A revised 87Sr/86Sr curve for the Silurian: Implications for global ocean chemistry and the Silurian timescale

Recent recalibration of the Silurian timescale and improved global chronostratigraphic correlation of Silurian strata significantly altered the Silurian ⁸⁷Sr/⁸⁶Sr curve and the temporal extent of available data. Whereas previous Silurian ⁸⁷Sr/⁸⁶Sr composites showed a generally monotonic increase throughout the Silurian, revisions to the Silurian timescale now require a major increase in the rate of change in ⁸⁷Sr/⁸⁶Sr at or near the onset of the Gorstian Age of the Ludlow Epoch. Similarly, improved chronostratigraphic correlations between Silurian outcrops on Anticosti Island, Canada, and Gotland, Sweden, indicate that the middle part of the Telychian Age, which is roughly 10%–15% of the total duration of the Silurian period, is undersampled and underrepresented in Silurian ⁸⁷Sr/⁸⁶Sr composites. A revised Silurian ⁸⁷Sr/⁸⁶Sr curve based on 241 new and published analyses confirms the significant increase in the rate of change of ⁸⁷Sr/⁸⁶Sr toward more radiogenic values near the base of the Ludlow Series. On the basis of these data, we propose that the rapid trend toward more radiogenic ⁸⁷Sr/⁸⁶Sr values is indicative of increased weathering of old sialic crust exposed during the Silurian uplift of portions of Baltica, Laurentia, and Avalonia. Importantly, however, the actual rate of change of ⁸⁷Sr/⁸⁶Sr will remain equivocal until the durations of Silurian epochs and ages are better constrained.