Precise timing of the Late Ordovician (Sandbian) super-eruptions and associated environmental, biological, and climatological events

Two of the largest known eruptions in the Phanerozoic produced the Ordovician Millbrig K-bentonite of North America and the Kinnekulle K-bentonite of Scandinavia, which have been previously suggested to be coeval. The Millbrig K-bentonite from Kentucky, USA and the Kinnekulle K-bentonite from Bornholm, Denmark yielded chemical abrasion thermal ionization mass spectrometry U-Pb zircon dates of 452.86 +/- 0.29 and 454.41 +/- 0.17 Ma (2 sigma analytical uncertainty), respectively, thus showing significant age differences contrary to what is generally held. These data and four additional newly dated K-bentonites directly establish the first radioisotopic age constraints for the Ordovician Katian-Sandbian global stage boundary, refine global stratigraphic correlations, date associated chemostratigraphic events, and suggest an alternative volcanic-climate hypothesis for the Late Ordovician.