Abstract In 1970, the National Committee for Geological Sciences accepted in principle the ISSC recommendations for stratigraphic classification and a South African Committee for Stratigraphy (SACS) was appointed. A local code was published in 1971 and, through working groups, SACS has revised and completely reclassified the South African stratigraphic column. The former and the revised principal stratigraphic subdivisions are presented in tables. The principal lithostratigraphic units in the main Precambrian basins of deposition are being termed supergroups, groups, and sequences; the former Swaziland, Witwatersrand, and Ventersdorp Systems" are now Supergroups; the Pongola, Dominion Reef, and Waterberg "Systems are Groups; and the Transvaal System" is now the Transvaal and Griqualand-West sequences with component groups. The term Bushveld Complex replaces Bushveld Igneous Complex. The Gariep and Nosib Groups (formerly "Systems") have been placed in the Damara Supergroup. The Nama "System" which spans the Precambrian-Phanerozoic boundary has become a Group; its counterpart in the southwestern Cape Province, which is intruded by the Cape Granite, is now termed the Malmesbury Group. For the Phanerozoic, SACS decided that the Cape "System" becomes the Cape Supergroup and the Karoo "System" a sequence. In the Cape Supergroup the major units are now termed the Table Mountain, Bokkeveld, and Witteberg Groups. In the Karoo sequence, the Dwyka Tillite Formation forms the base followed by the Ecca, Beaufort, and Drakensberg Groups. The widespread dolerites intrusive into the Karoo are still collectively referred to as Karoo Dolerites. In the Jurassic-Cretaceous, the term Beds has been abandoned and Suurberg, Uitenhage, and Zululand Groups are defined. The problem of subdividing the Precambrian chronostratigraphically is discussed. In South Africa there are unrivalled, relatively undisturbed, and only slightly metamorphosed Precambrian successions that cover, with only minor hiatuses, the time span from 3,750 m.y. to the Phanerozoic. A wide span of reliable radiometric age determinations, and absence of major facies changes, has led to their formal subdivision into the following erathems: Swazian (3,750+ to 2,870 m.y.), Randian (2,870 to 2,630 m.y.), Vaalian (2,630 to 2,070 m.y.), Mogolian (2,070 to 1,080 m.y.) and Namibian (1,080 to 570 m.y.).

Abstract Crustal heterogeneity is considered to play a critical role in the position of continental break-up, yet this can only be demonstrated when a fully constrained pre-break-up configuration of both conjugate margins is achievable. Limitations in our understanding of the pre-break-up crustal structure in the offshore region of many margins preclude this. In the southern South Atlantic, which is an archetypal conjugate margin, this can be achieved because of the high confidence in plate reconstruction. Prior to addressing the role of crustal heterogeneity, two questions have to be addressed: first, what is the location of the regionally extensive Gondwanan Orogeny that remains enigmatic in the Orange Basin, offshore South Africa; and, second, although it has been established that the Argentinian Colorado rift basin has an east–west trend perpendicular to the Orange Basin and Atlantic spreading, where is the western continuation of this east–west trend? We present here a revised structural model for the southern South Atlantic by identifying the South African fold belt offshore. The fold belt trend changes from north–south to east–west offshore and correlates directly with the restored Colorado Basin. The Colorado–Orange rifts form a tripartite system with the Namibian Gariep Belt, which we call the Garies Triple Junction. All three rift branches were active during the break-up of Gondwana, but during the Atlantic rift phase the Colorado Basin failed while the other two branches continued to rift, defining the present day location of the South Atlantic. In addressing these two outstanding questions, this study challenges the premise that crustal heterogeneity controls the position of continental break-up because seafloor spreading demonstrably cross-cuts the pre-existing crustal heterogeneity. Furthermore, we highlight the importance of differentiating between early rift evolution and subsequent rifting that occurs immediately prior to seafloor spreading.

Abstract The Taylor Group, the lower division of the Beacon Supergroup, comprises mainly quartzose sandstones of Devonian age deposited after the development of the Kukri Erosion Surface across the Cambrian Ross orogen. Devonian sediments accumulated in a McMurdo Basin that now incorporates most of the Transantarctic Mountains, and a larger Ellsworth Basin that extends from West Antarctica into southern Africa. In southern Victoria Land (McMurdo Basin) the seven formations total around 1200 m in thickness. Sequence stratigraphy suggests five sedimentary cycles, the lower four of which may show shallow marine influence. Provenance studies indicate derivation solely from Ross Orogen sources. The Taylor Group in the central Transantarctic Mountains consists of two thin formations, only one of which is extensive. In the Ellsworth Basin, Taylor Group equivalents rest concordantly on thick piles of post-Ross Palaeozoic sediment. Shallow-water Devonian sediments in the Ohio Range contain a marine fauna linked with those of the Ellsworth Mountains, southern Africa, South America, New Zealand and Australia. A seaway probably existed along the Pacific edge of the East Antarctic craton, allowing these faunal links, and may also have communicated with the McMurdo Basin to drive the five sedimentary sequences.