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.
39-604: Provenances/Regions that are included in the Owambo Basin are: 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: The breakup of Rodinia (Late Precambrian )
78-512: A class of sedimentary rocks composed primarily of carbonate minerals . The two major types are limestone , which is composed of calcite or aragonite (different crystal forms of CaCO 3 ), and dolomite rock (also known as dolostone), which is composed of dolomite (CaMg(CO 3 ) 2 ). They are usually classified on the basis of texture and grain size . Importantly, carbonate rocks can exist as metamorphic and igneous rocks, too. When recrystallized carbonate rocks are metamorphosed , marble
117-686: A large part of central southern Africa, extending from the Kasai region of the DRC into Sudan and Angola . It forms parts of the countries of Gabon , Cameroon , and the Central African Republic . A small portion extends into Zambia as well, where it is called the Bangweulu Block . The Congo Craton and the São Francisco Craton are stable Archaean blocks that formed a coherent landmass until
156-527: A layer of limestone and dolomite with interdispersed oolitic shoals . The Mulden Group was deposited after a major unconformity created by the uplift from the Kaoko Belt and Damara Belt collisions (580-530 Ma). During this time, the Owambo Basin was drained and exposed at the surface, causing massive erosion with minimal deposition. After 530 Ma, the rebound from the uplift of the Damara orogeny had caused
195-455: A short emplacement interval and resulted in a 3,000–4,000 m (9,800–13,100 ft) thick sequence. Mafic-felsic magma sequences (6,000 m (20,000 ft) thick) on the western edge of the Congo Craton are similar to those of the Paraná and Deccan LIPs, but in the Congo Craton the magma source became shallower with time. There was no geodynamic activity along the western Congo margin during
234-460: Is created. Rare igneous carbonate rocks even exist as intrusive carbonatites and, even rarer, there exists volcanic carbonate lava . Carbonate rocks are also crucial components to understanding geologic history due to processes such as diagenesis in which carbonates undergo compositional changes based on kinetic effects . The correlation between this compositional change and temperature can be exploited to reconstruct past climate as
273-402: Is doloimite which contains significant trace levels of iron. Due to the similar ionic radii of iron(II) and magnesium , iron(II) can easily substitute magnesium to form ferroan dolomite; manganese can also substitute this atom. The result can be defined as ankerite . The exact delineation between which minerals are considered ferroan dolomite and which are ankerite is unclear. Ankerite with
312-433: Is dolomite which has more calcium than magnesium in its mineral form. This is the most common form of dolomite found naturally and artificially from synthesis . This dolomite, when formed in the oceans, can prove to be metastable . The resultant structure of this mineral presents minimal differences from regular dolomite likely as a result of formation after initial crystal growth. Iron-rich dolomite, or ferroan dolomite,
351-465: Is done in paleoclimatology . Carbonate rocks can also be used for understanding various other systems as described below. Limestone is the most common carbonate rock and is a sedimentary rock made of calcium carbonate with two main polymorphs : calcite and aragonite. While the chemical composition of these two minerals is the same, their physical properties differ significantly due to their different crystalline form . The most common form found in
390-523: 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
429-467: 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
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#1732885162017468-758: The Keweenawan Rift in Laurentia (although the latter was located far from the other continental blocks). A series of 1500 Ma dyke swarms also support the close relation between Congo–São Francisco and Siberia: Kuonamka in Siberia and Curaçá and Chapada Diamantina in São Francisco and Angola. These dyke swarms radiate from a mantle plume centre located in what is now north-eastern Siberia. Magmatic events in Congo (Kunene) and Siberia (Chieress) at 1384 Ma also corroborate
507-593: 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. 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
546-578: The Palaeozoic -to-recent Congo Basin , is an ancient Precambrian craton that with four others (the Kaapvaal , Zimbabwe , Tanzania , and West African cratons) makes up the modern continent of Africa . These cratons were formed between about 3.6 and 2.0 billion years ago and have been tectonically stable since that time. All of these cratons are bounded by younger fold belts formed between 2.0 billion and 300 million years ago. The Congo Craton occupies
585-546: The copper ore from the Tsumeb mine. In the mid-Cretaceous, Africa shifted to closer to the equator with the Owambo Basin landing at near 30° South latitude (very close to its current location), causing rapid desertification . This is represented in the stratigraphic sequence by a large depositional sequence that continues through the Quaternary . Beginning in the mid-Cretaceous, deposition of sandstones occur. These are labeled as
624-544: The greenhouse effect . There is significant amount of research studying the ideal quantity of calcium carbonate (derived from limestone) in concrete and if other compounds can be used to provide the same economic and structural integrity benefits. Many forms of paleoclimatology exist whereby carbonate rocks can be used to determine past climate. Corals and sediments are well-known proxies for these reconstructions. Corals are marine organisms with calcium carbonate skeletons (rocks) which grow specific to oceanic conditions at
663-503: The "pure" CaFe(CO 3 ) 2 chemical formula has yet to be found in nature . Carbonate rocks are significant for both human understanding of Earth's atmospheric and geologic history, in addition to providing humans with significant resources for current civilizational endeavors such as concrete . Limestone is often used in concrete as powder due to its cheap cost. During the formation of concrete, however, breakdown of limestone releases carbon dioxide and contributes significantly to
702-529: The Congo and Kalahari Cratons during the formation of the Gondwana supercontinent. The Owambo Basin is thought to originate at this time as a pull-apart basin filled with sediment from the surrounding uplifted areas, and eventually as a shallow marine system. The Otavi Group is composed entirely of shallow marine deposits. During this time period, the Owambo Basin was part of a shallow marine system that resulted in deposition of carbonates and organics, resulting in
741-537: The Kalahari Sequence, so named after the sand origin, the Kalahari Desert . The earliest formation in the known stratigraphic history of the Owambo Basin comprises what is geologically termed the basement and is compositionally zoned with mostly granite and gneiss. There is a metamorphic overprint on the majority of the granite from the tectonic history of rifting and compression, causing mass devolitilization of
780-486: The Mesoproterozoic. [REDACTED] Africa [REDACTED] Antarctica [REDACTED] Asia [REDACTED] Australia [REDACTED] Europe [REDACTED] North America [REDACTED] South America [REDACTED] Afro-Eurasia [REDACTED] Americas [REDACTED] Eurasia [REDACTED] Oceania Carbonate rock Carbonate rocks are
819-566: 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 . The Damara Supergroup has a relatively abrupt end when Gondwana shifts under the South Pole . The entirety of the Congo Craton
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#1732885162017858-409: The Owambo Basin to sink and it again filled with water to create a shallow marine system with deposition from both continental and marine organic sources. The stages between when the Owambo Basin was a transgressive vs regressive deposition system are bounded by a black shale marker that runs through the "middle" of the Mulden Group. Though the center of the Owambo Basin is a wildlife preservation area,
897-603: The São Francisco–Congo continent. The West Congo Pan-African Belt includes major magmatic events at c. 1000 and 910 Ma. In the Early Neoproterozoic, the western edge of Congo Craton was the location for the initial rifting of Rodinia before its break-up. During the Neoproterozoic, Central Congo or Bas-Congo became a passive margin on which was deposited 4,000 m (13,000 ft) sediments. At
936-469: The aragonite of coral skeleton can be used, alongside other proxies like oxygen isotopic ratios , to reconstruct climate variability when the coral was growing. This is because Strontium will sometimes substitute for Calcium in the calcium carbonate molecule depending on temperature effects. Similar to the concept for using compositional changes in coral skeletons as proxies for climate conditions, compositional changes in marine sediments can be used for
975-510: The basement rock. This section is overlain by a layer of volcanics, a likely accompaniment to the compression involved in the formation of Rodinia. The Nosib Group is charactererized by interbedded marine and continental sediment capped by volcanics. In the USGS stratigraphic column this is associated with the uplift of the Katangan orogeny 880 Ma, created during the series of rifting and compression of
1014-476: The boom of the twenty-first century. In 2007, Angola was the third largest producer of diamonds in Africa with only 40% of the potential territory explored. It is also known as a major exporter of iron ore, with potential to market several other mineral resources including manganese, copper, gold, phosphates, marble, uranium, tin, fluorite, feldspar, gypsum, and talc. Congo Craton The Congo Craton , covered by
1053-626: The closeness of these two continents during at least 120 million years. It is possible that the 1110 Ma LIP in Congo–São Francisco, Amazonia, and India was part of a much larger event that also involved West Africa and Kalahari (with a possible but unlikely link to the 1075 Ma Warakurna LIP in Australia). However, while the palaeo-latitudes of India and Kalahari are well constrained, those of Amazonia and Congo–São Francisco are not, making any plate tectonic reconstruction speculative. At
1092-478: 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
1131-481: The end of the Neoproterozoic, Bas-Congo was only affected by the Pan-African orogeny at 566 Ma to a limited extent protected by this passive margin and by the thickness of the craton. At 1000 Ma peralkaline magmatism initiated an early transtensional setting along the western edge of the Congo Craton. An LIP at c. 930–920 Ma was followed by felsic magmatism between c. 920–910 Ma which had
1170-529: The existing rock grains together or it can fill fractures. Compared to calcite, aragonite is less stable and more soluble , and can thus be converted to calcite under certain conditions. In solution, magnesium ions can act as promoters of aragonite growth as they inhibit calcite precipitation . Often this inhibited precipitation occurs in biology where organisms aim to precipitate calcium carbonate for their structural features such as for skeleton and shells . The discovery of dolomite rock, or dolostone ,
1209-502: The melted glaciers and the Owambo Basin is again a shallow marine system with heavy carbonate and organic deposition . 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
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1248-598: The opening of the South Atlantic Ocean during the break-up of Gondwana ( c. 2000–130 Ma). They stabilised during the Transamazonian orogeny and Eburnean Orogeny and have been affected by a long series of orogens since resulting in similar sequences on both blocks. Congo–São Francisco experienced three large igneous province (LIP) events at 1380–1370 Ma, c. 1505 Ma, and c. 1110 Ma. The relative position of Congo–São Francisco within
1287-683: The opening of the South Atlantic the São Francisco and Congo cratons were connected by a "cratonic" bridge, the Bahia–Gabon Bridge. The most recent orogenic event on this bridge occurred at 2 Ga, so the connection between São Francisco and Congo must have formed during the Palaeoproterozoic. South of this cratonic bridge the Araçuaí–West Congo orogen evolved in the Neoproterozoic in a sea basin made of oceanic crust, an embayment in
1326-512: The seafloor is calcite, while aragonite is more found in biological organisms. Calcite can be either dissolved by groundwater or precipitated by groundwater, depending on several factors including the water temperature , pH , and dissolved ion concentrations. Calcite exhibits an unusual characteristic called retrograde solubility in which it becomes less soluble in water as the temperature increases. When conditions are right for precipitation, calcite forms mineral coatings that cement
1365-871: The supercontinent Nuna/Columbia can be reconstructed because these LIP events also affected other Precambrian continental blocks. Within Nuna the northern part of Siberia was located adjacent to western São Francisco. 1110 Ma dyke swarms in Angola are absent in Siberia but coincide with the Umkondo LIP on the Kalahari Craton and magmatic event in the Bundelkhand Craton in India, the Amazonian Craton in South America, and
1404-450: The surrounding uplifted areas are rich in mineral and ore deposits. In terms of revenue mining is the largest contributor to Namibia's economy, accounting for over 25% of the country's income. The majority of this revenue is centered around diamond mining, however, Namibia is also a large producer of copper, lead, zinc, cement, and uranium. Due to the highly volatile nature of Angola's political system, its resources have been vastly untapped by
1443-548: The time for the formation of the supercontinent Gondwana at c. 550 Ma the Congo Craton formed the already amalgamated central African landmass. The southern and eastern margins (modern coordinates) of this landmass was made of the Archaean Angola-Kasai block and Tanzanian Craton. These proto-Congo blocks were deformed in the Palaeoproterozoic Eburnean orogeny but later stabilised. Before
1482-404: The time of growth. Diagenesis refers to the process whereby sediments are being converted to sedimentary rock. This includes biological activity, erosion, and other chemical reactions. Due to the strong correlation between diagenesis and seawater temperature , coral skeletons can be used as proxies for understanding past climate effects. Specifically, the ratio of Strontium to Calcium in
1521-524: Was first published in 1791 and has been found across the Earth's crust from various different time periods . Because the rock is made of calcium , magnesium , and carbonate ions, the mineral crystalline structure can be visualized similar to calcite and magnesite . Due to this composition, the dolomite mineral present in dolostone can be classified by varying degree of calcium inclusion, and occasionally iron, too. Calcium-rich dolomite, or calcian dolomite,
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