Reappraisal of the GL‐O Reference Material for K‐Ar Dating: New Insight from Microanalysis, Single‐Grain and Milligram Ar Measurements - Université de Lorraine Access content directly
Journal Articles Geostandards and Geoanalytical Research Year : 2020

Reappraisal of the GL‐O Reference Material for K‐Ar Dating: New Insight from Microanalysis, Single‐Grain and Milligram Ar Measurements

Abstract

The homogeneity and Ar‐dating suitability of the GL‐O reference material were re‐evaluated to determine whether this material is sufficiently homogeneous to be suitable for the calibration of modern high sensitivity instruments. Based on new micro‐analyses and noble gas determinations, our contribution reveals several kinds of inhomogeneity at the grain scale: disparity in the glauconitisation among and within the pellets, variable occurrence of a phosphatic component within pellets (1% m/m on average), and rare occurrences of calcite and detrital grains. Measurements on test portions of ≤ 1 mg reflect such heterogeneity with variability in 40Ar* content that exceeds analytical uncertainty, including a few highly anomalous values. The lesser evolved glauconite population yielded 40Ar* contents ~ 15% lower than the value of 24.8 nl g−1 recommended by Odin et al. (1982, Numerical dating in stratigraphy. Wiley (Chichester, UK), 123–148). But the measured concentrations of 40Ar* converge towards the aforementioned value as test portion mass increased to > 3 mg. A few rare 3 mg experiments still yielded 40Ar* contents lower than the recommended value (down to 24.0 nl g−1), and we recommend using more conservative minimum masses of 5–10 mg. A further purification step for GL‐O or the intercalibration of its powder version could be considered to diminish the size of the test portions and the intensity of the measured signals.
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Dates and versions

hal-02477670 , version 1 (13-02-2020)

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Thomas Boulesteix, Jesús Solé, Teresa Pi, Michel Cathelineau. Reappraisal of the GL‐O Reference Material for K‐Ar Dating: New Insight from Microanalysis, Single‐Grain and Milligram Ar Measurements. Geostandards and Geoanalytical Research, 2020, ⟨10.1111/ggr.12306⟩. ⟨hal-02477670⟩
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