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Stratigraphy and Basin Analysis of the Mesoarchaean West Rand Group, Witwatersrand Supergroup, South Africa

The Mesoarchaean West Rand Group displays a layer-cake stratigraphy with lithostratigraphic units correlatable on a basin-wide scale. The ~5 km thick succession consists of fluvial braidplain and shelf deposits, which range from shallow inner shelf marine orthoquartzites, outer shelf argillites to starved shelf iron-formations. Three major sequences are present: Sequence I (Hospital Hill Subgroup), Sequence II (Government Subgroup) and Sequence III (Jeppestown Subgroup).

Sequence I was deposited during a period of highstand of sea-level, sequence II during a period of relative lowstand, and sequence III during a period of relative highstand coupled with high rates of sediment supply. Isopach, depofacies and palaeocurrent analyses indicate that strata in the western to northwestern parts of the basin were deposited under more proximal sedimentary conditions compared to those in the central or southeastern parts. Little relationship between the present outline of the basin and the distribution of depofacies suggests that the original sedimentary basin was significantly larger in areal extent.

Depofacies and thickness distribution, as well as synsedimentary deformation of strata, indicate that the basin was most probably of flexural tectonic origin. These findings support deposition in a wide, shallow, and rather stationary foreland basin, with an axial zone towards the west/northwest and low amplitude peripheral bulge to the east/southeast. Such shallow foreland basins, with abundant sediment bypassing, are thought to be associated with windward-facing orogenic fronts. High rates of erosion along such fold-thrust belts lead to ineffective loading and advancement of the orogenic front, as well as an oversupply of sediment.

Details

Author
Nicolas Johannes Beukes1, Bradley Martin Guy2, Sam Thiele3
Institutionen
1PPM Research Group, Department of Geology, University of Johannesburg, South Africa; 2PPM Research Group, Department of Geology, University of Johannesburg, South Africa;Helmholtz Institute Freiberg for Resource Technology, Helmholtz-Zentrum Dresden-Rossendorf, Germany; 3Helmholtz Institute Freiberg for Resource Technology, Helmholtz-Zentrum Dresden-Rossendorf, Germany
Veranstaltung
GeoSaxonia 2024
Datum
2024
DOI
10.48380/6dqd-5n45