Distribution of recent Foraminifera as depositional indicators in Yongle Atoll, Xisha Islands, South China Sea

The key to the utility of foraminifers as paleo-environmental indicators for coral reefs is the knowledge of modern assemblages in relation to environmental conditions. This study examined 44 surface-sediment samples from three small islands in Yongle Atoll, with the goal to investigate the relationship between foraminiferal distribution and environmental characterization. In samples, 192 foraminiferal species belonging to 74 genera were identified, among which the hyaline foraminifers totally dominated. Hierarchical Cluster Analysis resulted in the identification of three foraminiferal biofacies, representing different environmental settings and sedimentary regimes. (1) The Amphistegina (mainly Amphistegina lobifera) facies characterizes the upper fore-reef slope zone, which experiences strong wave action and currents from the open sea. (2) The Calcarina hispida–Neorotalia calcar facies represents the reef flat and lagoon slope zone, and patch reefs in the lagoon basin, which is the shallowest of all the biofacies, exposed to the strong solar radiation and strong hydrodynamic activity. (3) The Quinqueloculina crassa subcuneata–Elphidium advenum facies characterizes the lagoon basin, which is covered by fine sands and muds with abundant Halimeda fragments to water depths <15 m. Bivariate Correlation Analysis and Canonical Correspondence Analysis indicate that the spatial distributions of foraminifers in Yongle Atoll are associated with water depth and sediment texture. Other environmental factors, including hydrodynamic energy, substratum type and light intensity also influence the foraminiferal biofacies. Finally, we summarized our results into a foraminiferal distribution model for the purpose of interpreting modern and paleo environmental conditions in atolls in the South China Sea.