Stratified Soil on Dictioneme Shales in the Area of the Last Cover Glaciation (Southern Ladoga Region): Properties, Paleogeographic Interpretation, and Radiocarbon Dating Issues

In the Valdai glaciation area (the valley of the Lyubsha River, Leningrad region), the morphological features at the macro, meso, and micro levels and the properties of a unique virgin dark humus dark-profile stratified clay soil formed from locally redeposited dictionemic shales (the Lyubsha section) overlain by a thin late glacial fine sand and silty loams deposited by the Aeolian way are considered and enriched with carbonate crushed stone and glauconite material. The local redeposition of dictionemic shales in the thickness of the section is confirmed by the data of spore-pollen analysis of the layers at its base (tundra vegetation), where the shale layers are underlain by Cambrian sands. The shale thickness underwent cryogenic cracking, increasing from the lower horizons of the profile to the upper ones, which was diagnosed by the micromorphological method. The soil developed under subaerial conditions starting in the Late Pleistocene. Holocene pedogenesis, along with the allochthonous stratum, covers only the upper layer of shale (AUca horizon), in which structuration, decompression, and inclusion of fragments of shale with undisturbed microstructure are noticeable. Such a low manifestation of soil formation on dictionemic shales is determined by the large “buffering” of the parent material and the predominance of a difficult-to-oxidize fraction in the organic matter of shales. The definite radiocarbon age of the organic matter of the dictionemic layers, which varies from the lower horizons to the upper ones in the range of ~36–24 cal. BP. (the Lyubsha section) and ~35–26 cal. BP. (the section on the Kirchhoff Upland), does not reflect the real age of soil formation. The organic matter of these soils is heterogeneous and heterochronous. Both the “dead” organic matter of shales and younger organic matter of pedogenic origin contribute to the radiocarbon age. This should be taken into account when 14C-dating and interpreting the results obtained.