Inversion and exhumation of the St. George's Channel basin, offshore Wales, UK

G. A. Williams, J. P. Turner, S. P. Holford
2005 Journal of the Geological Society  
The western UK basins of the Irish Sea have provided one of the best natural laboratories for investigating the causes and consequences of intracratonic uplift and erosion (exhumation). To date, the emphasis has been on igneous underplating as the chief process driving their exhumation. In this paper, we demonstrate that tectonic inversion -the shortening of formerly extensional basins and reactivation of their constituent faults -dominated the exhumation of the St. George's Channel basin,
more » ... Channel basin, offshore Wales. Based on mapping of an extensive 2D seismic grid, evidence is presented for at least two major inversion episodes in the Late Cretaceous and the Neogene, plus minor shortening during the Eocene. Inversion was distinctly noncoaxial, especially during the Neogene when coeval transpression and transtension was focused at discrete bends and stepovers on the basin-bounding St. George's, Bala and Northwest Flank faults. That the principal mechanism driving these uplift episodes was inversion (as opposed to igneous underplating) is corroborated by analysis of thermal history data (apatite fission track and vitrinite reflectance). They reveal late Cretaceous and Neogene geothermal gradients that were comparable with the present day i.e. no significant increase in basal heatflow. Sonic velocity profiles logged in hydrocarbon boreholes constrain the minimum thickness of the eroded section which varies between c.1000m in the centre and c.2240m at the margins of the basin. Given the strength of evidence for tectonic inversion in the St. George's Channel basin, our favoured model invokes superimposition of the effects of inversion and igneous underplating to account for the complex exhumation history of the St. George's Channel basin in particular, and the western UK basins in general. KEYWORDS: ABBREVIATED TITLE: Inv. & Exh. of the SGCB inversion to regional uplift. First, it contains one of the thickest and most complete Jurassic successions on the UK continental shelf, and over a kilometre of Cenozoic rocks (Tappin et al. 1994). Unlike the East Irish Sea basin , where Triassic rocks outcrop at the seafloor, the geometry, kinematics and timing of post-Triassic inversion episodes can be mapped using seismic data. 2. Exhumation between 2.08 km-2.24 km (relative to the reference trend) for wells located near to the NW basin margin.
doi:10.1144/0016-764904-023 fatcat:palkjcmoc5bwtksf2pkstpy7fm