Nama Group

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Nama Group
Stratigraphic range: Vendian-Cambrian
~570–543 Ma
TypeGroup
Unit ofNama Basin
Sub-unitsSee text
UnderliesTable Mountain Sandstone
OverliesBasement
Area125,000 km2 (48,000 sq mi)
Lithology
PrimarySandstone
OtherSiltstone, mudstone, limestone
Location
Coordinates23°54′S 16°42′E / 23.9°S 16.7°E / -23.9; 16.7Coordinates: 23°54′S 16°42′E / 23.9°S 16.7°E / -23.9; 16.7
Approximate paleocoordinates41°24′S 179°12′W / 41.4°S 179.2°W / -41.4; -179.2
RegionOmaheke, Hardap & ǁKaras Regions
Country Namibia
Damara-Orogen mit Damara-Gürtel, Kaoko-Gürtel und Gariep-Gürtel.png
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[edit]

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[edit]

Paleogeographic reconstruction from 600 Ma to recent

The Nama Group is subdivided into:[8]

Subgroup Formation Member
Fish River
Schwarzrand Vergesig Formation
Nomtsas Formation
Urusis Formation Spitzkopf
Naldaus/Nudaus Formation Huns
Niederhagen
Kuibis Zaris Formation Urikos & Hoogland
Omkyk
Dabis Formation Kliphoek
Kanies

Ages[edit]

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[edit]

Fossil of Pteridinium simplex from the Nama Group

Nama-type Ediacaran fossils found in the group include:

Gallery[edit]

See also[edit]

References[edit]

  1. ^ 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
  2. ^ 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.
  3. ^ 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.
  4. ^ Meert et al., 1997, p.639
  5. ^ Grotzinger, 2000, p.252
  6. ^ Wood & Curtis, 2015, p.114
  7. ^ Pruss et al., 2018, p.763
  8. ^ Winterleitner et al., 2015
  9. ^ Buatois et al., 2018
  10. ^ Hahn, G.; Pflug, H. D. (1985). "Polypenartige Organismen aus dem Jung-Präkambrium (Nama-Gruppe) von Namibia". Geologica et Palaeontologica. 19: 1–13
  11. ^ a b c d e f g h i Crimes & Germs, 1982, p.890
  12. ^ a b Thrombolite Reef, Schwarzrand Subgroup at Fossilworks.org
  13. ^ a b c Niederhagen Member, Naldaus Fm., - Jenkins 1985 at Fossilworks.org
  14. ^ a b Kliphoek Member, Dabis Fm., - Jenkins 1985 at Fossilworks.org
  15. ^ Reefal biostrome, Kuibis Subgroup at Fossilworks.org
  16. ^ a b c Vendian fauna, Kuibis Formation, - Glaessner 1979 at Fossilworks.org
  17. ^ Rietoog, Driedoornvlagte pinnacle reef complex at Fossilworks.org
  18. ^ Aar Farm at Fossilworks.org
  19. ^ a b Farm Swartpunt at Fossilworks.org
  20. ^ Farm Swartpunt, Urusis Formation at Fossilworks.org
  21. ^ Sonntagsbrunn Farm, Nomtsas Fm., Valley Fill 2, Visionarium at Fossilworks.org

Bibliography[edit]

Further reading[edit]