Nama Group

The Nama Group is a 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. The Nama Group is made of fluvial and shallow-water marine sediments, both siliciclastic and carbonate. La Tinta Group in Argentina is considered equivalent to Nama Group.
Description.
The group extends from the Gariep Belt in the south to outcrops of pre-Damara basement in the north. 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. The Nama Group is a series of interbedded shallow marine carbonates and siliciclastics deposited in a storm-dominated ramp setting.
"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.
Stratigraphy.
The Nama Group is subdivided into:
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.
Fossil content.
Nama-type Ediacaran fossils found in the group include: