Evidence of Longshore Drift in Beach Sediment: Manzanillo, Costa Rica

Abstract

<p> The beach at Manzanillo, Costa Rica, is composed of a mixture of terrigenous siliciclastic and marine calcareous sediment. The most abundant siliclastic grains are magnetite and diopside. The most abundant calcareous grains are red algae and molluscan fragments. These grains are found in much greater abundance in the beach sediment then in their source areas as a result of their resistance to breakdown.</p> <p> The distribution of the siliclastic minerals on the beach shows longshore drift to be from east to west. The main source of siliclastic sediment is the Rio Sixaola. Local rivers provide small inputs of sediment.</p> <p> The trace element chemistry of the beach indicates the possibility that some elements may be absorbed on the surfaces of grains as opposed to being substituted for other elements in mineral lattices.</p>