed fens makes them suitable for detailed palaeoenvironmental studies. A newly investigated cupola spring-fed fen (Paw?ów site), located in the Lublin chalkland, eastern Poland, was the object of our study. This special karst region is characterised by the occurrence of Upper Cretaceous carbonate rocks in the substratum. Sedimentological observations indicated strong variability of biogenic-carbonate series in the deposits (=peat-tufa rhythmite), reflects changes of accumulation conditions (oxidising versus reducing), resulting from alternate occurrence of warmer and cooler periods. Difficulties in pollen analysis due to oxidising conditions necessitate a multidisciplinary approach for palaeoenvironmental reconstruction. We used a multidisciplinary approach (sedimentological, palaeobotanical, geochemical analyses and radiocarbon dating) to determine the main evolutionary stages of this unique fen ecosystem and to discuss the role of local or/and regional factors in its development. Pollen and plant macrofossil analyses, supported by radiocarbon dating, proved that the bottom part of the cores represents the Late Glacial–Early Holocene stages of the fen development. A comparative analysis of palaeoenvironmental data showed close resemblance between the Paw?ów fen and the earlier studied fens in eastern Poland and Central-Eastern Europe, and the connection between their development and supraregional hydrological-climatic factors. The results indicated also the influence of the morphological position of such a type of ecosystem on the development of a continuous deposit succession. The occurrence of a river valley in close proximity of the Paw?ów site resulted in the lack of tufa deposits from the Atlantic period, because of an erosional phase in the river valley.     

Possible origin of stromatactis-like cavities in Upper Jurassic sediments from the Wielkanoc quarry near Gołcza (Kraków–Częstochowa Upland,southern Poland)—experimental studies

Isolated stromatactis-like cavities were found in a microbial-sponge buildup exposed in the Wielkanoc quarry (eastern part of the Kraków-Częstochowa Upland). The cavities are filled with several generations of carbonate cements and with internal sediments. The top surfaces of internal sediments are flat or wavy, whereas the roofs of cavities are arcuate. The origin of cavities from the Kraków-Częstochowa Upland is difficult to constrain. It seems that the stromatactis-like cavities from the Wielkanoc quarry resulted, at least partly, from remodeling of open spaces left after dissolution of corals in incompletely lithified sediment. Dissolution of corals disturbed the primary stress field within the carbonate buildup and generated the secondary stress characterized by the appearance of compressional forces in the walls of cavities and tensional forces in their roofs. Thus, the lack of support of sediments over roofs of cavities after dissolution of corals resulted in their instability and collapse triggered by vibrations caused by various factors. One of such triggers might have been the rejuvenation of the Kraków-Lubliniec Fault Zone in the Late Jurassic or the collapse of reticular framework within the buildup. The material falling down from the roofs was deposited at the bottoms of cavities as an internal sediment. Results of experimental studies demonstrate that the arcuate shapes of the roof surfaces of cavities are related to compressional stress in the walls and tensional stress in their roofs.