We believe an explanation for this discrepancy lies in the numerous improvements in analytical technique in the intervening several decades, including improved monitoring of neutron fluence gradients in irradiation packages, and major improvements in mass resolution, sensitivity, and efficiency afforded by a new generation of multicollector mass spectrometers (e.g.
the Nu Instruments Noblesse 5-collectors instrument used herein).
This result is combined with prior The representative weighted-mean age for the CI eruption from this population is 39.85 ± 0.12 ka (95% confidence level, including error in J, the neutron-fluence parameter).
MSWD, the ‘mean square of weighted deviates’, is a reduced chi-squared statistic that should be approximately unity if the analytical errors are properly estimated and the observed scatter is due to the stated uncertainties.
The two outliers, excluded from the further calculations, may have been affected by contamination that was not successfully removed by the ABA method. Assuming no pre-aging of the wood, since all ages are in a good agreement this can be considered the statistically most robust radiocarbon age for an organic specimen free of reservoir effect, and virtually coeval to the CI eruption, so far obtained.
Ar laser incremental heating method (details on sample location and analytical procedure are provided in Materials and methods below).
With the notable exception of two grains that did not yield plateaus (e.g. S2n), there is no clear evidence of rising, saddle-shaped or otherwise heterogeneous release patterns that would indicate isotopic discordance.
Plateau steps are plotted on inverse isochrons (Ar) in Supplementary Figure S3.Age-probability density spectra and weighted-mean ages of the individual samples are shown in Figure S4.All four samples yield indistinguishable weighted-mean ages ranging from 39.72 to 40.17 ka, with an overall weighted-mean age of the four results of 39.88 ± 0.17 ka (standard error; ±0.28 ka 95% confidence level).These improved capabilities permit the adoption of single-grain incremental heating, whereas previously only single-grain total-fusion, or multi-grain step-heating approaches were possible.Additional previous ages for the CI were obtained from both the proximal equivalent C-13 (Y-5) layer, which yielded mean ages of 39.85 ± 0.11 ka and 41.4 ± 2.1 ka, respectively (also recalculated for consistency). 2 is virtually identical to the present result, and while that of ref.In the framework of western Eurasian tephrostratigraphy, the Campanian Ignimbrite (CI, southern Italy, circa 40 ka first recognized the large dispersal of the CI by correlating on-land outcrops to the widespread Y-5 marine layer.