The structure of the Neath disturbance between Bryniau Gleision and Glynneath, South Wales

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Abstract
Summary: The Neath disturbance is one of a number of compression belts which occur on the northern limb of the South Wales syncline, and caledonoid directions of which are at variance with the normal armoricanoid trend characteristic of South Wales structures. The main structural elements of the disturbance are (1) impersistent, caledonoid folds; (2) charnoid shear-faults which separate areas of contrasting fold pattern; (3) normal charnoid faults, some of which do not break the continuity of the folds; (4) a caledonoid, sinistral, shear-fault—the Dinas fault; (5) a caledonoid, normal fault—the Coed-Hir fault. In general, the caledonoid folds and accompanying charnoid shear-faults appear to have been formed before the Dinas fault. But local reversals of this general sequence and the partial or complete overlap of the phases indicate that they belong to a single period of earth-movement, believed to be of Armorican age. Subsequent vertical movements resulted in the formation of the Coed-Hir fault and some charnoid faults, and occurred also along the Dinas fault and many of the existing charnoid shear-faults. The Neath disturbance is a product of the resolution of a major Armorican force from the south-south-west into a compressional force directed towards the north-north-west and a sinistral shearing force along the Dinas fault. Such a resolution was probably due to a control exerted by the sub-Devonian foundation. A similar control was being exerted during late Avonian times along part of the disturbed area.

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