The timing of sea-level high-stands during Marine Isotope Stages 7.5 and 9: Constraints from the uranium-series dating of fossil corals from Henderson Island

• Published in: Geochimica et Cosmochimica Acta
• Main Authors: Andersen, M, Stirling, C, Potter, E, Halliday, A, Blake, S, McCulloch, M, Ayling, B, O'Leary, M
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2016
• Subjects: Henderson Island; Pacific; Stirling
• Online Access: https://doi.org/10.1016/j.gca.2010.03.020; https://ora.ox.ac.uk/objects/uuid:cf6c0fb6-a22b-4f13-8115-7d5f66515901

Direct dating of fossil coral reefs using the U-series chronometer provides an important independent test of the Milankovitch orbital forcing theory of climate change. However, well-dated fossil corals pre-dating the last interglacial period (>130 thousand years ago; ka) are scarce due to, (1) a lack of sampling localities, (2) insufficient analytical precision in U-series dating methods, and (3) diagenesis which acts to violate the assumption of closed-system U-series isotopic decay in fossil corals. Here we present 50 new high-precision U-series age determinations for fossil corals from Henderson Island, an emergent coral atoll in the central South Pacific. U-series age determinations associated with the Marine Isotope Stage (MIS) 9 interglacial and MIS 7.5 interstadial periods are reported. The fossil corals show relatively little open-system U-series behaviour in comparison to other localities with fossil coral reefs formed prior to the last glacial cycle, however, open-system U-series behaviour is still evident in most of the dated corals. In particular, percent-level shifts in the [230Th/238U]act composition are observed, leading to conventional U-series ages that are significantly younger or older than the true sample age. This open-system U-series behaviour is not accounted for by any of the open-system U-series models, indicating that new models should be derived. The new U-series ages reported here support and extend earlier findings reported in Stirling et al. (2001), providing evidence of prolific coral reef development on Henderson Island at ∼320ka, most likely correlated with MIS 9.3, and subsequent reef development at ∼307ka during MIS 9.1, while relative sea-level was potentially ∼20m lower than during MIS 9.3. The U-series ages for additional well-preserved fossil corals are suggestive of minor reef development on Henderson Island during MIS 7.5 (245-230ka) at 240.3±0.8 and 234.7±1.3ka. All U-series observations are consistent with the Milankovitch theory of climate change, in terms of the ...