Uranium-thorium dating potential of the marine bivalve Lithophaga lithophaga

Poor chronological control hampers efforts to constrain uplift event frequency in the Eastern Mediterranean Basin and develop regional tectonic models. Borings of the colonial marine mollusc Lithophaga lithophaga are commonly associated with uplifted Mediterranean shorelines and the suitability of its fossil shell for uranium-series dating is investigated to assess its potential for refining uplift chronologies. Living specimens contain very little uranium but Holocene fossils suggest rapid post-mortem uptake from a marine source. However, in common with many other mollusc species, Pleistocene samples show clear evidence of subsequent exchange with uranium from groundwater and although two out of eight samples returned ages compatible with their stratigraphic locations, these may be chance results given the compelling evidence for general open system behaviour. Detrital contamination appears not to be a significant problem in pre-Holocene samples. Open system modelling, using techniques developed to correct for alpha recoil effects in reef corals, shows that the recoil mechanism is inadequate to explain the magnitude of the isotopic alterations observed. Our results show that whilst uranium-series dating of Holocene L. lithophaga shells may be possible, Pleistocene specimens suffer from significant geochemical alteration and cannot be used to refine crustal uplift chronologies over longer timescales.