A new U-uptake model for combined ESR/U-series dating of tooth enamel

Abstract Combined ESR/U-series dating of tooth enamel using US model implies the calculation of a specific parameter p for each dental tissue to reconstruct its U-uptake history. The US model simulates this history as a continuous incorporation process without leaching, where the 238 U– 234 U– 230 Th system evolves towards secular equilibrium state. Consequently, the application of this model is restricted to the samples displaying 230 Th/ 234 U activity ratio below or close to equilibrium with maximum value of ∼1.05 for each tissue. In order to overcome this limitation, here, a new model named Accelerating Uptake (AU) model is proposed. This model describes U-uptake into dental tissue as an accelerating process by the introduction of two parameters, the initial uptake rate and the acceleration of this uptake rate. The AU model is then able to reconstruct a process combining incorporation followed by leaching, as well as continuous uptake one. With this model, the evolution of 230 Th/ 234 U activity ratio with time can reach values higher than unity, even beyond equilibrium. The AU model is useful in cases for which age estimates cannot be calculated by routine use of US model. The application of the AU model to the palaeoanthropological site of Mauer in Germany shows its potential for extending the applicability of the combined ESR/U-series dating of tooth enamel.