Testing the relationship between marine transgression and evolving island palaeogeography using 3D GIS: an example from the Late Triassic of SW England

The Rhaetian transgression marked a major landscape change. The Permian and Triassic had been a time of terrestrial conditions across Europe, including much of mainland UK, as well as the North Sea and Irish Sea, represented by red bed clastic successions. At 205.7 Ma, seas flooded across Europe, and the environmental shift from terrestrial to marine is marked in the UK by the switch from red beds of the Mercia Mudstone Group to black mudstones and shelly limestones and sandstones of the Penarth Group. The area around Bristol was marked by a complex landscape in which an archipelago of islands of Carboniferous Limestone was formed in the new shallow seas. Application of new methods in GIS allows a detailed exploration of a number of conformable surfaces, the unconformity between the underlying Palaeozoic rocks and overlying Mesozoic, as well as levels within the latest Triassic, marking the advance of the sea and interaction with coeval tectonics that caused some islands to rise and some basins to descend. The new GIS models show a sequence of palaeogeographic reconstructions of the archipelago and relate this to the tetrapod island faunas which show strong evidence of the species-area effect.