Structural analysis and kinematic evolution of the inverted central South Celtic Sea Basin

Abstract

The central South Celtic Sea Basin shows excellent examples of tectonics and sedimentation relationships as evidenced by detailed geological interpretation of a local grid of seismic profiles. These relationships together with balanced⧹restored geological cross-sections and block diagrams have been used to unravel the post-Variscan evolution of this part of the Celtic Sea basin. Three sedimentary mega-sequences separated by two erosional surfaces have been recognized overlying a deformed Palaeozoic basement in this area. (1) Permo?-Triassic-Jurassic syn-rift mega-sequence. Sedimentation of the lowest part of this succession is strongly controlled by extensional faults, whereas the rest of the sequence indicates much less fault control. Lateral extent of these rocks is also controlled by the disposition of the Palaeozoic basement which appears as an elevation in the Pembrokeshire Ridge area, where no sedimentation occurs. (2) Cretaceous post-rift mega-sequence. (3) Tertiary post-rift mega-sequence. The Cretaceous and Tertiary successions are more extensive than Permo?–Triassic–Jurassic sediments covering the central South Celtic Sea Basin and the Pembrokeshire Ridge. The structural framework displayed by the syn-rift and post-rift sequences is very different. Thus, the general structure beneath the Jurassic–Cretaceous (Late Cimmerian) unconformity consists of a WSW–ENE trending fault system and related folds. This resulted from an extensional phase, which led to a sub-basin compartmentalization of the area, and a subsequent inversional event, which caused significant reverse movement along previous extensional structures. Early Cretaceous erosion was responsible for an important and unequal denudation. The timing of the switch between extension and inversion cannot be determined due to Early Cretaceous erosion. Overlying the Jurassic–Cretaceous unconformity, Cretaceous sediments are slightly deformed by broad anticlines formed during Early Tertiary mainly as a result of tightening of previous folds. The Tertiary sequence shows a subhorizontal disposition responsible for the present-day, smooth bathymetric relief of the South Celtic Sea Basin.