BIOLOGICAL EVIDENCE OF SEA-LEVEL RISE DURING THE LAST 4500 YEARS ON THE ROCKY COASTS OF CONTINENTAL SOUTHWESTERN FRANCE AND CORSICA

On the rocky coasts of the northwestern Mediterranean basin, biogenic littoral rims built by the coralline rhodophyte Lithophyllum lichenoid es develop, whose remains may be preserved for millennia when submerge d in a rising sea environment. These remains can be used as biological indicators of recent sea-level variations. Our survey of the continen tal coasts of Var and Bouches du Rhone, west of Marseilles (southern F rance) and of northern Corsica shows that relative sea level rose abou t 1.6 m in the study area during the last 4500 years without exceeding the present datum. The rate of sea-level rise was 0.4 mm per year bet ween 4500 and 1500 yr B.P. and slowed down to 0.2 mm per year from 150 0 yr B.P. to present time. There are also morphological indications of an acceleration of the rate of sea-level rise during the last century , supporting the evidence of tide gauges. Regions at the periphery of the above zone (Alpes Maritimes, Italian border zone, and the French a nd Spanish Catalonia regions) were also surveyed, but a weaker develop ment of Lithophyllum rims and bad preservation of algal remains led to unconvincing dates which could also be linked to regional tectonic tr ends.