Lystrosaurus Assemblage Zone

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Lystrosaurus Assemblage Zone
Ma
↓
Karoo Basin
Type section
Named forLystrosaurus
Named byRobert Broom
Year defined1906, 1909

The Lystrosaurus Assemblage Zone is a

Queenstown, Aliwal North, Nieu-Bethesda) and in the southern and northeastern Free State (Bethulie, Gariep Dam, Mthatha, Harrismith). The Lystrosaurus Assemblage Zone is one of eight biozones found in the Beaufort Group, and is considered to be Early Triassic in age.[1][2]

The name of the biozone refers to

therapsid. It is characterized by the appearance of further Lystrosaurus subspecies which are confined to this biozone.[3] Lystrosaurus maccaigi and Lystrosaurus curvatus are the only two species found outside the Lystrosaurus Assemblage Zone in Upper Permian deposits of the underlying Daptocephalus Assemblage Zone.[4][5]

History

The first fossils to be found in the Beaufort Group rocks that encompass the current eight biozones were discovered by Andrew Geddes Bain in 1856.[6] However, it was not until 1892 that it was observed that the geological strata of the Beaufort Group could be differentiated based on their fossil taxa. The initial undertaking was done by Harry Govier Seeley who subdivided the Beaufort Group into three biozones,[7] which he named (from oldest to youngest):

  • Zone of "
    Pareiasaurians
    "
  • Zone of "
    Dicynodonts
    "
  • Zone of "highly specialized group of
    theriodonts
    "

These proposed biozones Seeley named were subdivided further by Robert Broom between 1906 and 1909.[8] Broom proposed the following biozones (from oldest to youngest):

These biozone divisions were approved by paleontologists of the time and were left largely unchanged for several decades.[9] The Lystrosaurus Assemblage Zone was first named by Robert Broom in 1906.[10] Initially Broom had subdivided the existing Lystrosaurus zone into the Lystrosaurus and Procolophon Assemblage Zones respectively. The biozone was later revised in 1976 by James Kitching where Kitching assimilated the Procolophon zone into the Lystrosaurus zone due to discovering that fossils of the small parareptile Procolophon were likewise found throughout the Lystrosaurus zone.[11][12]

Lithology

The Lystrosaurus Assemblage Zone ranges from the Palingkloof Member of the upper Balfour Formation west of 24°E. It comprises the entire Katberg Formation and the first third of the Burgersdorp Formation east of 24°E.[13] The Balfour Formation is located within the Adelaide Subgroup, while the Katberg and Burgersdorp are within the Tarkastad Subgroup of the Beaufort Group. Its contact with the underlying Daptocephalus Assemblage Zone marks the Permian-Triassic boundary.[14][15]

The boundary is defined by a change in the

pedogenic nodules and intrabasinal clasts are also found.[25][26]

Paleontology

There is a marked drop in

arid climate before their remains were buried by floods
.

The

ray-finned fish Caruichthys[50]
was also found in layers of this biozone.

Age and correlations

The Lystrosaurus Assemblage Zone dates to approximately 251 to 249 Ma, and correlates with the Kopanskaya and Staritskaya Formations of Russia,[51] and with the Jiucaiyuan Formation of China, the Knocklofty and Arcadia Formations of Australia, the Buena Vista Formation of the Paraná Basin, South America, and the Panchet Formation of India.[52]

See also

References

  1. ^ Keyser, A. W., & Smith, R. M. H. (1978). Vertebrate biozonation of the Beaufort Group with special reference to the western Karoo Basin. Geological Survey, Department of Mineral And Energy Affairs, Republic of South Africa.
  2. ^ Rubidge, B. S. (ed.) 1995b. Biostratigraphy of the Beaufort Group (Karoo Supergroup). South African Committee of Stratigraphy. Biostratigraphic Series 1. Pretoria, Council for Geoscience.
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  10. ^ Broom, R. (1906). V.—On the Permian and Triassic Faunas of South Africa. Geological Magazine, 3(1), 29-30.
  11. ^ Kitching, J. W. (1977). The distribution of the karroo vertebrate fauna: with special reference to certain genera and the bearing of this distribution on the zoning of the Beaufort Beds, Bernard Price Institute for Palaeontological Research, University of the Witwatersrand.
  12. ^ Kitching, J. W. (1984). A reassessment of the biozonation of the Beaufort Group. Paleo News, 4(1), 12-13.
  13. ^ Rubidge, B. S. (ed.) 1995b. Biostratigraphy of the Beaufort Group (Karoo Supergroup). South African Committee of Stratigraphy. Biostratigraphic Series 1. Pretoria, Council for Geoscience.
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  22. ^ Smith, R., Rubidge, B., & Van der Walt, M. (2012). Therapsid biodiversity patterns and paleoenvironments of the Karoo Basin, South Africa. Forerunners of Mammals: Radiation, Histology, Biology. Indiana University Press, Indianapolis, Indiana, 30-62.
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  39. ^ Day, Michael; Abdala, Fernando; Golubev, Valeriy; Sennikov, Andrey; Rubidge, Bruce (2017-12-19). "New insights on the correlation of Permo-Triassic terrestrial faunas of South Africa with those of European Russia". ResearchGate.
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  50. ^ Broom, Robert (1913). "On some fishes from the Lower and Middle Karroo, S. Africa". Annals of the South African Museum. 12: 1–5.
  51. ^ "Magnetostratigraphy - Background to stratigraphy across the PTB in Russia". Archived from the original on 2019-02-16. Retrieved 2019-03-15.
  52. ^ Ezcurra, 2016, p.8

Bibliography

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