Simulation Experiment Study on Impacting the δD Value of Aromatic Compounds

Abstract

Little is known about the effects of sedimentary environment and maturity on δD values of aromatic compounds deposited in geological bodies. Our simulation experiments showed that the δD value of pyrolytic polycyclic aromatic hydrocarbons (PAHs) was significantly different between the studied samples from high and low latitude regions. Comparative studies showed that the δD values of PAHs produced by pyrolysis were related to those of water in the two regions. With increasing maturity, the δD value of the PAHs becomes higher. Additionally, it was observed that some PAHs exhibited a propensity to increase the δD value upon demethylation. The thermodynamic fractionation of hydrogen isotopes between the PAHs produced by pyrolysis and both the n-alkanes and methane produced by pyrolysis indicated that the hydrogen isotopic value of the PAHs was higher than that of the n-alkanes or methane. The long-chain alkylbenzene produced by pyrolysis has a higher mean δD value compared with the n-alkanes produced by pyrolysis, but it is lower than that of the PAHs in the same sample. The lowest δD value among the aromatics was found in the ring A monoaromatic steroids produced by pyrolysis. The low δD values of these steroids should originate from isotopic fractionation during isoprenoid lipid biosynthesis.