Isotope Signature of Sand Calcites in the Paris Basin: A Proxy for Permafrost/Groundwater Paleoconditions

Sand calcites occurring as rhombohedral crystals and spherolitic concretions in several Tertiary sandstone formations in the Paris basin have been dated to the cooling periods of the four last glacial stages, using 14C and U-Th methods. Sand calcites constitute a novel proxy to estimate paleo-groundwater levels and the extension of permafrost conditions. The δ13C and δ18O compositions of sand calcites are a function of precipitation depth in relation with the warming of surface water during infiltration. Sand calcites appear as precious markers for Pleistocene paleo-landscape reconstructions.