Depositional and Diagenetic Controls on the Spatio-Temporal Variability of the Triassic Mercia Mudstone Group, UK

Summary The Middle-Upper Triassic Mercia Mudstone Group (MMG) of England and Wales, and equivalent units on the UK offshore continental shelf, is a successful top seal to hydrocarbon reservoirs and is now a potential host rock for radioactive waste disposal and top seal to Carbon Capture and Storage (CCS) reservoirs in the UK. A significant challenge for these projects is that the MMG is both vertically and laterally heterogeneous. The distribution and causes of heterogeneity are poorly understood. We will here show that this variability has arisen from spatial-temporal changes in depositional environments combined with complex differences in the temperature-time history of major UK Triassic basins. This research therefore takes an integrated approach by combining published compositional, sedimentological and burial diagenetic data to synthesise the depositional and diagenetic controls on the spatio-temporal variability of this heterogeneous rock. As well as improving general understanding of the variability of the MMG, the findings of this research provide crucial insights into the representativity of natural analogues for CCS and radioactive waste disposal projects in the UK.