Titel: Sequence stratigraphy of the Moodies Group (3.2 Ga), Barberton Greenstone Belt, South Africa
Deon J. Janse van Rensburg, Christoph Heubeck, Sebastian Reimann
Friedrich Schiller Universität Jena, Germany
Veranstaltung: GeoKarlsruhe 2021
The Moodies Group (~3.2 Ga) of the Barberton Greenstone Belt is one of the oldest and best-preserved shallow-water siliciclastic sequences. It also harbors one of the largest occurrences of Paleoarchean microbial mats and the oldest record of early Earth-Moon dynamics. The extent (ca. 40 km * 70 km), lithologic and alluvial-to-prodeltaic facies diversity (incl. paleosols, pedogenic concretions and microbial mats etc.) , good outcrop, and excellent preservation of Moodies strata allows the recognition of mappable systems tracts and sequence-stratigraphic surfaces. However, the lack of biostratigraphic constraints and the nonactualistic Archean surface conditions (absence of vegetation, aggressive chemical weathering, oceanic composition and temperatures, climate, tides) challenge the applicability of sequence-stratigraphic concepts. Well-studied Moodies strata north of the Inyoka Fault zone can be readily subdivided into several 3rd-order parasequence sets. Lower Moodies strata are characterized by an overall increase in accommodation space relative to sediment supply and comparative tectonic quiescence, whereas upper Moodies strata (above a basinwide volcanic unit) record an overfilled basin. Much less is known about the Moodies south of the Inyoka fault zone where the Masenjane Range exposes a section 600-2000 m thick of largely northeastward-prograding, coastal, deltaic and estuarine strata. They record at least five 4th-order shoaling-upward parasequences. Stacking patterns, paleocurrents and provenance indicators show an overall northeastward progradation of facies, likely controlled by local tectonothermal drivers, as evidenced by several syndepositional shallow sills, stockworks, and syndepositional normal faults. These may have been regionally related to the tightening and rotation of the Onverwacht Anticline and the formation of other paleogeographic features.
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