What is a Bedload Parting?

  1. B. W. Flemming and
  2. A. Bartholomä
  1. P. T. Harris1,*,
  2. C. B. Pattiaratchi2,
  3. M. B. Collins3 and
  4. R. W. Dalrymple4

Published Online: 14 APR 2009

DOI: 10.1002/9781444304138.ch1

Tidal Signatures in Modern and Ancient Sediments

Tidal Signatures in Modern and Ancient Sediments

How to Cite

Harris, P. T., Pattiaratchi, C. B., Collins, M. B. and Dalrymple, R. W. (1995) What is a Bedload Parting?, in Tidal Signatures in Modern and Ancient Sediments (eds B. W. Flemming and A. Bartholomä), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444304138.ch1

Author Information

  1. 1

    Ocean Sciences Institute, University of Sydney, Sydney NSW 2006, Australia

  2. 2

    Centre for Water Research, University of Western Australia, Nedlands WA 6009, Australia

  3. 3

    Department of Oceanography, University of Southampton, Southampton SO9 5NH, UK

  4. 4

    Department of Geological Sciences, Queen's University, Kingston, Ontario K7L 3N6, Canada

*Australian Geological Survey Organisation, Antarctic CRC, University of Tasmania, GPO Box 252C, Hobart, Tasmania 7001, Australia

Publication History

  1. Published Online: 14 APR 2009
  2. Published Print: 11 AUG 1995

ISBN Information

Print ISBN: 9780865429789

Online ISBN: 9781444304138

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Keywords:

  • bedload parting (BLP) - model for sand dispersal;
  • tidal current transport paths;
  • scour zones and bottom-stress maxima;
  • development of scour zones;
  • flow acceleration under amphidromic points;
  • flow acceleration, relating to coastal geometry;
  • spatial succession of facies

Summary

Net sediment transport paths and their associated bedload partings (BLPs) are important elements of sediment dispersion on tidally dominated continental shelves. The facies distribution associated with these paths is believed to reflect primarily a downcurrent decrease in tidal bottom stress. With decreasing tidal bottom stress, scour zones characterized by lag gravel and/or bedrock exposures give way to a mobile sand sheet facies, ending with a muddy sand facies at the lowest tidal energy. A review of available data on the distribution of these facies shows that they are developed at the location of local maximum bed stress, induced by either standing-wave nodal points (type A) or geomorphic constrictions (type B). Around the western European continental shelf, 22 different locations having a length scale exceeding 10 km are associated with local bottom-stress maxima (type A or B).

A model is proposed for the development of scour zones as a function of sediment supply, with consideration given to the movement of facies boundaries through time in relation to the bottom-stress maxima. Where sand is plentiful, the transport pattern is dominated by linear sand banks and associated dunes; these delimit a mutually evasive transport system. Incipient scour zones are those that occupy a significant (∼50%) portion of the channel width. Partial scour zones occupy nearly the entire channel, except for deposits along the margins which link the flanking depositional areas. Complete scour zones separate totally the mobile sand deposits located on opposite flanks of a channel, with no significant marginal sand deposits occurring. Only 11 of the 22 zones of local maximum bottom stress correlate with ‘complete’ scour zones.

Bedload partings are classified as a special case of scour zone, in which local bottom-stress maxima coincide with divergent patterns in sand transport (inferred from bedform asymmetries). A minimum scale of about 10 km is proposed for a ‘complete’ BLP which separates flanking depositional areas on the basis of the tidal excursion length of a sand grain. The model proposed for scour zone development applies also to BLPs, suggesting that only three of the six BLPs previously identified for the west European shelf are at a ‘complete’ stage of development.