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+ further reading, must be one of the best PhD theses I have read and needs to be incorporated in this article
 
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{{short description|Geological group in the Karoo Supergroup from South Africa}}
{{Karoo stratigraphy}}
{{Infobox rockunit
The '''Dwyka Group''' is the [[group (stratigraphy)|group]] of [[Sedimentary rock|sedimentary]] [[geological formation]]s laid down in the [[Karoo Basin]] of southern [[Africa]] in the [[Late Carboniferous]] and possibly extending into the [[Asselian]] of the early [[Permian]]. It consists mainly of [[tillite]]s, laid down along the sandy shorelines of swamplands. The Dwyka is the oldest and lowermost unit of the [[Karoo Supergroup]] that is recognized throughout sub-Saharan Africa.
| name = Dwyka Group
| period = Carboniferous
| age = [[Late Carboniferous]]-[[Early Permian]]<br />~{{fossilrange|317|288}}
| type = [[Geologic group]]
| prilithology = [[Diamictite]], [[tillite]], [[claystone]], [[mudstone]]
| otherlithology = [[Quartzite]], [[sandstone]] [[shale]]
| namedfor = Dwyka
| region = [[Western Cape|Western]], [[Northern Cape]], [[Free State (province)|Free State]], [[North-West]], [[Limpopo]], [[Eastern Cape]], and [[KwaZulu-Natal]]
| country = {{flag|South Africa}}<br>{{flag|Namibia}}<br>{{flag|Botswana}}<br>{{flag|Zimbabwe}}
| subunits = [[Mbizane Formation|Mbizane]], [[Elandsvlei Formation|Elandsvlei]] & [[Tshidzi Formation]]s
| overlies = [[Cape Supergroup]], [[Natal Supergroup]], Namaqua-Natal Province, Archean basement rocks
| underlies = [[Ecca Group]]
| coordinates = {{coord|26.0|S|29.5|E|display=inline,title}}
| paleocoordinates = {{coord|76.2|S|52.2|W|display=inline}}
| extent =
| area =
| map = Geology of Karoo Supergroup.png
| map_caption = A simplified geological map of the outcrops of Karoo Supergroup rocks in Southern Africa. The Dwyka Group deposits are represented by the red key on the map
}}


The '''Dwyka Group''' is one of four geological [[Stratigraphic unit|groups]] that compose the [[Karoo Supergroup]]. It is the lowermost geological group and heralds the commencement of [[sedimentation]] of the Karoo Supergroup. Based on [[Stratigraphy|stratigraphic]] position, [[Lithostratigraphy|lithostratigraphic]] correlation and [[Palynology|palynological]] analyses, these lowermost Karoo strata range between the Late [[Carboniferous]] ([[Pennsylvanian (geology)|Pennsylvanian]]) to Early [[Permian]] in age.<ref>{{cite journal | last1 = Visser | first1 = J.N.J. | year = 1986 | title = Lateral lithofacies relationships in the glacigene Dwyka Formation in the western and central parts of the Karoo Basin | journal = Transactions of the Geological Society of South Africa | volume = 89 | pages = 373–383 }}</ref><ref>Isbell, John L., Douglas I. Cole, and Octavian Catuneanu. "Carboniferous-Permian glaciation in the main Karoo Basin, South Africa: Stratigraphy, depositional controls, and glacial dynamics." In ''Resolving the Late Paleozoic ice age in time and space'', vol. 441, pp. 71–82. Geological Society of America Special Paper, 2008. Link: https://www.researchgate.net/profile/John_Isbell/publication/235926635_Carboniferous-Permian_glaciation_in_the_main_Karoo_Basin_South_Africa_Stratigraphy_depositional_controls_and_glacial_dynamics/links/00463514485423265a000000/Carboniferous-Permian-glaciation-in-the-main-Karoo-Basin-South-Africa-Stratigraphy-depositional-controls-and-glacial-dynamics.pdf</ref><ref>{{Cite journal|last=Smith, R.M.H., Eriksson, P.G., Botha, W.J.|date=1993-01-01|title=A review of the stratigraphy and sedimentary environments of the Karoo-aged basins of Southern Africa|journal=Journal of African Earth Sciences (and the Middle East)|language=en|volume=16|issue=1–2|pages=143–169|doi=10.1016/0899-5362(93)90164-L|bibcode=1993JAfES..16..143S |issn=0899-5362}}</ref><ref>{{Cite journal|last=Bamford|first=M. K.|date=2004-01-01|title=Diversity of the Woody Vegetation of Gondwanan Southern Africa|journal=Gondwana Research|language=en|volume=7|issue=1|pages=153–164|doi=10.1016/S1342-937X(05)70314-2|bibcode=2004GondR...7..153B |issn=1342-937X}}</ref>
== Formation ==
In the Carboniferous, southern Africa was part of [[Gondwana]]. During the Late Carboniferous the [[lithosphere]] underlying what is now the Karoo Basin migrated over the South Polar Region. This resulted in southern Gondwana being covered by a major ice sheet. As the ice sheet and subsequent [[glacier]]s melted, the sediments of the Dwyka Group were deposited in the newly formed basin. These [[glacial]] deposits include [[diamictite]], [[varve]]d [[shale]] and [[mudstone]] with dropstones, fluvioglacial gravel and conglomerates. The total thickness of the group ranges from {{convert|600|to|750|m|ft}}.<ref>SACS (South African Committee for Stratigraphy) (1980) Stratigraphy of South Africa. Part 1 (Comp. L.E. Kent). ''Lithostratigraphy of the Republic of South Africa, South West Africa/Namibia, and the Republics of Bophuthatswana, Transkei and Venda:'' Handbook Geological Survey of South Africa, 8, 690p.</ref>


== Background ==
The Dwyka Group is considered to be Permo-Carboniferous in age, but due to ambiguities in the fossil record, more precise dating is not available. Maximum age inferred from [[fossil]]s found in underlying strata is Late Devonian or Early Carboniferous, and minimum age inferred from fossils in the upper glacial deposits is Early Permian.<ref>M. J. Hambrey, W. B. Harland, ''Earth's pre-Pleistocene glacial record,'' International Geological Correlation Programme. Project 38: Pre-Pleistocene Tillites, p76</ref>


At the commencement of the deposition of the Dwyka Group, it is thought that the development of the Karoo supergroup [[Foreland basin|foreland system]] had begun approximately 30 million years prior. This foreland system was caused by [[Tectonic uplift|crustal uplift]] that had previously begun to take course due to the [[subduction]] of the Palaeo-pacific [[Plate tectonics|plate]] beneath the Gondwanan [[Plate tectonics|plate]]. This resulted in the rise of the Gondwanide mountain range in what is known as the [[Gondwanide orogeny]]. The continuation of the [[Orogeny|orogenic]] pulses from the growing Gondwanides mountain chain and associated subduction created accommodation space for sedimentation in the [[Karoo Supergroup|Karoo Basin]] which ran along an east to west trending foreland trough. The formation of the Karoo Basin resulted in the preservation of the Dwyka Group rocks and all succeeding rocks that make up the greater [[Karoo Supergroup]]. [[Southern Africa]] at this time was part of the [[supercontinent]], [[Gondwana]], and was positioned over the [[Antarctic Circle|antarctic circle]] at this time. The result was the development of the [[Permo-Carboniferous]] glacial environment where massive [[ice sheet]]s entombed the early Karoo Basin in the surrounding highlands and permanent, floating [[glacier]]s in the lowlands.<ref>{{Cite journal|date=1993-01-01|title=The tectonic evolution of southern Africa: an overview|journal=Journal of African Earth Sciences (and the Middle East)|language=en|volume=16|issue=1–2|pages=5–24|doi=10.1016/0899-5362(93)90159-N|issn=0899-5362|last1=Thomas|first1=R.J.|last2=von Veh|first2=M.W.|last3=McCourt|first3=S.|bibcode=1993JAfES..16....5T }}</ref><ref>{{Cite journal|last1=Catuneanu|first1=O.|last2=Hancox|first2=P.J.|last3=Rubidge|first3=B.S.|date=1998-12-01|title=Reciprocal flexural behaviour and contrasting stratigraphies: a new basin development model for the Karoo retroarc foreland system, South Africa|url=http://www.earthdoc.org/publication/publicationdetails/?publication=62697|journal=Basin Research|language=en|volume=10|issue=4|page=417 |doi=10.1046/j.1365-2117.1998.00078.x |bibcode=1998BasR...10..417C |s2cid=56420970 |issn=1365-2117}}</ref><ref>{{Cite journal|last=O. Catuneanu, P.J. Hancox and B.S. Rubidge|date=2002-11-01|title=Foredeep submarine fans and forebulge deltas: orogenic off-loading in the underfilled Karoo Basin|journal=Journal of African Earth Sciences|language=en|volume=35|issue=4|pages=489–502|doi=10.1016/S0899-5362(02)00154-9|bibcode=2002JAfES..35..489C |issn=1464-343X}}</ref><ref>{{Cite journal|last=Catuneanu|first=Octavian|date=2004|title=Basement control on flexural profiles and the distribution of foreland facies: The Dwyka Group of the Karoo Basin, South Africa|url=https://pubs.geoscienceworld.org/gsa/geology/article-abstract/32/6/517/29470|journal=Geology|language=en|volume=32|issue=6|pages=517|doi=10.1130/G20526.1|bibcode=2004Geo....32..517C |issn=0091-7613}}</ref><ref>{{Cite journal|date=1989-05-01|title=The Permo-Carboniferous Dwyka Formation of Southern Africa: Deposition by a predominantly subpolar marine ice sheet|journal=Palaeogeography, Palaeoclimatology, Palaeoecology|language=en|volume=70|issue=4|pages=377–391|doi=10.1016/0031-0182(89)90115-6|issn=0031-0182|last1=Visser|first1=J.N.J.|bibcode=1989PPP....70..377V }}</ref><ref>Thomas, R.J., Marshall, C.G.A., Du Plessis, A., Fitch, F.J., Miller, J.A., Von Brunn, V. and Watkeys, M.K., 1992. Geological studies in southern Natal and Transkei: implications for the Cape Orogen. ''Inversion Tectonics of the Cape Fold Belt, Karoo and Cretaceous Basins of Southern Africa. Balkema, Rotterdam'', pp.229–236.
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== Stratigraphic position ==
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 Formation|Molteno]], [[Elliot Formation|Elliot]], and [[Clarens Formation]]s and the igneous [[Drakensberg Group]]. The basin followed the typical evolution of [[foreland basin]]s, with the Ecca Group representing the ‘[[flysch]]’ component and the Beaufort Group, the overlying Molteno and Elliot Formations representing the ‘[[molasse]]’-fluvial type sediments.<ref>Johnson, M. R. (1991). Sandstone petrography, provenance and plate tectonic setting in Gondwana context of the south-eastern Cape Karoo basin, ''[[South African Journal of Geology]]'', 94, 137-154.</ref><ref>Catuneanu, O. (2004) ''Retroarc foreland systems – evolution through time,'' Journal of African Earth Sciences, 38, 225-242.</ref>


Link: https://www.researchgate.net/profile/Bob_Thomas4/publication/290693065_Geological_studies_in_southern_Natal_and_Transkei_implications_for_the_Cape_Orogen/links/5772141e08ae6219474a6519.pdf</ref>
In the [[Nama Basin|Nama or Kalahari Basin]] of southeastern [[Namibia]], the Dwyka Group contains the fossiliferous [[Ganigobis Formation]].

[[File:Snider-Pellegrini Wegener fossil map-i18n.png|340px|right|Caption: 1-South-America
2-Africa; 3-India; 4-Australia; 5-Antarctica; 6-Fossil remains of Cynognathus, a Triassic land reptile, approximately 3m long; 7- Fossil remains of the freshwater reptile Mesosaurus;
8-Fossil of the fern Glossopteris found in all of the southern continents show that they were once joined; 9-Fossil evidence of the Triassic land reptile Lystrosaurus]]

== Geographic extent ==

The [[geological formation]]s of the Dwyka Group are restricted to the edges of the [[Karoo Supergroup|Karoo Basin]] and achieve their greatest thickness in its southern deposits at approximately 800&nbsp;m, progressively thinning out towards the north. In the south outcrops and exposures are known from [[Prince Albert, Western Cape|Prince Albert]], [[Matjiesfontein]], [[Laingsburg, Western Cape|Laingsburg]], [[Sutherland, Northern Cape|Sutherland]], and as far south as [[Worcester, Western Cape|Worcester]]. Western to northern exposures are known from [[Calvinia]], [[Carnarvon, Northern Cape|Carnarvon]], [[Kimberley, Northern Cape|Kimberley]], and then from [[Vryheid]] and [[Durban]] in the east.

Dwyka Group deposits are also found outside of and north of the Karoo Basin. These deposits found north of the Karoo Basin are found as the lowermost geological formation of the Springbok Flats, Tshipise, northern Lebombo, Tuli, and [[Ellisras Basin|Ellisras]] ([[Lephalale]]) Basins of north-northeastern [[South Africa]].

In its southern, western, and eastern deposits, the Dwyka Group conformably overlies rocks of the [[Cape Supergroup]], which includes the [[Cape Fold Belt]], and the Natal Supergroup. It also unconformably overlies the Namaqua-Natal Metamorphic Province in some localities in the west-northwest of South Africa. Its north and northeastern Karoo Basin deposits and all deposits found north of the Karoo Basin [[Unconformity|unconformably]] overlie the [[Transvaal Supergroup]], Ventersdorp Group, or [[Archean]] and [[Proterozoic]] basement rocks. In all South African localities, the Dwyka Group underlies rocks of the [[Ecca Group]].

The geographical range of the Dwyka Group is large with its deposits also being found in other localities in [[southern Africa]]. Dwyka-aged deposits that are considered to correlate in age to those found in South Africa have been located in the southern Karasburg and [[Kalahari Basin]]s of southern [[Namibia]] – in and around the [[Fish River Canyon]] – in the Huab Basin of northern-western [[Namibia]], the Waterberg and [[Owambo Basin]]s of northern Namibia, the Dukwi Formation of the [[Kalahari Basin]] of [[Botswana]], and the Save Basin of southeastern [[Zimbabwe]].<ref>{{Cite journal|date=1999-07-01|title=The geochronology and significance of ash-fall tuffs in the glaciogenic Carboniferous-Permian Dwyka Group of Namibia and South Africa|journal=Journal of African Earth Sciences|language=en|volume=29|issue=1|pages=33–49|doi=10.1016/S0899-5362(99)00078-0|issn=1464-343X|last1=Bangert|first1=Berthold|last2=Stollhofen|first2=Harald|last3=Lorenz|first3=Volker|last4=Armstrong|first4=Richard|bibcode=1999JAfES..29...33B }}</ref>

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== Stratigraphic units ==

The Dwyka Group deposits have been categorized by those found as part of the [[Karoo Supergroup|Karoo Basin]] and smaller formations found in different basins north of the Karoo Basin. In the [[Karoo Supergroup|Karoo Basin]], the Dwyka Group is known by two distinctive [[Lithology|lithological]] [[facies]]. These two facies are represented in its northern and southern deposits respectively and are recognized as the two [[geological formation]]s below:
* '''Elandsvlei Formation''' is the southern [[facies]] and it is considered to represent the earliest [[Foreland basin|foredeep]] deposits of the Karoo foreland system. This portion is restricted to the southern areas of South Africa and is characterized by uniform, high, massive, and [[Clastic rock|clast]]-poor [[diamictite]]s and rarer [[mudrock]] deposits.
[[File:Drop pebble in varves of the Elandsvlei Fm, Dwyka Group, near Laingsburg, RSA.jpg|thumb|Greenish laminated siltstones of the Elandsvlei Fm, Dwyka Group, near Laingsburg, RSA, containing a solitary pebble which was apparently a dropstone, with thinned laminae draped over the top.]]
The [[diamictite]]s are highly compacted and overlie stratified diamictites and mudrocks. The southern facies is interpreted as suspension or melt-out deposits that were deposited in low energy [[Subglacial lake|subglacial]] or subaqueous rain-out from either semi-grounded or floating [[ice sheet]]s. All sedimentation occurred below the water surface in a deep [[Ocean|marine]] environment. More evidence to support this is that [[turbidite]]s are often found in Elandsvlei Formation deposits.<ref>Theron, J.N. and Blignault, H.J., 1975. A model for the sedimentation of the Dwyka glacials in the southwestern Cape. ''Gondwana Geology'', pp.347–356.</ref><ref>{{Cite journal|date=1990-12-01|title=Major element geochemistry and paleoclimatology of the Permo-Carboniferous glacigene Dwyka Formation and postglacial mudrocks in southern Africa|journal=Palaeogeography, Palaeoclimatology, Palaeoecology|language=en|volume=81|issue=1–2|pages=49–57|doi=10.1016/0031-0182(90)90039-A|issn=0031-0182|last1=Visser|first1=Johan N.J.|last2=Young|first2=Grant M.|bibcode=1990PPP....81...49V }}</ref>
* '''Mbizane Formation''' is the northern [[facies]] and is considered to represent [[forebulge]] deposits of the Karoo [[Foreland basin|foreland system]]. This portion of the formation is restricted to the northern and northeastern sections of the [[Karoo Supergroup|Karoo Basin]]. It is composed of thinly bedded [[mudstone]]s and claystones, stratified [[Conglomerate (geology)|conglomerates]], [[Pebble|pebbly]] [[sandstone]]s, and diamictites. The [[Clastic rock|clasts]] were sourced from [[Erosion|eroded]] material from the much older basement rocks and comprise numerous different rock types. These include [[Quartzite|quarzites]], [[Quartz|vein quartz]], [[Ironstone|banded ironstone]], [[Dolomite (rock)|dolomite]], [[gneiss]], [[granite]], and [[Amygdule|amygdaloidal lavas]]. It is currently accepted that the northern facies represents valley-fill deposits, [[Proglacial lake|proglacial]] [[outwash fan]]s, and [[Subglacial lake|subglacial]] [[till]] deposits left by [[Ice sheet|continental glaciers]] retreating towards the south of the early [[Karoo Supergroup|Karoo Basin]]. [[Glacial striation|Glacial pavements]] where striation marks are left on the surface of basement rocks are known from this formation in numerous localities.<ref>Von Brunn, V. and Visser, J.N.J., 1999. Lithostratigraphy of the Mbizane Formation (Dwyka group). South African Committee for Stratigraphy. ''Lithostratigraphic Series'', (32), p.10.</ref><ref>{{Cite journal|date=2001-06-15|title=Geochemistry and petrology of Witwatersrand and Dwyka diamictites from South Africa: search for an extraterrestrial component|journal=Geochimica et Cosmochimica Acta|language=en|volume=65|issue=12|pages=2007–2016|doi=10.1016/S0016-7037(01)00569-5|issn=0016-7037|last1=Huber|first1=Heinz|last2=Koeberl|first2=Christian|last3=McDonald|first3=Iain|last4=Reimold|first4=Wolf Uwe|bibcode=2001GeCoA..65.2007H }}</ref><ref>{{Cite journal|last=Brunn|first=V. Von|date=1977-08-01|title=A furrowed intratillite pavement in the Dwyka Group of northern Natal|url=https://journals.co.za/content/sajg/80/2/AJA10120750_1313|journal=South African Journal of Geology|language=en|volume=80|issue=2|issn=1012-0750}}</ref><ref>{{Cite journal|last=Gravenor, V., von Brunn, C.P.|date=1983-09-01|title=A model for late Dwyka glaciomarine sedimentation in the Eastern Karoo basin|url=https://journals.co.za/content/sajg/86/3/AJA10120750_305|journal=South African Journal of Geology|language=en|volume=86|issue=3|issn=1012-0750}}</ref><ref>{{Cite journal|last1=Brunn|first1=V. von|last2=Marshall|first2=C. G. A.|date=1989-12-01|title=Glaciated surfaces and the base of the Dwyka Formation near Pietermaritzburg, Natal|url=https://pubs.geoscienceworld.org/gssa/sajg/article-abstract/92/4/420/122206|journal=South African Journal of Geology|language=en|volume=92|issue=4|issn=1012-0750}}</ref><ref>{{Cite thesis|last=Berthold|first=Bangert|title=Tephrostratigraphy, petrography, geochemistry, age and fossil record of the Ganigobis Shale Member and associated glaciomarine deposits of the Dwyka Group, Late Carboniferous, southern Africa|year=2000 |publisher=Universität Würzburg |url=https://opus.bibliothek.uni-wuerzburg.de/frontdoor/index/index/docId/179|language=en}}</ref>

North of the [[Karoo Supergroup|Karoo Basin]] outcrops of another [[geological formation]] that correlates in age to the main Karoo Basin's Dwyka-aged deposits. This formation is the lowermost unit of the Springbok Flats, Tshipise, northern Lebombo, Tuli, and [[Ellisras Basin|Ellisras]] ([[Lephalale]]) Basins. This geological formation is recognized and differentiated below due to its unique [[Lithology|lithological]] [[facies]] from its main [[Karoo Supergroup|Karoo Basin]] counterparts:<ref>{{Cite journal|date=1984-03-01|title=Nature and classification of waterlain glaciogenic sediments, exemplified by Pleistocene, Late Paleozoic and Late Precambrian deposits|journal=Earth-Science Reviews|language=en|volume=20|issue=2|pages=105–166|doi=10.1016/0012-8252(84)90023-0|issn=0012-8252|last1=Gravenor|first1=C.P.|last2=von Brunn|first2=V.|last3=Dreimanis|first3=A.|bibcode=1984ESRv...20..105G }}</ref><ref>{{Cite journal|date=1996-10-01|title=The Dwyka Group in the northern part of Kwazulu/Natal, South Africa: sedimentation during late Palaeozoic deglaciation|journal=Palaeogeography, Palaeoclimatology, Palaeoecology|language=en|volume=125|issue=1–4|pages=141–163|doi=10.1016/S0031-0182(96)00028-4|issn=0031-0182|last1=von Brunn|first1=V.|bibcode=1996PPP...125..141V }}</ref><ref>{{Citation|last=Von Brunn|first=V.|chapter=Glaciogenic deposits of the Permo-Carboniferous Dwyka Group in the eastern region of the Karoo Basin, South Africa|date=1994|chapter-url=http://cco.cup.cam.ac.uk/chapter.jsf?bid=CBO9780511628900&cid=CBO9780511628900A045|pages=60–69|publisher=Cambridge University Press|language=en|doi=10.1017/CBO9780511628900.005|isbn=9780511628900|access-date=2018-11-23|title=Earth's Glacial Record}}</ref>

* '''Tshidzi Formation''' : Deposits of this formation represent [[Foreland basin|backbulge]] basin deposits of the Karoo [[Foreland basin|foreland system]]. In the Tshipise and Tuli Basins, this formation is known as the Madzaringwe Formation. This formation consists of [[Pebble|pebbly]] [[mudstone]]s that are [[Interbedding|interbedded]] with mainly coarse-grained [[diamictite]]s. These deposits are considered to be [[Lake|lacustrine]] [[facies]], which show that the rock sediments were deposited in [[Glacial lake|glacial]] or [[Periglaciation|periglacial]] lakes. The northernmost Dwyka Group deposits are considered to have been most proximal to the shoreline of the shallow interior sea that was present at this time in southern Africa.<ref>{{Cite journal|last=Bordy|first=E.M.|date=2018-03-01|title=Lithostratigraphy of the Tshidzi Formation (Dwyka Group, Karoo Supergroup), South Africa|url=https://pubs.geoscienceworld.org/gssa/sajg/article-abstract/121/1/109/543205|journal=South African Journal of Geology|language=en|volume=121|issue=1|pages=109–118|doi=10.25131/sajg.121.0008|issn=1996-8590}}</ref>

== Paleontology ==

The Dwyka Group is mainly known for [[petrified wood]] which increase in [[species diversity]] in the younger sequences.<ref>{{Cite journal|last=Bamford|first=M. K.|date=2000-07-01|title=Fossil woods of Karoo age deposits in South Africa and Namibia as an aid to biostratigraphical correlation|journal=Journal of African Earth Sciences|language=en|volume=31|issue=1|pages=119–132|doi=10.1016/S0899-5362(00)00077-4|bibcode=2000JAfES..31..119B |issn=1464-343X}}</ref><ref>{{Cite journal|date=2004-01-01|title=Diversity of the Woody Vegetation of Gondwanan Southern Africa|journal=Gondwana Research|language=en|volume=7|issue=1|pages=153–164|doi=10.1016/S1342-937X(05)70314-2|issn=1342-937X|last1=Bamford|first1=Marion K.|bibcode=2004GondR...7..153B }}</ref> The cold, [[Glacial period|glacial]] environment that the [[Sedimentary rock|sedimentary]] rocks of the Dwyka Group were deposited in was not conducive for high plant diversity. Fossil wood species identified include [[Lycopodium|lycopods]], especially from the Karasburg, [[Kalahari Basin|Kalahari]], and Huab Basins in [[Namibia]]. ''[[Glossopteris]]'' leaf impressions, the [[Petrifaction|petrified]] remains of ''[[Dadoxylon]]'', [[coprolite]]s, fossil [[pollen]], and [[trace fossil]]s of [[Osteichthyes|bony fishes]], [[crustacean]]s, and other [[arthropod]]s have been found from the Dwyka Group and correlated [[geological formation]]s from other basins.<ref>{{Cite journal|last1=R.|first1=McLachlan, I.|last2=Ann|first2=Anderson|date=1973|title=A REVIEW OF THE EVIDENCE FOR MARINE CONDITIONS IN SOUTHERN AFRICA DURING DWYKA TIMES|journal=Palaeontologia Africana|url=http://146.141.12.21/handle/10539/16040|language=en|issn=0078-8554|access-date=2018-11-23|archive-date=2018-11-24|archive-url=https://web.archive.org/web/20181124055010/http://146.141.12.21/handle/10539/16040|url-status=dead}}</ref><ref>{{Cite journal|last=Barbolini, N., Bamford, M.K.|date=2014-12-01|title=Palynology of an Early Permian coal seam from the Karoo Supergroup of Botswana|journal=Journal of African Earth Sciences|language=en|volume=100|pages=136–144|doi=10.1016/j.jafrearsci.2014.06.008|bibcode=2014JAfES.100..136B |issn=1464-343X}}</ref><ref>{{Cite journal|last1=Bangert|first1=B|last2=Bamford|first2=Marion|date=2001-01-01|title=Carboniferous pycnoxylic woods from the Dwyka group of Southern Namibia|url=https://www.researchgate.net/publication/286583560|journal=Palaeontologia Africana|pages=13–23}}</ref><ref>{{Cite journal|last1=Scheffler|first1=K.|last2=Hoernes|first2=S.|last3=Schwark|first3=L.|date=2003|title=Global changes during Carboniferous–Permian glaciation of Gondwana: Linking polar and equatorial climate evolution by geochemical proxies|url=https://pubs.geoscienceworld.org/gsa/geology/article-abstract/31/7/605/188341/global-changes-during-carboniferous-permian?redirectedFrom=fulltext|journal=Geology|language=en|volume=31|issue=7|pages=605|doi=10.1130/0091-7613(2003)031<0605:GCDCGO>2.0.CO;2|bibcode=2003Geo....31..605S |issn=0091-7613}}</ref><ref>{{Cite journal|last=Smith, R.M.H., Eriksson, P.G., Botha, W.J.|date=1993-01-01|title=A review of the stratigraphy and sedimentary environments of the Karoo-aged basins of Southern Africa|journal=Journal of African Earth Sciences (and the Middle East)|language=en|volume=16|issue=1–2|pages=143–169|doi=10.1016/0899-5362(93)90164-L|bibcode=1993JAfES..16..143S |issn=0899-5362}}</ref>


== See also ==
== See also ==
{{portal|Geology|Carboniferous|Permian|Prehistory of Africa}}
* {{annotated link|Geology of South Africa}}
* {{annotated link|Geography of South Africa}}
* [[Geology of Namibia]]
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* [[Geology of South Africa]]
* [[List of fossiliferous stratigraphic units in Namibia]]
* [[List of fossiliferous stratigraphic units in South Africa]]


== References ==
== References ==
{{Reflist}}
{{Reflist}}


{{Major African geological formations}}
== Further reading ==
⚫
{{Geology of South Africa|formations}}
* {{cite LSA |last=Werner |first=Mario |year=2006 |title=The stratigraphy, sedimentology, and age of the Late Palaeozoic Mesosaurus Inland Sea, SW-Gondwana - New implications from studies on sediments and altered pyroclastic layers of the Dwyka and Ecca Group (lower Karoo Supergroup) in southern Namibia (PhD thesis) |url=https://opus.bibliothek.uni-wuerzburg.de/opus4-wuerzburg/frontdoor/deliver/index/docId/1918/file/00-Complete_thesis-STD.pdf |publisher=[[University of Würzburg|Julius-Maximilians-Universität Würzburg]] |pages=1–428 |accessdate=2018-08-26}}
{{Portal bar|Geology}}


[[Category:Geologic formations of Africa]]
[[Category:Geologic groups of Africa]]
[[Category:Geologic formations of Namibia]]
[[Category:Geologic formations of Namibia]]
[[Category:Geologic formations of South Africa]]
[[Category:Geologic formations of South Africa]]
[[Category:Carboniferous Africa]]
[[Category:Geologic formations of Zimbabwe]]
[[Category:Karoo]]
[[Category:Carboniferous System of Africa]]
[[Category:Carboniferous South Africa]]
[[Category:Permian System of Africa]]
[[Category:Permian South Africa]]
[[Category:Carboniferous south paleopolar deposits]]
[[Category:Permian south paleopolar deposits]]
[[Category:Karoo Supergroup]]
[[Category:Karoo Supergroup]]

Latest revision as of 21:38, 3 November 2024

Dwyka Group
Stratigraphic range: Late Carboniferous-Early Permian
~317–288 Ma
TypeGeologic group
Sub-unitsMbizane, Elandsvlei & Tshidzi Formations
UnderliesEcca Group
OverliesCape Supergroup, Natal Supergroup, Namaqua-Natal Province, Archean basement rocks
Lithology
PrimaryDiamictite, tillite, claystone, mudstone
OtherQuartzite, sandstone shale
Location
Coordinates26°00′S 29°30′E / 26.0°S 29.5°E / -26.0; 29.5
Approximate paleocoordinates76°12′S 52°12′W / 76.2°S 52.2°W / -76.2; -52.2
RegionWestern, Northern Cape, Free State, North-West, Limpopo, Eastern Cape, and KwaZulu-Natal
Country South Africa
 Namibia
 Botswana
 Zimbabwe
Type section
Named forDwyka

A simplified geological map of the outcrops of Karoo Supergroup rocks in Southern Africa. The Dwyka Group deposits are represented by the red key on the map

The Dwyka Group is one of four geological groups that compose the Karoo Supergroup. It is the lowermost geological group and heralds the commencement of sedimentation of the Karoo Supergroup. Based on stratigraphic position, lithostratigraphic correlation and palynological analyses, these lowermost Karoo strata range between the Late Carboniferous (Pennsylvanian) to Early Permian in age.[1][2][3][4]

Background

[edit]

At the commencement of the deposition of the Dwyka Group, it is thought that the development of the Karoo supergroup foreland system had begun approximately 30 million years prior. This foreland system was caused by crustal uplift that had previously begun to take course due to the subduction of the Palaeo-pacific plate beneath the Gondwanan plate. This resulted in the rise of the Gondwanide mountain range in what is known as the Gondwanide orogeny. The continuation of the orogenic pulses from the growing Gondwanides mountain chain and associated subduction created accommodation space for sedimentation in the Karoo Basin which ran along an east to west trending foreland trough. The formation of the Karoo Basin resulted in the preservation of the Dwyka Group rocks and all succeeding rocks that make up the greater Karoo Supergroup. Southern Africa at this time was part of the supercontinent, Gondwana, and was positioned over the antarctic circle at this time. The result was the development of the Permo-Carboniferous glacial environment where massive ice sheets entombed the early Karoo Basin in the surrounding highlands and permanent, floating glaciers in the lowlands.[5][6][7][8][9][10]

Caption: 1-South-America 2-Africa; 3-India; 4-Australia; 5-Antarctica; 6-Fossil remains of Cynognathus, a Triassic land reptile, approximately 3m long; 7- Fossil remains of the freshwater reptile Mesosaurus; 8-Fossil of the fern Glossopteris found in all of the southern continents show that they were once joined; 9-Fossil evidence of the Triassic land reptile Lystrosaurus
Caption: 1-South-America 2-Africa; 3-India; 4-Australia; 5-Antarctica; 6-Fossil remains of Cynognathus, a Triassic land reptile, approximately 3m long; 7- Fossil remains of the freshwater reptile Mesosaurus; 8-Fossil of the fern Glossopteris found in all of the southern continents show that they were once joined; 9-Fossil evidence of the Triassic land reptile Lystrosaurus

Geographic extent

[edit]

The geological formations of the Dwyka Group are restricted to the edges of the Karoo Basin and achieve their greatest thickness in its southern deposits at approximately 800 m, progressively thinning out towards the north. In the south outcrops and exposures are known from Prince Albert, Matjiesfontein, Laingsburg, Sutherland, and as far south as Worcester. Western to northern exposures are known from Calvinia, Carnarvon, Kimberley, and then from Vryheid and Durban in the east.

Dwyka Group deposits are also found outside of and north of the Karoo Basin. These deposits found north of the Karoo Basin are found as the lowermost geological formation of the Springbok Flats, Tshipise, northern Lebombo, Tuli, and Ellisras (Lephalale) Basins of north-northeastern South Africa.

In its southern, western, and eastern deposits, the Dwyka Group conformably overlies rocks of the Cape Supergroup, which includes the Cape Fold Belt, and the Natal Supergroup. It also unconformably overlies the Namaqua-Natal Metamorphic Province in some localities in the west-northwest of South Africa. Its north and northeastern Karoo Basin deposits and all deposits found north of the Karoo Basin unconformably overlie the Transvaal Supergroup, Ventersdorp Group, or Archean and Proterozoic basement rocks. In all South African localities, the Dwyka Group underlies rocks of the Ecca Group.

The geographical range of the Dwyka Group is large with its deposits also being found in other localities in southern Africa. Dwyka-aged deposits that are considered to correlate in age to those found in South Africa have been located in the southern Karasburg and Kalahari Basins of southern Namibia – in and around the Fish River Canyon – in the Huab Basin of northern-western Namibia, the Waterberg and Owambo Basins of northern Namibia, the Dukwi Formation of the Kalahari Basin of Botswana, and the Save Basin of southeastern Zimbabwe.[11]

Stratigraphic units

[edit]

The Dwyka Group deposits have been categorized by those found as part of the Karoo Basin and smaller formations found in different basins north of the Karoo Basin. In the Karoo Basin, the Dwyka Group is known by two distinctive lithological facies. These two facies are represented in its northern and southern deposits respectively and are recognized as the two geological formations below:

  • Elandsvlei Formation is the southern facies and it is considered to represent the earliest foredeep deposits of the Karoo foreland system. This portion is restricted to the southern areas of South Africa and is characterized by uniform, high, massive, and clast-poor diamictites and rarer mudrock deposits.
Greenish laminated siltstones of the Elandsvlei Fm, Dwyka Group, near Laingsburg, RSA, containing a solitary pebble which was apparently a dropstone, with thinned laminae draped over the top.

The diamictites are highly compacted and overlie stratified diamictites and mudrocks. The southern facies is interpreted as suspension or melt-out deposits that were deposited in low energy subglacial or subaqueous rain-out from either semi-grounded or floating ice sheets. All sedimentation occurred below the water surface in a deep marine environment. More evidence to support this is that turbidites are often found in Elandsvlei Formation deposits.[12][13]

North of the Karoo Basin outcrops of another geological formation that correlates in age to the main Karoo Basin's Dwyka-aged deposits. This formation is the lowermost unit of the Springbok Flats, Tshipise, northern Lebombo, Tuli, and Ellisras (Lephalale) Basins. This geological formation is recognized and differentiated below due to its unique lithological facies from its main Karoo Basin counterparts:[20][21][22]

  • Tshidzi Formation : Deposits of this formation represent backbulge basin deposits of the Karoo foreland system. In the Tshipise and Tuli Basins, this formation is known as the Madzaringwe Formation. This formation consists of pebbly mudstones that are interbedded with mainly coarse-grained diamictites. These deposits are considered to be lacustrine facies, which show that the rock sediments were deposited in glacial or periglacial lakes. The northernmost Dwyka Group deposits are considered to have been most proximal to the shoreline of the shallow interior sea that was present at this time in southern Africa.[23]

Paleontology

[edit]

The Dwyka Group is mainly known for petrified wood which increase in species diversity in the younger sequences.[24][25] The cold, glacial environment that the sedimentary rocks of the Dwyka Group were deposited in was not conducive for high plant diversity. Fossil wood species identified include lycopods, especially from the Karasburg, Kalahari, and Huab Basins in Namibia. Glossopteris leaf impressions, the petrified remains of Dadoxylon, coprolites, fossil pollen, and trace fossils of bony fishes, crustaceans, and other arthropods have been found from the Dwyka Group and correlated geological formations from other basins.[26][27][28][29][30]

See also

[edit]

References

[edit]
  1. ^ Visser, J.N.J. (1986). "Lateral lithofacies relationships in the glacigene Dwyka Formation in the western and central parts of the Karoo Basin". Transactions of the Geological Society of South Africa. 89: 373–383.
  2. ^ Isbell, John L., Douglas I. Cole, and Octavian Catuneanu. "Carboniferous-Permian glaciation in the main Karoo Basin, South Africa: Stratigraphy, depositional controls, and glacial dynamics." In Resolving the Late Paleozoic ice age in time and space, vol. 441, pp. 71–82. Geological Society of America Special Paper, 2008. Link: https://www.researchgate.net/profile/John_Isbell/publication/235926635_Carboniferous-Permian_glaciation_in_the_main_Karoo_Basin_South_Africa_Stratigraphy_depositional_controls_and_glacial_dynamics/links/00463514485423265a000000/Carboniferous-Permian-glaciation-in-the-main-Karoo-Basin-South-Africa-Stratigraphy-depositional-controls-and-glacial-dynamics.pdf
  3. ^ Smith, R.M.H., Eriksson, P.G., Botha, W.J. (1993-01-01). "A review of the stratigraphy and sedimentary environments of the Karoo-aged basins of Southern Africa". Journal of African Earth Sciences (and the Middle East). 16 (1–2): 143–169. Bibcode:1993JAfES..16..143S. doi:10.1016/0899-5362(93)90164-L. ISSN 0899-5362.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  4. ^ Bamford, M. K. (2004-01-01). "Diversity of the Woody Vegetation of Gondwanan Southern Africa". Gondwana Research. 7 (1): 153–164. Bibcode:2004GondR...7..153B. doi:10.1016/S1342-937X(05)70314-2. ISSN 1342-937X.
  5. ^ Thomas, R.J.; von Veh, M.W.; McCourt, S. (1993-01-01). "The tectonic evolution of southern Africa: an overview". Journal of African Earth Sciences (and the Middle East). 16 (1–2): 5–24. Bibcode:1993JAfES..16....5T. doi:10.1016/0899-5362(93)90159-N. ISSN 0899-5362.
  6. ^ Catuneanu, O.; Hancox, P.J.; Rubidge, B.S. (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. Bibcode:1998BasR...10..417C. doi:10.1046/j.1365-2117.1998.00078.x. ISSN 1365-2117. S2CID 56420970.
  7. ^ O. Catuneanu, P.J. Hancox and B.S. Rubidge (2002-11-01). "Foredeep submarine fans and forebulge deltas: orogenic off-loading in the underfilled Karoo Basin". Journal of African Earth Sciences. 35 (4): 489–502. Bibcode:2002JAfES..35..489C. doi:10.1016/S0899-5362(02)00154-9. ISSN 1464-343X.
  8. ^ Catuneanu, Octavian (2004). "Basement control on flexural profiles and the distribution of foreland facies: The Dwyka Group of the Karoo Basin, South Africa". Geology. 32 (6): 517. Bibcode:2004Geo....32..517C. doi:10.1130/G20526.1. ISSN 0091-7613.
  9. ^ Visser, J.N.J. (1989-05-01). "The Permo-Carboniferous Dwyka Formation of Southern Africa: Deposition by a predominantly subpolar marine ice sheet". Palaeogeography, Palaeoclimatology, Palaeoecology. 70 (4): 377–391. Bibcode:1989PPP....70..377V. doi:10.1016/0031-0182(89)90115-6. ISSN 0031-0182.
  10. ^ Thomas, R.J., Marshall, C.G.A., Du Plessis, A., Fitch, F.J., Miller, J.A., Von Brunn, V. and Watkeys, M.K., 1992. Geological studies in southern Natal and Transkei: implications for the Cape Orogen. Inversion Tectonics of the Cape Fold Belt, Karoo and Cretaceous Basins of Southern Africa. Balkema, Rotterdam, pp.229–236. Link: https://www.researchgate.net/profile/Bob_Thomas4/publication/290693065_Geological_studies_in_southern_Natal_and_Transkei_implications_for_the_Cape_Orogen/links/5772141e08ae6219474a6519.pdf
  11. ^ Bangert, Berthold; Stollhofen, Harald; Lorenz, Volker; Armstrong, Richard (1999-07-01). "The geochronology and significance of ash-fall tuffs in the glaciogenic Carboniferous-Permian Dwyka Group of Namibia and South Africa". Journal of African Earth Sciences. 29 (1): 33–49. Bibcode:1999JAfES..29...33B. doi:10.1016/S0899-5362(99)00078-0. ISSN 1464-343X.
  12. ^ Theron, J.N. and Blignault, H.J., 1975. A model for the sedimentation of the Dwyka glacials in the southwestern Cape. Gondwana Geology, pp.347–356.
  13. ^ Visser, Johan N.J.; Young, Grant M. (1990-12-01). "Major element geochemistry and paleoclimatology of the Permo-Carboniferous glacigene Dwyka Formation and postglacial mudrocks in southern Africa". Palaeogeography, Palaeoclimatology, Palaeoecology. 81 (1–2): 49–57. Bibcode:1990PPP....81...49V. doi:10.1016/0031-0182(90)90039-A. ISSN 0031-0182.
  14. ^ Von Brunn, V. and Visser, J.N.J., 1999. Lithostratigraphy of the Mbizane Formation (Dwyka group). South African Committee for Stratigraphy. Lithostratigraphic Series, (32), p.10.
  15. ^ Huber, Heinz; Koeberl, Christian; McDonald, Iain; Reimold, Wolf Uwe (2001-06-15). "Geochemistry and petrology of Witwatersrand and Dwyka diamictites from South Africa: search for an extraterrestrial component". Geochimica et Cosmochimica Acta. 65 (12): 2007–2016. Bibcode:2001GeCoA..65.2007H. doi:10.1016/S0016-7037(01)00569-5. ISSN 0016-7037.
  16. ^ Brunn, V. Von (1977-08-01). "A furrowed intratillite pavement in the Dwyka Group of northern Natal". South African Journal of Geology. 80 (2). ISSN 1012-0750.
  17. ^ Gravenor, V., von Brunn, C.P. (1983-09-01). "A model for late Dwyka glaciomarine sedimentation in the Eastern Karoo basin". South African Journal of Geology. 86 (3). ISSN 1012-0750.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  18. ^ Brunn, V. von; Marshall, C. G. A. (1989-12-01). "Glaciated surfaces and the base of the Dwyka Formation near Pietermaritzburg, Natal". South African Journal of Geology. 92 (4). ISSN 1012-0750.
  19. ^ Berthold, Bangert (2000). Tephrostratigraphy, petrography, geochemistry, age and fossil record of the Ganigobis Shale Member and associated glaciomarine deposits of the Dwyka Group, Late Carboniferous, southern Africa (Thesis). Universität Würzburg.
  20. ^ Gravenor, C.P.; von Brunn, V.; Dreimanis, A. (1984-03-01). "Nature and classification of waterlain glaciogenic sediments, exemplified by Pleistocene, Late Paleozoic and Late Precambrian deposits". Earth-Science Reviews. 20 (2): 105–166. Bibcode:1984ESRv...20..105G. doi:10.1016/0012-8252(84)90023-0. ISSN 0012-8252.
  21. ^ von Brunn, V. (1996-10-01). "The Dwyka Group in the northern part of Kwazulu/Natal, South Africa: sedimentation during late Palaeozoic deglaciation". Palaeogeography, Palaeoclimatology, Palaeoecology. 125 (1–4): 141–163. Bibcode:1996PPP...125..141V. doi:10.1016/S0031-0182(96)00028-4. ISSN 0031-0182.
  22. ^ Von Brunn, V. (1994), "Glaciogenic deposits of the Permo-Carboniferous Dwyka Group in the eastern region of the Karoo Basin, South Africa", Earth's Glacial Record, Cambridge University Press, pp. 60–69, doi:10.1017/CBO9780511628900.005, ISBN 9780511628900, retrieved 2018-11-23
  23. ^ Bordy, E.M. (2018-03-01). "Lithostratigraphy of the Tshidzi Formation (Dwyka Group, Karoo Supergroup), South Africa". South African Journal of Geology. 121 (1): 109–118. doi:10.25131/sajg.121.0008. ISSN 1996-8590.
  24. ^ Bamford, M. K. (2000-07-01). "Fossil woods of Karoo age deposits in South Africa and Namibia as an aid to biostratigraphical correlation". Journal of African Earth Sciences. 31 (1): 119–132. Bibcode:2000JAfES..31..119B. doi:10.1016/S0899-5362(00)00077-4. ISSN 1464-343X.
  25. ^ Bamford, Marion K. (2004-01-01). "Diversity of the Woody Vegetation of Gondwanan Southern Africa". Gondwana Research. 7 (1): 153–164. Bibcode:2004GondR...7..153B. doi:10.1016/S1342-937X(05)70314-2. ISSN 1342-937X.
  26. ^ R., McLachlan, I.; Ann, Anderson (1973). "A REVIEW OF THE EVIDENCE FOR MARINE CONDITIONS IN SOUTHERN AFRICA DURING DWYKA TIMES". Palaeontologia Africana. ISSN 0078-8554. Archived from the original on 2018-11-24. Retrieved 2018-11-23.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  27. ^ Barbolini, N., Bamford, M.K. (2014-12-01). "Palynology of an Early Permian coal seam from the Karoo Supergroup of Botswana". Journal of African Earth Sciences. 100: 136–144. Bibcode:2014JAfES.100..136B. doi:10.1016/j.jafrearsci.2014.06.008. ISSN 1464-343X.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  28. ^ Bangert, B; Bamford, Marion (2001-01-01). "Carboniferous pycnoxylic woods from the Dwyka group of Southern Namibia". Palaeontologia Africana: 13–23.
  29. ^ Scheffler, K.; Hoernes, S.; Schwark, L. (2003). "Global changes during Carboniferous–Permian glaciation of Gondwana: Linking polar and equatorial climate evolution by geochemical proxies". Geology. 31 (7): 605. Bibcode:2003Geo....31..605S. doi:10.1130/0091-7613(2003)031<0605:GCDCGO>2.0.CO;2. ISSN 0091-7613.
  30. ^ Smith, R.M.H., Eriksson, P.G., Botha, W.J. (1993-01-01). "A review of the stratigraphy and sedimentary environments of the Karoo-aged basins of Southern Africa". Journal of African Earth Sciences (and the Middle East). 16 (1–2): 143–169. Bibcode:1993JAfES..16..143S. doi:10.1016/0899-5362(93)90164-L. ISSN 0899-5362.{{cite journal}}: CS1 maint: multiple names: authors list (link)
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