A new interpretation of soft-sediment deformation features (SSDs) in the Parktown Formation (lower West Rand Group); the physical processes of deformation during deposition.

In the Parktown Formation of the lower West Rand Group (Witwatersrand Supergroup), remarkably well-preserved soft-sedimentary deformation features (SSDs) occur in a number of locations in three stratigraphic horizons across the Vredefort Mountainland and in key sites in Johannesburg. The SSDs were the inevitable products of static liquefaction during early deposition in the Witwatersrand Basin. The trigger to static liquefaction is interpreted to be autogenic and related to cyclic fluctuations in pore fluid pressure(s) during capped dewatering. Allogenic triggers are not indicated. We suggest that static liquefaction was an integral physical process to sediment deposition on the Parktown Formation offshore platform, but a process not previously recognised as important to the modification of the West Rand Group stratigraphy across the Witwatersrand Basin. [ABSTRACT FROM AUTHOR]