TRIPLING YOUR PLEASURE: ESR DATING MOLLUSCS AND TEETH WITH STANDARD AND ISOCHRONS

ESR dating for molluscs uses one of several carbonate ESR signals that grow with dose near g = 2.007-2.000, while dating teeth uses the HAP signal at g = 2.0018. Since the two signals respond differently to dose both in nature and artificially, the methods act as independent geochronometers. In standard ESR dating teeth, uncertainty arises from the external dose rate, D_ext(t), and the tooth’s U uptake rate, p. Isochron analyses use 4-8 subsamples from large teeth having different U concentrations to assess the time-averaged external dose rate, D^I_ext(t), seen by the tooth, given a p value. Since the isochron depends on p, it also indicates secondary U mobilization. If one knows the time-averaged and volumetrically averaged external dose rate measured at the site, D^BG_ext(t), setting D^I_ext(t) = D^BG_ext(t) will reveal the tooth's p. Using isochrons to find p is faster than doing coupled ESR-²³⁰Th/²³⁴U dating analyses. From an archaeological site with Paleolithic tools and associated fauna, five subsamples from a single cervid molar, AT39, were dated, as were molluscs, AM66, from an overlying layer. The standard ESR ages were calculated using time-averaged and volumetrically averaged external dose rates, modelling the dose rates by assuming typical sedimentation rates and cover thicknesses estimated from the geological strata. AM66 dates indicated that the tooth had to predate 414 ± 42 ka. The standard ESR tooth analyses indicated a maximum age for AT39 at 637 ka. The isochron analysis, however, suggested that AT39 had experienced some secondary U remobilization. Equating D^I_ext(t) = D^BG_ext(t) gave p = 2. Assuming p = 2, AT39 dated at 484 ± 13 ka, which correlates with Marine (Oxygen) Isotope Stage 13. This age agrees with the vertebrate paleontology biozone attribution and other dating results. Here, using molluscan dating, standard tooth dating, and isochron analyses gave us a firm age for the Paleolithic site.