Biogenic Assemblage and Hydrodynamic Settings of the Tidally Dominated Reef Platform Sediments of the Zanzibar Channel

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The biogenic assemblage and hydrodynamic settings of the tidally dominated reef platform sediments (TDRPS) east of the Zanzibar channel were investigated in order to characterise the carbonate sediments. Benthic foraminifera were found to be the most important group, both in terms of average abundance (> 60 % by weight) and also in terms of spatial distribution, with common occurrence in all sediments samples. Pelecypods, with an average abundance of 8 % were slightly less widely distributed. The remaining groups occurred at lower average abundance and less frequently in the sediments. Current measurements indicated that the maximum current speed is higher during spring than during neap tides. The direction is phase-dependent with flood tidal current flowing from the northern and southern tips of the island towards Zanzibar town. The ebb current flows in the opposite direction. The geomorphological setting of the carbonate platforms together with the present investigation of the currents and biogenic assemblage of the clastic sediments permits us to subdivide the reef platform area in the Zanzibar Channel into two sub-provinces: the northern and the southern. The northern sub-province contains significantly higher proportion of lithogenic particles, pelecypods, gastropod and ostracods than the southern sub-province. Some samples from the southern subprovince had significantly higher proportion of corals, than those from northern sub-province.
Biogenic assemblage, Hydrodynamics, carbonate sediments,, Reef platforms, Zanzibar channel
Wannas, K.O., Mahongo, S.B. and Shaghude, Y.W., 2002. Biogenic assemblage and hydrodynamic settings of the tidally dominated reef platform sediments of the Zanzibar Channel.