Geochemical and petrographical analyses for selecting Quaternary marine shells for radiometric dating and paleoclimate reconstructions: examples...

The selection of suitable samples is a fundamental target in order to obtain reliable results in the field of radiometric dating and paleoclimate. Marine molluscs are particularly interesting in this respect in what different radiometric methods (e.g. U/Th, ESR) can be applied coupled with chemical analyses to reconstruct past environment. For this kind of material is imperative that the samples have not undergone any alteration. We present, as example, the study of marine molluscs from Quaternary beach ridges from the Atlantic Patagonian coast. Multiproxy analyses show that the degree of weathering is quite variable but not enough for undermining the paleoclimatic values of the stable isotopes content and of some trace element, but enough severe to make problematic the application of U/Th dating methods. However, the careful petrographic observation and trace element analyses can support the selection of suitable samples for U/Th dating.