CORAL GROWTH RATES, SEDIMENTATION RATES AND SEDIMENT COMPOSITION IN THE CAÑADA HONDA HOLOCENE REEF, DOMINICAN REPUBLIC

The Cañada Honda outcrop found in the Enriquillo Lake, Southwestern Dominican Republic is an excellent example of a Holocene shallow water coral reef. The high degree of preservation of the fossil corals and the reef structure makes this exposure a unique one. This outcrop presents a unique opportunity to study a fossil marine ecosystem without human induced variables with many of the same coral species assemblages present today. Annual growth rates were measured from four coral samples of the species Montastraea faveolata collected from a previously defined reef zone (Massive Coral Zone 2) in the Cañada Honda Outcrop. The four colonies measured of Montastraea faveolata showed average annual growth rates of 0.13, 0.18, 0.34, and 0.45 cm/yr. The corals with the lower growth rates were located stratigraphically higher in the section. These growth rates are very similar to growth rates of the same species in modern shallow water reefs. The coral species Montastraea faveolata has a foliated morphology. Each of those foliations was interpreted as a period of re-growth after episodes of high sedimentation. Based on this assumption the foliations were used to calculate sedimentation rates. The selected coral has 10 foliations and the growth rate in the foliations varied from 0.11cm/yr to 0.26cm/yr. The average sedimentation rate was calculated to be 0.17cm/yr. for an average reef accretion of 1.7m/1000yrs. This value is consistent with the 1m per1000yrs of reef accretion commonly cited in the literature. The composition of the sediments within the Cañada Honda Reef Outcrop was also measured (n=13). The sediments within the reef contain over 90% carbonate material, with 0.80% to 9.40% insoluble material.