These proposed biozones
Seeley named were subdivided further by
Robert Broom between 1906 and 1909.[9]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.[10] The rocks composing the current Eodicynodon Assemblage Zone were previously included in the upper Waterford Formation of the underlying
Ecca Group.[11] This was due to prior observations of the
biozone rock colours not being consistent with the known reddish to purple colours that are diagnostic of the
Beaufort Group. After further
stratigraphic reorganization of the
Beaufort Group was conducted from the 1970s,[12][13][14][15][16][17] it was discovered that the Eodicynodon Assemblage Zone correlated with the lower Abrahamskraal Formation, the lowermost
geological formation of the
Beaufort Group, and that the fossils of Eodicynodon sp. were only known from these specific rocks.[18] The Eodicynodon Assemblage Zone is currently accepted as the oldest
biozone of the
Beaufort Group.[19][20][21][22][23]
Lithology
The Eodicynodon Assemblage Zone correlates with the lower Abrahamskraal Formation, Adelaide Subgroup of the
Beaufort Group.
Outcrops of this
biozone are only known from the south-western margins of the Abrahamskraal Formation and is considered to be Middle
Permian (
Guadalupian) in age.
The rocks of the Eodicynodon Assemblage Zone comprise
mudstones,
siltstones, and fine-grained,
siliceoussandstone. The
mudstones are olive green to moderate yellowish brown in colour and contain thinner light reddish-brown layers. The reddish-brown layers frequently contain
calcareousnodules.
Desiccation cracks - indicative of seasonal dry periods - and raindrop impressions are sometimes found in the
mudstone layers.
Argillaceous layers are also common. The
siltstones are extremely fine-grained, often containing
ripple marks from being deposited in low energy streams, and vary from being dark grey, greenish-grey, and blueish-grey in colour. Thin sheets of
chert occur in the
mudstone and less commonly in the
siltstone layers. The
sandstones are fine-grained and vary from being greyish olive green to dark yellowish brown. Some
sandstone layers either contain or are capped by pebble-sized
mudstone-
clastconglomerates. These
conglomerates also contain isolated
fossils in some localities. The
sandstones are more common and at their thickest towards the upper sections of the
biozone. The rocks of this
biozone were likely deposited in a
subaerialdeltaic environment which included
floodplains. The presence of
calcareousnodules also indicates that the environment was warm with seasonal dry periods.[24][25][26]
The depositional environment of the Eodicynodon Assemblage Zone was formed by sedimentary material being deposited in the Karoo Basin - a
retro-arc foreland basin - by vast, low-energy
alluvial plains flowing northwards from a southerly source area in the rising the Gondwanide mountains. The Gondwanides were the result of
crustal uplift that had previously begun to take course due to
subduction of the Palaeo-pacific plate beneath the Gondwanan Plate.
Orogenic pulses from the growing Gondwanides mountain chain and associated
subduction created accommodation space for sedimentation in the
Karoo Basin where the deposits of the Eodicynodon Assemblage zone, and all other succeeding assemblage zones, were deposited over millions of years.[27][28][29]
^Rubidge, B. S. (ed.) 1995b. Biostratigraphy of the Beaufort Group (Karoo Supergroup). South African Committee of Stratigraphy. Biostratigraphic Series 1. Pretoria, Council for Geoscience
^Jirah, Sifelani; Rubidge, Bruce S. (2014-12-01). "Refined stratigraphy of the Middle Permian Abrahamskraal Formation (Beaufort Group) in the southern Karoo Basin". Journal of African Earth Sciences. 100: 121–135.
doi:
10.1016/j.jafrearsci.2014.06.014.
ISSN1464-343X.
^Rubidge, B.S.; King, G.M.; Hancox, P.J. (1994). "The posteranial skeleton of the earliest dicynodont synapsid Eodicynodon from the Upper Permian of South Africa". Palaeontology. 37 (2): 397–408.
^Rubidge, B.S.; Modesto, S.; Sidor, C.; Welman, J. (1999). "Eunotosaurus africanus from the Ecca-Beaufort contact in Northern Cape Province, South Africa-implications for Karoo basin development". South African Journal of Science. 95 (11/12): 553–554.
^Kitching, J.W., 1970. A short review of the Beaufort zoning in South Africa. In Second
Gondwana Symposium Proceedings and Papers (Vol. 1, pp. 309-312)
^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.
^Keyser, A.W. (1979). "A review of the biostratigraphy of the Beaufort Group in the Karoo Basin of South Africa". Geocongress, Geological Society of South Africa. 2: 13–31.
^Kitching, J.W. (1984). "A reassessment of the biozonation of the Beaufort Group". Paleo News. 4 (1): 12–13.
^Hancox, P.J; Rubidge, B.S (2001-01-01). "Breakthroughs in the biodiversity, biogeography, biostratigraphy, and basin analysis of the Beaufort group". Journal of African Earth Sciences. 33 (3–4): 563–577.
doi:
10.1016/S0899-5362(01)00081-1.
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^Rubidge, B. S. (ed.) 1995b. Biostratigraphy of the Beaufort Group (Karoo Supergroup). South African Committee of Stratigraphy. Biostratigraphic Series 1. Pretoria, Council for Geoscience.
^van der Walt, M., Day, M., Rubidge, B., Cooper, A.K. and Netterberg, I., 2010. A new GIS-based biozone map of the Beaufort Group (Karoo Supergroup), South Africa.
^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.
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^Rubidge, B. S. (ed.) 1995b. Biostratigraphy of the Beaufort Group (Karoo Supergroup). South African Committee of Stratigraphy. Biostratigraphic Series 1. Pretoria, Council for Geoscience.
^Rubidge, Bruce S.; Day, Michael O.; Barbolini, Natasha; Hancox, P. John; Choiniere, Jonah N.; Bamford, Marion K.; Viglietti, Pia A.; McPhee, Blair W.; Jirah, Sifelani (2016), "Advances in Nonmarine Karoo Biostratigraphy: Significance for Understanding Basin Development", Origin and Evolution of the Cape Mountains and Karoo Basin, Springer International Publishing, pp. 141–149,
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^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.
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^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.
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^Hopson, James A. (1994). "Synapsid Evolution and the Radiation of Non-Eutherian Mammals". Short Courses in Paleontology. 7: 190–219.
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^N.F.H. (November 1984). "J. M. Anderson & H. M. Anderson 1983. Palaeoflora of Southern Africa. Molteno Formation (Triassic). Volume 1. Part 1. Introduction; Part 2, Dicroidium. ix + 227 pp. Rotterdam: A. A. Balkema. Price Dfl. 135.00, £31.40. ISBN 90 6191 283 0 (for complete set of six volumes ISBN 90 6191 282 2)". Geological Magazine. 121 (6): 659–660.
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^Rubidge, B.S.; Day, M.O. (2020). "Biostratigraphy of the Eodicynodon Assemblage Zone (Beaufort Group, Karoo Supergroup), South Africa". South African Journal of Geology. 123 (2): 141–148.
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