FOSSILIZED CORAL REEF UPLIFT ON ROATAN ISLAND, HONDURAS

The differential nature of uplifted fossilized coral reef on the western end of Roatan Island, Honduras is representative of the ongoing earthquake activity of subsidiary faults along the American/Caribbean plate boundary in Central America. Surveying elevations and mapping the distribution of fringing coral reefs, fossil reefs, wave cut terraces, exposed beach rock, beach sediments, and cave dripstones that have been uplifted and/or tilted by fault movements was performed in an area of approximately 10km². At five dispersed locations subsurface samples were taken down to a depth of 2.5m. These samples were analyzed by XRD and ESR at intervals of 20cm. Ohio State University’s Nuclear Reactor Lab analyzed selected samples for U, Th, and K content, and also irradiated annealed samples at six intervals of intensity. The irradiated samples were used to establish a regression curve of radiation exposure to ESR signal. Using radionuclide content and this regression curve, ESR signals of field samples were analyzed to estimate their crystallization and/or recrystallization ages. All ESR signals of the field samples were below the limit of resolution of the regression curve (i.e. >20k years). Recrystallization of the coral may have accompanied differential uplift across the study area. Locally as much as 10m of relief can be observed in the beach rock terraces that trend from sea level in the southwest to over 10m in the northeast segment. Differential local and regional uplift coupled with sea level variability have influenced coastal geology and morphology in the study area, and obtaining quantitative results has proved problematic.