Geochemistry of deposits from spring-fed fens in West Pomerania (Poland) and its significance for palaeoenvironmental reconstruction

The cupolas of the spring-fed fens at Bobolice and Ogartowo (West Pomerania, Northern Poland) are composed of alternating peat and calcareous tufa layers. The geology of those two fens, together with the geochemistry of their deposits and radiocarbon dating results, made it possible: (1) to determine the source of water and mineral matter, and (2) to reconstruct the main stages in their development. The distinguished five main stages of development of the fens (four at Ogartowo) reflected varying depositional environments resulting, among other things, from the proportion of groundwater supply and its physico-chemical properties. On the basis of principal components analysis, the sources supplying elements of the peat-tufa rhythmite were found to be chemical denudation and sedentation of peat deposits, while mechanical denudation and atmospheric supply were considerably less important. The geochemistry of deposits was also influenced by local conditions of the geochemical environment, such as its pH, redox potential, CO2 content in water, and the occurrence of organic matter.