FACIES ANALYSIS AND DEPOSTIONAL ENVIRONME NTS OF THE FLUVIAL DEPOSITSIN THE CARBONIFEROUS BASIN OF SALVAN-DORENAZ

During the Late Palaeozoic, mainly during the Westphalian and Stephani an a small elongate basin formed between the cristalline massifs of Ar pille-Fully and Aiguilles Rouges located south of lake Geneva. The bas in fill was deformed during alpine orogeny and it is now preserved in a syncline; it is a few kilometers wide and about 20 km are exposed al ong strike. The sediment fill is about 1.7 km thick. Four fluvial accu mulation systems were distinguished which very probably respond to int rabasinal tectonic changes: At the base of the basin, sediments of a s and-dominated braided river document a palaeo-flow direction from NW t o SE which is perpendicular to present-day basin elongation, probably within a palaeo-valley. At this time basin subsidence and sediment acc umulation were nearly in equilibrium. Thereafter, basin subsidence inc reased and the basin was drained along axis to the NE; muddy sediments were deposited by an anastomosed river with slightly switching fluvia l channels. Simultaneously, alluvial fans prograded into the basin, ma inly from the NW. The sediments of the following, third fluvial system provide no evidence for a palaeodrainage direction, instead palustrin e muds, point to a sere-tilt and very rapid subsidence of the basin fl oor at this time in the investigation area. Finally, basin gradient in creased and sediments of a meandering river display palaeoflow along b asin axis to the SW. No indications of climatic changes have been iden tified.