The Holocene drowned reef of Les Saintes plateau as witness of a long-term tectonic subsidence along the Lesser Antilles volcanic arc in Guadeloupe

Resulting from the interplay between tectonics and eustatism, reef terraces are powerful markers of vertical movements at a scale of 1000 to 100,000 years. In the Lesser Antilles, they grow around every island of the archipelago and record both local and subduction-related tectonics. The recent acquisition and interpretation of very high-resolution bathymetry of Les Saintes submarine plateau, French West Indies, together with seismic reflection profiles, are a unique opportunity to study one of these submarine structures, at metric to kilometric scales, addressing the questions of its nature, age and growth environment, but also of the control of active tectonics on its formation. The 20 km wide Les Saintes reef plateau lies at about 45 mbsl. It is crosscut by NW–SE striking, north-dipping normal faults that belong to Les Saintes fault system and graben, which produced a Mw 6.3 earthquake in 2004. The plateau is composed of four 20 m thick reef units, piled up in “layer cake” morphology down to 110 mbsl. The upper unit has a fresh morphology and presents typical reef features, like barrier and lagoon, spurs and grooves, pinnacles, etc. From its morphology we propose that it grew during the Holocene last transgression. Below, the three other units likely formed during Pleistocene sea level highstands and were eroded during the low stands, as evidenced in seismic reflection profiles. This scenario would imply that Les Saintes plateau formed in a context of subsidence with a rate we evaluate to be of the order of tenths of mm/yr. Probably linked to local tectonics, we believe that this deformation is also related to plate-scale subduction processes, similarly to deformations occurring on the other islands of the Guadeloupe archipelago.