Lead


Lay summary
Fossil reefs and coastal deposits contain direct information on sea-level and climate fluctuations during the late Cenozoic that supplement data derived from the study of deep-sea sediments and ice cores. Such knowledge is critical to decipher the mechanisms of sea-level and climate variations, and better constrain future global changes. Fossil reefs are precise indicators of former sea stands and can further be accurately dated with the U-series method. The sedimentological and petrographic characteristics of ancient coastal deposits register high-frequency sea-level and water-table changes, as well as climatic conditions during early diagenesis. These deposits may all undergo phases of dolomitization. This is interesting per se (e.g. because dolomitization changes the reservoir properties of parent rocks), but also because the mode of dolomitization is constrained by the degree of carbonate-platform flooding. Dolostones may thus provide also information regarding ancient climate and sea-level fluctuations. Fossil reefs and coastal deposits have been already studied in details in Bermuda, Barbados, Florida, and the northern Bahamas. The basic framework of middle/late Quaternary sea-level and climate changes in these areas is rather well established, but many uncertainties still remain regarding earlier time periods. By contrast, the southeastern Bahamas have not been much studied in this respect, possibly because of their relative inaccessibility. During our first expedition to the SE Bahamas in 2007, we discovered one large reef tract of last interglacial age, widespread lower Pleistocene coastal deposits, and outcropping, massive Miocene and Pliocene dolostones on the surface of Mayaguana Island. The spatial distribution of these exposures suggests that the internal architecture of this small platform must be indeed complex. We therefore intend to focus our study on the nature and geometry of these newly discovered rock units.In addition to refining our understanding on the timing of key sea-level and climate events during the late Cenozoic, a critical piece of information for better resolving the dynamics of ice ages, this study will enable us to complement existing knowledge on coastal sedimentation, dolomitization processes, and the architecture of small carbonate platforms. This first topic is becoming a key scientific and political issue in the current context of anthropogenic global warming and sea-level rise; the other two pertain to rock reservoir properties, which is fundamental for oil exploration and CO2 storage.