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Grain size distribution and composition of modern dune and beach sediments, Malindi Bay coast, Kenya
Abuodha, J.O.Z. (2003). Grain size distribution and composition of modern dune and beach sediments, Malindi Bay coast, Kenya. J. Afr. Earth Sci. 36(1-2): 41-54
In: Journal of African Earth Sciences. Elsevier: Oxford & Amsterdam. ISSN 1464-343X, more
Peer reviewed article  

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Keywords
    Coasts; Eolian dust; Grain size; Heavy metals; Monsoons; ISW, Kenya [Marine Regions]; Marine

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  • Abuodha, J.O.Z.

Abstract
    Grain size distribution and heavy mineral content of beach and dune sediments from the Malindi Bay coast, Kenya were determined. Grain sizes were determined by dry sieving sediments; samples represent the upper 5 mm of surficial sediment, collected from the four main geomorphological units (beach, berm zone, foredune and dunefield), during three observation periods, covering the southeast and northeast monsoon seasons. Sediment samples were grouped according to whether they were collected from the northern or southern sector of the Sabaki river. The heavy mineral content of several samples collected from the beach, berm zone and sand dunes was obtained by using separating funnels and tetrabromomethane to gain insight into the mineral distribution, the mineralogy and comment on the economic potential of prospecting for the heavy minerals. The petrographic parameters determined include the heavy mineral weight percentages and the mineral composition of the heavy fractions obtained using a petrographic microscope. The Malindi Bay shore is dominated by terrigenous deposits brought in by the Sabaki river which consist mainly of fine- to medium-grained quartz sand. The sediments also contain heavy minerals averaging about 15%, with highest concentration being 67% by weight for the samples analyzed. The heavy mineral suite here is dominated by opaque iron–titanium minerals as well as some red garnet and zircon. The results demonstrate a good relationship between the heavy mineral concentrations and the corresponding geomorphological elements. There are some differences between the various geomorphological units, with a subtle trend from the beach to the dunes. During all three observation periods grain size decreases slightly from the beach to the foredune. The sediment size fraction 0.625£, present on the beach, was absent in the immediate aeolian environments, except for the steep slopes of sand sheets and interdune valleys. The berm zone rarely has sediments coarser than 1.125£. The grain size parameters at different beach locations do not suggest a general trend of longshore variations, except on the beach close to the river mouth. The differences between the seasons were larger than those between the geomorphological units. During the northeast monsoon the mean size was coarser, sorting was worse and the distribution was more positively skewed.

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