13C variation in limestone on an aquifer-wide scale and its effects on groundwater 14C dating models.

Abstract

In modeling the initial 14C activity of ground waters, the 813C 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 1^(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.