Last interglacial reef facies and late Quaternary subsidence in the Maldives, Indian Ocean

To date, there is hardly any knowledge of facies and age of Pleistocene reef limestone in the Maldives. Likewise, there are no robust estimates of Quaternary subsidence in this major shallow-water carbonate platform and reef area. In a core recovered on the windward margin of Rasdhoo Atoll in the central part of the archipelago, Pleistocene coralgal grainstone facies belonging to marine isotope stage (MIS) 5e were recovered underlying a Holocene reef succession, 14.5 m below modern sea level. Based on the occurrence of shallow-water stony corals such as Isopora palifera and possibly Acropora gr. robusta, high-energy coralline algae including Porolithon onkodes, in part associated with vermetids, and grain-supported limestone texture, the paleoenvironment is interpreted as a shallow back reef area with a paleo-waterdepth of <10 m. Based on a reliable U-series age from a Pleistocene acroporid coral of 136.9 kyr BP and assuming a + 7.5 m higher-than-present peak sea level during MIS 5e, late Quaternary subsidence is estimated to 0.09 m/kyr (minimum)-0.16 m/kyr (maximum value). A sea level of +2.5 m during the early MIS 5e would reduce the rates to 0.05 m/kyr (minimum)-0.12 m/kyr (maximum). These numbers are significant for reconstructions of depositional environments of this major carbonate platform area in the Quaternary. The subsidence estimates are not as crucial for historical reconstruction of relative sea level and for predictions of the near future in this low-lying archipelago, because they will add only a minor portion to the predicted rates of 21st century sea-level rise.