|
Regional Studies |
1 Department of Geology, Imperial College, Prince Consort Road, London SW7 2BP, UK
2 Kerr-McGee Oil (UK) plc, 75 Davies Street, London W1Y 1FA, UK
Inversion in Lyme Bay and West Dorset was characterized by the reversal of motion on major Jurassic faults, and regional uplift which resulted in the widespread loss of the mid-Cretaceous to Tertiary post-rift cover throughout the area. North-south contraction during the Tertiary resulted in the development of a major anticline in the hanging wall of the Lyme-Portland faults, which was accompanied by widespread folding within the footwall of these faults. Northeast-southwest sinistral and northwest-southeast dextral strike-slip faults were also developed throughout the Lyme Bay-West Dorset area and accommodated much of the north-south contraction. These features are considered to be a consequence of the mechanical effects of an extensive salt interval within the Triassic Mercia Mudstone Group of this area. Major Early Jurassic faults appear to have been directly linked with basement through the salt interval, although smaller faults within the footwall apparently detached on this horizon. The major faults were inverted in a complex manner during the Tertiary, commencing with simple reversal of motion on these faults, followed by detachment of the post-salt carapace as the footwall and hanging wall salt layers were brought into close proximity, thereby resulting in the widespread deformation observed in the footwall of these faults.
