3.4 Ga biostructures from the Barberton greenstone belt of South Africa: New insights into microbial life

Raman spectroscopy is a molecule-specific technique allowing the investigation of the chemical structure of organic and inorganic geological materials. Being a nobiostructures from the Barberton greenstone belt of South An-invasive analytical procedure, Raman spectroscopy is ideally suited to palaeontology. Raman spectroscopy is herein applied to the study of carbonaceous chert facies of the ~3.4 Ga old Buck Reef Chert of South Africa, which contains some of the oldest well-preserved evidence of early life. Laminated chert typically consists of microbands composed of microcrystalline quartz (chert) and an association of siderite and carbonaceous material (CM) in the form of mat-like laminations, simple carbonaceous grains, vein infills and diffuse CM. Using Raman spectroscopy, the structural characteristics of CM in mat-rich chert were investigated and compared with CM-rich grains from the same unit, which were deposited as layers that bear no evidence for mat construction. All CM retains a structural organisation consistent with the lower greenschist grade regional metamorphic imprint, however, a detailed study of the Raman signal of CM revealed some heterogeneity between different sedimentary facies, indicating the presence of different types of CM. Multiple CM precursors are indicated and may reflect different sources or different alteration chemistries of various microbial metabolic pathways.