Benton Fault
The Benton Fault is a geological fault in southern Pembrokeshire in southwest Wales that was active as a normal fault during the deposition of the Old Red Sandstone during the Devonian period, forming a thick half graben.[1] During the Carboniferous, the Benton Fault was strongly inverted as part of the Variscan Orogeny.[2]
Geological history
[edit]The Benton Fault probably originated during the early Palaeozoic era (over 400 million years ago) as a boundary fault of a horst—a raised block of land between faults. During this period, it formed part of the margin of a raised block of Precambrian igneous rocks. Following the Caledonian orogeny (mountain-building event) in the late Silurian period, the Benton Fault became an active normal fault during the deposition of Old Red Sandstone sediments. As a normal fault, it allowed the land on its southern side to drop down relative to the northern side. At its maximum, the fault achieved a downthrow to the south of at least 1,500 metres. This movement helped create space for thicker sedimentary deposits to accumulate on the southern side of the fault. The fault's displacement varied along its length, with evidence suggesting that movement increased eastward. This differential movement contributed to the varying thickness and composition of sedimentary rock units across the region.[3]
By the Carboniferous period, the Benton Fault had become inactive, as evidenced by undisturbed Carboniferous Limestone series rocks that overlie it at the eastern end of its outcrop. During the Variscan orogeny in the late Carboniferous (about 300 million years ago), the Benton Fault was reactivated, but this time with reverse movement—meaning the southern side was pushed up relative to the northern side. This reactivation was particularly significant in the western portion of the fault. Later in the Variscan deformation, the western portion of the Benton Fault was transected and displaced northward by the Johnston Thrust, a younger fault structure.[3]
See also
[edit]References
[edit]- ^ Hillier, R.D.; Williams, B.P.J. (2006). "The alluvial Old Red Sandstone: fluvial basins". In Brenchley P.J. & Rawson P.F. (ed.). The geology of England and Wales (2 ed.). London: Geological Society. pp. 155–172. ISBN 978-1-86239-200-7. Retrieved 9 December 2010.
- ^ Coward, M.P. (1996). "Balancing sections through inverted basins". In Buchanan P.G. & Nieuwland D.A. (ed.). Modern developments in structural interpretation, validation and modelling. Special Publication. Vol. 99. London: Geological Society. pp. 51–78. ISBN 978-1-897799-43-7. Retrieved 9 December 2010.
- ^ a b Dunne, William M. (1983). "Tectonic evolution of SW Wales during the Upper Palaeozoic". Journal of the Geological Society. 140 (2): 257–265. doi:10.1144/gsjgs.140.2.0257.