Process and pattern of sediment mixing in a microtidal coastal lagoon along the west coast of South Africa
Flemming, B.W. (1988). Process and pattern of sediment mixing in a microtidal coastal lagoon along the west coast of South Africa, in: de Boer, P.L. et al. (Ed.) Tide-influenced sedimentary environments and facies. Extended versions of papers presented at the Symposium on Classic Tidal Deposits, held August 1985 in Utrecht, Netherlands. pp. 275-288 In: de Boer, P.L. et al. (Ed.) (1988). Tide-influenced sedimentary environments and facies. Extended versions of papers presented at the Symposium on Classic Tidal Deposits, held August 1985 in Utrecht, Netherlands. D. Reidel Publishing: Dordrecht. ISBN 90-277-2622-1. ix, 530 pp., more |
| Abstract | Langebaan Lagoon is a microtidal environment along the west coast of South Africa. The sediments consist of a mixture of carbonate-siliciclastic sands with little or no mud. Scatter diagrams of textural parameters reveal clearly defined patterns which reflect progressive sediment mixing between two hydraulic populations, one consisting of fine to very fine sand and the other of medium sand. Both parent populations are slightly skewed. In the process of mixing the textural relationships of the sediments follow a clear and predictable pattern. The coarse population becomes progressively finer and initially less well sorted as the proportion of finer material increases, whereas the fine population shows the reverse trend. At the point of equal proportional mixing the sorting is poorest, whereas a symmetrical distribution occurs when the inherited skewness of the one endmember is counterbalanced by a sufficient amount of the other. If the parent populations are lognormal then a symmetrical grain size distribution coincides with the point of equal proportional mixing, i.e., where sorting is poorest. Such mixing patterns are produced by the areal overlap of different sedimentary facies and have been identified in other depositional environments. In Langebaan Lagoon, the mixing model provides a rational explanation of sediment dispersal. It identifies the local sediment sources and demonstrates that textural characteristics of sediments can be a direct function of proportional mixing between two sediment populations rather than the result of a single population undergoing progressive size sorting. |
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