Middleton Formation

The Middleton Formation is a geological formation that extends through the Northern Cape, Western Cape, and Eastern Cape provinces of South Africa. It overlies the lower Abrahamskraal Formation, and is the eastern correlate, East of 24ºE, of the Teekloof Formation. Outcrops and exposures of the Middleton Formation range from Graaff-Reinet in the Eastern Cape onwards. The Middleton Formation's type locality lies near the small hamlet, Middleton, approximately 25 km south of Cookhouse. Other exposures lie in hillsides along the Great Fish River in the Eastern Cape. The Middleton Formation forms part of the Adelaide Subgroup of the Beaufort Group, which itself forms part of the Karoo Supergroup.[1][2][3][4]

Middleton Formation
Stratigraphic range: Middle Permian
~265–256 Ma
Middleton Formation exposures are found in the Eastern Cape of South Africa
TypeGeological formation
Unit ofAdelaide Subgroup, Beaufort Group
UnderliesBalfour Formation
OverliesAbrahamskraal Formation
Thicknessup to 300 m (980 ft)
Lithology
PrimaryMudstone, siltstone
OtherSandstone
Location
Coordinates32.949°S 25.816°E / -32.949; 25.816
RegionEastern Cape
Country South Africa

Geology

The Middleton Formation is the eastern correlate of the Teekloof Formation. Both these formations overlie the Abrahamskraal Formation. The upper Middleton Formation correlates with eastern exposures of the uppermost Pristerognathus Assemblage Zone, and is late Middle Permian (Guadalupian) in age. Current thought posits that the eruption of the Emeishan Large Igneous Province caused the middle Permian (end-Guadalupian) extinction event, during which the Middleton Formation rocks formed.[5][6]

The Middleton Formation, like the underlying Abrahamskraal Formation, is rich in mudstone. However, the mudstones are notably redder in colour in the Middleton formation than in the Abrahamskraal Formation. The Middleton mudstones contain wave-and current-ripples, as well as calcareous nodules, which weather out brown. Minor sandstones, containing argillaceous layers, interspace the mudstones. These sandstone layers are important stratigraphic markers for geologists and paleontologists.[7][8] The mudstones were deposited in a shallow, low-energy, freshwater lacustrine environment. Observation of the sandstones reveals that high-energy fluvial events infrequently disturbed this low-energy depositional environment. These disturbances are associated with extensive argillaceous overbank deposits. The argillaceous sandstone deposits contain many trace fossils of invertebrates, suggesting that the deposits were nutrient-rich.[9][10][11][12]

Paleontology

The Middleton Formation does not contain as many fossils as its western correlate, the Teekloof Formation. This is particularly true of vertebrate fossils. The end-Guadalupian extinction event caused a drop in species diversity in the Middleton Formation compared to the Abrahamskraal Formation. However, vertebrate fossils yielded from the Middleton Formation are the same as those associated with the Pristerognathus Assemblage Zone.[13][14][15] When found, vertebrate fossils appear most frequently in the mudstone and calcareous nodule deposits.

Trace fossils are more commonly found in this formation than vertebrate fossils. These trace fossils lie in the sandstones and include preserved burrows, track ways, feeding trails and other evidence of shallow-water-dwelling invertebrates. The invertebrates include annelids, aquatic oligochaetes, nematodes, insect larvae, and planolites. The formation's trace fossils also offer evidence for the presence of the bony fishes Namaichthys and Atherstonia.[16]

References
  1. 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.
  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.
  3. Bordy, Emese M.; Linkermann, Sean; Prevec, Rose (2011-10-01). "Palaeoecological aspects of some invertebrate trace fossils from the mid- to Upper Permian Middleton Formation (Adelaide Subgroup, Beaufort Group, Karoo Supergroup), Eastern Cape, South Africa". Journal of African Earth Sciences. 61 (3): 238–244. doi:10.1016/j.jafrearsci.2011.06.002. ISSN 1464-343X.
  4. Day, Michael Oliver (2014-03-04). Middle Permian continental biodiversity changes as reflected in the Beaufort Group of South Africa: a bio-and lithostratigraphic review of the Eodicynodon, Tapinocephalus and Pristerognathus assemblage zones (Thesis thesis).
  5. Sami, K. (1992-11-01). "Recharge mechanisms and geochemical processes in a semi-arid sedimentary basin, Eastern Cape, South Africa". Journal of Hydrology. 139 (1): 27–48. doi:10.1016/0022-1694(92)90193-Y. ISSN 0022-1694.
  6. Day, M.O., Ramezani, J., Bowring, S.A., Sadler, P.M., Erwin, D.H., Abdala, F. and Rubidge, B.S. (2015-02-22). "When and how did the terrestrial mid-Permian mass extinction occur? Evidence from the tetrapod record of the Karoo Basin, South Africa". ResearchGate. Retrieved 2019-02-06.CS1 maint: multiple names: authors list (link)
  7. Keyser, A. W., and 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.
  8. Mason, Richard (2008-10-27). A bio- and litho- stratigraphic study of the Ecca-Beaufort contact in the southeastern Karoo basin (Albany District, Eastern Cape Province) (Thesis thesis).
  9. Catuneanu, Octavian; Bowker, Duncan (2001-01-01). "Sequence stratigraphy of the Koonap and Middleton fluvial formations in the Karoo foredeep South Africa". Journal of African Earth Sciences. African Renaissance and Geosciences. 33 (3): 579–595. doi:10.1016/S0899-5362(01)00095-1. ISSN 1464-343X.
  10. Catuneanu, Octavian; Elango, Henry N (2001-04-15). "Tectonic control on fluvial styles: the Balfour Formation of the Karoo Basin, South Africa". Sedimentary Geology. 140 (3): 291–313. doi:10.1016/S0037-0738(00)00190-1. ISSN 0037-0738.
  11. Rubidge, B. S.; Hancox, P. J.; Catuneanu, O. (1998-12-01). "Reciprocal flexural behaviour and contrasting stratigraphies: a new basin development model for the Karoo retroarc foreland system, South Africa". Basin Research. 10 (4): 417–439. doi:10.1046/j.1365-2117.1998.00078.x. ISSN 1365-2117. Archived from the original on 2018-09-17. Retrieved 2019-02-06.
  12. Day, Michael Oliver; Rubidge, Bruce Sidney (2014-12-01). "A brief lithostratigraphic review of the Abrahamskraal and Koonap formations of the Beaufort Group, South Africa: Towards a basin-wide stratigraphic scheme for the Middle Permian Karoo". Journal of African Earth Sciences. 100: 227–242. doi:10.1016/j.jafrearsci.2014.07.001. ISSN 1464-343X.
  13. Damiani, Ross J. (2004-01-01). "Temnospondyls from the Beaufort Group (Karoo Basin) of South Africa and Their Biostratigraphy". Gondwana Research. 7 (1): 165–173. doi:10.1016/S1342-937X(05)70315-4. ISSN 1342-937X.
  14. Modesto, Sean P.; Smith, Roger M. H.; Campione, Nicolás E.; Reisz, Robert R. (2011-12-01). "The last "pelycosaur": a varanopid synapsid from the Pristerognathus Assemblage Zone, Middle Permian of South Africa". Naturwissenschaften. 98 (12): 1027–1034. doi:10.1007/s00114-011-0856-2. ISSN 1432-1904. PMID 22009069.
  15. Cisneros, J.C., Abdala, F., Jashashvili, T., de Oliveira Bueno, A. and Dentzien-Dias, P. (2015-07-01). "Tiarajudens eccentricus and Anomocephalus africanus, two bizarre anomodonts (Synapsida, Therapsida) with dental occlusion from the Permian of Gondwana". ResearchGate. Retrieved 2019-02-06.CS1 maint: multiple names: authors list (link)
  16. Bordy, Emese M.; Linkermann, Sean; Prevec, Rose (2011-10-01). "Palaeoecological aspects of some invertebrate trace fossils from the mid- to Upper Permian Middleton Formation (Adelaide Subgroup, Beaufort Group, Karoo Supergroup), Eastern Cape, South Africa". Journal of African Earth Sciences. 61 (3): 238–244. doi:10.1016/j.jafrearsci.2011.06.002. ISSN 1464-343X.
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