Sequence stratigraphy of the Precambrian Rooihoogte–Timeball Hill rift succession, Transvaal Basin, South Africa

Abstract

Third-order sequence stratigraphic analysis is performed on the Rooihoogte–Timeball Hill second-order rift succession of the Paleoproterozoic Transvaal Basin, South Africa. This provides a case study for systems tract and sequence development during a time of glacio-eustatic fall, when accommodation was generated by subsidence related to syn-rift and post-rift tectonic processes. Two third-order depositional sequences have been identified, separated by a basin-wide subaerial unconformity. The lower third-order sequence includes the complete succession of lowstand, transgressive, and highstand systems tracts (LST, TST, and HST), whereas the upper third-order sequence only preserves lowstand and transgressive systems tracts. This indicates that the fall in base level associated with the upper second-order boundary of the Rooihoogte–Timeball Hill sequence was of higher magnitude relative to the third-order subaerial unconformity, which is in agreement with the principles of boundary hierarchy based on the magnitude of base-level changes. The position of the lower boundary of the Rooihoogte–Timeball Hill second-order sequence has been revised from the base of the chert breccias to the contact between the breccias and the overlying chert conglomerates. This is because a major tilting event occurred between the deposition of the two facies, which are genetically unrelated, and which are separated by a subaerial unconformity. The lithostratigraphic contact between the Rooihoogte and Timeball Hill formations is interpreted as a diachronous transgressive surface of erosion. In this interpretation, the Polo Ground Member of the Rooihoogte Formation may be coeval with the basal black shales of the Timeball Hill Formation, the two facies (fluvial and marine, respectively) forming together a transgressive systems tract.