中国科学院南京地质古生物研究所机构知识库

Conodont microfossils record seawater strontium isotope values (Sr-87/Sr-86), permitting chemostratigraphic correlation for tectonic and climatic reconstructions of the Paleozoic and early Mesozoic (541-201 Ma). Laser ablation multiple collection inductively coupled plasma mass spectrometry (LA MC-ICP-MS) can provide rapid, high spatial resolution Sr-87/Sr-86 analysis of conodont bioapatite but has not been validated by comparison with solution analysis. Validation of LA MC-ICP-MS should be completed in order to use the conodont Sr-87/Sr-86 values for age-correlations and environmental interpretations. Here, for the first time, we compare solution and LA MC-ICP-MS Sr-87/Sr-86 analyses of Carboniferous-age conodonts. Furthermore, we use quadrupole LA ICP-MS to determine concentrations of trace elements potentially responsible for isobaric interferences. Using increased mass resolving power (m/Delta m = similar to 7500) and analyzing conodont tissue with low Rb-85/Sr-88 (< 0.001), we find laser ablation copacetic with solution Sr-87/Sr-86 values. The two-standard-deviation of these LA Sr-87/Sr-86 ratios (average 2SD = 0.00105) are within the two-standard-error uncertainty of solution measurements (average 2SE = 0.00001) on conodonts from the same stratigraphic level. The LA measurements are at a higher spatial resolution and on average 0.00015 higher than solution measurements. Uncertainty of the mean calculations, made on duplicate LA MC-ICP-MS analyses of individual conodonts from the same stratigraphic level, exhibit Sr-87/Sr-86 variability beyond the precision of reference materials (2SE = 0.00001). This finding suggests that solution Sr-87/Sr-86 values determined by dissolving multiple conodonts are homogenizing the conodont Sr-87/Sr-86 signal. As such, the precision of these solution measurements does not capture the geologic variability of conodont Sr-87/Sr-86 within a stratigraphic level, which may originate from differential diagenetic alteration. Conodont Sr-87/Sr-86 measurements that do not account for this variability are at risk of false calibrations with the paleo-seawater Sr-87/Sr-86 curve, which has implications for the timing of geologic events and reconstructions of paleo-environmental changes.