1:45 PM - 2:00 PM
[BPT02-01] Thermal maturation experiments of lichen materials: Origin and diagenetic alternation of aromatic furans in sedimentary rocks
Keywords:aromatic furans, biomarker, thermal maturation experiment, lichen
Aromatic furans such as dibenzofuran (DBF) have been reported to be detected in sedimentary rocks throughout geological ages. These compounds have been thought to be of terrestrial origin, although their origin is still under debate. There are two possible origins of DBFs in sedimentary rocks; 1) polysaccharides and lignin from higher plants (Sephton et al., 2005; Fenton et al., 2007; Wang and Visscher, 2007), and 2) DBF derivatives in lichens (Watson et al., 2005; Sawada et al., 2012). In catalytic combustion experiments, Fullana and Sidhu (2005) demonstrated that the DBFs could be produced from fluorene and biphenyls. In nature, DBFs were found as antimicrobial components of higher plants (Kokubun et al., 1995; Dixon, 2001) and lichens. Radke et al. (2000) statistically analyzed the distribution of methyl DBFs in sedimentary rocks and reported that 1-methyl DBF might have a different origin from other isomers, especially in lichens. Thus, there are several possible origins for the aromatic furans in the sediments, and some compounds have been suggested to have a specific origin.
We conducted the thermal maturation experiments. As a specific experimental technique, montmorillonite and water were added with each sample of possible precursor compounds of DBF, degassed, sealed, and heated at 200 ℃. Samples obtained from the experiment were extracted in organic solvents and identified by GC-MS analysis, and their composition and distribution were investigated for changes over time.
As a result, we confirmed that alkyl furans, benzofurans, and DBFs were generated from cellobiose, cellulose, lignin, and biphenol, while alkyl dibenzofurans were not detected. On the other hand, it was found that alkyl DBFs such as 1-methyl DBF, dimethyl DBF, and C3 alkyl DBF were obtained as the thermal maturation products of Cladonia rangiferina, which is a lichen producing the DBF as its metabolite. We interpret that these alkyl DBFs were generated as a result of preserving the alkyl chain attached to position 1 (and position 9), unique to the lichen producing DBFs, which may provide new insight into the origin of aromatic furans in sedimentary rocks.
We conducted the thermal maturation experiments. As a specific experimental technique, montmorillonite and water were added with each sample of possible precursor compounds of DBF, degassed, sealed, and heated at 200 ℃. Samples obtained from the experiment were extracted in organic solvents and identified by GC-MS analysis, and their composition and distribution were investigated for changes over time.
As a result, we confirmed that alkyl furans, benzofurans, and DBFs were generated from cellobiose, cellulose, lignin, and biphenol, while alkyl dibenzofurans were not detected. On the other hand, it was found that alkyl DBFs such as 1-methyl DBF, dimethyl DBF, and C3 alkyl DBF were obtained as the thermal maturation products of Cladonia rangiferina, which is a lichen producing the DBF as its metabolite. We interpret that these alkyl DBFs were generated as a result of preserving the alkyl chain attached to position 1 (and position 9), unique to the lichen producing DBFs, which may provide new insight into the origin of aromatic furans in sedimentary rocks.