What is a Bedload Parting?
- B. W. Flemming and
- A. Bartholomä
Published Online: 14 APR 2009
Copyright © 1995 The International Association of Sedimentologists
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
- Published Online: 14 APR 2009
- Published Print: 11 AUG 1995
Print ISBN: 9780865429789
Online ISBN: 9781444304138
- 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
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.