The purpose of the research is to investigate two hypotheses involving sedimentation associated with the emplacement of shallow marine ash-flow tuffs. Specifically, these hypotheses are: 1) that Ordovician ash-flow tuffs of the Capel Curig Volcanic Formation were emplaced and welded underwater, and 2) that explosive volcanism has a significant impact on influencing patterns of shallow marine sedimentation. Ordovician volcanic and volcaniclastic rocks of the Capel Curig Volcanic Formation provide an ideal laboratory for testing these hypotheses. Sedimentary rocks associated with ash-flow tuffs in the Ordovician of North Wales are well exposed and contain numerous sedimentary structures. Detailed mapping by the British Geological Survey has provided a well-defined stratigraphic context for this work. Furthermore, many of these ash-flow tuffs have been interpreted to have been emplaced and welded underwater, although this hypothesis has been controversial. Yet the tuffs of the Capel Curig Volcanic Formation have remained one of the textbook examples of welding in shallow marine water. The study will determine environments of deposition in the associated sedimentary rocks beneath the tuffs and paleowater depths from numerous bedding plane exposures of wave ripples. Determination of the environments of deposition will test the likelihood of subaqueous welding. Comparing pre-tuff environments with ones that existed following tuff emplacement will determine the effect that these tuffs had on patterns of sedimentation. Successful completion of this work will provide data far beyond that of solving a local geological problem in Wales. This project will bear directly on the question of subaqueous welding and on the specific examples that have been most often to support welding in intermediate depth water. Also, models of volcaniclastic sedimentation from the Capel Curig Volcanic Formation will be developed that can be applied in many future studies and used to determine the influence that explosive volcanism plays on patterns of marine shelf sedimentation.
