The chronology of Funafuti Atoll: revisiting an old friend

The drill core of Funafuti Atoll, collected by The Royal Society Coral Reef Expedition in 1896–1898, has been dated using high–precision 14C and Sr isotope measurements determined by mass spectrometry. The core top is a Holocene reef deposit, reflecting 26.4 m of reef growth since 8 ka, and is underlaid by Pleistocene reef–lagoonal deposits separated by a series of inferred hiatuses at 26.4 m, ca.30 m, ca.65 m and ca.80 m (ca.0.1 Ma, ca.0.2 Ma, ca.0.3 Ma and ca.0.6 Ma, respectively), reflecting atoll carbonate deposits associated with late Quaternary sea–level changes. In turn, the underlying sequence below ca.80 m comprises an upper section of additional Pleistocene reef–lagoonal deposits, having a high accumulation rate greater than 100 m Ma−1, and a heavily dolomitized lower section. Sr isotope data in the lower section provide maximum (oldest) ages for dolomite formation and, depending on the extent of the isotopic memory from precursor CaCO3, reflect ongoing diagenetic alteration from ca.2.3 Ma (i.e. the oldest dolomite) or in one or more discrete diagenetic events at ca.1 Ma, and possibly at ca.2 Ma. This sequence reflects interaction between atoll carbonate sedimentation, tectonic subsidence and eustatic sea–level change.