Syn-rift lacustrine carbonates; cycles, microbial mounds, and brackish to hypersaline facies models; Purbeck Group, Wessex Basin, UK. Analogues for south Atlantic pre-salt carbonates?
The lacustrine limestones of the Purbeck Group were deposited in a shallow lake on the western margin of the Wessex Basin during its late syn-rift phase of basin evolution. The field trip will demonstrate the palaeoenvironmental setting of these limestones in the latest Jurassic and show how this lake was firstly brackish water and later hypersaline. The lower, brackish phase, of the Purbeck limestones are characterised by in-situ, highly porous, thrombolitic microbial mounds that reveal complex and irregular shapes. These microbial mounds are surrounded by, and interdigitate with, an inter-mound packstone-grainstone facies and together are arranged in high-frequency lacustrine cycles capped by paleosols. This fieldtrip will demonstrate these complex and highly variable carbonate facies and compare them with the pre-salt carbonates of the South Atlantic. This new work on the Dorset Purbecks represents the results of a 4-year industry funded research project at Royal Holloway University of London.
Find out more at