FTIR microspectroscopy of carbonaceous matter in ~ 3.5 Ga seafloor hydrothermal deposits in the North Pole area, Western Australia

Abstract

Carbonaceous matter in~3.5 Ga hydrothermal vein deposits from the Dresser Formation, Western Australia, was analyzed using Fourier transform infrared (FTIR) microspectroscopy. Based on the spectroscopy, the carbonaceous matter was mainly composed of disordered aromatic structures, with minor aliphatic C-H functional groups. Spatially resolved analysis supports that the aliphatic C-H signatures are derived from kerogenous macromolecule and not from free bitumen or other artificial sources. The intensity ratios of the asymmetric aliphatic CH 3 to the asymmetric aliphatic CH 2 (R 3/2 value) in the carbonaceous clots range from 0.22 to 0.51. Thermal alteration may increase or not change the R 3/2 value of organic matter, as suggested by previous experiments, but it is unlikely to be the cause of the substantially lower R 3/2 values when compared with those of primary organic matter. In particular, the low R 3/2 values (<~0.4) suggest that the carbonaceous matter mainly contains aliphatic C-H bonds derived from bacterial cells. The carbonaceous clots may have been possibly produced by abiotic reaction such as Fischer-Tropsch-type (FTT) synthesis. However, the organic matter source only produced by the FTT synthesis is inconsistent with the R 3/2 values for the analyzed carbonaceous clots. The results obtained by combining these spectroscopic features of the carbonaceous clots together with the previously reported isotopic features may possibly suggest that both bacteria and archaea were colonized in thẽ 3.5 Ga Dresser hydrothermal system.

Diverse communities of Bacteria and Archaea flourished in Palaeoarchaean (3.5–3.3 Ga) microbial mats

“…(2015) and Igisu et al . (2009, 2018). Numerous peaks within the 1400–2000 cm −1 range are interpreted as Si–O (Igisu et al .…”

“…Igisu et al . 2009, 2018; this study) is an in situ IR approach that mitigates the potential contamination by volatile hydrocarbons in laboratory air inherent to studies of powdered samples (e.g. Derenne et al .…”

“…2017), however, studies on older palaeontological materials of higher metamorphic grade (Igisu et al . 2006, 2009, 2018) have also yielded informative palaeobiological datasets unavailable through other vibrational spectroscopy approaches.…”

“…(2005) and Igisu et al . (2006, 2009, 2012, 2018), can distinguish the nature of precursor membrane lipids. As noted above, the composition of membrane lipids is considered the most fundamental distinction between extant Archaea and Bacteria (Albers & Meyer 2011).…”

“…2012; Olcott Marshall & Marshall 2015) even through low‐grade metamorphism (Igisu et al . 2018). Naturally matured kerogens have been shown to undergo only a small initial change in aliphatic compositions due to scission of the C–C bond adjacent to aromatic moieties (Lin & Ritz 1993; Lis et al .…”