Permo-Triassic Lacustrine Deposits in the Eastern Karoo Basin, Natal, South Africa

  1. Albert Matter and
  2. Maurice E. Tucker
  1. D. E. van Dijk,
  2. D. K. Hobday and
  3. A. J. Tankard

Published Online: 29 JUN 2009

DOI: 10.1002/9781444303698.ch12

Modern and Ancient Lake Sediments

Modern and Ancient Lake Sediments

How to Cite

van Dijk, D. E., Hobday, D. K. and Tankard, A. J. (1978) Permo-Triassic Lacustrine Deposits in the Eastern Karoo Basin, Natal, South Africa, in Modern and Ancient Lake Sediments (eds A. Matter and M. E. Tucker), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444303698.ch12

Author Information

  1. Department of Zoology and Department of Geology, University of Natal, Pietermaritzburg, South Africa 3200, South African Museum, Cape Town, South Africa 8000

  1. Bureau of Economic Geology, University of Texas at Austin, Austin, Texas 78712, USA

Publication History

  1. Published Online: 29 JUN 2009
  2. Published Print: 24 NOV 1978

ISBN Information

Print ISBN: 9780632002344

Online ISBN: 9781444303698



  • diachronous relationship between Ecca and Beaufort Groups;
  • The Clarens Formation (Cave sedimentation);
  • Trace fossils- paired arthropod tracks, burrows and trails of sediment-ingesting organisms;
  • Permo-Triassic lacustrine deposits;
  • substrate- highly reducing, with plant decay generating anaerobic conditions.favouring the formation of pyrite


Beaufort strata of the eastern Karoo Basin contain a classic lacustrine assemblage of freshwater fish, amphibians, reptiles, therapsids, crustaceans, insects and plants. The basin was subject to sediment influx from the south and east, with a subordinate contribution from the north. Maximum water depth was about 150 m. Fine-grained sediments settled over wide areas of the lake floor and were reworked by organisms. A predominantly massive lacustrine siltstone facies contains occasional complete skeletons of reptiles. A complex, shifting pattern of fluvio-deltaic progradation produced a highly irregular shoreline characterized by broad, open embayments, with smaller isolated ponds on the coastal plain. Lake shore encroachment generated upward-coarsening sequences with wave ripples, coprolites and fish trails in the silty lower part and traction-current structures in the sandstone above. Coarse-grained sediments were concentrated as mouth bars, distributary channel fills and overbank splays. Thin, upward-coarsening bay-fill sequences contain a great variety of fossils. Three bay-fill subtypes are recognized. One shows a gradual upward increase in grain size into fine-grained silty sandstones and is attributed to overbank flooding. The second contains erosively-based, lenticular crevasse-splay sandstones near the top, while the third was sediment-starved and has a high organic content.

The lakes were eventually infilled by northward-prograding fluvial systems, and fluvial sedimentation finally ceased with the onset of arid conditions. Arid conditions also characterized the later Stormberg environment of dunefields, playa lakes and ephemeral streams. Typically the playa lake deposits show shallow water and emergence structures, together with intercalated evaporites. These lakes were a favourable habitat for dinosaurs, and ten different types of vertebrate footprints are present, including quadrupedal and bipedal walking tracks and bipedal hopping prints. Karoo sedimentation was terminated by widespread Jurassic volcanism.