Correlation of the Triassic and Jurassic successions proved in the Lyme Regis (1901) borehole with those exposed on the nearby Devon and Dorset coasts

Abstract

The Lyme Regis (1901) Borehole was one of numerous coal-exploration boreholes drilled in southern England during the late 19th and early 20th centuries. It is one of the few deep boreholes (>200 m depth) in the east Devon-west Dorset area and, unlike more recent hydrocarbon-exploration boreholes, was continuously cored. The borehole was sited [NGR SY 3364 9297] on the floodplain of the River Lim on the outcrop of the Jurassic Blue Lias Formation, and was continuously cored to a final depth of 396.85 m within the Triassic Mercia Mudstone Group. Selected samples and some of the cores were examined by the Geological Survey geologists Jukes-Browne and Woodward who were working in the area at the time of drilling. The former published a description of the succession based on his and Woodward’s notes and the driller’s log, and correlated it with the succession of Triassic and Jurassic rocks that are almost wholly exposed in the cliffs between Sidmouth and Lyme Regis. A recent revision of the stratigraphy of the coastal successions has enabled that proved in the borehole to be reassessed and placed more accurately into its regional stratigraphical context