Reverse Flow in Turbidity Currents: The Role of Internal Solitons

  1. Dorrik A. V. Stow
  1. H. M. Pantin1 and
  2. M. R. Leeder2

Published Online: 29 APR 2009

DOI: 10.1002/9781444304473.ch7

Deep-Water Turbidite Systems

Deep-Water Turbidite Systems

How to Cite

Pantin, H. M. and Leeder, M. R. (1991) Reverse Flow in Turbidity Currents: The Role of Internal Solitons, in Deep-Water Turbidite Systems (ed D. A. V. Stow), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444304473.ch7

Editor Information

  1. Department of Geology, University of Southampton, UK

Author Information

  1. 1

    British Geological Survey, Keyworth, Nottingham NG12 5GG, UK

  2. 2

    Department of Earth Sciences, University of Leeds, Leeds LS2 9JT, UK

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:

  • reverse-flow units;
  • thick-bedded calcareous wacke;
  • probable nature of primary turbidity flow;
  • sediment concentration;
  • rate of momentum loss of the flow

Summary

Pickering & Hiscott, (1985) have demonstrated amply the presence of reverse-flow units within the thick-bedded calcareous wacke (TCW) beds of the turbiditic Cloridorme Formation (Middle Ordovician, Gaspé Peninsula, Quebec, Canada). These reverse-flow units are underlain and overlain by units which reveal flow in the primary (obverse) direction.

In this paper, a model is proposed for this reverse flow, based on the probable nature of the primary turbidity flow. It appears that the initial flow was highly elongated (thickness h < < length L), with h ≈ 500 m, velocity U ≈ 2 m s−1 and sediment concentration C ≈ 1.25 ‰. The rate of momentum loss of the flow is estimated by means of a useful parameter which we call the ‘drag distance’, symbol dD, defined by

dD = hL/(L.cCd + h.fCd),

where h and L are the thickness and length of the flow, respectively; cCd is a combined drag coefficient representing friction on the bottom and at the upper interface; and fCd is a form-drag coefficient related to the shape and size of the head. dD is the distance travelled by a current of constant h and L, flowing over a horizontal bottom and obeying a quadratic friction law, for an e-fold reduction in velocity.

Simple considerations, confirmed by our own experiments (described in this paper), show that such an elongated turbidity current cannot be reflected as a whole from an adverse slope; when the nose of the current reaches the slope, it forms a hump, which surges backwards and sooner or later breaks up into a series of internal solitons. The latter, probably numbering 4–7, will cause reverse flow at a given point as they pass by, provided that the residual velocity in the tail is not too great. Flow in the original (obverse) direction will be re-established after the passage of the solitons. Quiescent periods in front of, between and behind the solitons, when soliton-associated currents cancelled out the residual obverse flow, would allow the deposition of thin mud-drapes.

Additional flow reversals observed in a few of the TCW beds cannot be explained readily by the re-passage of solitons, since wave breaking at the ends of the basin would cause massive energy loss; internal seiches are the preferred explanation for these later reversals.