Aspects of the Revised South African Stratigraphic Classification and a Proposal for the Chronostratigraphic Subdivision of the Precambrian
Published:January 01, 1978
L. E. Kent, P. J. Hugo, 1978. "Aspects of the Revised South African Stratigraphic Classification and a Proposal for the Chronostratigraphic Subdivision of the Precambrian", Contributions to the Geologic Time Scale, George V. Cohee, Martin F. Glaessner, Hollis D. Hedberg
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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.).
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Contributions to the Geologic Time Scale
Containing papers given at the Geological Time Scale Symposium in 1976, this volume begins with a review of dating and correlation, and includes papers on the topics of: geochronoloic scales, biochronology, the magnetic polarity time scale, the potassium-argon isotopic dating method, isotopic methods, and worldwide Permian chronostratigraphy, among others.