Discovery of a composite reefal terrace of middle and late Pleistocene age in Great Inagua Island, Bahamas. Implications for regional tectonics and sea-level history

摘要

We provide here new ~(234)U/~(230)Th ages measured on coral samples collected from a reefal terrace exposed on Great Inagua Island (Bahamas) that was, up to now, wholly attributed to the last interglacial period (Marine Isotope Stage 5e). Our results from the upper part of the terrace confirm the previously reported MIS 5e age, whereas ages obtained from the lower part range between 139,000 and 193,000 years BP, spanning most of MIS 6. Petrographic examination showed that secondary aragonite cement and internal sediment occur in the coral chambers of these samples, indicating they were rejuvenated and likely date from the penultimate interglaciation (MIS 7). The studied terrace is thus a composite build-up and its lower part represents the first coral reef of MIS 7 age ever described in the Bahamas archipelago. Our results further suggest (1) that Great Inagua Island recently underwent a phase of tilting, and (2) that sea level was close present datum during MIS 7.