Middle pleistocene deposits at La Cote, Val-de-Lans, Isere department, France: plant macrofossil, palynological and fossil insect investigations

International audienceplant macrofossils, pollen and spores, and Coleoptera remains were analysed from high altitude, lacustrine, interglacial deposits collected from La Cote, Val-de-Lans, Isere, western French Alps. The investigation concentrated on the second half of the temperate stage (locally called the La Cote Interglacial Stage). Palaeoecological, palaeoenvironmental and quantitative climatic reconstructions for the termination of the interglacial period and the onset of cold conditions are presented. Because the different fossils were affected in varying ways by taphonomic processes they provide a range of complementary data about the palaeoenvironment, and illustrate the importance of multi-disciplinary studies. As conditions became cooler at the end of the temperate stage the lake levels fluctuated, and the water's trophic status changed. The occurrence of Pterocarya and the dominance of Abies support a correlation with the temperate Holsteinian Stage (oxygen isotope stage 11). At the top of the core an interstadial event characterised by Pinus, Picea and Betula is represented. This could have occurred either directly after the La Cote Interglacial Stage or the event may have occurred during the following cold La Bourns Stage after a hiatus. The climate fluctuations represented at the end of the La Gate Interglacial Stage in the Val-de-Lans basin prompt comparisons with the end of the Eemian Stage (Late Pleistocene) and suggest that such oscillations are characteristic for the end of temperate stages. An understanding of the changes represented here aids the evaluation of present trends as we possibly enter the final phases of the Holocene Stage. Sites of this age and located at this altitude are rare in Europe; therefore, it is proposed that the La Cote site should be considered as a high altitude, alpine parastratotype for the Holsteinian Stage in western Europe. (C) 2000 Elsevier Science B.V. All rights reserved