U-series and radiocarbon cross dating of speleothems from Nerja Cave (Spain): Evidence of open system behavior. Implication for the Spanish rock art chronology

Two stalagmites from Nerja cave (Andalusia, Spain) were studied. The is well known because of its long human occupation the Upper Palaeolithic to Chalcolithic and abundant parietal prehistoric Art. aims this study twofold: i) compare uranium/thorium (230Th/234U) Carbon-14 (14C) ages obtained all along growth axis in order understand consequences diagenetic processes on validity radiometric ages; ii) as one contains black layers, attributed combustion soot, establish when these intense hearths used by which culture. 230Th/234U 14C coupled with mineralogical studies using FTIR (Fourier-transform infrared spectroscopy) thin section observations. first stalagmite (GN16-9b) displays stratigraphic order, compatible corrected for a few percent dead carbon. Homogeneous composition aragonitic crystals characterized their needle-like texture observed throughout speleothem. For second (GN16-7), contrast, display large significant inversions discordant results upper part at base stalagmite, suggesting possible open system behavior chronometer. Interestingly, are only central part. Mineralogical evidence aragonite calcite transformation top complex assemblage interlayered silicates (possibly clays) calcitic mineralogy GN16-7. In parts, measured. middle however, where fibrous preserved, agree. Our data suggest that case shown here, biased, but seem remain accurate, already marine bio minerals. chronology soot layer, determined here between 7900 5500 years Cal BP, coherent previous analysis charcoals same sector cave. This highlights importance working least two chronometers age verification not possible, some CaCO3 layers rock art dating. Recent published carbonate deposits Spanish Art discussed light demonstration.