New ESR/U-series data for the early Middle Pleistocene site of Isernia la Pineta, Italy

Located in Southern Italy, the Early Palaeolithic site of Isernia la Pineta has provided numerous palaeontological remains and artefacts in well-defined fluvio-lacustrine sequence. The normal magnetization of the main archaeological layer t3a and 39Ar/40Ar date of 610 ± 10 (2σ) ka, obtained from the immediately overlaying geological level, put the Isernia assemblage in the first part of the Middle Pleistocene. Previous ESR/U-series analyses of Isernia fossil teeth have displayed both recent U-uptake and severe underestimation of the ESR/U-series dates in comparison with the 39Ar/40Ar age. In order to identify the cause of this age underestimation, new analyses were realized in the present study on four bovid teeth directly recovered from the archaeological surface t3a. The ESR/U-series dates obtained were once again strongly underestimated, with an error weighted mean age of 435 ± 24 (1σ) ka. These too young dates could be associated to a change of the environmental γ-dose rate during the geological history of the Isernia site, related to the revealed recent U-uptake into the palaeontological remains of the archaeological level. If we consider that this dose rate change was coeval with a wet interglacial period and taking the 39Ar/40Ar age as geochronological reference, simulations with two dose rate steps indicate that this change could be correlated with marine isotopic stage 7 (MIS 7).