Both aquatic and land snails are common in the geologic record, but their utility in dating is greatly restricted by their well-documented tendency to yield 14C dates inconsistent with true 14C ages. In this study, we examine the use of 14C ages from (1) small, previously unstudied, terrestrial snails to date hosting spring deposits and from (2) cooccuring aquatic snails to constrain ground-water travel times during the last glacial period. Our study area in the southern Great Basin encompasses Yucca Mountain, site of the proposed high-level nuclear waste repository, where information on the age and extent of past high water tables and on ground-water flow times is crucial to several licensing issues. Our results show that shells of small terrestrial snails belonging to Vallonia sp. yield 14C dates consistent with 14C ages of associated carbonized wood. These results imply that these taxa can provide reliable 14C age control on the broadly distributed deposits in which they have been described. In contrast, cooccurring aquatic snails from fossil spring deposits yield 14C ages generally greater than the control age. This is because the aquatic shells often formed in spring waters that had an initial 14C deficiency. However, the magnitude of the deficiency is much less than that observed in nearby modern springs, arguing for much higher average 14C contents in late Pleistocene groundwaters in these basins. If representative, this implies shorter groundwater travel times through aquifers in southern Nevada during late-glacial time.
ASJC Scopus subject areas
- Arts and Humanities (miscellaneous)
- Earth-Surface Processes
- Earth and Planetary Sciences(all)