13 C Variation in Limestone On An Aquifer-Wide Scale and Its Effects On Groundwater 14 C Dating Models

Abstract

In modeling the initial 14 C activity of ground waters, the δ 13 C of marine limestone is taken conventionally to vary little about 0‰ PDB. This variation was found to be 6.28‰ in samples taken over intervals from 10 -2 to 10 5 m in the Mooney Falls Member of the Redwall Limestone in northern Arizona. Such a variation will cause appreciable variability in the results of all four initial activity models tested. The variability, due primarily to a numerical instability in the models dependent on this parameter, can introduce significant uncertainty into groundwater “age” calculations.