A new correction model for C ages in aquifers with complex geochemistry – Application to the Neogene Aquifer,Belgium

The objective of this paper is to build a general correction model that takes into account all the different radiocarbon-dilution reactions and resolving the processes that are geochemically “aging” the groundwater in the Neogene Aquifer. For this, δ¹³C and radiocarbon in groundwater are investigated with their relationship to other chemical components in groundwater. The δ¹³C values in the Neogene Aquifer are influenced by various geochemical reactions like calcite dissolution, oxidation of organic matter and methanogenesis. Calcite dissolution and CH₄ production increase δ¹³C while the oxidation of organic matter decreases δ¹³C in the groundwater. The reactions that modify δ¹³C also influence the ¹⁴C activity. Due to the complex geochemical environment, existing correction models are not applicable to this situation. A correction model for initial ¹⁴C activity is formulated in which the different C sources that influence ¹⁴C activity are taken into account. It is observed that recent dissolved organic matter plays an important role in redox reactions. The corrected ¹⁴C ages lie between −0.792 and 6.425 ka representing the maximum age. If a part of the organic matter that oxidises is fossil, the determined age will represent an overestimated age.