Hydrocarbon status of soils in zones of active tectonic faults of Baikal rift

Abstract

Some parameters of the hydrocarbon status of two soils of the Ulyunkhan depression (North-Western part of the Barguzin depression, Western Transbaikalia) within the Baikal rift system formed under the endogenous effect in the zone of hydrothermal waters active discharge, were studied. Soil samples were analyzed for the organic carbon, total content of hydrocarbons, concentrations of polyсyclic aromatic hydrocarbon compounds. The preliminary results of the study showed that total content of hydrocarbons in soils varied from 15 to 115 mg/kg and had no common profile distribution and evident correlation with other studied soil properties. Polycyclic aromatic hydrocarbons (PAHs) accumulation was marked within humus horizons and lower impregnated layers with high content of easily soluble salts that do not correspond to the total hydrocarbons amount. Total PAHs concentrations positively tightly correlated with the soil texture parameters (r = 0.89). Several typical features characterizing the HC state in the zone of active discharge of gas-hydrothermal fluids were revealed: increased HC content, the predominance of phenanthrene in the total PAHs, and the presence of a wide range of PAHs, including heavy ones, consisting of 4–6 rings as well as the high benz(a)pyrene concentration that was revealed in the gley alluvial soil.