CONTRIBUTION OF MESO-CENOZOIC ORGANIC-MATTER IN A LATE AND POSTGLACIAL DETRITAL ORGANIC SUPPLY (CHAILLEXON LAKE, DOUBS, FRANCE)

Chaillexon lake (Doubs, France) has been settled by a rock collapse ab out 12,000 years ago. That trap represents a continuous sedimentary re cord for the late and post-glacial period. The optical analysis of the organic matter settled in the Meso-Cenozoic substratum of the watersh ed and in the sedimentary infilling points out the incorporation of Me so-Cenozoic organic matter in the late and post-glacial organic detrit al supply. This incorporation mainly occurred from late glacial to Pre boreal periods (12,000-9,000 B.P.) showing that during this time veget al and soil covers were poorly developed and did not allow a significa nt protection of the bedrock from erosional processes. This protection started only at the beginning of Boreal (9 000 B.P.). These results a nd besides the presence of Meso-Cenozoic organic matter mainly compose d with opaque particles (coal debris) allow us two remarks: - such par ticles found in recent sediments must not be systematically interprete d as fire signals, - a watershed without any vegetal cover can neverth eless provide organic carbon.