Dearing, John, Hu, Yuquan, Doody, Pippa, James, Peter A. and Brauer, Achim
Preliminary reconstruction of sediment-source linkages for the past 6000 yr at the Petit Lac d'Annecy, France, based on mineral magnetic data
Journal of Paleolimnology, 25, (2), . (doi:10.1023/A:1008186501993).
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An 8 m core from the central plain of the Petit Lac d’Annecy, France, two floodplain cores, river bedload sediments
and several hundred soil samples from the catchment have been studied using magnetic techniques. The soils, mainly
developed on limestones and local glacial tills, show widespread magnetic enhancement with higher ferrimagnetic
concentrations and contents of superparamagnetic grains than found in the lake sediments. Some soils show
significant concentrations of canted antiferromagnetic minerals (mainly haematite). Using magnetic quotient
parameters the surface soils are classified into four mineralogical types. The lake and floodplain sediment properties
over the past 6000 yrs can largely be explained by the erosion and deposition of these sources, with a smaller
superimposed biogenic (magnetosomes) signal. Derived sediment-source linkages allow the construction of several
hypotheses about geomorphological changes in the catchment system: (i) the long-term erosion of high altitude
unweathered substrates has gradually increased towards the present day; (ii) the erosion of high altitude soils has
increased within the last 1000 yrs, possibly during the period of the ‘Little Ice Age’; (iii) shifts towards an increased
erosion of surface lowland soil occurred ~2000 and 1000 yrs ago and may be linked to an accelerated accretion of
floodplain overbank deposits; (iv) there has been a significant storage of surface soil within floodplains, which
leads to an underestimation of the importance of soil erosion in the lake sediment records; (v) the sediment transported
by high magnitude, low frequency flood events has shifted in source from high altitude soils before ~1000 cal. yr
BP to lowland and mid-altitude free draining soils after ~1000 cal. yr BP.
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