| Nama Group | |
|---|---|
| Stratigraphic range: Ediacaran ~ | |
| Type | Group |
| Unit of | Nama Basin |
| Sub-units | See text |
| Underlies | Table Mountain Sandstone |
| Overlies | Basement |
| Area | 125,000 km2 (48,000 sq mi) |
| Lithology | |
| Primary | Sandstone |
| Other | Siltstone, mudstone, limestone |
| Location | |
| Coordinates | 23°54′S 16°42′E / 23.9°S 16.7°E |
| Approximate paleocoordinates | 41°24′S 179°12′W / 41.4°S 179.2°W |
| Region | Omaheke, Hardap & ǁKaras Regions |
| Country |  Namibia |
 Geologic map of Namibia with the Nama Group in beige | |
The Nama Group is a 125,000 square kilometres (48,000 sq mi) megaregional Vendian to Cambrian group of stratigraphic sequences deposited in the Nama foreland basin in central and southern Namibia. The Nama Basin is a peripheral foreland basin, and the Nama Group was deposited in two early basins, the Zaris and Witputs, to the north, while the South African Vanrhynsdorp Group was deposited in the southern third.[1] The Nama Group is made of fluvial and shallow-water marine sediments, both siliciclastic and carbonate.[2] La Tinta Group in Argentina is considered equivalent to Nama Group.[3]
Description
The group extends from the Gariep Belt in the south to outcrops of pre-Damara basement in the north.[4] Thrombolite-stromatolite reefs in the Nama Group are best developed in the Kuibis Subgroup of the Zaris subbasin, and in the Huns platform of the Witputs subbasin.[5] The Nama Group is a series of interbedded shallow marine carbonates and siliciclastics deposited in a storm-dominated ramp setting.[6]
"Nama-type preservation" is an Ediacaran type preservation that presents sandstone castings of fossil creatures in which organisms are preserved in three dimensions, within fine-grained beds that were deposited in single storm or mudflow events: an example is Ausia fenestrata. Analysis performed in 2018 on Namacalathus and Cloudina skeletons from the Ediacaran Omkyk Member of the Nama Group demonstrates that both organisms originally produced aragonitic skeletons, which later underwent diagenetic conversion to calcite.[7]
Stratigraphy
The Nama Group is subdivided into:[8]
| Subgroup | Formation | Member |
|---|---|---|
| Fish River | ||
| Schwarzrand | Vergesig Formation | |
| Nomtsas Formation | ||
| Urusis Formation | Spitskop | |
| Naldaus/Nudaus Formation | Huns | |
| Niederhagen | ||
| Kuibis | Zaris Formation | Urikos & Hoogland |
| Omkyk | ||
| Dabis Formation | Kliphoek | |
| Kanies | ||
Ages
The lower and upper part of the Spitskop Member of the Urusis Formation, Schwarzrand Subgroup, had originally been dated on the basis of zircons to 545.1 ± 1 Ma and 543.3 ± 1 Ma respectively. Recalibration of the Spitskop radiometric data indicates revised dates of 542.68 ± 1.25 Ma (terminal Ediacaran) and 540.61 ± 0.67 Ma (within error of the Ediacaran–Cambrian boundary), respectively. An ash bed from the Hoogland Member towards the base of the Nama Group (Zaris Formation, Kuibus Subgroup) has yielded an age of 547.4 ± 0.3 Ma, in 2018 slightly modified to 547.32 ± 0.31 Ma. The lower part of the Nomtsas Formation has yielded an age of 539.4 ± 1 Ma, in the same year recalibrated to 538.18 ± 1.11 Ma.[9]
Fossil content
Nama-type Ediacaran fossils found in the group include:
- Ausia fenestrata[10]
- Bergaueria - Kuibis Subgroup[11]
- Brooksella - Schwarzrand Subgroup[11]
- ?Chondrites - Schwarzrand Subgroup[11]
- Cloudina - Zaris Formation[12]
- ?Diplichnites - Nomtsas Formation[11]
- Neonereites biserialis, N. uniserialis - Nomtsas Formation[11]
- Diplocraterion - Schwarzrand Subgroup[11]
- Enigmatichnus africani - Fish River Subgroup[11]
- Ernietta - Naldaus & Dabis Formations[13][14]
- Namacalathus hermanastes - Zaris Formation[15][12]
- Namalia villiersiensis - Kuibis Quartzite[16]
- Namapoikia rietoogensis - Dabis Formation[17]
- Nereites - Schwarzrand Subgroup[11]
- Protechiurus edmondsi - Kuibis Quartzite & Dabis Formation[16][18]
- Pteridinium carolinaense, P. simplex - Naldaus & Dabis Formations[13][16][19]
- Rangea schneiderhoehni - Naldaus & Dabis Formations[13][14]
- Skolithos - Fish River & Schwarzrand Subgroups[11]
- Streptichnus narbonnei - Urusis Formation[20]
- Swartpuntia germsi - Urusis Formation[19]
- Treptichnus pedum - Nomtsas Formation[21]
Gallery
Reconstruction of Swartpuntia germsi
Reconstruction of Namacalathus hermanastes
Reconstruction of Cloudina
See also
References
- ↑ Gresse, P. G., G. J. B. Germs. The Nama foreland basin: sedimentation, major unconformity bounded sequences and multisided active margin advance. 1993, Precambrian Research, 63(3-4):247-252, 259-272
- ↑ Saylor, Beverly Z., John P. Grotzinger, Gerard J. B. Germs. Sequence stratigraphy and sedimentology of the Neoproterozoic Kuibis and Schwarzrand Subgroups (Nama Group), southwestern Namibia. 1995 Precambrian Research 73:153-171.
- ↑ Iacumin, M.; Piccirillo, E.M.; Girardi, V.A.V.; Teixeira, W.; Bellieni, G.; Echeveste, H.; Fernández, R.; Pinese, J.P.P.; Ribot, A. (2001). "Early proterozoic calc-alkaline and middle proterozoic tholeiitic Dyke Swarms from Central–Eastern Argentina: petrology, geochemistry, Sr–Nd isotopes and tectonic implications". Journal of Petrology. 42 (11): 2109–2143. doi:10.1093/petrology/42.11.2109.
- ↑ Meert et al., 1997, p.639
- ↑ Grotzinger, 2000, p.252
- ↑ Wood & Curtis, 2015, p.114
- ↑ Pruss et al., 2018, p.763
- ↑ Winterleitner et al., 2015
- ↑ Buatois et al., 2018
- ↑ Hahn, G.; Pflug, H. D. (1985). "Polypenartige Organismen aus dem Jung-Präkambrium (Nama-Gruppe) von Namibia". Geologica et Palaeontologica. 19: 1–13
- 1 2 3 4 5 6 7 8 9 Crimes & Germs, 1982, p.890
- 1 2 Thrombolite Reef, Schwarzrand Subgroup at Fossilworks.org
- 1 2 3 Niederhagen Member, Naldaus Fm., - Jenkins 1985 at Fossilworks.org
- 1 2 Kliphoek Member, Dabis Fm., - Jenkins 1985 at Fossilworks.org
- ↑ Reefal biostrome, Kuibis Subgroup at Fossilworks.org
- 1 2 3 Vendian fauna, Kuibis Formation, - Glaessner 1979 at Fossilworks.org
- ↑ Rietoog, Driedoornvlagte pinnacle reef complex at Fossilworks.org
- ↑ Aar Farm at Fossilworks.org
- 1 2 Farm Swartpunt at Fossilworks.org
- ↑ Farm Swartpunt, Urusis Formation at Fossilworks.org
- ↑ Sonntagsbrunn Farm, Nomtsas Fm., Valley Fill 2, Visionarium at Fossilworks.org
Bibliography
- Buatois, Luis A.; Almond, John; Mángano, M. Gabriela; Jensen, Sören; Germs, Gerard J.B. (2018). "Sediment disturbance by Ediacaran bulldozers and the roots of the Cambrian explosion". Scientific Reports. 8 (1): Article number 4514. Bibcode:2018NatSR...8.4514B. doi:10.1038/s41598-018-22859-9. PMC 5852133. PMID 29540817.
- Crimes, T. Peter; Germs, Gerard J.B. (1982). "Trace Fossils from the Nama Group (Precambrian-Cambrian) of Southwest Africa (Namibia)". Journal of Paleontology. 56 (4): 890–907. JSTOR 1304708.
- Grotzinger, John P (2000). "Facies and paleoenvironmental setting of Thrombolite-Stromatolite Reefs, Terminal Proterozoic Nama Group (ca. 550-543 Ma), central and southern Namibia" (PDF). Communications of the Geological Survey of Namibia. 12: 251–264. Retrieved 2018-08-25.
- Meert, Joseph G.; Eide, Elizabeth A.; Torsvik, Trond H. (1997). "The Nama Group revisited" (PDF). Geophysical Journal International. 129 (3): 637–650. Bibcode:1997GeoJI.129..637M. doi:10.1111/j.1365-246X.1997.tb04499.x. Retrieved 2018-08-25.
- Pruss, Sara B.; Blättler, Clara L.; Macdonald, Francis A.; Higgins, John A. (2018). "Calcium isotope evidence that the earliest metazoan biomineralizers formed aragonite shells". Geology. 46 (9): 763–766. Bibcode:2018Geo....46..763P. doi:10.1130/G45275.1.
- Winterleitner, G.; Le Heron, D.P.; Mapani, B.; Vining, B.A.; McCaffrey, K.J.W. (2015). "Styles, origins and implications of syndepositional deformation structures in Ediacaran microbial carbonates (Nama Basin, Namibia)". Geological Society, London, Special Publications. 418 (1): 87–109. Bibcode:2015GSLSP.418...87W. doi:10.1144/SP418.12. S2CID 131352816. Retrieved 2018-08-25.
- Wood, R.; Curtis, A. (2015). "Extensive metazoan reefs from the Ediacaran Nama Group, Namibia: the rise of benthic suspension feeding" (PDF). Geobiology. 13 (2): 112–122. doi:10.1111/gbi.12122. hdl:20.500.11820/5f33c6b7-a2ac-4d1b-9f8d-a0ee6409af28. PMID 25556318. S2CID 904616. Retrieved 2018-08-25.
Further reading
- 2009 - Cohen, Phoebe A., Alexander Bradley, Andrew H. Knoll, John P. Grotzinger, Soren Jensen, John Abelson, Kevin Hand, Gordon Love, Joannah Metz, Nicola McLoughlin, Patrick Meister, Rebekah Shepard, Mike Tice, and Jonathan P. Wilson - Tubular compression fossils from the Ediacaran Nama Group, Namibia. Journal of Paleontology 83, no. 1: 110-122
- M. F. Glaessner. 1979. An echiurid worm from the Late Precambrian. Lethaia 12(2):121-124
- D. Grazhdankin and A. Seilacher. 2002. Underground Vendobionta from Namibia. Palaeontology 45(1):57-78
- J. P. Grotzinger, W. A. Watters, and A. H. Knoll. 2000. Calcified metazoans in thrombolite-stromatolite reefs of the terminal Proterozoic Nama Group, Namibia. Paleobiology 26(3):334-359
- R. J. F. Jenkins. 1985. The enigmatic Ediacaran (Late Precambrian) genus Rangea and related Forms. Paleobiology 11(3):336-355
- S. Jensen and B. N. Runnegar. 2005. A complex trace fossil from the Spitskop Member (terminal Ediacaran–? Lower Cambrian) of southern Namibia. Geological Magazine 142(5):561-569
- G. M. Narbonne, B. Z. Saylor, and J. P. Grotzinger. 1997. The youngest Ediacaran fossils from southern Africa. Journal of Paleontology 71(6):953-967
- J. P. Wilson, J. P. Grotzinger, W. W. Fischer, K. P. Hand, S. Jensen, A. H. Knoll, J. Abelson, J. M. Metz, N. Mcloughlin, P. A. Cohen, and M. M. Tice. 2012. Deep-water incised valley deposits at the Ediacaran-Cambrian boundary in Southern Namibia contain abundant Treptichnus pedum. Palaios 27:252-273
- R. A. Wood, J. P. Grotzinger, and J. A. D. Dickson. 2002. Proterozoic Modular Biomineralized Metazoan from the Nama Group, Namibia. Science 296(5577):2383-2386