Depositional setting and metabolism of microbial mats in the Archean Moodies Group, Barberton Greenstone Belt, South Africa
Year: 2015
Type: dissertation
Abstract: The Archean eon encompasses about one-third of Earth’s history. During its 1.5 Ga time span, most of the principal biochemical pathways had evolved, including cyanobacterial oxygenic photosynthesis, which keeps dominating the modern biosphere. Biological oxygen production provided the physiological base for the expansion of life, particularly the evolution of complex multicellular organisms. However, the antiquity and origin of oxygenic photosynthesis is vigorously debated. Hence, the study of Earth’s oldest well-preserved microbial mats and their paleoenvironmental setting has the potential to unravel earliest evolution photosynthesis. An ideal place to tackle this issue is the Paleoarchean (~3.22 Ga) Moodies Group of the Barberton Greenstone Belt, South Africa, which contains widespread remains of remarkably well-preserved microbial mats and sedimentary structures in shallow-water sandstones. In the Saddleback Syncline of the central BGB, kerogenous laminae representing fossilized microbial mats occur abundantly in a ~1000-m-thick succession of fine- to coarse-grained sandstones and conglomerates, which can be traced laterally for >15 km. Microbial mats were thriving in coastal floodplain, inter-, and supratidal paleoenvironments. In situ δ13C PDB measurements of the kerogen range from -32.3‰ to -21.3‰ and are consistent with a biogenic origin. The exclusive occurrence of mats in shallow-water, high-energy setting, and their tufted micro-morphology suggest that they were photosynthetic and most likely build by ancestral cyanobacteria. However, the ultimate question whether the microbes were producing free oxygen or not still needs to be resolved. The identification of cavity-dwelling microbial communities beneath these microbial mats, has extended the geological record of coelobionts by ~500 Ma, while the occurrence of microbial mats in fluvial-alluvial conglomerates and sandstones extends the record of terrestrial life by ~400 Ma.
Author: Homann, Martin
Language: English
Subfield: Paleontology
Field: Earth and Planetary Sciences
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W2339443362