The application of chemostratigraphy and proximality trends to the Silurian Coralliferous Formation of SW Wales: rhythmical sedimentation during the transgression of a palaeo-shoreline

Abstract

The Silurian Coralliferous Formation of Pembrokeshire comprises 94–143 m of shelfal sediments deposited on the southern margin of the Welsh Basin, UK. The succession begins with rudites (Renney Slip Member), which are overlain by interbedded silty mudstone and sandstone (Deadman's Bay Member). Biostratigraphical control is weak between the two principal sections (Renney Slip and Marloes Sands), but high-resolution chemostratigraphy permits 11 subdivisions to be distinguished. Some chemostratigraphical units can be traced between the sections, whereas others are locally absent. The correlation of the chemostratigraphical units has been compared with sea-level cycles identified by a study of the frequency, distribution and characteristics of storm-beds using proximality trend analysis. This suggests a synchroneity of traceable chemostratigraphical units within the Deadman's Bay Member, indicating that deposition began in the Renney Slip Section, and that a greater water depth was achieved there. A holistic assessment shows that the Coralliferous Formation onlaps an unconformity surface with a palaeo-relief of 57 m, over a current distance of 3 km. Further considerations of benthic assemblages, subsidence rates and global sea-level fluctuations support the presence of a late Telychian transgression with glacio-eustasy contributing between 40 and 70 m to that sea-level rise.