MESO-CENOZOIC ORGANIC-MATTER IN PRESENT H UMUS LAYERS (CHAILLEXON BASIN, DOUBS, FRANCE)

The optical analysis in the Chaillexon water-shed (Doubs, France), of the present soils 'humus layers' organic matter-points out the contrib ution of Meso-Cenozoic organic matter in addition to the one produced by vegetal cover. Their relative occurrence varies in each layer: in t he reverse of that of vegetal organic matter, the relative amount of M eso-Cenozoic organic matter increases according to the depth. That res ult shows that the total organic matter amounts in soils (and its eval uation) do not only depend on the net primary production and that geol ogical formations have to be taken into account. Moreover, it suggests that present and past detrital supplies are concerned with 'old' orga nic matter incorporation. (C) Academie des sciences/Elsevier, Paris.