Revising the late Cambrian time scale and the duration of the SPICE event using a novel Bayesian age modeling approach

We present a refined global Furongian (late Cambrian) time scale derived through the application of Bayesian age modeling, using an integrative assemblage of conditioning likelihoods (age constraints) including U-Pb zircon maximum depositional ages in the Steptoean positive isotopic carbon excursion (SPICE) reference section in Smithfield Canyon (Utah, USA) and nearby McPherson Canyon (Idaho, USA); Re-Os geochronology from the SPICE-bearing interval of the Andrarum- 3 core (Scania, Sweden); and new high-precision chemical abrasion–isotope dilution– thermal ionization mass spectrometry U-Pb zircon tuff ages from Avalonian Wales. We embed these radioisotopic ages within a novel probabilistic treatment of biozones to establish temporal constraints on rock accumulation rates in the Great Basin (USA), the duration of the SPICE event, and Laurentian trilobite biozones correlated to the global Cambrian time scale. Results reveal a beginning of 494.5 (+0.7/−0.6) Ma and an end of 487.3 ± 0.08 Ma for the Furongian Epoch, representing a reduction of the traditional late Cambrian by ∼30% and an extension of the Ordovician by nearly half a million years. Furthermore, the SPICE is confined to a duration of 2.6 (+0.9/−0.8) m.y. Our new approach to integrating faunal succession into Bayesian age modeling can help to constrain rock accumulation rates and possible hiatuses in sections with limited radioisotopic ages. Additionally, it offers a robust calibration tool for further refining the numerical calibration of the geologic time scale, for testing hypotheses about the rates of trilobite evolution and extinction, for evaluating causes of the SPICE, and for constraining paleoclimatic conditions including atmospheric O2 levels.