SEDIMENT PRODUCTION, WEATHERING, AND TRANSPORT ON THE DENNERY AND CHOC RIVERS, ST. LUCIA

Saint Lucia is a tropical island located in the center of the Lesser Antilles Volcanic Arc, produced by subduction of the North American Plate beneath the Caribbean Plate. The Choc and Dennery river basins are each a collection of small streams which flow into a larger river, cutting across andesitic and basaltic terrains. The Choc River drains westward into the Caribbean Sea and the Dennery River flows mainly eastward into the Atlantic Ocean. In this study, we investigate weathering and sediment transport in these two tropical stream systems.

River sediment from both rivers was collected to determine the evolution of sediment from source to mouth. Bedrock material was collected at upstream sites to determine source rock composition. Thin sections of source rock were created to determine mineralogy. Grain count analyses of river sediments were performed to determine the composition of clastic sediment at several sites along each stream. The results show that sediment is less evolved with respect to chemical weathering in the Dennery River Basin than in the Choc River Basin, resulting in compositionally more mature sediment on the Caribbean mouth of the Choc River than on the Atlantic beaches of the Dennery River. Beach sediment at the mouth of the Dennery River Basin retains mineralogy similar to source rocks at the river's head. In contrast, sediments from the Choc River Basin display a greater degree of enrichment in resistant minerals such as quartz and magnetite. It is likely that the natural weathering and erosion in these streams are further influenced by anthropogenic processes. We hope that the study of the erosional processes of the main river systems of Saint Lucia can provide insight into these issues.