Variability of the ancient organic supply in modern humus

The particulate organic matter isolated from soils and from underlying geol ogic formations from Various french watersheds was studied under the light microscope to determine palynofacies composition. The results reveal that m odern humus contain notable amounts of ancient organic constituents inherit ed from the geologic substratum. This ancient contribution varies both qual itatively and quantitatively, mainly as function of the substratum composit ion. This implies that the cartography of surface formations and the knowle dge of their composition is a prerequisite to the evaluation of the soil or ganic carbon reservoir and to the determination of its turnover. A more imm ediate conclusion is to remind us that the coaly debris that occur naturall y in soils does not always derive from modern biologic production and from pollution.