Carbon isotope (δ13Ccarb) and facies variability at the Wenlock–Ludlow boundary (Silurian) of the Midland Platform, UK

Abstract

The Wenlock–Ludlow series boundary (Silurian) has been recognized as a time of pronounced sea-level rise and the end of a globally recognized Late Homerian Stage (Mulde) positive carbon isotope excursion (CIE). However, the precise timing and synchronicity of the end of the excursion with respect to the Wenlock–Ludlow boundary is debated. Within the type Wenlock and Ludlow areas (UK), high-resolution δ13Ccarb isotope data are presented across the Wenlock–Ludlow boundary, and within a range of carbonate platform settings. Correlation between sections and depositional settings has been based upon the characteristics of high-order sea-level fluctuations (parasequences). Comparisons between parasequence-bounded δ13Ccarb values reveal clear spatial variations, with lighter values recorded from more distal settings and heavier values from shallower settings. Temporal variations in the δ13Ccarb values are also documented and appear to reflect local variations in carbonate provenance and productivity in response to sea-level rise. While δ13Ccarb values converge in all sections towards the Wenlock–Ludlow boundary, the apparent end of the Mulde CIE appears diachronous and is progressively older within more distal settings.