HOLOCENE SEA-LEVEL CHANGES AND REEF DEVELOPMENT IN THE SOUTHWESTERN INDIAN-OCEAN

The sedimentological and chronological study of Holocene reef sequence s recovered in drill cores through modern reefs of Mauritius, Reunion Island and Mayotte allows the reconstruction of sea level changes and reef growth patterns during the Holocene. The branching-coral facies s ystematically predominates over coral head facies throughout the Holoc ene reef sequences, and Acropora is the main frame builder among the b ranching forms. The reconstructed sea level curves, based both on iden tification of coral assemblages and on radiometric U/Th ages, are char acterized by a rapid rise between 10 and 7.5 ky BP, followed by a clea r inflection between 7.5 and 7 ky BP. The stabilization of sea level a t its present level occurred between 2000 and 3000 years ago, probably without a higher sea level stand. Rates of vertical reef accretion ra nge between 0.9 and 7 mm. y(-1). In Mauritius, and also probably in Re union Island, the reef first tracked, then caught-up to sea level to r each an equilibrium position (''catch-up'' growth), while the barrier reef margin off Mayotte has been able to keep pace with rising sea lev el (''keep-up'' growth).