Reef coralgal assemblages as recorders of paleobathymetry and sea level changes in the Indo-Pacific province

Abstract

The coralgal framework within the outer reef margin of many Indo-Pacific reefs exhibits three main shallow-water communities, the environmental significance of which can be inferred by comparison with their modern counterparts. A community dominated by tabular Acropora gr. hyacinthus/ cytherea with branching Pocillopora damicornis, P. eydouxi, Montipora digitata, occasional domal faviids and mm-thick crusts of the coralline algae Lithophyllum and Mesophyllum (mainly), typical of the 6 – 15 m paleodepth range; a community including robust-branching Acropora gr. danai/ robusta, A. humilis, A. digitifera and subordinate Favia stelligera, Echinopora gemmacea, associated to vermetid gastropods and thick coralline crusts of Hydrolithon cf. onkodes and Neogoniolithon cf. fosliei flourishing in depths less than 6 m; in medium-to-high water-energy settings, a community composed of domal Porites cf. lutea and P. cf. lobata with occasional Acropora gr. danai/ robusta and cm-thick crusts of coralline algae in sheltered habitats in depths less than 10 m. These biological assemblages allow us to determine relationships between reef growth and paleobathymetry and, consequently, to reconstruct regional relative sea-level curves. High water-energy reefal assemblages provide stronger evidence for reconstructing sea-level curves than low-energy buildups, because they have generally been controlled by a keep-up growth mode. Subsiding reef sites seem to be more reliable indicators of sea-level variations because they usually present expanded reef sequences.