| The Wenlock Series of the Midland Platform, England, comprise three conformably successive formations, the Buildwas, Coalbrookdale and Much Wenlock Limestone, totalling 291–447m of strata. Though well constrained within the type localities, the graptolite biozonal framework does not provide a clear means of correlation elsewhere on the platform or beyond. Based on the geochemical and geophysical correlation of several K-bentonites, time lines within the basal and uppermost formations have now been established which allow direct correlation across the Midland Platform and the development of a platform wide sea-level curve. From the basal Wenlock there is a clear synchronous regression (C. centrifuges-C. murchisoni), represented by the limestones and shales of the Buildwas Formation. The overlying monotonous shales (M. riccartonensis-C. lundgreni) of the Coalbrookdale Formation represent a major transgression, though within the southern half of the platform (?C. rigidus-C. linnarsoni) regressive sandstones and limestones occur in the middle Coalbrookdale. The successive Much Wenlock Limestone (G. nassa-M. ludensis) famous for its rich fauna and bioherms, consists of two shallow water carbonates separated by a deep water shale interval in the northwest part of the platform and a coarser siliciclastic dominated equivalent to the south. Within the type locality at Wenlock Edge, carbonate deposition does not start until the M. ludensis biozone and is associated with localised uplift along the platform margin and the onset of the upper platform-wide regression. The Much Wenlock Limestone-Elton Shale contact appears both conformable and synchronous across the platform, indicating rapid transgression. Sedimentation throughout the Midland Platform can be regarded as being largely eustatically controlled while other factors such as platform slope, siliciclastic input and variations in subsidence are of lesser importance. |
