Variations in sediment yield from the Upper Doubs River carbonate watershed (Jura, France) since the Late-Glacial period

The Upper Doubs River Valley is a 910-km(2) watershed feeding into Lake Cha illexon, The lake was formed by a natural rockfall at the end of the Bollin g Chronozone (around 14,250 cal yr B.P.) and since then has trapped materia l eroded from the watershed. The filling process and variations in sediment yield have been investigated by mechanical coring, seismic surveys, and el ectric soundings. The detrital sediment yield of the upstream watershed can be calculated by quantifying the sedimentary stocks for each climatic stag e of the Late-Glacial period and Holocene Epoch and estimating the lake's e ntrapment capacity. This enables us to determine the intensity of the erosi on processes in relation to climate and environmental factors. The Bolling- Allerod Interstade produced the greatest yields with mean values of 19,500 metric tons per calendar year (t/yr). The Younger Dryas Chronozone saw a sh arp fall (8900 t/yr) that continued into the Preboreal (2100 t/yr). Clastic supply increased during the Boreal (4500 t/yr) before declining again in t he Early Atlantic (2400 t/yr), Since then, yields have risen from 4500 t/yr in the Late Atlantic to 6800 t/yr in the Subboreal and 11,100 t/yr in the Subatlantic, Comparison of quantitative data with the qualitative analysis of the deposits and with the paleohydrologic curve of the watershed based o n level fluctuations in lakes around Chaillexon shows that climate was the controlling factor of sediment yield until the Late Atlantic. From the Late Atlantic-Subboreal around 5400 cal yr B.P. (4700 C-14 yr B.P,) and especia lly from the end of the Subboreal Chronozone and during the Subatlantic Chr onozone (2770 cal yr B.P./2700 C-14 yr B.P.-present) climatic constraints h ave been compounded by human activity related to forest clearing and land u se. (C) 1999 University of Washington.