Abstract

The area to the north of Barnstaple (north Devon) was covered by a detailed gravity survey. The main gravity gradient of the Bouguer anomaly map (estimated to be 1.2 mgals per mile) confirmed the conclusions drawn by Bott et al. (1958), who attributed it to a basin of possibly Carboniferous sediments and/or Old Red Sandstone, about 4 miles thick, separated from the outcropping Devonian rocks by an assumed thrust plane. A negative residual gravity anomaly is located over the outcrop of the Pickwell Down sandstone. Analyses of the anomaly show that it is caused by the southwards dipping belt of sandstone and that the angle of dip of the formation decreases with depth. At a depth of about 2 miles the formation becomes nearly horizontal. Alternatively, it may terminate against an assumed thrust plane underlying the whole outcropping Devonian. The aeromagnetic map of the area shows an elongated magnetic 'high' following the outcrop of the Morte slates. The anomaly is probably caused by near surface, highly magnetized rocks in association with the Morte slates.

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