Dense-media separation as a more efficient pollen extraction method for use with organic sediment/deposit samples: comparison with the conventional method

Dense-media separation, frequently adopted as a standard pollen extraction method for use with minerogenic sediment samples, was adapted for use with organic-rich sediment and peat samples. A total of 15 organic-rich sediment samples, obtained from sites in Corsica and the Southern European Alps, was treated using both dense-media separation and the conventional preparation method in order to compare the relative efficiencies of the two methods. The dense-media separation method consistently achieved a remarkably higher purity of extracted pollen grains. This was especially true for the Corsican peat samples, the dense-media separations being quite pure, whereas the classical method produced samples that were so severely polluted with organic fragments that it was impossible to carry out a satisfactory pollen analysis. The percentage values of each taxon were generally similar using both methods, showing that the two methods are compatible for pollen analytical studies. Total pollen concentrations were generally higher with the dense-media separation method (especially for gyttja samples). In conclusion, dense-media separation is an efficient method for pollen extraction from organic as well as from minerogenic sediments and deposits.     

Holocene palaeoenvironments at the timberline in the French Alps—a multidisciplinary approach

An attempt is made to reconstruct the palaeoenvironmental Holocene history at the timberline on the basis of the analysis of various palaeoecological proxy indicators available on a marshy area and its surroundings in the Taillefer Massif (Isère. France). The multidisciplinary approach involves analyses of pollen assemblages. plant macrofossils, coleoptera remains. subfossil trunks extracted from lakes or peat-bogs. and charcoals derived from the surrounding soils. This enables definition of the respective roles of five forest taxa ( Pinus uncinata Mill., Pinus cembra L., Larix decidua Mill., Abies alba Mill, and Picea abies L. Karsten) in the evolution of high altitude forests during the Holocene. Pinus uncinata was present on the plateau throughout the Holocene. Larix and Pinus cembra were present only during two periods: 7500-5000 BP and 3500-2000 BP. All trees disappeared from the plateau at about 2000 BP, while, at lower altitude. Abies was replaced by Picea. The action of both climate and early human impact can explain these changes.     

A long Upper Pleistocene pollen record from Les Echets, near Lyon, France

Analysis of 732 samples through 39 m of sediments from the ancient lake of Les Echets, 15 km northeast of Lyon, France, resulted in a long, continuous pollen diagram covering the interval from the Late Rissian to the Holocene. Above a complete Ecmian sequence, there are two Early Wiirmian temperate cycles (the older one including two climatic optima separated by a brief deterioration) with forest successions characterized by the spread of Carpinus at the end of the early temperate phase. These episodes, whose exact equivalents are found at Grande Pile in the Vosges area, are correlated with the Early Wiirmian trilogy Amersfoort-Brorup-Odderade of northern Europe. The absolute dates proposed for the Grande Pile sequence arc accepted, whereas those for the three northern European stratotypes are rejected. The Early Wiirmian is thus placed between 115,000 and 70,000 years B.P. In the Middle Wiirm, three undated intcrstadials arc characterized by a sparse forest cover. The long Late Wiirmian section is a characteristic feature of the sediment history at Les Echets. Very cold and arid conditions prevailed during this interval, without any unequivocal indications of intcrstadial episodes. A rise in Artemisia around 15,000 B.P. marks the transition from the Pleniglacial to the Oldest Dryas.     

The lithostratigraphy of the Les Echets basin, France: tentative correlation between cores

Two new long sediment cores (EC1 and EC3), recovered from different locations within the infilled basin at Les Echets, France, provide a new high-resolution record of terrestrial and lacustrine responses to climatic changes during Marine Isotope Stages (MIS) 3 and 2. The lithologies of the cores are described in detail and correlated with each other by stratigraphic marker horizons, fluctuations in organic matter and AMS radiocarbon ages. The tentative correlation of the new cores to those described and analysed by de Beaulieu et al. (1980) and de Beaulieu & Reille (1984a) provides a preliminary chronostratigraphic framework. Sedimentation during MIS3 started with accumulation of sands and silts and was followed by alternating gyttja and clayey gyttja silts. Exceptionally high sedimentation rates during MIS2 led to the infilling of the basin. Alternating organic-rich and minerogenic-rich sediments appear to coincide with changes in pollen assemblages (de Beaulieu & Reille 1984a) and suggest that millennial-scale climatic changes controlled lake productivity and catchment stability during most of MIS3.