Sundays River Formation
Stratigraphic range: Valanginian-Hauterivian
~139–131 Ma

PreЄ

Sandstone layer overlying siltstone/mudstone

Type| Geological formation
Unit of| Uitenhage Group
Underlies| Algoa Group
Overlies| Kirkwood Formation
Thickness| Up to 2,000 m (6,600 ft)
Lithology
Primary| Sandstone, claystone
Other| Siltstone, mudstone
Location
Coordinates|  [ ⚑ ] : 33°36′S 25°36′E﻿ / ﻿33.6°S 25.6°E﻿ / -33.6; 25.6
Paleocoordinates|  [ ⚑ ] 45°06′S 11°30′W﻿ / ﻿45.1°S 11.5°W﻿ / -45.1; -11.5
Region| Eastern & Western Cape
Country| South Africa
Type section
Named for| Sundays River

Map showing extent of the Sundays River Formation in the Algoa Basin

The Sundays River Formation is a geological formation found in the Eastern and Western Cape provinces in South Africa. It is the second youngest of the four formations found within the Uitenhage Group of the Algoa Basin, its type locality, and the only location where outcrops have been located. The Sundays River has been measured at a maximum thickness of 2,000 metres (6,600 ft).[1]

## Contents

* 1 Geology
* 2 Paleontology
* 3 Fossil content
* 3.1 Plesiosaurs
* 4 References

## Geology

The Sundays River Formation overlies the Kirkwood Formation which it grades laterally into in certain areas, meaning that they correlate in age in some localities.[2][3] The sedimentary rock of the Sundays River comprises mainly fine to medium grained grey sandstones which often contain shell fragments, siltstones, and mudstones. The sandstone layers are frequently cemented with calcite layers. These were deposited in a shallow marine environment which likely included estuarine and lagoonal settings.[4][5]

## Paleontology

The Sundays River is highly fossiliferous and a variety of fossil flora and fauna have been discovered. Invertebrate shells from ammonites, bivalves, and microfossils such as species of forams and ostracods[6] are commonly found cemented within the calcite layers in the sandstone deposits.[7][8][9] Trace fossils of gastropod tracks which are infilled with siltstone are also frequently found.[10][11] Some vertebrate fossils have been found, most notably a near-complete skeleton of a marine plesiosaur, Leptocleidus capensis.[12] However, very little study has been done on the plesiosaur specimen discovered here. Plant remains[13] and non-diagnostic vertebrate fossils have also been recovered.[14]

## Fossil content

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Color key
| Taxon | Reclassified taxon | Taxon falsely reported as present | Dubious taxon or junior synonym | Ichnotaxon | Ootaxon | Morphotaxon

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| Notes
Uncertain or tentative taxa are in small text; ~~crossed out~~ taxa are discredited.

### Plesiosaurs

Plesiosaurs of the Sundays River Formation

Genus  | Species  | Location  | Stratigraphic position  | Material  | Notes  | Images
Leptocleidus | L. capensis |  |  |  | A leptocleidid plesiosaur |

## References

1. ↑ Shone, R.W. (2006-01-01). "Onshore post-Karoo Mesozoic deposits". The Geology of South Africa: 541–552. https://www.researchgate.net/publication/284594629.
2. ↑ Shone, R.W. (2006-01-01). "Onshore post-Karoo Mesozoic deposits". The Geology of South Africa: 541–552. https://www.researchgate.net/publication/284594629.
3. ↑ McLachlan, I.R.; McMillan, I.K. (1979-01-01). "Microfaunal biostratigraphy, chronostratigraphy and history of Mesozoic and Cenozoic deposits on the coastal margin of South Africa.". Geological Society of South Africa, Special Publication 6: 161–181. https://www.researchgate.net/publication/280824976.
4. ↑ McMillan, I.K.; Brink, G.I.; Broad, D.S.; Maier, J.J. (1997-01-01). "Chapter 13 Late Mesozoic Sedimentary Basins Off the South Coast of South Africa" (in en). Sedimentary Basins of the World 3: 319–376. doi:10.1016/S1874-5997(97)80016-0. ISBN 9780444825711. ISSN 1874-5997.
5. ↑ Muir, R.A.; Bordy, E.M.; Reddering, J.S.V.; Viljoen, J.H.A. (2017-06-01). "Lithostratigraphy of the Kirkwood Formation (Uitenhage Group), including the Bethelsdorp, Colchester and Swartkops Members, South Africa" (in en). South African Journal of Geology 120 (2): 281–293. doi:10.25131/gssajg.120.2.281. ISSN 1012-0750. Bibcode: 2017SAJG..120..281M.
6. ↑ Brenner, P; HJ, Oertli (1976-01-01). "Lower Cretaceous Ostracodes (Valanginian to Hauterivian) from the Sundays River Formation, Algoa Basin, South Africa". Bulletin Centre Recherches Pau-SNPA 10: 471–533. https://www.researchgate.net/publication/281179925.
7. ↑ Brenner, P.W. McLachlan, I.R., McMillan, I.K. & (1976-09-01). "Micropalaeontological study of the Cretaceous beds at Mbotyi and Mngazana, Transkei, South Africa" (in en). South African Journal of Geology 79 (3). ISSN 1012-0750. https://journals.co.za/content/sajg/79/3/AJA10120750_2825.
8. ↑ Shone, R.W. (2006-01-01). "Onshore post-Karoo Mesozoic deposits". The Geology of South Africa: 541–552. https://www.researchgate.net/publication/284594629.
9. ↑ McMillan, I.K. (2003-01-01). "The Foraminifera of the Late Valanginian to Hauterivian (Early Cretaceous) Sundays River Formation of the Algoa Basin, Eastern Cape Province, South Africa". Annals of the South African Museum 106: 1–274. https://www.researchgate.net/publication/292770856.
10. ↑ Shone, R.W. (2006-01-01). "Onshore post-Karoo Mesozoic deposits". The Geology of South Africa: 541–552. https://www.researchgate.net/publication/284594629.
11. ↑ McMillan, I.K.; Brink, G.I.; Broad, D.S.; Maier, J.J. (1997-01-01). "Chapter 13 Late Mesozoic Sedimentary Basins Off the South Coast of South Africa" (in en). Sedimentary Basins of the World 3: 319–376. doi:10.1016/S1874-5997(97)80016-0. ISBN 9780444825711. ISSN 1874-5997.
12. ↑ Andrews, C.W. (2018-04-26). "Description of a new plesiosaur (Plesiosaurus capensis, sp. nov.) from the Uitenhage Beds of Cape Colony". Annals of the South African Museum 7: 309–322. https://www.researchgate.net/publication/284255099.
13. ↑ Bamford, Marion (1986-01-01). Aspects of the palaeoflora of the Kirkwood and Sundays River Formations, Algoa Basin, South Africa. https://www.researchgate.net/publication/35640573.
14. ↑ McMillan, I.K.; Brink, G.I.; Broad, D.S.; Maier, J.J. (1997-01-01). "Chapter 13 Late Mesozoic Sedimentary Basins Off the South Coast of South Africa" (in en). Sedimentary Basins of the World 3: 319–376. doi:10.1016/S1874-5997(97)80016-0. ISBN 9780444825711. ISSN 1874-5997.

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