Abstract

Since its designation as the Global Stratotype Section and Point (GSSP) for the base of the Silurian System, the choice of Dob's Linn, Southern Scotland, has received criticism due to the difficulties of relating its well-constrained graptolite biostratigraphy to shallow-water sequences elsewhere. Kerogen samples from across the Ordovician-Silurian boundary interval at Dob's Linn have yielded carbon stable-isotope signatures consistent with those recorded elsewhere, in particular showing a clear positive δ13C excursion in the terminal Ordovician. The architecture of the δ 13C curve from Dob's Linn enables very high-resolution stratigraphic subdivision and direct correlation between the deep water Dob's Linn section and time-equivalent carbonate shelf deposits. An integrated stratigraphic scheme using isotope stratigraphy and biostratigraphy of graptolites, conodonts and shelly faunas has been constructed. This direct correlation shows that the shallow water successions, including the former stratotype candidate at Anticosti Island, are generally incomplete, with hiatuses related to the rapid sea-level changes during the Hirnantian stage. This confirms and greatly increases the global utility of Dob's Linn as a boundary stratotype.

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