Ganigobis Formation

Ganigobis Formation
Stratigraphic range: Gzhelian-Artinskian
Type	Geological formation
Unit of	Dwyka Group
Sub-units	Ganigobis Shale Member
Underlies	Ecca Group
Overlies	Nama Group
Thickness	up to 240 m (790 ft)
Lithology
Primary	Shale, conglomerate, sandstone
Other	Tuff
Location
Coordinates	25.9°S 18.0°E / -25.9; 18.0
Approximate paleocoordinates	56.0°S 35.9°W / -56.0; -35.9
Region	ǁKaras Region Northern Cape
Country	Namibia South Africa
Extent	Aranos & Karoo Basins Kalahari Craton
Type section
Named for	Ganigobis
Location	Ganigobis, Fish River Canyon
Thickness at type section	155 m (509 ft)
Geologic map of Namibia with the Ganigobis Formation partly cropping out in the southern area (orange)

The Ganigobis Formation is a Late Carboniferous (Gzhelian) to Early Permian (Artinskian) geologic formation of the Dwyka Group in the ǁKaras Region of southeastern Namibia and the Northern Cape of South Africa. The widespread formation was deposited in the Aranos and Karoo Basins of southern Africa.

Description

The Ganigobis Formation is an extensive unit with a maximum thickness of 240 metres (790 ft) evidenced in the Vreda borehole. The conglomerates, sandstones, shales and tuff of the formation were deposited in a glacio-lacustrine to marine environment. The Ganigobis Formation provides fossil fish as well as bivalves (e.g. Nuculopsis), gastropods (e.g. Peruvispira), scyphozoa (e.g. Conularia), crinoid stalks, foraminifera (Hyperammina, Ammodiscus, Glomospira, Ammobacculites and Spiroplectammina), sponges and sponge spicules, radiolaria, coprolites and permineralised wood.

Zircons of the Ganigobis Shale Member yield SHRIMP-ages of 302-300 Ma. This dates the uppermost part of the second deglaciation sequence in southern Namibia to the Late Carboniferous (Gzelian) and provides a minimum age for the onset of Karoo-equivalent marine deposition. The age of the uppermost argillaceous part of the third deglaciation sequence (297 Ma) was determined from zircons of a tuffaceous bed sampled in a roadcut in the Western Cape Province, South Africa.

Fossil content

Among others, the following fossils are reported from the formation:

Fish

• Acrolepis addamsi
• Namaichthys schroederi
• Watsonichthys lotzi

See also

• List of fossiliferous stratigraphic units in Namibia
• List of fossiliferous stratigraphic units in South Africa
• Geology of Namibia
• Geology of South Africa
• Irati Formation

References

Bibliography

• Bangert, B.; Stollhofen, H.; Geiger, M.; Lorenz, V. (2000), "Fossil record and high-resolution tephrostratigraphy of Carboniferous glaciomarine mudstones, Dwyka Group, southern Namibia" (PDF), Communications of the Geological Survey of Namibia, 12: 265–276, retrieved 2018-08-26
• Bangert, Berthold (2000), Tephrostratigraphy, petrography, geochemistry, age and fossil record of the Ganigobis Shale Member and associated glaciomarine deposits of the Dwyka Group, Late Carboniferous, southern Africa (PhD thesis) (PDF), Julius-Maximilians-Universität Würzburg, pp. 1–242, retrieved 2018-08-26

Further reading

• B. G. Gardiner. 1962. Namaichthys schroederi Gürich and other Palaeozoic Fishes from South Africa. Palaeontology 5(1):9-21