Structure and deformation history of the Central Wales Synclinorium, northeast Dyfed: Evidence for a long-lived basement structure

The Central Wales Synclinorium in northeast Dyfed is markedly asymmetrical, dominated by strongly southeast verging NE–SW trending F1 folds with an axial planar to mildly clockwise‐transecting cleavage. Within the Pysgotwr Fault Belt, a narrow braided array of steep faults developed in the core of the structure, the F1 folds and S1 cleavage are locally refolded into en echelon ENE–WSW F2 folds with an associated S2 cleavage. F2 and S2 geometry and orientation strongly suggest development in response to an important element of oblique simple shear involving components of sinistral strikeslip and NW‐down dip‐slip. The Pysgotwr Fault Belt is anomalous in the context of fold‐dominated mid‐Wales and appears to be associated with a long‐lived basement structure which significantly influenced Welsh Basin topography in early Silurian time.