The Homerian (Silurian) stratigraphy of the May Hill and Gorsley inliers of England, UK: integration of carbon isotope data, sedimentology, and sequence stratigraphy

The globally-recognised Homerian (Silurian) carbon isotope excursion (CIE) occurs in the Much Wenlock Limestone Formation and Gorsley Limestone of the May Hill and Gorsley inliers of the southern part of the Midland Platform (eastern Avalonia), England. This CIE is associated with eustatic sea-level fluctuations and time-specific facies, and is documented in limestone facies formed in a tropical shallow marine setting, that crop out at the key localities of Hobbs Quarry, Hobbs Lane, and Linton Quarry. Carbon isotope trends and values from these localities identify the falling limbs of the first and second peaks of the Homerian CIE at Hobbs Quarry and Hobbs Lane, respectively, and the low between these peaks at Linton Quarry. The identification and correlation of these parts of the Homerian CIE, alongside the correlation of lithofacies, bentonites and sea-level changes, indicate that at May Hill, the Much Wenlock Limestone Formation began near the top of Silurian stage slice Ho1 and ended near the top of Ho3 (i.e., middle to end Homerian), as is the case for the inner part of the Midland Platform to the north of the study area. Lithofacies of the Gorsley Limestone (Gorsley Inlier), alongside carbon isotope values, correlate to the middle of the Much Wenlock Limestone Formation, as developed at May Hill and across the inner part of the Midland Platform. This indicates that the unconformity at the top of the Gorsley Limestone omits the latest Homerian limestones and second peak of the Homerian CIE, as well as the overlying Gorstian. Furthermore, the uplift, subaerial exposure, and weathering of pyrite-rich sediments in the Gorsley area, to form the Gorsley High, may have supplied iron into the surrounding marine environment, and resulted in the localised development of the latest Homerian ferruginous crinoidal grainstones of the neighbouring May Hill Inlier and Ledbury Hills. These results demonstrate that the CIE and associated strata in the study sites are consistent with regional trends, and therefore add to the global database of these mid-Silurian stratigraphic changes.