SKELETAL COMPOSITION OF MODERN LAGOON SEDIMENTS IN NEW-CALEDONIA - CORAL, A MINOR

The skeletal composition of 273 sediment samples, collected within 146 15 km(2) of lagoon habitat in New Caledonia (Ouvea and Chesterfield at olls and eastern and northern lagoons of the main island), was analyze d. Major constituents were molluscs (bivalves and gastropods), foramin ifers, and Halimeda plates. The quantitative examination showed that, even in a pure coralline structure such as the two atolls studied, cor al debris and calcareous algae, potentially produced within the barrie r reef, never constituted a dominant element in the lagoonal sediments . Distribution of coral debris showed that coral is significant only c lose to the barrier reef (i.e. passes and back-reef slope). From the p oint of view of sedimentology, this suggests that the major role of th e barrier reef is to provide a physical barrier that allows the develo pment and preservation of lagoon sediments. Sedimentation within the l agoon of grains coarser than 63 mu m is the result of in situ organic production combined with low hydrodynamic control.