A Geomorphological Reconnaissance of Tromelin Island, Indian Ocean
Résumé
Tromelin is a small coral reef island (1 km2) located in the Indian Ocean, approximately 440 km E of Madagascar and 580 km N of La Réunion. Despite the presence of a permanent Météo France weather station on Tromelin since the 1950s, a detailed geomorphological study of the island has never been undertaken. In this paper, we describe the geomorphology of the atoll, detailing seven geomorphological zones from the outer reef to the atoll crown. We also discuss Holocene relative sea-level changes in the light of new radiometric datings. Uranium-thorium dating of a remnant mid-Holocene reef-flat yielded an age of 5700 ± 400 years and could be interpreted as a relative sea level approximately 1.2 m above present. Subsequent possible sea-level positions have been inferred from coral conglomerates left by high-energy waves. These conglomerates might be interpreted as a beachrock, cemented mainly in the former intertidal zone when sea level was still approximately 1.2 m above present. The radiocarbon dating of three coral fragment samples collected from these conglomerates has yielded ages spanning 4200 to 2900 calibrated years BP.