Kirkwood Formation

The Kirkwood Formation is a geological formation found in the Eastern and Western Cape provinces in South Africa. It is one of the four formations found within the Uitenhage Group of the Algoa Basin – its type locality – and in the neighbouring Gamtoos Basin. Outcrops of the Kirkwood are also found along the Worcester-Pletmos, Herbertsdale-Riversdale, Heidelberg-Mossel Bay, and Oudtshoorn-Gamtoos basin lines.^[1][2] At these basins the Kirkwood Formation underlies the Buffelskloof Formation and not the Sundays River Formation.^[3]

Kirkwood Formation
Stratigraphic range: Berriasian-Hauterivian ~140–125 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Type	Geological formation
Unit of	Uitenhage Group
Sub-units	Swartkops Member, Colchester Member, Bethelsdorp Member, Wood beds
Underlies	Sundays River Formation, Buffelskloof Formation
Overlies	Enon Formation
Thickness	up to 2,210 m (7,250 ft)
Lithology
Primary	Sandstone, claystone
Other	Mudstone, siltstone
Location
Coordinates	33°24′S 25°30′E / 33.4°S 25.5°E / -33.4; 25.5
Approximate paleocoordinates	45°00′S 11°30′W / 45.0°S 11.5°W / -45.0; -11.5
Region	Western & Eastern Cape
Country	South Africa
Type section
Named for	Kirkwood, Eastern Cape
Map showing extent of the Kirkwood Formation (green) in the Algoa and Gamtoos Basins

Geology

The Kirwood Formation was formed along the southern section of South Africa during the break up of Gondwana. Dating it has proven tricky, with some regarding it as a Late Jurassic (~145 Ma)^[4][5] or Early Cretaceous deposit (~135 Ma).^[6][7][8] However, dating the Kirkwood's abundant volcanic ash layers by U-Pb methods is currently underway.

The Kirkwood Formation is composed of sedimentary rocks deposited under fluvial conditions at or near sea level, such as variegated mudstone (an iconic feature), medium-grained lithic sandstone (often being charcoal-rich), and sporadic conglomerates. At its base, the Kirkwood Formation includes a significant deposit of fine-to-medium grained, poorly-sorted (often quartzitic) estuarine sandstone with subordinate dark grey to brow shale layers. This deposit was described as the Swartkops Member. The lower portion of the remainder of the Formation is composed predominantly of siltstones, but includes a smaller sandstone layer (described as part of the Bethelsdorp Member). The upper portion of the Formation is composed predominantly of fine, clay-rich mudstones, with multiple smaller layers of estuarine sandstone.^[9][10]

The Kirkwood is the second formation of the Uitenhage Group, positioned between the overlying Sundays River Formation and the underlying Enon Formation. Only three geological members have been described within it: the Swartkops Member which contains estuarine sandstone deposits and lacks fossils. The Colchester Member is the most fossil-rich containing terrestrial and lacustrine fossils and is composed of dark grey shale, siltstones and sandstones. The third, the Bethelsdorp Member, resembles the Colchester in containing dark-grey shales and sandstone, and contains marine microfossils.^[11] The upper section of the member is overlain by mudstone and siltstone.^[12]

Paleontology

The Kirkwood Formation is the most fossil-rich formation of Late Jurassic - Early Cretaceous age known in South Africa. It has yielded disarticulated remains of theropod and ornithopod dinosaurs, and several sauropod species in which the Kirkwood is particularly rich, and includes indeterminate members of Diplodocidae, Dicraeosauridae and Brachiosauridae, as well as Algoasaurus, a eusauropod of uncertain affinities.^[13] A partial skull and teeth of a stegosaur, Paranthodon, has also been discovered.^[14] In addition to Paranthodon, an ankylosaur vertebra has also been described.^[15] Fossils belonging to a dryosaurid ornithopod were unearthed in three expeditions between 1995 and 1999. In 2022, these remains were described as a new genus and species, Iyuku raathi. Iyuku is primarily known from remains belonging to hatchling and juvenile individuals.^[16] Indeterminate members of Rhynchocephalia and Squamata have also been discovered.^[17] Mesozoic-aged amber has also been recovered from the Kirkwood.^[18] The most well-known find from the Kirkwood is Nqwebasaurus, a basal ornithomimosaur.^[19] Fragmentary remains of various reptile,^[20] frog, insect, and mammal fossils have also been found, including fish scales and freshwater bivalves.^[21] In addition several plant species such as bryophytes, ferns, conifers, cycads, and bennettitaleans have been discovered, including silicified fossil tree trunks in the sandstone sections which show evidence of being burned.^[22][23]

References

1. Shone, R.W. (2006-01-01). "Onshore post-Karoo Mesozoic deposits". The Geology of South Africa: 541–552.
2. 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". South African Journal of Geology. 120 (2): 281–293. Bibcode:2017SAJG..120..281M. doi:10.25131/gssajg.120.2.281. ISSN 1012-0750.
3. John Pether (April 2014) Extension of quarrying on Portion 12 of Farm Hartenbosch 217 (Maandagskop Crusher), Mossel Bay, Western Cape. Brief Palaeontological Assessment (Desktop Study). Link:http://www.phsconsulting.co.za/uploads/7593872PIA%20Brief%20Maandagskop.pdf
4. 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.
5. 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". South African Journal of Geology. 79 (3). ISSN 1012-0750.{{cite journal}}: CS1 maint: multiple names: authors list (link)
6. 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". Sedimentary Basins of the World. 3: 319–376. doi:10.1016/S1874-5997(97)80016-0. ISBN 9780444825711. ISSN 1874-5997.
7. Gomez, Bernard; Bamford, Marion; Delclòs, Xavier (2002-03-01). "Lower Cretaceous plant cuticles and amber (Kirkwood Formation, South Africa)". Comptes Rendus Palevol. 1 (2): 83–87. Bibcode:2002CRPal...1...83G. doi:10.1016/S1631-0683(02)00014-3.
8. W. McPhee, Blair; Mannion, Philip; De Klerk, William; Choiniere, Jonah (2016-04-01). "High diversity in the sauropod dinosaur fauna of the Lower Cretaceous Kirkwood Formation of South Africa: Implications for the Jurassic–Cretaceous transition". Cretaceous Research. 59: 228–248. Bibcode:2016CrRes..59..228M. doi:10.1016/j.cretres.2015.11.006. hdl:10044/1/27470.
9. 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". South African Journal of Geology. 120 (2): 281–293. Bibcode:2017SAJG..120..281M. doi:10.25131/gssajg.120.2.281. ISSN 1012-0750.
10. Rich, Tom; Molnar, R.E.; Vickers Rich, Patricia (1983-01-01). "Fossil vertebrates from the Late Jurassic or Early Cretaceous Kirkwood Formation, Algoa Basin, southern Africa". 86: 281–291. {{cite journal}}: Cite journal requires |journal= (help)
11. 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". South African Journal of Geology. 120 (2): 281–293. Bibcode:2017SAJG..120..281M. doi:10.25131/gssajg.120.2.281. ISSN 1012-0750.
12. A. Fcrster, C; Frost, S; Ross, Callum (1995-01-01). "NEW DINOSAUR MATERIAL AND PALEOENVIRONMENT OF THE EARLY CRETACEOUS KIRKWOOD FORMATION, ALGOA BASIN, SOUTH AFRICA". Journal of Vertebrate Paleontology. 15: 29A.
13. W. McPhee, Blair; Mannion, Philip; De Klerk, William; Choiniere, Jonah (2016-04-01). "High diversity in the sauropod dinosaur fauna of the Lower Cretaceous Kirkwood Formation of South Africa: Implications for the Jurassic–Cretaceous transition". Cretaceous Research. 59: 228–248. Bibcode:2016CrRes..59..228M. doi:10.1016/j.cretres.2015.11.006. hdl:10044/1/27470.
14. "Table 16.1," in Weishampel, et al. (2004). Page 345
15. Rozadilla, Sebastián; Agnolín, Federico; Manabe, Makoto; Tsuihiji, Takanobu; Novas, Fernando E. (September 2021). "Ornithischian remains from the Chorrillo Formation (Upper Cretaceous), southern Patagonia, Argentina, and their implications on ornithischian paleobiogeography in the Southern Hemisphere". Cretaceous Research. 125: 104881. Bibcode:2021CrRes.12504881R. doi:10.1016/j.cretres.2021.104881. ISSN 0195-6671.
16. Forster CA, de Klerk WJ, Poole KE, Chinsamy-Turan A, Roberts EM, Ross CF (2022). "Iyuku raathi, a new iguanodontian dinosaur from the Early Cretaceous Kirkwood Formation, South Africa". The Anatomical Record. doi:10.1002/ar.25038. PMID 35860957. S2CID 250730794.
17. Ross, Callum F.; Sues, Hans-Dieter; De Klerk, William J. (1999-03-15). "Lepidosaurian remains from the Lower Cretaceous Kirkwood Formation of South Africa". Journal of Vertebrate Paleontology. 19 (1): 21–27. Bibcode:1999JVPal..19...21R. doi:10.1080/02724634.1999.10011119. ISSN 0272-4634.
18. Gomez, Bernard; Bamford, Marion; Delclòs, Xavier (2002-03-01). "Lower Cretaceous plant cuticles and amber (Kirkwood Formation, South Africa)". Comptes Rendus Palevol. 1 (2): 83–87. Bibcode:2002CRPal...1...83G. doi:10.1016/S1631-0683(02)00014-3.
19. De Klerk, William; Forster, Catherine; Sampson, Scott; Chinsamy-Turan, Anusuya; Ross, Callum (2000-06-27). "A new coelurosaurian dinosaur from the Early Cretaceous of South Africa". Journal of Vertebrate Paleontology. 20 (2): 324–332. doi:10.1671/0272-4634(2000)020[0324:ANCDFT]2.0.CO;2. S2CID 128622530.
20. Ross, Callum; Sues, Hans-Dieter; De Klerk, William (1999-03-15). "Lepidosaurian remains from the Lower Cretaceous Kirkwood Formation of South Africa". Journal of Vertebrate Paleontology. 19: 21–27. Bibcode:1999JVPal..19...21R. doi:10.1080/02724634.1999.10011119.
21. 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". South African Journal of Geology. 120 (2): 281–293. Bibcode:2017SAJG..120..281M. doi:10.25131/gssajg.120.2.281. ISSN 1012-0750.
22. Bamford, Marion (1986-01-01). "Aspects of the palaeoflora of the Kirkwood and Sundays River Formations, Algoa Basin, South Africa". {{cite journal}}: Cite journal requires |journal= (help)
23. Muir, Robert A.; Bordy, Emese M.; Prevec, Rose (2015-09-01). "Lower Cretaceous deposit reveals first evidence of a post-wildfire debris flow in the Kirkwood Formation, Algoa Basin, Eastern Cape, South Africa". Cretaceous Research. 56: 161–179. Bibcode:2015CrRes..56..161M. doi:10.1016/j.cretres.2015.04.005. ISSN 0195-6671.