9:30 AM - 9:45 AM
[BCG05-03] Oxygen-containing aromatic compounds detected in the Mesoproterozoic sedimentary rocks, Northwest Greenland: The origins and significance for earth’s history
Keywords:aromatic furans, biomarker, Mesoproterozoic, Greenland
The middle Proterozoic (1.8 - 0.8 Ga), which was sandwiched between two major oxidation events (GOE and NOE), has been called the "barren billion" because of the lack of carbon isotope excursions and glaciations (Young, 2013). However, molecular phylogenetic analyses suggest that the emergence and rapid dispersal of a eukaryotic common ancestor occurred (Parfrey et al., 2011; Eme et al., 2014), and geochemical evidence suggests that microbes may have preceded higher plants on land during this period, promoting terrestrial weathering (e.g. Kump, 2014). In the present study, we discuss the origin of aromatic furans detected in Mesoproterozoic sedimentary rocks in northwestern Greenland and their potential as biomarkers.
In this study, we analyzed the organic matter in the shaley mudstone of the Qaanaaq Formation, Baffin Bay Group, distributed in northwestern Greenland, using GC-MS. The Qaanaaq Formation is composed of sand-dominated sand and mud alternations, and previous studies suggest that it is regarded as dep an alluvial plain to marine shoreline deposit in the late Mesoproterozoic (Samuelsson et al., 1999; Dawes, 2006).
Although their distribution varied, several aromatic furans, which are oxygen-containing aromatic compounds, were detected in each sample. The origin of dibenzofurans, in particular, has been discussed in several ways, including lignin from higher plants and polysaccharides from terrestrial soils (Sephton et al., 2005; Fenton et al., 2007; Wang & Visscher, 2007), and secondary metabolites from lichens (Radke, 2000; Watson et al., 2005; Sawada et al., 2012). Fullana & Sidhu (2005) reported that dibenzofurans are produced from fluorene and biphenyl in catalytic combustion experiments. As a natural product, dibenzofurans have been reported as antimicrobial agents produced by higher plants (Kokubun et al., 1995; Dixon, 2001) in addition to the lichens. In this sample, the origin of higher plants can be dismissed among these theories, and Watanabe (2000) reported that dibenzofurans were produced from cellulose, lignin, and saccharide in heating experiments simulating aging in sediments, but dibenzofurans with alkyl groups were not produced. Therefore, we believe that the origin of polysaccharides is also unlikely. In addition, the distribution of isomers of alkyl dibenzofurans fluctuates each sample, suggesting that they may be derived from compounds that originally have aromatic furan structures and thus from specific organisms of origin such as lichens. However, studies of molecular clocks in lichens suggest that they first appeared in the Late Paleozoic (e.g. Nelsen et al., 2019). Our proposal is considerably older than that discussion and needs to be considered.
In this study, we analyzed the organic matter in the shaley mudstone of the Qaanaaq Formation, Baffin Bay Group, distributed in northwestern Greenland, using GC-MS. The Qaanaaq Formation is composed of sand-dominated sand and mud alternations, and previous studies suggest that it is regarded as dep an alluvial plain to marine shoreline deposit in the late Mesoproterozoic (Samuelsson et al., 1999; Dawes, 2006).
Although their distribution varied, several aromatic furans, which are oxygen-containing aromatic compounds, were detected in each sample. The origin of dibenzofurans, in particular, has been discussed in several ways, including lignin from higher plants and polysaccharides from terrestrial soils (Sephton et al., 2005; Fenton et al., 2007; Wang & Visscher, 2007), and secondary metabolites from lichens (Radke, 2000; Watson et al., 2005; Sawada et al., 2012). Fullana & Sidhu (2005) reported that dibenzofurans are produced from fluorene and biphenyl in catalytic combustion experiments. As a natural product, dibenzofurans have been reported as antimicrobial agents produced by higher plants (Kokubun et al., 1995; Dixon, 2001) in addition to the lichens. In this sample, the origin of higher plants can be dismissed among these theories, and Watanabe (2000) reported that dibenzofurans were produced from cellulose, lignin, and saccharide in heating experiments simulating aging in sediments, but dibenzofurans with alkyl groups were not produced. Therefore, we believe that the origin of polysaccharides is also unlikely. In addition, the distribution of isomers of alkyl dibenzofurans fluctuates each sample, suggesting that they may be derived from compounds that originally have aromatic furan structures and thus from specific organisms of origin such as lichens. However, studies of molecular clocks in lichens suggest that they first appeared in the Late Paleozoic (e.g. Nelsen et al., 2019). Our proposal is considerably older than that discussion and needs to be considered.