A Basin Reappraisal of the Proterozoic Torridon Group, Northwest Scotland

  1. L. E. Frostick3 and
  2. R. J. Steel4
  1. P. G. Nicholson

Published Online: 16 APR 2009

DOI: 10.1002/9781444304053.ch11

Tectonic Controls and Signatures in Sedimentary Successions

Tectonic Controls and Signatures in Sedimentary Successions

How to Cite

Nicholson, P. G. (1994) A Basin Reappraisal of the Proterozoic Torridon Group, Northwest Scotland, in Tectonic Controls and Signatures in Sedimentary Successions (eds L. E. Frostick and R. J. Steel), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444304053.ch11

Editor Information

  1. 3

    Reading, UK

  2. 4

    Bergen, Norway

Author Information

  1. Department of Geology and Applied Geology, University of Glasgow, Glasgow, Scotland G12 8QQ, UK

  1. Thai Shell Exploration and Production Company, P.O. Box 345, Bangkok 10501, Thailand

Publication History

  1. Published Online: 16 APR 2009
  2. Published Print: 28 FEB 1994

ISBN Information

Print ISBN: 9780632037452

Online ISBN: 9781444304053

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Keywords:

  • basin reappraisal of Proterozoic Torridon group, northwest Scotland;
  • Torridonian;
  • Torridon group deposition;
  • applecross alluvium;
  • applecross sandbodies - description and terminology;
  • syndepositional tectonic activity

Summary

Existing models of Torridon Group (Applecross Formation) genesis suggest deposition by at least two large alluvial fans within a 75-100-km-wide rift graben cutting Archaean crust. Results presented here reveal the presence of large-scale bar structures (up to 9 m thick) within the alluvium, indicating the occurrence of major rivers within the fluvial system. Palaeocurrent analyses show a greater degree of variability in sediment transport direction, at outcrop level, than previously recognized, whereas regional palaeoflow vectors do not exhibit radial patterns nor do they suggest that any active basin-bounding faults influenced sedimentation.

An alluvial braidplain origin for the Applecross Formation is preferred to the existing alluvial fan model, based on the evidence for rivers over 500 km long (determined by a palaeohydrological reconstruction), together with the consistently E–SE regional palaeoflow. These scale considerations, combined with the lack of evidence for both syndepositional tectonism within the basin and for active basin-bounding fault margins, collectively favour deposition within a significantly larger basin than the relatively self-contained rift graben previously proposed. A larger scale, later stage, extensional basin formed by post-rifting thermal relaxation processes, accompanied by a component of passive subsidence-driven normal faulting along the Outer Isles Fault, is proposed for deposition of the Torridon Group.