CENTIMETER-SCALE ALTERNATION WITHIN A LATE ARCHAEAN CARBONATE PLATFORM: USING STRATIGRAPHIC ANALYSES TO INTERPRET PALEOENVIRONMENTAL VARIATION

Understanding the vertical structure of ocean oxygenation prior to the Great Oxygenation Event (~2.4 Ga) is critical to decipher the environmental impacts of the GOE, and requires accurate determination of depositional environments and their relationship to water depth. Here we explore late Archaean strata of the Transvaal Supergroup and show remarkable similarity in bedding thickness, sedimentation patterns, and microbially-influence in carbonate fabrics from inferred shallow- to deep-water facies that have previously been interpreted to reflect depositional environments that differed in water depth by more than 500m.

In this study, we use high-resolution analysis of cm-scale stratigraphy in inferred “platform” and “basin” facies to place more precise constraint on environments of deposition, and to develop a refined paleoenvironmental model of this Archaean carbonate platform. Detailed, cm-scale measurements and photographic documentation of the strata in “platform” facies of the Reivilo Formation and “basin” facies of the Nauga Formation were used to construct detailed stratigraphic columns. Statistical analysis was then used to explore our ability to reconstruct fine-scale facies changes, estimate the similarity of strata behavior in different sections, and to assess the potential controls on repetitive bedding alternations. Additionally, modified Fischer plots were utilized to assess changes in accommodation through time and evaluate contribution of depositional components to couplet thickness. Initial results show that patterns within cm-scale bedding can be readily identified and are consistent across multiple stratigraphic sections. Despite past interpretation of facies that range shallow to deep-water environments, these patterns reveal a striking similarity between localities, and, ultimately, these observations may necessitate rethinking of depositional environments exposed in the Transvaal Supergroup.