COASTAL SEDIMENTARY EVOLUTION OF ST. THOMAS AND ST. JOHN, US VIRGIN ISLANDS: A FUNCTION OF DRAINAGE BASIN DIVERSITY
The record of anthropogenic activities is most evident in surface sediments of heavily developed areas such as along the west coast of St. John and east and southeast coasts of St. Thomas. The anthropogenic signal manifested in surface sediments is highly variable in both magnitude and type (e.g., coarsening, fining, and/or changes in sediment composition) due to the type of activity, as well as the natural character of each basin. Although the suite of sediment textures and compositions is highly variable, all record a similar history of coastal evolution: a) terrigenous deposition during the last sea-level low stand; b) carbonate deposition reflecting open marine conditions during initial flooding associated with the last sea-level rise; c) paralic deposition as sites became isolated by mangrove construction and/or reef growth; and, d) infilling by terrigenous input, which is often anthropogenically enhanced. Consequently, the final stages include the natural infilling of coastal depocenters by island runoff, but anthropogenic activities appear to be accelerating this process, possibly causing the premature destruction of island coastal wetlands.