ABSTRACT

Carbonaceous matter (CM) in silica veins contained in the ~3.5 billion-year-old (Ga) Dresser Formation, Western Australia, can offer insights into biological activity in Earth’s oldest seafloor hydrothermal deposits, although a biological origin for this material remains debated. Herein, CM from Dresser hydrothermal vein deposits was analyzed using carbon X-ray absorption near edge structure (C-XANES) and Raman microspectroscopy. The CM is mainly composed of disordered aromatic structures, potentially containing minor aliphatic/ketonic/phenolic and carboxylic groups. These characteristics resemble those of biogenic Phanerozoic kerogen with high maturation, CM from the ~2.7 Ga Tumbiana Formation and the ~3.5 Ga Mount Ada Basalt in the Pilbara Craton, and abiotically synthesized graphite, but differ from those of CM produced via Fischer-Tropsch-type synthesis. Our observations indicate the presence of heteroatoms (hydrogen and possibly oxygen); however, the observed C-XANES spectra can be explained by either biotically or abiotically produced organic matter at this stage.