Geology of Mauritania

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The geology of Mauritania is built on more than two billion year old Archean crystalline basement rock in the Reguibat Shield of the West African Craton, a section of ancient and stable continental crust. Mobile belts and the large Taoudeni Basin formed and filled with sediments in the connection with the Pan-African orogeny mountain building event 600 million years ago and a subsequent orogeny created the Mauritanide Belt. In the last 251 million years, Mauritania has accumulated additional sedimentary rocks during periods of marine transgression and sea level retreat. The arid country is 50% covered in sand dunes and has extensive mineral resources, although iron plays the most important role in the economy.

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Stratigraphy, tectonics and geologic history

The oldest rocks in Mauritania date to the Archean, over two billion years old in the Reguibat Shield of the West African Craton. The extremely old crystalline basement rock of the shield is almost entirely Neoarchean age and metamorphosed to hornblende or granulite grade in the metamorphic facies sequence. These Saouda Series rocks include gneiss, with different endmembers enriched in leptynite garnet, hypersthene and sillimanite garnet, as well as pyroxene amphibolite, magnetite quartzites and marble. The Saouda Series is intruded by younger basalts, anorthosite and gabbros along with serpentinite.

Saouda Series rocks appear to be restite, the residual material left at a location after in situ granite production through intense metamorphism and are part of a larger group of anatectic and magmatic granites in the Rag el Abiod complex. In Mauritania, metamorphic and igneous crystalline basement rock is exposed as the Kenieba and Kayes inliers, sections of older rock surrounded by younger rock. They show signs of multiple phases of deformation and intrusion by tectonic and post-tectonic granites, dated at 2.05 billion years, lining up with the Eburnean orogeny. Geologists have found pebbles within microsyenites and microgranites, in a folded conglomerate, that form part of a metasedimentary unit, which may be the remnants of even older Archean rocks. [1]

Proterozoic (2.5 billion-539 million years ago)

In the Neoproterozoic, the Pan-African orogeny began to form mobile belts across Africa. The Taoudeni Basin in Mauritania, Mali, Algeria, Burkina Faso, Guinea, Senegal and Guinea-Bissau began to form as a foreland basin to the surrounding mobile belts—a process that continued into the Paleozoic. Also known as the Bove Basin further south, the Taoudeni Basin is a slightly dipping sag basin filled with two to three kilometers of clastic sedimentary rocks. The rocks are grouped into three sequences. Sequence 1 deposited in the Middle Neoproterozoic and includes sandstones and carbonates formed from stromatolites. Supergroup 2 also dates to the Neoproterozoic and contains dolomite rich in barite, basal tillite, marine chert and sandstones.

Paleozoic (539-251 million years ago)

The deposition of Supergroup 2 continued with the formation of sandstones containing brachiopod fossils, in the Cambrian and Ordovician, followed by Late Ordovician tillites, graptolite Silurian sandstones and shales, as well as Devonian shales with reef limestones.

The Mauritanide Belt formed in an orogeny between 320 and 270 million years ago that is allochthonous, lying on top of the Reguibat Shield crystalline basement rocks and the sedimentary rocks of the Taoudeni Basin. The Mauritanide Belt was thrust on top of the Taoudeni Basin during the Hercynian orogeny, which also folded and fractured the edge of the basin. It is one of several West African fold belts along with the Bassarides and Rokelides. [2]

Mesozoic-Cenozoic (251 million years ago-present)

Mauritania is part of the Senegal Basin and its Mesozoic sedimentary sequence begins with Late Jurassic dolomite formed in a shallow marine environment. Offshore research has found Early Cretaceous detrital sediments lying atop Early Jurassic evaporites. The ocean receded in the region in the Maastrichtian near the end of the Cretaceous, followed by a large marine transgression in the early Cenozoic. The country's sedimentary rocks interfinger between continental sediments and silicate marine sediments in the west. [3]

Hydrogeology

Mauritania has two interconnected groundwater systems, the Continental Terminal coastal system and the interior Taoudeni Basin. Most groundwater flow happens in porous sedimentary rock, although some moves through fractured crystalline basement rock. The Continental Terminal system have very limited recharge, while the Taoudeni Basin has three main areas of recharge on the northwest edge of the shield, in tillites in the south and in the vicinity of Tidjikdja.

Fresh groundwater discharges east into Mali and saltwater intrusions affect the coastal areas of Mauritania. [4]

Natural resource geology

Iron ore mining plays an important role in the economy of Mauritania. Banded iron formations with 64% iron hematite lenses were discovered at F'Derik-Segazou, Tazadit hills and Rouessa, close to the border with Western Sahara in the 1970s. Mining began 25 kilometers north of Zouerate, as part of the Guelb project in the mid-1980s. The site has itabirite with 37% iron. Dust storms and problems at the site's mill have limited production. A different Guelb project site 12 kilometers east of El Rhein became active in the early 1990s, extracting 64% iron ore. A Neoproterozoic carbonate unit, part of a synformal nappe overturned in the Paleozoic, now forms a major copper deposit 250 kilometers northeast of Nouakchott in the Mauritanides Belt. The one kilometer, 250 meter wide deposit spans the West and East Moghrein Guelb hills.

Forty meters below the deposit is a secondary deposit of cuprite, azurite, malachite and tenorite, with an additional 2.25% copper, some gold and sulfide mineralization including cubanite, chalcopyrite, pyrrohitite and aresnopyrite. In the 2000s, mining at the site had mostly ceased except for gold mining in the tailings pile. Gypsum is extracted from the N'Drahamcha quarry, 50 kilometers northeast of Nouakchott, used to produce concrete blocks and plaster. Bofal and Loubboira in southern Mauritania have up 150 megatons of phosphate, at 20% concentration. [5]

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Geology of the Republic of the Congo

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The geology of Western Sahara includes rock units dating back to the Archean more than two billion years old, although deposits of phosphorus formed in the Mesozoic and Cenozoic have helped to prompt the current Moroccan occupation of most of the country.

The geology of Guinea-Bissau is oldest in the east and becomes younger toward the west, with sediments from the past 66 million years nearer the coast. Some rock units in the northeast are as much as 680 million years old and throughout the geologic past Guinea-Bissau was influenced by the Mauritanide Belt orogeny and was submerged or partially submerged as a marine shelf or river delta for most of its existence.

The geology of Liberia is largely extremely ancient rock formed between 3.5 billion and 539 million years ago in the Archean and the Neoproterozoic, with some rocks from the past 145 million years near the coast. The country has rich iron resources as well as some diamonds, gold and other minerals in ancient sediment formations weathered to higher concentrations by tropical rainfall.

The geology of Somalia is built on more than 700 million year old igneous and metamorphic crystalline basement rock, which outcrops at some places in northern Somalia. These ancient units are covered in thick layers of sedimentary rock formed in the last 200 million years and influenced by the rifting apart of the Somali Plate and the Arabian Plate. The geology of Somaliland, the de facto independent country recognized as part of Somalia, is to some degree better studied than that of Somalia as a whole. Instability related to the Somali Civil War and previous political upheaval has limited geologic research in places while heightening the importance of groundwater resources for vulnerable populations.

Geology of Ghana

The geology of Ghana is primarily very ancient crystalline basement rock, volcanic belts and sedimentary basins, affected by periods of igneous activity and two major orogeny mountain building events. Aside from modern sediments and some rocks formed within the past 541 million years of the Phanerozoic Eon, along the coast, many of the rocks in Ghana formed close to one billion years ago or older leading to five different types of gold deposit formation, which gave the region its former name Gold Coast.

Geology of the Democratic Republic of the Congo

The geology of the Democratic Republic of the Congo is extremely old, on the order of several billion years for many rocks. The country spans the Congo Craton: a stable section of ancient continental crust, deformed and influenced by several different mountain building orogeny events, sedimentation, volcanism and the geologically recent effects of the East Africa Rift System in the east. The country's complicated tectonic past have yielded large deposits of gold, diamonds, coltan and other valuable minerals.

The geology of Cameroon is almost universally Precambrian metamorphic and igneous basement rock, formed in the Archean as part of the Congo Craton and the Central African Mobile Zone and covered in laterite, recent sediments and soils. Some parts of the country have sequences of sedimentary rocks from the Paleozoic, Mesozoic and Cenozoic as well as volcanic rock produced by the 1600 kilometer Cameroon Volcanic Line, which includes the still-active Mount Cameroon. The country is notable for gold, diamonds and some onshore and offshore oil and gas.

Geology of Ivory Coast

The geology of Ivory Coast is almost entirely extremely ancient metamorphic and igneous crystalline basement rock between 2.1 and more than 3.5 billion years old, comprising part of the stable continental crust of the West African Craton. Near the surface, these ancient rocks have weathered into sediments and soils 20 to 45 meters thick on average, which holds much of Ivory Coast's groundwater. More recent sedimentary rocks are found along the coast. The country has extensive mineral resources such as gold, diamonds, nickel and bauxite as well as offshore oil and gas.

The geology of Malawi formed on extremely ancient crystalline basement rock, which was metamorphosed and intruded by igneous rocks during several orogeny mountain building events in the past one billion years. The rocks of the Karoo Supergroup and newer sedimentary units deposited across much of Malawi in the last 251 million years, in connection with a large rift basin on the supercontinent Gondwana and the more recent rifting that has created the East African Rift, which holds Lake Malawi. The country has extensive mineral reserves, many of them poorly understand or not exploited, including coal, vermiculite, rare earth elements and bauxite.

The geology of Mozambique is primarily extremely old Precambrian metamorphic and igneous crystalline basement rock, formed in the Archean and Proterozoic, in some cases more than two billion years ago. Mozambique contains greenstone belts and spans the Zimbabwe Craton, a section of ancient stable crust. The region was impacted by major tectonic events, such as the mountain building Irumide orogeny, Pan-African orogeny and the Snowball Earth glaciation. Large basins that formed in the last half-billion years have filled with extensive continental and marine sedimentary rocks, including rocks of the extensive Karoo Supergroup which exist across Southern Africa. In some cases these units are capped by volcanic rocks. As a result of its complex and ancient geology, Mozambique has deposits of iron, coal, gold, mineral sands, bauxite, copper and other natural resources.

The geology of Niger comprises very ancient igneous and metamorphic crystalline basement rocks in the west, more than 2.2 billion years old formed in the late Archean and Proterozoic eons of the Precambrian. The Volta Basin, Air Massif and the Iullemeden Basin began to form in the Neoproterozoic and Paleozoic, along with numerous ring complexes, as the region experienced events such as glaciation and the Pan-African orogeny. Today, Niger has extensive mineral resources due to complex mineralization and laterite weathering including uranium, molybdenum, iron, coal, silver, nickel, cobalt and other resources.

Geology of Sierra Leone

The geology of Sierra Leone is primarily very ancient Precambrian Archean and Proterozoic crystalline igneous and metamorphic basement rock, in many cases more than 2.5 billion years old. Throughout Earth history, Sierra Leone was impacted by major tectonic and climatic events, such as the Leonean, Liberian and Pan-African orogeny mountain building events, the Neoproterozoic Snowball Earth and millions of years of weathering, which has produced thick layers of regolith across much of the country's surface.

Geology of Tanzania

The geology of Tanzania began to form in the Precambrian, in the Archean and Proterozoic eons, in some cases more than 2.5 billion years ago. Igneous and metamorphic crystalline basement rock forms the Archean Tanzania Craton, which is surrounded by the Proterozoic Ubendian belt, Mozambique Belt and Karagwe-Ankole Belt. The region experienced downwarping of the crust during the Paleozoic and Mesozoic, as the massive Karoo Supergroup deposited. Within the past 100 million years, Tanzania has experienced marine sedimentary rock deposition along the coast and rift formation inland, which has produced large rift lakes. Tanzania has extensive, but poorly explored and exploited natural resources, including coal, gold, diamonds, graphite and clays.

The geology of Uganda extends back to the Archean and Proterozoic eons of the Precambrian, and much of the country is underlain by gneiss, argillite and other metamorphic rocks that are sometimes over 2.5 billion years old. Sedimentary rocks and new igneous and metamorphic units formed throughout the Proterozoic and the region was partially affected by the Pan-African orogeny and Snowball Earth events. Through the Mesozoic and Cenozoic, ancient basement rock has weathered into water-bearing saprolite and the region has experienced periods of volcanism and rift valley formation. The East Africa Rift gives rise to thick, more geologically recent sediment sequences and the country's numerous lakes. Uganda has extensive natural resources, particularly gold.

The geology of Morocco formed beginning up to two billion years ago, in the Paleoproterozoic and potentially even earlier. It was affected by the Pan-African orogeny, although the later Hercynian orogeny produced fewer changes and left the Maseta Domain, a large area of remnant Paleozoic massifs. During the Paleozoic, extensive sedimentary deposits preserved marine fossils. Throughout the Mesozoic, the rifting apart of Pangaea to form the Atlantic Ocean created basins and fault blocks, which were blanketed in terrestrial and marine sediments—particularly as a major marine transgression flooded much of the region. In the Cenozoic, a microcontinent covered in sedimentary rocks from the Triassic and Cretaceous collided with northern Morocco, forming the Rif region. Morocco has extensive phosphate and salt reserves, as well as resources such as lead, zinc, copper and silver.

Geology of Senegal

The geology of Senegal formed beginning more than two billion years ago. The Archean greenschist Birimian rocks common throughout West Africa are the oldest in the country, intruded by Proterozoic granites. Basins formed in the interior during the Paleozoic and filled with sedimentary rocks, including tillite from a glaciation. With the rifting apart of the supercontinent Pangaea in the Mesozoic, the large Senegal Basin filled with thick sequences of marine and terrestrial sediments. Sea levels declined in the Eocene forming large phosphate deposits. Senegal is blanketed in thick layers of terrestrial sediments formed in the Quaternary. The country has extensive natural resources, including gold, diamonds, and iron.

The geology of Nigeria formed beginning in the Archean and Proterozoic eons of the Precambrian. The country forms the Nigerian Province and more than half of its surface is igneous and metamorphic crystalline basement rock from the Precambrian. Between 2.9 billion and 500 million years ago, Nigeria was affected by three major orogeny mountain-building events and related igneous intrusions. Following the Pan-African orogeny, in the Cambrian at the time that multi-cellular life proliferated, Nigeria began to experience regional sedimentation and witnessed new igneous intrusions. By the Cretaceous period of the late Mesozoic, massive sedimentation was underway in different basins, due to a large marine transgression. By the Eocene, in the Cenozoic, the region returned to terrestrial conditions.

Geology of Sweden

The geology of Sweden is the regional study of rocks, minerals, tectonics, natural resources and groundwater in the country. The oldest rocks in Sweden date to more than 2.5 billion years ago in the Precambrian. Complex orogeny mountain building events and other tectonic occurrences built up extensive metamorphic crystalline basement rock that often contains valuable metal deposits throughout much of the country. Metamorphism continued into the Paleozoic after the Snowball Earth glaciation as the continent Baltica collided with an island arc and then the continent Laurentia. Sedimentary rocks are most common in southern Sweden with thick sequences from the last 250 million years underlying Malmö and older marine sedimentary rocks forming the surface of Gotland.

References

  1. ↑ Schlüter, Thomas (2008). Geological Atlas of Africa. Springer. p. 166.
  2. ↑ Schlüter 2008, p. 166.
  3. ↑ Schlüter 2008, pp. 166–167.
  4. ↑ Friedel & Finn (2008). "Hydrogeology of the Islamic Republic of Mauritania". USGS.
  5. ↑ Schlüter 2008, pp. 168–169.
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