Abstract

The abundance and size distribution of ecologically diagnostic foraminiferal species are ideal tracers of sediment transportation and storm processes on the windward shelf of Grand Cayman. During storm peak, sediment in the lagoon and fore-reef is suspended by large storm waves. Sediments of sand size and finer, including forereef foraminifera species, are moved shoreward by wind-driven currents and deposited in a blanket behind the reef. The fore-reef foraminiferal assemblage is winnowed and the mean and median sizes of Amphistegina gibbosa progressively decrease from the shelf edge into the inner lagoon. As the storm wanes, water piled in the lagoon drains via channels and sediment is transported offshore. Consequently, lagoonal sediment that includes lagoonal foraminiferal tests is carried out of the lagoon and deposited on the fore-reef terrace and down the shelf escarpment. This process produces winnowed lagoonal sediments because suspended fine sediments are preferentially transported. During the long inter-storm periods, tranquil conditions are once again established and sediment exchange between the lagoon and on the fore-reef terrace ceases. During this time, lagoonal organisms once again colonize the lagoon and bioturbation causes mixing of surface and subsurface sediments.

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