M. Campy et al., EVOLUTION OF THE MATTER FLUXES SINCE 12,0 00 YEARS IN THE HIGH DOUBS VALLEY (FRANCE), Bulletin de la Societe geologique de France, 165(4), 1994, pp. 381-400
At the end of the last glacial period, about 12,000 years B.P., a land
side blocked the upper part of the Doubs valley. It results in a natur
al reservoir which is nowadays filled up to 9/10 of its initial volume
by inputs from the Doubs drainage basin. Geometry and nature of the l
acustrine infilling are known owing to some 40 drillings and its chron
ology is based on palynological data and 17 radiocarbon datings. Sedim
entological analyses (major components, granulometry, clays minerals),
geochemical analyses (Mg/Ca ratio), isotopes (delta18C, deltaC-13), a
s well as organic matter analyses (Rock Eval pyrolysis and palynofacie
s) point to an evolution of the behaviour of the system supplying drai
nage basin/collecting lacustrine trap, since the onset of its working.
Three major periods are distinguished, showing changes in sources of
material, erosion types and sedimentary fluxes. During a first period
(12,000 to 9,000 years B.P.), mechanical erosion is predominant and af
fects the Mesozoic substratum and morainic cover. Vegetation is scarse
and soils are not much developed in the drainage basin. Matter fluxes
are dominated by particulate elements (coarse bed load and suspended
matter). During a second period (9,000 to 6,000 years B.P.), chemical
erosion is predominant (karstic dissolution). Forests (oak association
) colonize the drainage basin and soils develop. Matter fluxes are dom
inated by solute elements. During the last period (6,000 years B.P. to
Present), mechanical erosion, bearing essentially on soils, starts ag
ain. This renewal of soil erosion is due either to development of coni
fer forests, and/or to anthropic deforestations.