Nama Group

Nama Group
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	23.9°S 16.7°E
Approximate paleocoordinates	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

Fish River Canyon and Huns Mountains, where the Nama Group crops out

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
	Naldaus/Nudaus Formation	Niederhagen
Kuibis	Zaris Formation	Urikos & Hoogland
	Zaris Formation	Omkyk
	Dabis Formation	Kliphoek
	Dabis Formation	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

Fossil of Pteridinium simplex from the Nama Group

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

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
Crimes & Germs, 1982, p.890
Thrombolite Reef, Schwarzrand Subgroup at Fossilworks.org
Niederhagen Member, Naldaus Fm., - Jenkins 1985 at Fossilworks.org
Kliphoek Member, Dabis Fm., - Jenkins 1985 at Fossilworks.org
Reefal biostrome, Kuibis Subgroup at Fossilworks.org
Vendian fauna, Kuibis Formation, - Glaessner 1979 at Fossilworks.org
Rietoog, Driedoornvlagte pinnacle reef complex at Fossilworks.org
Aar Farm at Fossilworks.org
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. 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. Retrieved 2018-08-25.