EVOLUTION OF THE MATTER FLUXES SINCE 12,0 00 YEARS IN THE HIGH DOUBS VALLEY (FRANCE)

Citation
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
Citations number
41
Categorie Soggetti
Geology
ISSN journal
00379409
Volume
165
Issue
4
Year of publication
1994
Pages
381 - 400
Database
ISI
SICI code
0037-9409(1994)165:4<381:EOTMFS>2.0.ZU;2-V
Abstract
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.