Inversion tectonics in S.W. Dyfed

Abstract

Inverted sedimentary basins form when basin-controlling extensional faults reverse their movement during contractional tectonics. The structural evolution of S.W. Dyfed is considered in terms of a model of positive inversion tectonics. A change in deformation mode from Devonian extension to Late Carboniferous contraction gave rise to renewed movement on pre-existing extensional faults. The stratigraphy of S.W. Dyfed is categorized into stratigraphic sequences according to their deposition before, during and after extensional fault movement. Excellent stratigraphical control enables the interrelationship of sedimentation and tectonics through time to be documented, growth fault geometries calculated and the pre- Variscan extensional system defined. Variscan contraction combines a thin-skinned tectonic style with a deeper level system of reactivated extensional faults. Small scale evidence for reactivation along individual faults is documented and theoretical methods for positive inversion are applied to the geology of S.W. Dyfed.