A Physical Model for the Transport and Sorting of Fine-Grained Sediment by Turbidity Currents

  1. Dorrik A. V. Stow
  1. Dorrik A. V. Stow and
  2. Anthony J. Bowen

Published Online: 29 APR 2009

DOI: 10.1002/9781444304473.ch2

Deep-Water Turbidite Systems

Deep-Water Turbidite Systems

How to Cite

Stow, D. A. V. and Bowen, A. J. (2009) A Physical Model for the Transport and Sorting of Fine-Grained Sediment by Turbidity Currents, in Deep-Water Turbidite Systems (ed D. A. V. Stow), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444304473.ch2

Editor Information

  1. Department of Geology, University of Southampton, UK

Author Information

  1. Departments of Geology and Oceanography, Dalhousie University, Halifax, N.S., Canada

  1. British National Oil Corporation, 150 St Vincent Street, Glasgow, Scotland

Publication History

  1. Published Online: 29 APR 2009
  2. Published Print: 11 NOV 1991

ISBN Information

Print ISBN: 9780632032624

Online ISBN: 9781444304473

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Keywords:

  • graded laminated units, representing single depositional events;
  • downslope lateral sorting occurs with preferential deposition of coarser silt grains;
  • large-scale turbidity currents;
  • fine-grained sediment dynamics;
  • Laurentian fan;
  • Scotian continental margin;
  • downslope lateral sorting, occurring with deposition of coarser silt grains and larger mud floes

Summary

Turbidite muds in cores from the outer Scotian continental margin, off eastern Canada, contain abundant thin silt laminae. Graded laminated units are recognized in parts of this sequence. These represent single depositional events, and show a regular decrease in modal grain size and thickness of the silt laminae through the unit. A similar fining trend is shown by both silt and mud layers over hundreds of kilometres downslope. Textural analysis of individual laminae allows the construction of a dynamically consistent physical model for transport and sorting in muddy turbidity currents. Hydraulic sorting aggregates finer material to the top and tail regions of a large turbidity flow which then overspills its channel banks. Downslope lateral sorting occurs with preferential deposition of coarser silt grains and larger mud flocs. Depositional sorting by increased shear in the boundary layer separates clay flocs from silt grains and results in a regular mud/silt lamination. Estimates can be made of the physical parameters of the turbidity flows involved. They are a minimum of several hundreds of metres thick, have low concentrations (of the order of 10−3 or 2500 mg 1−1), and move downslope at velocities of 10–20 cm s−1. A 5 mm thick, coarse silt lamina takes about 10 h to deposit, and the subsequent mud layer ‘blankets’ very rapidly over this. A complete unit is deposited in 2–6 days which is the time it takes for the turbidity flow to pass a particular point. These thick, dilute, low-velocity flows are significantly different from the ‘classical’ turbidity current. However, there is mounting evidence in support of the new concept from laboratory observations and direct field measurements.