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Sedimentological core and field study of the Fluvial-Marine Transition Zone preserved in the 3.2 Ga Moodies Group from the Barberton Greenstone Belt, South Africa

The ca. 3.22 Ga Paleoarchean Moodies Group in the Barberton Greenstone Belt (South Africa) represents one of the oldest shallow-marine quartzose sedimentary systems on Earth. Due to early silicification, sedimentary structures in the 3.7 km thick succession are usually well-preserved, allowing a detailed analysis of environments and surface conditions during the development of early life on Earth. The Moodies Group was cored in the framework of International Continental Drilling Project (ICDP) “Barberton Archean Surface Environments” (BASE). Here, we focus on the fluvial-marine transition zone in the Moodies Group using outcrop data and cores recently extracted in the so-called Lomati Delta Complex (LDC, Sites 4A-C). To reveal the dominant sedimentary processes within this dynamic depositional environment, we present results from petrography and detailed sedimentological logging in cores and outcrops.

The LDC is a stratigraphic unit with a wedge-shaped geometry that is approximately 300 m thick at its thickest point and pinches out over a distance of 7 km. The deposits consist of cross-bedded siliciclastic coarse-grained sandstones and conglomerates that transition into finer-grained and tuffaceous sandstones. Sedimentary structures include tangential and tabular cross bedding, desiccation cracks, conglomeratic beds, rare microbial mats, and soft-sediment deformation related to fluid escapes. Based on these features, the LDC has been interpreted as a fluvial-marine system with highly variable energy conditions, likely linked to the ephemerality of local rivers. This analysis provides the sedimentological context for follow-up geochemical and stratigraphic work, aiming at a detailed reconstruction of Paleoarchean environmental dynamics and conditions under which early life spread.

Details

Author
Dennis J. Schreiber1, David De Vleeschouwer2, Christoph Heubeck3, Nina M.A. Wichern2, Marcello Gugliotta1
Institutionen
1Institute of Geosciences and Geography, Martin Luther University Halle-Wittenberg, Halle, Germany; 2Institute of Geology and Paleontology, University of Münster, Germany; 3Department of Geosciences, Friedrich-Schiller-Universität Jena, Germany
Veranstaltung
GeoSaxonia 2024
Datum
2024
DOI
10.48380/jvrj-f443