High-Precision U-Pb Zircon Age Constraints on the Duration of Rapid Biogeochemical Events During the Ludlow Epoch (Silurian Period)

Bradley D. Cramer, University of Iowa
Mark D. Schmitz, Boise State University
Warren D. Huff, University of Cincinnati
Stig M. Bergström, Ohio State University


Precise determinations of the rates and durations of Palaeozoic biogeochemical events are largely unavailable. Here, we present two new high-precision U-Pb (zircon) dates from volcanic ash deposits from the Ludlow Series (Silurian System) of Podolia, Ukraine, that yielded weighted mean 206Pb/238U dates of 424.08 ± 0.20 (0.29) [0.53] Ma and 422.91 ± 0.07 (0.21) [0.49] Ma (analytical, tracer and total uncertainties). These new dates bracket the largest post-Cambrian global carbon cycle perturbation (Lau Excursion) and constrain the ‘Ludlow Rise’ in 87Sr/86Sr. These chronostratigraphically well-controlled dates improve the calibration of the Silurian time scale and provide the first determinations of the rates of biogeochemical change during the Ludlow Epoch.