Geomorphology and sedimentology of a modern isolated carbonate platform: The Glorieuses archipelago, SW Indian Ocean

Abstract

The study of modern carbonate systems commonly helps in improving facies interpretation in fossil reefs and in providing analogues of sediment distribution depending on the specific platform configuration (i.e. rimmed shelves and isolated carbonate platforms). This paper deals with a geomorphological and sedimentological study of the Glorieuses Archipelago, an isolated carbonate platform located between the northern tip of Madagascar and Mayotte. The dataset consists of Digital Terrain Model, satellite imagery, and box-sediment samples. Analyses of grain-size and composition of carbonate grains are used to characterize the distribution and heterogeneity of sediment accumulated on the isolated platform. Main results show that the Glorieuses Archipelago is organized in distinctive morphological units, including a reef flat developed along the windward side, an apron, and a semi-enclosed (<12m water depth) to open lagoon (>12m and up to 15m water depth). The lack of carbonate mud in sediments deposited on the archipelago can be explained by the direct connection between the lagoon and the open ocean. The main carbonate grains include Halimeda segments, coral fragments, large benthic foraminifers, red algae, and molluscs. According to the shape and the position of intertidal sandwaves, the current arrangement of moderately sorted fine to medium sands appears to be strongly influenced by tidal currents. The in-situ sediment production, accumulation and transport on the platform finally contribute to carbonate sand export to distinct deep marine areas depending on wind regimes and currents.