Development patterns of fringing and barrier reefs in New Caledonia (southwest Pacific)

In New Caledonia, core data indicate that the fringing reefs grew during th e last interglacial and the Holocene, while the barrier reefs developed dur ing several high sea level stands of the Quaternary. These growth periods a re archived in a 128-m-long core from Ilot Amedee, offshore of Noumea. Dire ctly upon the peridotitic substrate (reached at 126.50 m), a basal unit com prising abundant rhodoliths, molluscs and rare corals is characteristic of the pioneer stage of barrier reef development. Above it, a severely calciti zed unit contains corals, molluscs and abundant micritic levels. Then, a se quence punctuated by several minor discontinuities and by a downward increa se in diagenetic alteration is found. At 47 m core depth, a unit, which is thought to be related to isotopic stages 7 and 9, contains thin beds of cor algal frameworks and muddy detritus. The 125 ka-old reef, from 14 to 37 m c ore deep, is predominantly composed of biocalcarenites and rare coral colon ies. Finally, the Holocene reef is composed of sands and scarce coral build ups. Drilling results indicate that the distributional patterns of the 125- ka-old reef bodies around New Caledonia express an increasing tendency of i sland subsidence northward, southwestward and more markedly seaward, mainly controlled by isostatic readjustments and margin collapse. (C) 1999 Ifreme r / CNRS / IRD / Editions scientifiques et medicales Elsevier SAS.