Simultaneous Dispersal of Volcaniclastic and Non-Volcanic Sediment in Fluvial Basins: Examples from the Lower Old Red Sandstone, East-Central Scotland

  1. M. Marzo and
  2. C. Puigdefábregas
  1. P. D. W. Haughton

Published Online: 14 APR 2009

DOI: 10.1002/9781444303995.ch29

Alluvial Sedimentation

Alluvial Sedimentation

How to Cite

Haughton, P. D. W. (1993) Simultaneous Dispersal of Volcaniclastic and Non-Volcanic Sediment in Fluvial Basins: Examples from the Lower Old Red Sandstone, East-Central Scotland, in Alluvial Sedimentation (eds M. Marzo and C. Puigdefábregas), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444303995.ch29

Editor Information

  1. Barcelona, Spain

Author Information

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

Publication History

  1. Published Online: 14 APR 2009
  2. Published Print: 16 SEP 1993

ISBN Information

Print ISBN: 9780632035458

Online ISBN: 9781444303995

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Keywords:

  • dispersal of volcaniclastic and non-volcanic sediment;
  • lower ors non-volcaniclastic fluvial deposits;
  • Coeval volcaniclastic and fluvial deposition;
  • lower ors volcaniclastic facies;
  • ‘Crystal-rich’ volcaniclastic deposits

Summary

Fluvial basins flanking active volcanoes can preserve complex sequences in which intervals of volcaniclastic sediment alternate with mixed provenance or non-volcaniclastic sediments. Transport mechanisms, the pattern and rate of sediment supply, and depositional processes can be markedly different for these deposits. Deposition of polymict Lower Old Red Sandstone fluvial deposits in central Scotland was repeatedly interrupted by the dispersal of units of volcaniclastic sediment. These were emplaced by a combination of fluvial, debris flow and fluidal sediment flow processes. The nature of the transitions to and from these volcaniclastic intervals is documented and three recurring types of sequence are identified. In the first, contacts between volcaniclastic and mixed fluvial deposits are sharp and the structure, composition and palaeoflow of the fluvial sediments are unperturbed above and below the intervals of volcaniclastic sediment. In the second, the volcaniclastic intervals appear to determine a component of the structure of the enclosing non-volcanic deposits, with evidence for periods of aggradation and degradation associated with volcaniclastic and non-volcaniclastic sequences respectively. A third type of sequence, closely related to the second, shows that degradation on return to normal fluvial sedimentation was at first suppressed, with flat stratified units of mixed provenance intervening between the volcaniclastic and non-volcaniclastic deposits. The various sequences appear to be specific to one or other margin of a fault-controlled basin, and can be related to contrasting aggradation rates, the type of non-volcanic fluvial system and the nature of the volcaniclastic sources. The synchroneity or otherwise of eruption and volcaniclastic deposition was particularly important, with the latter recording both episodic, syn-eruption flushing of parts of the basin with volcanic sand, and normal degradation of volcanic sourcelands.