Lefort Jean-Pierre

The article considers changes of paleoenvironment on the western edge of continental Europe using the example of the Nantua section deposits, the formation period of which falls on the Middle Pleistocene cryochron corresponding to MIS 6 and, possibly, the transition to MIS 5e. The approach used is based on a set of characteristics of specific carbonaceous (humus) substances contained in the deposits, including its most reflective component – humic acids (HA). It is shown that the correlation coefficients of the indicator parameters of the composition and properties of modern humic acids in soils, obtained using different methods for studying their molecular features, are within 0.78–0.90. Based on the changes in the characteristics of the humus component of the deposits, it was established that the latter were formed in changing conditions, when, against the background of general coldness of the climate, there were five relative warmings of varying severity, which caused the appearance of clear signs of pedogenesis and primitive paleosols formation. A trend towards increasing moisture conditions was revealed, which is manifested in an increase in the proportion of fulvic acids relative to humic acids and a decrease in the absolute values of Cha:Cfa. Preliminary calculations of the average long-term air temperatures and the duration of the biological activity period (BAP) showed that their possible limits, respectively, lay between minus 5.9°C and –7.8°C and 52–80 days. The terms “humus” and “humus substance system” are used as synonyms in this paper.