CURRENT AND FUTURE RADIOISOTOPIC CALIBRATION OF THE GEOLOGICAL TIME SCALE

The radioisotopic calibration of the latest geological time scale (GTS2012) represents improvements related to: a) the propagation of systematic uncertainties; b) the rejection of legacy ages which could not be reproduced from data in the published literature; c) recalculation of ages and their errors from primary isotope ratios reported in the literature; d) harmonization of U-Pb and Pb-Pb ages using a new estimate for the uranium decay constant ratio of (Mattinson, 2010); e) and recalculation of all ⁴⁰Ar/³⁹Ar data to a new adopted age for the FC sanidine monitor standard age of 28.201 ± 0.046 Ma (Kuiper et al., 2008) using the total K decay constant, l_total = 0.5463 ± 0.0107 Ga^-1 (Min et al., 2000), which intercalibrates ⁴⁰Ar/³⁹Ar and astronomical clocks.

The radioisotopic calibration of the geological time scale is a work in progress. While entailing a major overhaul in methodology and foundational data, the calibration promulgated in GTS2012 is not necessarily more accurate than that of earlier time scales where there have been no new geochronological contributions. Dramatic increases over the past decade in the number of radioisotopic calibration tie points for the Carboniferous Period or the Permo-Triassic boundary contrast with moribund progress for much of the Early Paleozoic, the Late Mesozoic and Paleogene. Similarly, a surprising number of key volcanic ash horizons throughout the Phanerozoic have yet to be revisited with modern analytical methods like CA-TIMS (U-Pb), or single grain laser fusion (⁴⁰Ar/³⁹Ar).

The future holds much promise for a more highly resolved geological time scale as community-wide efforts at improved accuracy, precision, and intercalibration of chronometers bear fruit. In ⁴⁰Ar/³⁹Ar geochronology, a new generation of multi-collector mass spectrometers will soon be in widespread use. In U-Pb geochronology, all new time scale related ages will utilize a combination of CA-TIMS methods and EARTHTIME spikes and standards, most in tandem with cathodoluminescence imaging and in situ analysis via ion probe or LA-ICPMS. Key to the next decade will the integration of radioisotopic and astronomical dating methods—much like the efforts of the recently completed GTSNext Marie Curie Initial Training Network in Europe—as well as magnetostratigraphy and quantitative biostratigraphy.