Evidence for kilometre-scale Neogene exhumation driven by compressional deformation in the Irish Sea basin system
Published:January 01, 2008
Simon P. Holford, Paul F. Green, Jonathan P. Turner, Gareth A. Williams, Richard R. Hillis, David R. Tappin, Ian R. Duddy, 2008. "Evidence for kilometre-scale Neogene exhumation driven by compressional deformation in the Irish Sea basin system", The Nature and Origin of Compression in Passive Margins, Howard Johnson, Tony G. Doré, Robert W. Gatliff, Robert W. Holdsworth, Erik R. Lundin, J. Derek Ritchie
Download citation file:
Large tracts of the NW European continental shelf and Atlantic margin have experienced kilometre-scale exhumation during the Cenozoic, the timing and causes of which are debated. There is particular uncertainty about the exhumation history of the Irish Sea basin system, Western UK, which has been suggested to be a focal point of Cenozoic exhumation across the NW European continental shelf. Many studies have attributed the exhumation of this region to processes associated with the early Palaeogene initiation of the Iceland Plume, whilst the magnitude and causes of Neogene exhumation have attracted little attention. However, the sedimentary basins of the southern Irish Sea contain a mid–late Cenozoic sedimentary succession up to 1.5 km in thickness, the analysis of which should permit the contributions of Palaeogene and Neogene events to the Cenozoic exhumation of this region to be separated. In this paper, an analysis of the palaeothermal, mechanical and structural properties of the Cenozoic succession is presented with the aim of quantifying the timing and magnitude of Neogene exhumation, and identifying its ultimate causes. Synthesis of an extensive apatite fission-track analysis (AFTA), vitrinite reflectance (VR) and compaction (sonic velocity and density log-derived porosities) database shows that the preserved Cenozoic sediments in the southern Irish Sea were more deeply buried by up to 1.5 km of additional section prior to exhumation which began between 20 and 15 Ma. Maximum burial depths of the preserved sedimentary succession in the St George’s Channel Basin were reached during mid–late Cenozoic times meaning that no evidence for early Palaeogene exhumation is preserved whereas AFTA data from the Mochras borehole (onshore NW Wales) show that early Palaeogene cooling (i.e. exhumation) at this location was not significant. Seismic reflection data indicate that compressional shortening was the principal driving mechanism for the Neogene exhumation of the southern Irish Sea. Coeval Neogene shortening and exhumation is observed in several sedimentary basins around the British Isles, including those along the UK Atlantic margin. This suggests that the forces responsible for the deformation and exhumation of the margin may also be responsible for the generation of kilometre-scale exhumation in an intraplate sedimentary basin system located >1000 km from the most proximal plate boundary. The results presented here show that compressional deformation has made an important contribution to the Neogene exhumation of the NW European continental shelf.
Figures & Tables
The Nature and Origin of Compression in Passive Margins
Increasingly, researchers have reported that passive margins do not show a simple uninterrupted thermal sag pattern of post-rift subsidence following continental separation. Rather, the structural and stratigraphic development of such margins may record evidence of complex phases of differential subsidence, exhumation and fold development. Some of the fold structures observed on passive continental margins appear to be related to regional stresses transmitted through basement rocks, whereas others are related to gravitational sliding and toe-thrusting. This special publication concentrates on the first of these categories. The morphology and distribution of such folds, together with potential mechanisms for generation of regional stress, are described in a series of papers by authorities in the field. As well as being an enigmatic feature of passive margin geology, the compressive folds have significance in the exploration for petroleum.