A gravity survey of the western English Channel between Lyme Bay and St Brieuc Bay

Abstract
A gravity map of the area between Lyme Bay and St Brieuc Bay drawn up from the results of surveys by the Institute of Geological Sciences in 1972 and 1973 shows the following main features: (i) There is an east-west regional gradient of about 0.2 mGal/km over the entire survey area north of the Channel Isles. This may be due to a westward thinning o the crust. (ii) A region of low gravity in Lyme Bay is attributed to a Mesozoic basin at least 1 km thick. An anticline runs approximately east—west across this basin. (iii) A ridge of high gravity extends eastward from Start Point and is probably associated with thrusting of dense Metamorphic rocks over the Devonian strata. (iv) South of 50° N the gravity field is complex due mainly to the emplacement of granites in an area of shallow basement. The Hurd Deep Fault is, however, clearly visible, possibly owing to its having controlled Mesozoic basin formation.

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