Carbonate cementation in Pleistocene sediments of the mid-western part of the Polish Lowlands: Origin, macroforms, and microstructure characteristics

In the mid-western Polish Lowlands, 14 sites of Pleistocene sediments were examined within the region of maximal extent of the Weichselian Glaciation with regard to the occurrence of different forms of carbonate cementation. Out of these sites, five were examined in detail using grain size, petrographic, calcium carbonate content, and thin-section analyses. Rhizoliths, cemented deposits on the underside of pebbles, lumps, or blocks of conglomerates, and concretions in glacial till were found. Rhizoliths are formed in the course of calcium carbonate precipitation on the root surface (cemented sediment zone) and in root canals after their decay (micritic and microsparitic cemented zone). Some of the cementation forms are of infiltration origin (downward leaching of calcium carbonate by meteoric waters), examples of which include sub-pebble cementation forms and some conglomerates (cemented by meniscus cements). Some of the conglomerates may have formed on the boundary between the vadose and phreatic zone (few generations of cements). Concretions in glacial till-forming horizons of unclear origin were formed by calcite displacing sediment in dry weathering conditions of till.