Architecture et morphologie coralienne.Modélisation et observations des îles ensurrection de SE Sulawesi, Indonésie

National audienceDuring the Late Neogene, sea level oscillations have profoundlyshaped the morphology of the coastlines of intertropicalzones, wherein relative sea level simultaneously controlled reef expansionand erosion of earlier reef bodies. In uplifted domainslike SE Sulawesi, the sequences of fossil reefs display a variety offossil morphologies. Similarly, the morphologies of the modernreefs are highly variable, including cliff notches, narrow fringingreefs, wide flat terraces, and barriers reefs. In this region, whereuplift rates vary rapidly laterally, the entire set of morphologiesis displayed within short distances. We developed a numericalmodel that predicts the architecture of fossil reefs sequences andapply it to observations from SE Sulawesi, accounting -amongstother parameters- for reef growth, coastal erosion, and uplift rates.The observations that we use to calibrate our models are mostlythe morphology of both the onshore (dGPS and high-resolutionPleiades DEM) and offshore (sonar) coast, as well as U-Th radiometricallydated coral samples. Our method allows unravelling thespatial and temporal evolution of large domains on map view. Ouranalysis indicates that the architecture and morphology of upliftingcoastlines is almost systematically polyphased (as attested bysamples of different ages within a unique terrace), which assigns aprimordial role to erosion, comparable to reef growth. Our modelsalso reproduce the variety of modern morphologies, which arechiefly dictated by the uplift rates of the pre-existing morphologyof the substratum, itself responding to the joint effects of reefbuilding and subsequent erosion. In turn, we find that fossil andmodern morphologies can be returned to uplift rates rather precisely,as the parametric window of each specific morphology isoften narrow