THE SWAMPY GROUNDS IN WESTERN PROVENCE, I NDICATORS OF THE HOLOCENE MORPHOGENESIS

The damp endoreic basins of the coastline of the western low Provence formed the sedimentary geosystems highly damaged by an early and impor tant human occupation. Their hydrological variations free of these of the sea-level, depend on the local climatic evaluation of which they a re a good indicatory. The sedimentological analysis of a sample carrie d out of one of then (Etang du Pourra) is confronted with paleobotanic al informations and with the geomorphical investigation in others basi ns and their basin-versants. A rich archeological documentation and th ree isotopic datings back up the chronostratigraphic argument. The sur roundings seem to have been early stabilized as far back as the tardig lacial interstage, the settings of which are capped with a brown soil inclosing altered smectites. The late Dryas does not seem to suspend t his evolution. The Holocene is characterized by a damp climatic fluctu ation at the starting Subboreal, that induces a raising of sheets of w ater, and then by a dryer period between Bronze Age and Middle Ages. T he effects of anthropization upon morphogenesis depend at the same tim e on climatic changes and conditions of ground filling. Two unequally important erosive crises are separated by a two or three millenaries m orphogenic interval. They are characterized, upon slopes and talwegs, by alluval detritics silts enriched in altered minerals from scouring of pedological toppings. The first erosive crise, during last Neolithi c, shows the convergence of reclaiming extent and new spell of dampnes s. It ends with a vertic evolution, connected with the highly swampy l evel in hydromorphic low zone. Between Bronze Age and Roman times, the environment become steady in spite of an increasing anthropization: t he dryer climatic context and protecting cultural practices alter the morphodynamic process; fossilized farmings terraces have been discover ed, The post-antic period coincides with an erosive crise of first imp ortance, generating of thick colluvial deposits upon slopes. The inves tigation in that area shows then there are intricate connections of ca usality between anthropization, the history of climate and the startin g of erosive crises.