Polycyclic Aromatic Hydrocarbons in Rocks and Soils of the Siljan Impact Crater, Sweden

New data were used to analyze the distribution of polycyclic aromatic hydrocarbons (PAH) in the lithological complex and soils of the Siljan impact crater area (Scandinavian Shield, central Sweden). Ten individual unsubstituted PAHs were identified, including diphenyl, fluorene, phenanthrene, anthracene, pyrene, chrysene, fluoranthene, benzo[a]anthracene, benzo[a]pyrene, benzo[ghi]perylene, as well as a number of substituted naphthalene homologs. The PAHs were analyzed using the Shpolsky spectroscopy. The studies were carried out at the crater edge (an annular morphostructural depression) and in the adjacent areas. The depression is characterized by traces of hydrothermal activity and modern oil and gas seepages. In the gas seepage area at depths of 267‒485 m, nine out of eleven studied PAHs were identified (concentration from 20 to 890 μg/kg in total) in the igneous rock complex. Sedimentary rocks at depths from 10 to 250 m contain only naphthalene homologs, phenanthrene, and pyrene. The PAH concentration in sedimentary rocks in the oil seepage area is two times higher than in the gas seepage area, and its composition (naphthalene homologs, phenanthrene, pyrene, diphenyl, chrysene) is close to the PAH composition in oil. In general, soils of the crater show a hydrocarbon dispersal halo, which is presumably caused by the oil and gas seepages and traces of hydrothermal activity. Characteristics of this halo are differentiated in space and make it possible to predict hydrocarbon seepages in unexplored areas.