Puneet Varma (Editor)

Beaufort Group

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Joining the beaufort group


The Beaufort Group is the third of the main subdivisions of the Karoo Supergroup of geological strata in Southern Africa. It follows conformably after the Ecca Group and consists essentially of sandstones and shales, deposited in the Karoo Basin from the Middle Permian to the early part of the Middle Triassic periods.

Contents

In the Eastern Cape Province the Karoo Basin fill commenced with the deposition of the Dwyka Group, followed by the Ecca Group, the Beaufort Group, the Molteno, Elliot, and Clarens formations of the Stormberg Group and the igneous Drakensberg Group. The basin followed the typical evolution of foreland basins, with the Ecca Group representing the ‘flysch’ component and the Beaufort Group, the overlying Molteno and Elliot Formations representing the ‘molasse’-fluvial type sediments.

Deposits in this group include (in order of deposition):

  • Lower Adelaide Subgroup comprising:
  • Koonap Formation: Transitional brackish lacustrine to fluvial. Greenish-grey sandstones grading upwards into fine-grained siltstones and mudstones.
  • Middleton Formation: Semi-arid climate supported a lush flora and fauna that thrived along meander belts and semi-permanent lakes. Cyclic deposits of lenticular sandstone bodies grading into greenish-grey mudstone. The thickest formation in this succession, constituting 37% of the Beaufort Group and 47% of the Adelaide Subgroup. The formation has lenses of red mudstone which are likely to have been deposited in a sub-aerial fluvial environment.
  • Balfour Formation: The upper part of the Adelaide Subgroup and part of what was called lower to middle Beaufort.
  • Upper Tarkastad Subgroup comprising:
  • Katberg Formation: Arenaceous deposits of red and olive-yellow mudstones. Deposited in a braided fluvial system.
  • Burgersdorp Formation: Deposited in a low-sinuosity fluvial system.

    • Growing the beaufort group


    Paleontology

    Fossils of tetrapods, especially therapsids, are common, and the vertebrate biostratigraphy has been mapped out in detail, beginning with the work of Robert Broom at the start of the 20th century and developed and revised a number of times since. Currently eight faunal zones are recognised, tracing the development of terrestrial life through the Permo-Triassic, and named after a characteristic genus that serves as an index fossil.

    In order the assemblage zones are:

  • Cynognathus Assemblage Zone (Youngest)
  • Lystrosaurus Assemblage Zone
  • Dicynodon Assemblage Zone
  • Cistecephalus Assemblage Zone
  • Tropidostoma Assemblage Zone
  • Pristerognathus Assemblage Zone
  • Tapinocephalus Assemblage Zone
  • Eodicynodon Assemblage Zone (Oldest)

    • The Beaufort Group deposits also yield numerous plant and insect fossils.

    References

    Beaufort Group Wikipedia
    (Text) CC BY-SA