Sedimentation and Tectonics in the Dinantian Limestones of South Wales

  1. David I. M. Macdonald
  1. A. T. S. Ramsay

Published Online: 14 APR 2009

DOI: 10.1002/9781444303896.ch26

Sedimentation, Tectonics and Eustasy: Sea-Level Changes at Active Margins

Sedimentation, Tectonics and Eustasy: Sea-Level Changes at Active Margins

How to Cite

Ramsay, A. T. S. (1991) Sedimentation and Tectonics in the Dinantian Limestones of South Wales, in Sedimentation, Tectonics and Eustasy: Sea-Level Changes at Active Margins (ed D. I. M. Macdonald), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444303896.ch26

Editor Information

  1. British Antarctic Survey, Cambridge, UK

Author Information

  1. Department of Geology, University of Wales College of Cardiff, P.O. Box 914, Cathays Park, Cardiff, CF1 3YE, UK

Publication History

  1. Published Online: 14 APR 2009
  2. Published Print: 13 JUN 1991

ISBN Information

Print ISBN: 9780632030170

Online ISBN: 9781444303896

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Keywords:

  • sedimentation and tectonics in Dinantian limestones of South Wales;
  • limestone sedimentation and tectonics;
  • Arundian—Holkerian boundary nature;
  • Asbian and Brigantian;
  • sedimentation and NE-SW trending structures;
  • nature of marine transgression, regression, and facies successions;
  • causal mechanisms of Dinantian cyclicity and tectonics;
  • eustatic tectonic mechanisms

Summary

The Dinantian succession in South Wales was deposited on the southward-sloping hanging wall of a half-graben, which probably formed by northerly downthrow on a major fault system in the Bristol Channel. This basin formed and evolved in a N—S orientated extensional stress field, which pervaded Britain during the Dinantian. Deposition was controlled by movements on basement faults or fault complexes that formed active hinge lines with E—W, NE—SW, NNW—SSE, and N—S trends, and by a buoyant palaeohigh that developed along the Carreg Cennen Disturbance. The hinge-lines and palaeohigh influenced the thickness of the succession, and patterns of onlap during transgression. Erosion was enhanced on uplifted fault footwalls and over the active Caledonoid-trending palaeohigh. Variations in the geometry of the basin-margin floor (ramp or platform) are attributed to variations in the regional pattern of asymmetrical subsidence and to rifting phases associated with E—W orientated structures. The N—S stress field, half-graben basin, and tectonic activity on the south-sloping hanging wall developed in response to subduction and/or lithospheric loading associated with an orogeny to the south.

The pattern of Dinantian cyclicity is attributed to the interaction between uplift, episodic (pulsed subsidence) sedimentation rates, and changes in relative base level, which were probably tectonic and related to rifting and subsidence. The process of marine transgression involved rifting subsidence and shoreface and barrier retreat. Regressive phases are progradational and contain barrier and back barrier deposits when progradation coincided with high sedimentation rates and relative rise in sea level. Progradation and high sedimentation rates during relatively static base levels produced regressive sequences minus a back-barrier lagoonal—peritidal facies.