Organic matter geochemistry of Quaternary sediments of the Seyda River valley (northeast of the Pechora Lowland)

The hydrocarbon composition of extracts and pyrolysis products of peat from interglacial deposits of the Seida River basin, 200 ± 30 thousand years old, have been studied. To study the hydrocarbon composition, the peat extract is separated into saturated and aromatic fractions, the composition of which is analyzed by gas chromatography-mass spectrometry. The organic matter of the peat is analyzed by pyrolytic gas chromatography-mass spectrometry. The distribution of n-alkanes in the peat extracts, high Pwax and low Paq values, indicate a high contribution of woody vegetation within the studied peat section. According to palynological data, deciduous trees (Betula sp.), as well as conifers (Pinus sylvestris and Picea sp.), were widespread during this period. Triterpenoid derivatives of higher plants with oleanane and ursane carbon skeletons, markers of angiosperms, are identified in the aromatic fraction. Based on their distribution, it is established that the vegetation composition was uniform; the observed changes in component ratios are conditioned by changes in the proportions of different plant species, most likely by changing climatic conditions. The pyrolysis products contain phenolic derivatives of the guaiacyl series, considered biomarkers of gymnosperm lignin, confirming the presence of coniferous vegetation in the peat. The detection of n-alkenes in peat extracts may indicate the presence of lichens, and the presence of diploptene may indicate the involvement of sphagnum in peat formation. Data on the hydrocarbon composition of the extract and the pyrolysis products of peat organic matter support palynological data indicating the presence of coniferous and deciduous pollen in the peat.