NanoSIMS as an analytical tool for measuring oxygen and hydrogen isotopes in clay minerals from palaeosols: Analytical procedure and preliminary results

Oxygen and hydrogen isotope composition of neoformed clay minerals is commonly used as a palaeoclimatic proxy. Usually, sediments rocks (including palaeosols) contain not only minerals, but also detrital and/or diagenetic ones. Together with the usually small size (micro- or nanometric) in these materials, this can generate difficulties during isotopic analyses by conventional spectrometry. To avoid problem, we nanoscale secondary ion mass spectrometry (NanoSIMS) to analyse included palaeosol levels early Barremian continental profiles located NE Spain. The bottom are rich kaolinite, whereas top smectite (beidellite-type). compositions pure powder standards kaolinite beidellite were measured bulk obtain reference values for calibrating instrumental fractionation. Two common preparation techniques geological samples tested (thin sections thick polished sections), revealing that thin more suitable NanoSIMS analysis due their lower resin content. high spatial resolution instrument allowed elemental mapping samples, permitting localization interest measurement ratios at selected points (1 x 1 μm 2 ) within samples. preliminary results distinguish decrease average 18 O/ 16 O D/H from levels, reflecting change climatic conditions. δ δD obtained (δ SMOW =18±15‰; =-82±36‰ =14±4‰; =-97±37‰) =13±14‰; =-167±87‰ =11±6‰; =-180±40‰;), respectively, consistent crystallization clays weathering Despite uncertainties measures, estimate an temperature formation 21-22°C, 16-17°C smectite. Given calibration using adequate sample preparation, thus have great applicability studies involving oxygen nanometre-sized palaeosols • was single point H isotopes paleosols without contamination other phases. Preliminary document profiles, conditions Lower Barremian. O=18±15‰; δD=-82±36‰ O=14±4‰; δD=-97±37‰) O=13±14‰; δD=-167±87‰ O=11±6‰; δD=-180±40‰) agree formation. shows promise minerals.