Lignin Phenols in Soils as Biomarkers of Paleovegetation

It has been shown by the methods of biochemistry, nuclear magnetic resonance, and isotope geochemistry that the proportions of lignin phenols may be used as molecular traces of paleovegetation due to their biochemical and physiological specificity and high resistance to decomposition. Lignin structures have been detected in iron–manganese concretions. The comparison of the 13 NMR spectra of native lignin preparations isolated from different woody and herbaceous species with those of soil humic acids makes it possible to identify many characteristic shifts of lignin nature in humic acids at 56, 102, 115, 119, 131, 147, 151–152, 160, and 166 ppm. The information role of biomarker has been tested at the reconstruction of paleovegetation in the uplands of the Russian Plain: an upward shift of the forest boundary has been recorded on the Northern Caucasus; the hypothesis about the steppe period of landscape development in the Tien Shan mountain valleys during the middle Holocene has been confirmed, and molecular traces of tropical flora have been revealed in the buried soils of Pleistocene age. The representativeness of information has been increased using the isotope analysis (δ13C); a new parameter—the composition of lignin phenols—has been introduced in the existed system of biomarkers.