Palaeogroundwater of glacial origin in the Cambrian-Vendian aquifer of northern Estonia

Vaikmäe, R.; Vallner, L.; Loosli, H. H.; Blaser, P. C.; Juillard-Tardent, M. (2001). Palaeogroundwater of glacial origin in the Cambrian-Vendian aquifer of northern Estonia. In: Edmunds, W. M.; Milne, C. J. (eds.) Palaeowaters in Coastal Europe: evolution of groundwater since the late Pleistocene. Special Publications: Vol. 189 (pp. 17-27). London: Geological Society 10.1144/GSL.SP.2001.189.01.03

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A strongly depleted stable isotope composition, absence of 3H and a low radiocarbon concentration are the main indicators of glacial origin of groundwater in the Cambrian-Vendian aquifer in northern Estonia. It is concluded from noble gas analyses that palaeorecharge occurred at temperatures c. 0°C. In some wells unexpectedly high gas concentrations have been found. Excess air, up to c. 50 %, is common but two-five times oversaturation is very unusual, requiring special processes and explanations, e.g. oversaturation may indicate recharge under highpressure conditions, perhaps by subglacial meltwater recharge through the aquifers. Analyses of the gas composition in some groundwater samples also showed a rather high concentration of CH4, indicating the influence of biogenic reactions in the subsurface that could cause the rather negative δ13C values. Results of δ13C analyses in two CH4 samples also show that the CH4 is most likely of a biogenic origin. Based on the isotope data, the results of noble gas analyses, and considering the palaeoclimatic and palaeoenvironmental situation in Estonia during the late Weichselian time, it is concluded that palaeorecharge of Cambrian-Vendian aquifer most probably occurred during the last glaciation, probably by subglacial drainage through the tunnel valleys.

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