ASSESSMENT OF THE RESPONSE OF A HOLOCENE FOSSIL CORAL REEF TO HIGH SEDIMENT INPUT: IMPLICATIONS TO MODERN TRENDS OF REEF DEGRADATION IN HIGH SEDIMENTATION ENVIRONMENTS

Many modern coral reefs are in decline, in many areas related to high sedimentation rates and sediment resuspension. However, there is evidence in the fossil record of reefs developed in high sedimentation environments, such as the Cañada Honda outcrop in the Dominican Republic, with a record of accretion spanning over a thousand years. The Holocene coral reefs of the Enriquillo Valley, Dominican Republic provide a unique record of coral development in an environment that seems to have been exposed to high sediment input. They exhibit excellent preservation and offer an exceptional opportunity to examine in detail the internal coral assemblage and sedimentary patterns of a Holocene coral reef. The Cañada Honda outcrop, on the northern shore of Lago Enriquillo reveals several sediment layers that appear to represent single depositional events such as storms, probably with elevated rainfall as is typical of the region today. One particular layer (MD layer), rich in coral, bivalve and gastropod fragments can be traced several meters within the outcrop, where a paleoreef surface can be followed. Coral and sediment samples were collected below and above this sedimentary horizon for the purpose of dating and documenting any changes in the coral-species assemblage, growth rate, siltation stress and carbon isotopes before and after deposition of the MD layer. Additional coral and sediment samples were collected throughout the entire outcrop to observe similar changes through time. Quantitative measurements of coral importance, diversity and sediment were obtained throughout the whole stratigraphic section using quadrats along vertical transects. In addition, sediments incorporated in coral skeleton and from the reef matrix are being examined to quantify the input and variations in terrigenous sedimentation through the section. The information obtained from this study will be instrumental to better understand modern reefs since direct comparisons of this fossil reef with modern counterparts (with high sedimentation in a restricted environment) will be possible.