Carbon isotope (delta C-13(carb)) and facies variability at the Wenlock-Ludlow boundary (Silurian) of the Midland Platform, UK

摘要

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 delta C-13(carb) 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 delta C-13(carb) values reveal clear spatial variations, with lighter values recorded from more distal settings and heavier values from shallower settings. Temporal variations in the delta C-13(carb) values are also documented and appear to reflect local variations in carbonate provenance and productivity in response to sea-level rise. While delta C-13(carb) 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.