Uitenhage Group
{{short description|Geological group of post-Karoo Mesozoic rocks in South Africa}}
{{Infobox rockunit
| name = Uitenhage Group
| period = Early Cretaceous
| age = Late Early Jurassic-Early Cretaceous
~{{fossilrange|183|100}}
| type = Geologic group
| prilithology = Sandstone, mudstone, siltstone, shale, conglomerate
| otherlithology = Calcite
| namedfor = Uitenhage area
| region = Western & Eastern Cape
| country = South Africa
| subunits = Enon, Kirkwood, Sundays River & Buffelskloof Formations
| overlies = Suurberg Group
| underlies = Algoa Group
| map = Uitenhage Group Algoa Gamtoos map.png
| map_caption = Map showing extent of the Uitenhage Group in the Algoa and Gamtoos Basins}}
The Uitenhage Group is one of three geological groups, which comprise the onshore and offshore post-Karoo middle to lower Upper Mesozoic geological rock units in South Africa.{{Cite journal|last=Shone|first=R.W.|date=2006-01-01|title=Onshore post-Karoo Mesozoic deposits|url=https://www.researchgate.net/publication/284594629|journal=The Geology of South Africa|pages=541–552}}{{Cite journal|last1=McLachlan|first1=I.R.|last2=McMillan|first2=I.K.|date=1979-01-01|title=Microfaunal biostratigraphy, chronostratigraphy and history of Mesozoic and Cenozoic deposits on the coastal margin of South Africa.|url=https://www.researchgate.net/publication/280824976|journal=Geological Society of South Africa, Special Publication|volume=6|pages=161–181}}{{Cite journal|date=1997-01-01|title=Chapter 13 Late Mesozoic Sedimentary Basins Off the South Coast of South Africa|journal=Sedimentary Basins of the World|language=en|volume=3|pages=319–376|doi=10.1016/S1874-5997(97)80016-0|issn=1874-5997|last1=McMillan|first1=I.K.|last2=Brink|first2=G.I.|last3=Broad|first3=D.S.|last4=Maier|first4=J.J.|isbn=9780444825711}}{{cite web| url=http://www.mme.gov.na/files/publications/66e_Dingle_Continental%20margin.pdf | title=Structural and sedimentary development of the continental margin off Southwestern Africa | access-date=2024-02-03}} Stratigraphically, the Uitenhage Group overlies the Suurberg Group and is overlain by the Algoa Group.{{Cite book|title=Origin and Evolution of the Cape Mountains and Karoo Basin|last=Marsh|first=J. S. Goonie|date=2016|publisher=Springer, Cham|isbn=9783319408583|series=Regional Geology Reviews|pages=59–65|language=en|doi=10.1007/978-3-319-40859-0_6|chapter = New Evidence for the Correlation of Basalts of the Suurberg Group with the Upper Part of the Karoo Basalt Sequence of Lesotho}}Klinger, H. C., & Kennedy, W. J. (1977). Cretaceous faunas from Zululand, South Africa, and southern Mozambique. The Aptian Ancyloceratidae (Ammonoidea). Annals of the South African Museum, 73(9), 215-359. It contains four formations that range in age from late Early Jurassic and late Early Cretaceous in age (~183 - 100 Ma).
Geographic extent
In the onshore part of the southern Cape, deposits of the Uitenhage Group occur predominantly in the Algoa and Gamtoos Basins, which are situated north/north-west of Port Elizabeth in the Eastern Cape, South Africa. Smaller deposits also occur in the Baviaanskloof, Georginda, Vlakteplaas, Oudtshoorn, Plettenberg Bay, Knysna, Herbertsdale-Mossel Bay, Heidelberg-Riversdale, Swellendam, and Worcester-Robertson Basins.{{Cite journal|last1=Muir|first1=R.A.|last2=Bordy|first2=E.M.|last3=Reddering|first3=J.S.V.|last4=Viljoen|first4=J.H.A.|date=2017-06-01|title=Lithostratigraphy of the Enon Formation (Uitenhage Group), South Africa|journal=South African Journal of Geology|language=en|volume=120|issue=2|pages=273–280|doi=10.25131/gssajg.120.2.273|bibcode=2017SAJG..120..273M |issn=1012-0750}} These are grabens and half-grabens (rift basins) that opened up due to mainly normal faulting processes during the break-up of Gondwana.{{Cite journal|last1=Gresse|first1=P.G.|last2=Theron|first2=J.N.|last3=Fitch|first3=F.J.|last4=Miller|first4=J.A.|date=1992-01-01|title=Tectonic inversion and radiometric resetting of the basement in the Cape Fold Belt|url=https://www.researchgate.net/publication/279708057|journal=Inversion Tectonics of the Cape Fold Belt, Karoo and Cretaceous Basins of Southern Africa|pages=217–228}}
Stratigraphic units
Stratigraphic units in this group include (from oldest to youngest):
- Enon Formation: Contains subordinate sandstones and different types of thickly-bedded conglomerates, which consist mainly of quartzite and sometimes slate, shale, and charcoal. The clasts are poorly-sorted, sub-rounded to rounded pebbles and cobbles. Deposition occurred mainly in high-energy alluvial environments (e.g., alluvial fans, low sinuosity rivers).
- Kirkwood Formation: Contains mainly medium-grained sandstone that is locally charcoal-rich, sporadic conglomerates, and variegated mudstone. Out of the three formations of the Uitenhage Group, the Kirkwood is the most well-studied, and is extremely fossil-rich. Deposition occurred under mainly fluvial conditions at or near sea level.{{Cite journal|last1=Muir|first1=R.A.|last2=Bordy|first2=E.M.|last3=Reddering|first3=J.S.V.|last4=Viljoen|first4=J.H.A.|date=2017-06-01|title=Lithostratigraphy of the Kirkwood Formation (Uitenhage Group), including the Bethelsdorp, Colchester and Swartkops Members, South Africa|journal=South African Journal of Geology|language=en|volume=120|issue=2|pages=281–293|doi=10.25131/gssajg.120.2.281|bibcode=2017SAJG..120..281M |issn=1012-0750}}{{Cite web|last1=Rich|first1=Tom|last2=Molnar|first2=R.E.|last3=Vickers Rich|first3=Patricia|date=1983-01-01|title=Fossil vertebrates from the Late Jurassic or Early Cretaceous Kirkwood Formation, Algoa Basin, southern Africa.|url=https://www.researchgate.net/publication/291859449|volume=86|pages=281–291}}{{Cite journal|last1=W. McPhee|first1=Blair|last2=Mannion|first2=Philip|last3=De Klerk|first3=William|last4=Choiniere|first4=Jonah|date=2016-04-01|title=High diversity in the sauropod dinosaur fauna of the Lower Cretaceous Kirkwood Formation of South Africa: Implications for the Jurassic–Cretaceous transition|url=https://www.researchgate.net/publication/285386536|journal=Cretaceous Research|volume=59|pages=228–248|doi=10.1016/j.cretres.2015.11.006|bibcode=2016CrRes..59..228M |hdl=10044/1/27470|hdl-access=free}}{{Cite web|last=Bamford|first=Marion|date=1986-01-01|title=Aspects of the palaeoflora of the Kirkwood and Sundays River Formations, Algoa Basin, South Africa|url=https://www.researchgate.net/publication/35640573}}{{Cite journal|last1=Gomez|first1=Bernard|last2=Bamford|first2=Marion|last3=Delclòs|first3=Xavier|date=2002-03-01|title=Lower Cretaceous plant cuticles and amber (Kirkwood Formation, South Africa)|url=https://www.researchgate.net/publication/235355687|journal=Comptes Rendus Palevol|volume=1|issue=2|pages=83–87|doi=10.1016/S1631-0683(02)00014-3|bibcode=2002CRPal...1...83G }}{{Cite journal | doi=10.1671/039.029.0101|title = A "basal" tetanuran from the Lower Cretaceous Kirkwood Formation of South Africa| journal=Journal of Vertebrate Paleontology| volume=29| pages=283–285|year = 2009|last1 = Forster|first1 = Catherine A.| last2=Farke| first2=Andrew A.| last3=McCartney| first3=Jacob A.| last4=De Klerk| first4=William J.| last5=Ross| first5=Callum F.| issue=1 | bibcode=2009JVPal..29..283F | s2cid=131280290 }}
- Sundays River Formation: Contains fine- to medium-grained grey sandstones, siltstones, and mudstones. The sandstone layers are frequently cemented with calcite and contain shell fragments. The Sundays River is also highly fossiliferous. Deposition occurred under shallow marine and estuarine conditions.{{Cite journal|last1=Brenner|first1=P|last2=HJ|first2=Oertli|date=1976-01-01|title=Lower Cretaceous Ostracodes (Valanginian to Hauterivian) from the Sundays River Formation, Algoa Basin, South Africa|url=https://www.researchgate.net/publication/281179925|journal=Bulletin Centre Recherches Pau-SNPA|volume=10|pages=471–533}}{{Cite web| last=Bamford|first=Marion|date=1986-01-01|title=Aspects of the palaeoflora of the Kirkwood and Sundays River Formations, Algoa Basin, South Africa|url=https://www.researchgate.net/publication/35640573}}{{Cite journal|last=Andrews|first=C.W.|date=2018-05-08|title=Description of a new plesiosaur (Plesiosaurus capensis, sp. nov.) from the Uitenhage Beds of Cape Colony|url=https://www.researchgate.net/publication/284255099|journal=Annals of the South African Museum|volume=7|pages=309–322}}
- Buffelskloof Formation: Deposited in a high energy braided river system with conglomerate deposits, similar to that of the Enon Formation. Some fossil material such as petrified wood and scant remains of fossil dinosaur teeth and claws have been recovered. In the Herbertsdale/Mossel Bay Basin this formation, with the overlying Hartenbos Formation, forms the lateral equivalent of the Sundays River Formation.{{Cite web |url=http://www.phsconsulting.co.za/uploads/7648806Annex%20D%20-%20PIA%20Brief%20Maandagskop.pdf |title=Extension of quarrying on portion 12 of farm Hartenbosch 217 (Maandagskop crusher), Mossel bay, Western cape |access-date=2018-05-08 |archive-date=2018-05-08 |archive-url=https://web.archive.org/web/20180508185332/http://www.phsconsulting.co.za/uploads/7648806Annex%20D%20-%20PIA%20Brief%20Maandagskop.pdf |url-status=dead }}
Paleontology
Fossils are especially common in the Kirkwood and Sundays River Formations, although regarding the Sundays River Formation the most common fossils are of invertebrates. Past expeditions within the Kirkwood Formation have uncovered several dis-articulated remains of theropod, sauropod, and ornithopod dinosaurs,{{Cite web| last1=Rich|first1=Tom|last2=Molnar|first2=R.E.|last3=Vickers Rich|first3=Patricia|date=1983-01-01|title=Fossil vertebrates from the Late Jurassic or Early Cretaceous Kirkwood Formation, Algoa Basin, southern Africa.|url=https://www.researchgate.net/publication/291859449|volume=86|pages=281–291}}{{Cite journal|last1=De Klerk|first1=William|last2=Forster|first2=Catherine|last3=Sampson|first3=Scott|last4=Chinsamy-Turan|first4=Anusuya|last5=Ross|first5=Callum|date=2000-06-27|title=A new coelurosaurian dinosaur from the Early Cretaceous of South Africa|url=https://www.researchgate.net/publication/233184192|journal=Journal of Vertebrate Paleontology|volume=20|issue=2|pages=324–332|doi=10.1671/0272-4634(2000)020[0324:ANCDFT]2.0.CO;2|s2cid=128622530 }}{{Cite journal|last1=Choiniere|first1=Jonah|last2=Forster|first2=Catherine|last3=De Klerk|first3=William|date=2012-08-01|title=New information on Nqwebasaurus thwazi, a coelurosaurian theropod from the Early Cretaceous Kirkwood Formation in South Africa|url=https://www.researchgate.net/publication/257588809|journal=Journal of African Earth Sciences|volume=s 71–72|pages=1–17|doi=10.1016/j.jafrearsci.2012.05.005|bibcode=2012JAfES..71....1C }} and a plesiosaur fossil is known from the Sundays River Formation. Fossil remains of amphibians, lizards, fishes, and small mammals have also been recovered.{{Cite journal|last1=Ross|first1=Callum|last2=Sues|first2=Hans-Dieter|last3=De Klerk|first3=William|date=1999-03-15|title=Lepidosaurian remains from the Lower Cretaceous Kirkwood Formation of South Africa|url=https://www.researchgate.net/publication/241731004|journal=Journal of Vertebrate Paleontology |volume=19|issue=1 |pages=21–27|doi=10.1080/02724634.1999.10011119|bibcode=1999JVPal..19...21R }} A variety of bivalve, gastropod, ammonites, and ostracods are likewise known from these deposits. The fossil flora is equally diverse and silicified tree trunks - some with evidence of being charred by fire{{Cite journal|date=2015-09-01|title=Lower Cretaceous deposit reveals first evidence of a post-wildfire debris flow in the Kirkwood Formation, Algoa Basin, Eastern Cape, South Africa|journal=Cretaceous Research|language=en|volume=56|pages=161–179|doi=10.1016/j.cretres.2015.04.005|issn=0195-6671|last1=Muir|first1=Robert A.|last2=Bordy|first2=Emese M.|last3=Prevec|first3=Rose|bibcode=2015CrRes..56..161M }} - have also been found.
References
{{reflist}}
{{Geology of South Africa|formations}}
Category:Geologic groups of Africa
Category:Geologic formations of South Africa
Category:Cretaceous South Africa
Category:Jurassic South Africa
Category:Shallow marine deposits