The chronology and structure of the western New Caledonian barrier reef tracts

The mainland of New Caledonia (“Grande Terre”) is surrounded by one of the largest continuous barrier reef system in the world. In order to study the development history and internal structure of this system, drilling operations have been carried out at two sites (Amédée and Kendec islets), located on the barrier reef tract extending from the south-west 33 to the north-west of New Caledonia. The extracted cores are 128.50 and 148.75 m in length respectively. Lithological and paleoecological descriptions, combined with Uranium / Thorium dating, magnetostratigraphy and nannofossil-based biostratigraphy allowed a reef evolutionary scheme to be drawn. As a result of the interplay between margin subsidence and sea-level changes, 11 reef units formed successively during interglacial episodes at high sea levels in both sites. Depending on the subsidence rate of the western shelf-margin, major building in New Caledonia appears to have started during the MIS 11 (400,000 yr) from shallow-water carbonate platform deposits older than 780,000 yr. Comparing development patterns between the New Caledonian barrier reef and the Australian Great Barrier Reef clearly indicates that both global climate and regional tectonic history have been the major controls on reef initiation and growth along both sides of the Coral Sea. Climatic conditions are likely to have not been optimal before the late Quaternary, probably resulting in luxuriant reef expansion only during the last 400,000 yr.