Les bioconstructions à Lithophyllum Lichenoides, indicatrices des variations relatives du niveau de la mer.

Abstract

The problem of the altitude of contemporary sea level is an important one for the field archaeologist in coastal areas of the northwestern Mediterranean basin, where sedimentary and archaeological indicators are scarce or lack accuracy. Littoral algal rims built up by Lithophyllum lichenoides may be used as accurate biological sea level indicators on rocky coasts. Submersed and eroded remains are levelled and dated by radiocarbon ; a subsequent plotting of age/depth data allows a reconstitution of the sea level rise during the last four millenia. It appears from our study that, on rocky coasts of western Provence, relative sea level rose during the first millenium before Christ (approximately between 3000 and 2000 BP in radiocarbon years) with an average rate of 0,4 mm/year from - 100 cm under present datum to about - 60 cm, then slowed off to an average rate of 0,24 mm/year between - 68 cm and present datum from 1500 BP onwards. This apparent sea level rise represents the combined effect of eustatic rise and local tectonic components. Regional differences between western Provence, alpine and pyrenean regions, as well as local discrepancies may be noted.