Drilling Earth's early surface environments: Moodies Group, Barberton Greenstone Belt, South Africa

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Continuous coring by scientific drilling in volcanic and sedimentary units of greenstone belts has the potential to obtain new insights in Earth's earliest surface environments due to access to fresh lithologies and textures. Such a proposal has been submitted to ESF funding agencies (Arndt et al.) and has been submitted to IGCP in January, 2008. The current proposal aims to contribute to that objective by identifying potential drill sites and prepare predictive stratigraphic profiles for the Moodies Group of the Barberton Greenstone Belt (ca. 3.22-73.20 Ga), the world's oldest well-preserved quartzose and shallow-water sedimentary sequence. Although the overall degree of metamorphism in the Moodies Group is low, multiple regional alteration events following its deposition, deep burial, Cretaceous exhumation and weathering have affected its deep and near-surface composition and texture. Thus, only samples free from surface effects will help to distinguish between primary, diagenetic and weathering effects. Scientific issues to be clarified by the proposed drilling include the identification of datable ash-fall tuffs, the petrographic and geochemical characterization of weathering-sensitive lithologies and the clarification of the tectonic setting of the Moodies Group by verifying a progressive unconformity near its top. These data will bear on the reconstruction of Archean (and prediction of extraterrestrial) surface conditions and processes such as the intensity of chemical weathering, the role of bacterial mats, and early diagenesis.