STABLE ISOTOPIC COMPOSITION OF PALEOSOLS IN THE LOWER VISEAN OF EASTERN BELGIUM - EVIDENCE OF EVAPORATION AND SOIL-GAS CO2

Numerous paleosols occur in the Lower Visean peritidal limestones of e astern Belgium. At the top of the peritidal unit, a widespread paleoso l horizon occurs which has been analysed for its carbon and oxygen iso topic composition. In spite of the Paleozoic age of the pedogenic carb onates, the influence of evaporation and soil-ps CO2 on the stable iso topic composition of the paleosol is very pronounced. This has been as signed to the long exposure time in a semi-arid seasonal climate. Evap oration caused an enrichment in O-18 in the paleosol compared with the over- and underlying limestones, which were cemented and mineralogica lly stabilized in meteoric pore waters. The influence of soil-PS CO2 i n the soil formation is clearly indicated by the depletion in C-13 of the pedogenic carbonates (deltaC-13 = - 5 parts per thousand(PDB)) com pared with the carbon isotopic composition of Lower Visean marine lime stones (deltaC-13 = +4 parts per thousand(PDB)). The possible effect o f carbon derived from atmospheric CO2 on the deltaC-13-values of the p aleosols is discussed.