Lateglacial paleoenvironmental reconstruction using subfossil chironomid assemblages from Lake Lautrey (Jura, France)
Résumé
Chironomid assemblages were studied in Lake Lautrey (Jura, France) along a 2.50m long core spanning the whole Lateglacial period. A stratigraphical constraint cluster analysis showed 7 biozones and 13 sub-biozones within the chironomid biostratigraphy. Characteristic taxa were allocated to each of the 7 biozones by simple analysis of the relative abundance diagram whereas several Correspondence Analyses (C.A.) were needed for the remaining 13 sub-biozones. Characteristic taxon compositions were interpreted using available quantitative inference models for total phosphorus concentration ([T.P.]), chlorophyll-a concentration ([Chl-a]), hypolimnetic oxygen conditions, and water temperature. Optimum ranks of the characteristic taxa against the environmental factors provided by these inference models were used to deduce an evaluation of environmental conditions. Paleoenvironmental interpretations of chironomid assemblage changes showed the Lateglacial climatic event succession (Oldest Dryas, Bolling/Allerod Interstadial, and Younger Dryas) commonly recognized in the area. Moreover, a bipartition of the Oldest Dryas, the occurrence of two minor oscillations during the Bolling/Allerod Interstadial and a trend in environmental changes (climatic improvement) during the Younger Dryas were also found