Abstract
The four fossil terraces of the Glorieuses Islands are described, and new dates are provided to resolve their stratigraphy, depositional setting, and tectonic behavior. Most outcrops consist of a single sedimentary unit that represents the remains of an extensive reef flat dominated by Isopora palifera corals. At Lys Island, this unit is locally overlain by dipping layered beds composed of Halimeda segments, tentatively interpreted as storm overwash. Reliable U/Th dates obtained from corals sampled from the fossil outcrops mostly fall between 127 and 123 kyr, suggesting that these reefs formed exclusively during the first MIS-5e sea-level highstand, when sea level reached +3 m. The mean elevation of these terraces being +4.5 m, an uplift of 0.012 ± 0.002 mm year−1 is inferred. This relative tectonic stability contrasts with the subsidence reported from Mayotte Island, suggesting a different geologic setting for the nearby Comoros and Glorieuses archipelagoes.
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Acknowledgments
Field work has benefited from financial and/or logistic support by the Daniel Jouvance company (Auracea mission), Direction de l’Environnement, de l’Aménagement et du Logement (DEAL) Réunion, Forces Armées de la Zone Sud de l’Océan Indien (FAZSOI), Center National de la Recherche Scientifique CNRS (Institut écologie et environnement INEE and UMR-8591) and Terres Australes et Antarctiques Françaises (TAAF). The assistance of Cédric Marteau, Thierry Périllo, and the officers of Marion Dufresne is much appreciated. We further thank Christophe Colin (Orsay) for XRD analyses, Bruno Roump (SHOM) for tide predictions, Jean-François Ternon (IRD) for Fig. 1a, Carden Wallace (MTQ) for the identification of 3 badly preserved Acropora, and Guilhem Barruol (CNRS) and Laurent Michon (UR) for fruitful discussions.
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Communicated by Geology Editor Prof. Bernhard Riegl
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Guillaume, M.M.M., Reyss, JL., Pirazzoli, P.A. et al. Tectonic stability since the last interglacial offsets the Glorieuses Islands from the nearby Comoros archipelago. Coral Reefs 32, 719–726 (2013). https://doi.org/10.1007/s00338-012-1006-9
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DOI: https://doi.org/10.1007/s00338-012-1006-9