The Owambo Basin is a sedimentary basin located on the Congo Craton in Southern Africa that extends from southern Angola into Namibia and includes the Etosha Pan. It is bound on the southern and western sides by the Damara Belt in Northern Namibia, and by the Cubango River to the East. The northern boundary is scientifically disputed, but is currently mapped by most stratigraphers to include southern Angola with the boundary set at the Kunene River. The Owambo Basin is host to two famous regions: Tsumeb, a major Namibian city and site of a formerly active copper mine with exceptional mineralogical variability producing museum quality rare specimens, and Etosha National Park, the largest protected wildlife sanctuary in Namibia centered around Etosha Pan.
Local area
Provenances/Regions that are included in the Owambo Basin are:
Namibia
Kunene
Osmusati
Oshana
Ohangwena
Oshikoto
Kavango West
Kavango East
Otjozondjupa
Angola
Cuando Cubango
Cunene
Tectonic history
Congo Craton origin
The Owambo Basin's basement is the Congo Craton, composed of solid granite and gneiss that likely devolatilized during magmatic events over 2.2BYA, meaning that it is exceptionally old and highly rigid. Since its original formation, the Congo Craton has undergone a series of collisional and rifting events including: 2.1 Ga - Collision into continent Atlantica 1.8 Ga - Collision into supercontinent Columbia 1.3 Ga - Rifting apart and formation of an independent continent with the Sao Francisco Craton 1.1 Ga - Collision and incorporation into supercontinent Rodinia
Creation of the Owambo Basin
The breakup of Rodinia (Late Precambrian) is the origin of the original depositional series of the Owambo Basin. The rifting apart of the Congo Craton from the Rodinean shallow sea created a classic pull-apart basin. Pull-apart basins are characterized by faults that create an area of crustal extension, causing uplift at the edges and a sinking of the center, which is infilled by sediment or, in this case, a shallow sea (See Image 3). The deposition of the Nosib Formation (900-750 Ma) is the original deposition from the mass wasting of the newly uplifted edges of the Congo Craton, followed by the Otavi Formation (750-650 Ma), composed of dolomite and limestone from the formation of the shallow sea.
Formation of Gondwana
The pull-apart basin was then compressed when the Congo Craton was forced back together in the formation of the Gondwana supercontinent. This caused extensive uplift of the Owambo Basin edges and deepening of the basin's center(see Image 4), resulting in a massive erosional event that formed the Mulden Group (600-560 Ma). These three groups (Nosib, Otavi, and Mulden) compose the sedimentary package known as the Damara Supergroup.
Glaciation
The Damara Supergroup has a relatively abrupt end when Gondwana shifts under the South Pole. The entirety of the Congo Craton is overlain by large glaciers from 420 Ma until around 280 Ma, when the continent shifted far enough away from the South Pole to allow deglaciation. As the glaciers melted, deep valleys are carved into the sedimentary Mulden group depositing glacial till along their path. This glacial till is included in the sedimentary package known as the Karoo Group (280-130 Ma). The valleys are filled with water from the melted glaciers and the Owambo Basin is again a shallow marine system with heavy carbonate and organic deposition.
Breakup of Gondwana
The breakup of Gondwana began in the early Cretaceous (about 184-132 Ma). South America began to drift westward from Africa as the South Atlantic Ocean opened, resulting in complete open marine conditions by 110 Ma. During this, the Owambo Basin was reactivated as a pull-apart rift basin pulling apart from the east to the west, but received compression from the opening of the Damara Belt to its south. This created rotational seismic wrench systems across the basin profile. These wrench systems allowed for intrusions of continental igneous deposits: sills and dikes, along with pegmatites from metasomatized country rock. This intrusion of igneous material and hydrothermal activity led to heavy mineral depositions like the copper ore from the Tsumeb mine.