Kerogen density fractions separated by the sequential density centrifugation of kerogens from Cretaceous Leenhardt and Miocene Onnagawa shales were analyzed using pyrolysis-GC/MS. The pyrolysates from both kerogens mainly comprised aliphatic compounds, such as n-alkane/n-alkene doublets and acyclic isoprenoid hydrocarbons, along with aromatic compounds including alkylbenzenes, alkylnaphthalenes, and alkylphenanthrenes. The sporomorph-concentrate obtained from the Onnagawa kerogen was mainly composed of sporopollenin geomacromolecules, consistent with the dominances of long-chain (C₂₂–C₂₅) n-alkane/n-alkene doublets. In the algae/sporomorph-abundant fraction from the Leenhardt kerogen, mid-chain-length (C₁₆–C₂₀) n-alkane/n-alkene dominances suggested a larger contribution of dinoflagellate-derived algaenan. Pyrolysis of the weakly fluorescent amorphous kerogen (WFA)-containing fractions of the Onnagawa kerogen generated C₁₃–C₂₀ acyclic isoprenoid hydrocarbons (except C₁₇), as well as alkylbenzenes including 1,2,3,5- and 1,2,3,4-tetramethylbenzenes. The isoprenoid hydrocarbons and the alkylbenzenes were components of fossil geomacromolecules likely derived from marine microalgae (diatoms and cyanobacteria). Non-fluorescent amorphous kerogen (NFA), the major kerogen of the Leenhardt shale, contained terrigenous suberin geomacromolecules, consistent with the dominance of terrigenous organic matter in the Leenhardt kerogen and the abundance of long-chain even carbon-numbered (C₂₂ and C₂₄) n-alkanes. The distributions of the pyrolytic isoprenoid alkanes (C₁₃, C₁₆, and C₁₈–C₁₉) from the Leenhardt kerogen suggested their distinctive fossil geomacromolecular sources, such as freshwater/coastal microalgae and cyanobacteria.

Riverbed sediments from 19 Hayakawa River sites in Hakone Caldera Japan were analyzed for 37 elements, categorized into three groups by location: Group-1 (nine mainstream samples), Group-2 (five tributary samples with somma upstream), and Group-3 (five tributary samples with central volcanic cones upstream). Principal component analysis (PCA) showed the 3PCs explain approximately 77% of the total variance. The first principal component (PC1) is derived from the inverse correlation between Al and a group including Na, K, and rare earths elements (REE), likely due to their weathering, and their acidic alteration. Groups 1 and 2 sediments might be more influenced by this weathering or acidic alteration than Group-3. The PC2 was characterized by elements enriched in volcanic ash, such as Sc, V, Mn, Fe, and Cu, showing no significant score differences among the three groups. The PC3 was characterized by the correlation among Li, Al, Cu, Ga, Rb, and Sr, with no significant score variations among the three groups. Arsenic showed loadings below 0.5 in PC1 to PC3, indicating its limited contribution to the overall sample characteristics. However, a specific site with upstream volcanic hot spring discharge exhibited high As content, implying possible sediment contamination by As-bearing minerals like pyrite. This suggests the possibility of using As content in riverbed sediments to detect volcanic activity. This study’s results indicate that the elemental composition of riverbed sediments could be associated with the weathering and acidic alteration of volcanic rocks from Hakone Volcano, indicating the potential to identify areas influenced by geothermal activity.