STRUCTURAL-ANALYSIS AND KINEMATIC EVOLUTION OF THE INVERTED CENTRAL SOUTH-CELTIC SEA BASIN

The central South Celtic Sea Basin shows excellent examples of tectoni cs and sedimentation relationships as evidenced by detailed geological interpretation of a local grid of seismic profiles. These relationshi ps together with balanced/restored geological cross-sections and black diagrams have been used to unravel the post-Variscan evolution of thi s part of the Celtic Sea basin. Three sedimentary mega-sequences separ ated by two erosional surfaces have been recognized overlying a deform ed Palaeozoic basement in this area. (1) Permo?-Triassic-Jurassic syn- rift mega-sequence. Sedimentation of the lowest part of this successio n is strongly controlled by extensional faults, whereas the rest of th e 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) T ertiary post-rift mega-sequence. The Cretaceous and Tertiary successio ns are more extensive than Permo?-Triassic-Jurassic sediments covering the central South Celtic Sea Basin and the Pembrokeshire Ridge. The s tructural framework displayed by the syn-rift and post-rift sequences is very different. Thus, the general structure beneath the Jurassic-Cr etaceous (Late Cimmerian) unconformity consists of a WSW-ENE trending fault system and related folds. This resulted from an extensional phas e, which led to a sub-basin compartmentalization of the area, and a su bsequent inversional event, which caused significant reverse movement along previous extensional structures. Early Cretaceous erosion was re sponsible for an important and unequal denudation. The timing of the s witch between extension and inversion cannot be determined due to Earl y 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 fol ds. The Tertiary sequence shows a subhorizontal disposition responsibl e for the present-day, smooth bathymetric relief of the South Celtic S ea Basin. (C) 1998 Elsevier Science Ltd. All rights reserved.