PRELIMINARY COMPARISONS OF GRAIN SIZE AND MULTI-PROXY DATA FROM A MEDIEVAL LAKE SEDIMENT CORE, EAST CENTRAL FRANCE

Radiocarbon dating of basal sediments in a core from étang Lucenier, located in southern Burgundy, France, indicates that it has served as a small reservoir since 1300 A.D. The sediment core was recovered to examine the impact of humans and climate on the landscape as recorded in lacustrine/reservoir sediments. Previous work utilizing x ray fluorescence (XRF) provided elemental proxies of detrital and authigenic mineral fluxes within the basin, however the effect of particle size was unknown. Detailed grain size distributions were obtained using laser diffraction, at 5 cm intervals for 1.3 m. of the core, for comparison with element data and to examine changing land use and hydrologic regimes within the watershed.

Comparison of grain size data (e.g. percentages of sand:silt:clay) with elemental abundance as determined by XRF did not yield statistically significant relationships. Instead, variations in these values are likely due to differences in the ratio of total mineral:organic content. In contrast, there are correlations in grain size and seasonal precipitation data. High but variable sand percentages between ~1700 and 1900 A.D. suggest either frequent, large magnitude flood events, or localized hillslope instability. Summer precipitation correlates well with sand content at that time as well, possibly the result of strong summer convective storms. Much lower sand contents between ~1600 and 1700 A.D. attest to more stable conditions and/or less turbulent flows. Silt percentages are high at that time, and co-vary with fall precipitation, typically generated by frontal storms in southern Burgundy. The largest sand percentages occur during the late 1800’s, correlative with wide-spread pasturing of Charolais cattle.