Contribution of microbialites to the development of coral reefs during the last deglacial period: Case study from Vanuatu (South-West Pacific)

Coral reefs have grown continuously during the Last 24 ka on the island of Espiritu Santo (Vanuatu, South-West Pacific) in a setting characterized by frequent tectonic uplifts related to subduction of the Australia plate beneath the Vanuatu Island arc. Sedimentological and geochemical studies of two neighbouring areas having much different mean uplift rates and environmental settings provides an opportunity to analyze the environmental factors that promoted the widespread development of microbialite crusts from about 24 to 6 ka B.P. Nutrient supplies, and probably the rapidity of the sea level rise, are critical to an explanation of the distinctive distribution of microbialites in reef cores. Nutrient flux has been related to terrigenous fluxes in the Tasmaloum reef system that fringed the south-west uplifting coast of Espiritu Santo and possibly to upwelling in the Urélapa sequence that was isolated from the main island during its growth. A peak in microbialite abundance occurred between 16 and 10 ka B.P., a time window characterized by increasing erosional processes and/or more intense upwelling during a very rapid rise in sea-level.