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.
The oldest rock units in Somalia date back over 700 million years to the Proterozoic, forming the crystalline basement rock of northern Somalia. Many rock units date to the Mesozoic and the current Cenozoic eons.
Northern Somalia preserves the best examples of Proterozoic rocks. As basement rocks, they form a composite terrane, with younger rocks in the east and older rocks in the west. The older rocks pre-date the Pan-African orogeny and were affected by both igneous and metamorphic activity 840, 800 to 760 and 720 million years ago.
The early geology of Somalia is divided into four major events. The Qabri Bahar Complex formed in the Paleoproterozoic through the Mesoproterozoic with mafic and granitoid units, as well as rocks metamorphosed to granulite grade (part of the concept of metamorphic facies). Some geologists propose that the Qabri Bahar complex may preserve rocks from before the Pan-African orogeny. Major Event II, more than 700 million years ago, marked deformation, partial melting (also known as anataxis) and rocks metamorphosed up to amphibolite grade.
Major Event III happened 700 to 640 million years ago, bringing crustal thinning and extension, mafic volcanism in the Abdulkadir complex and Mait complex, regional heating, metamorphism and the emplacement of gabbro and syenite through the thinned crust. Major Event IV continued for 100 million years, from 600 to 500 million years ago, spanning into the Paleozoic Era of the Phanerozoic Eon. Granites were emplaced and the deposition of the low-grade, metasedimentary Inda Ad sequence occurred, followed by more deformation and regional heating.
The sequence of events in Somalia in the Proterozoic are correlated with the Arabian-Nubian Shield to the north, which experienced igneous activity related to subduction and witnessed the formation of marginal basins and island arcs. [1]
In the Early Jurassic, the supercontinent Gondwana, which included Africa, began to break apart. The marine transgression of the Tethys Ocean flooded large parts of East Africa and Arabia and new sedimentary rock units were deposited. In the west of Somalia, the Cretaceous at the end of the Mesozoic brought crustal upwarping, which is preserved in the Yesomma Sandstone.
Two major sedimentary basins began to form in Somalia during the Mesozoic, the Somali Coastal Basin and the Luuq-Mandera Basin, both filled with up to five kilometers of sedimentary rock. The basins formed due to the movements of India, Madagascar and East Africa and the opening of the Indian Ocean. Research on the basins came out of geophysical surveys in search of oil. Much of the seven kilometers of sedimentary rock in the Somali Coastal Basin was laid down in Jurassic and Cretaceous. In the Luuq-Mandera Basin, oil exploration found Late Triassic to Early Jurassic clastic sediments, evaporite and carbonate deposits, overlain by shales from the Tethys marine transgression. The Late Jurassic through the Cretaceous left marl and ammonite fossils, from an open sea environment, followed by shales and belemnite fossils from an epicontinental sea. [2]
The two basins are separated by the Bur Region, where crystalline basement rock from the Proterozoic comes close to the surface. In the Bur Region, basement rock only outcrops as a few small hills. Even though the region covers 30,000 square kilometers, most basement rock remains hidden by one to 30 meters of recently eroded and unconsolidated sediments.
Geologic research has found that there are two rock units in the Bur Region, the Olontole Complex and Dinsor Complex. The Olontole Complex includes gneiss, migmatite, granulite facies amphibolite and quartzite, cross-cut by bodies of granitoid rock. The Dinsor Complex consists of metapsammite and metapelite, migmatite, iron-rich quartzite and marble. Rubidium-strontium dating indicates that the young granites and granitoids date to the Paleozoic. [3]
Sedimentation continued in the Cenozoic. Deposition of the Yesomma Sandstone continued until another regional marine transgression in the Middle Eocene. The opening of the Gulf of Aden and the uplift of the Somali Plateau created brackish basins, which filled with marine deposits in the Miocene and Oligocene. Outcrops of these rock units are limited to a few coastal areas in Somalia, but rapid faulting created offshore basins with up to two kilometers of sediments from the late Cenozoic.
Both the Luuq-Mandera Basin and the Somali Coastal Basin continued to fill with a mix of clastic sediments, marl and carbonates. Since the Late Cretaceous, uplift in these basins created lake depressions and formed the Jubba valley. [3]
The formation of the Somali Plate began 60 million years ago and accelerated at the end of the Oligocene, approximately 23 million years ago. As the Arabian Plate and Somali Plate rifted apart, forming the Gulf of Aden through sea floor spreading in the Late Miocene, magma intruded between the two plates. [4]
At least 287 springs have been found in northern Somalia,[ citation needed ] where they are more common in karst aquifers. Ninety-five percent of Somalis get their drinking water from aquifers,[ citation needed ] although poor quality water often means that boreholes go abandoned.
The Eocene Karkar limestone, Auradu limestone and Taalex limestone are important karstic aquifers in Somaliland and Puntland, along with thick, unconsolidated sediment aquifers up to 100 meters thick formed in the past 2.5 million years of the Quaternary in wadi locations throughout the county. Fractured Pleistocene basalt flows, particularly near Las Dhure and Agabar have potential as aquifers. The Yesomma Sandstone in northern Somalia is a high productivity aquifer, but sandstones in the south remain poorly studied for groundwater potential.[ citation needed ]
Fourteen water utilities serve towns in Somaliland and Puntland, although at least 750,000 people on the outskirts of Hargeisa lack piped water. [5]
Mining is not a significant part of the economy of Somalia, with little extraction aside from sand, gravel and stone for construction. Small amounts of gypsum, limestone, sea salt and sepiolite were mined during the instability brought on by the ongoing Somali Civil War, although the conflict halted oil exploration which had taken place in the 1980s.
The geology of Germany is heavily influenced by several phases of orogeny in the Paleozoic and the Cenozoic, by sedimentation in shelf seas and epicontinental seas and on plains in the Permian and Mesozoic as well as by the Quaternary glaciations.
The geology of the Republic of the Congo, also known as Congo-Brazzaville, to differentiate from the Democratic Republic of the Congo, formerly Zaire, includes extensive igneous and metamorphic basement rock, some up to two billion years old and sedimentary rocks formed within the past 250 million years. Much of the country's geology is hidden by sediments formed in the past 2.5 million years of the Quaternary.
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.
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.
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 understood or not exploited, including coal, vermiculite, rare earth elements and bauxite.
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.
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.
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 geological history of Zambia begins in the Proterozoic eon of the Precambrian. The igneous and metamorphic basement rocks tend to be highly metamorphosed and may have formed earlier in the Archean, but heat and pressure has destroyed evidence of earlier conditions. Major sedimentary and metamorphic groups formed in the mid-Proterozoic, followed by a series of glaciations in the Neoproterozoic and much of the Paleozoic which deposited glacial conglomerate as well as other sediments to form the Katanga Supergroup and rift-related Karoo Supergroup. Basalt eruptions blanketed the Karoo Supergroup in the Mesozoic and Zambia shifted to coal and sandstone formation. Geologically recent windblown sands from the Kalahari Desert and alluvial deposits near rivers play an important role in the modern surficial geology of Zambia. The country has extensive natural resources, particularly copper, but also cobalt, emeralds, other gemstones, uranium and coal.
The geology of Somaliland is very closely related to the geology of Somalia. Somaliland is a de facto independent country within the boundaries that the international community recognizes as Somalia. Because it encompasses the former territory of British Somaliland, the region is historically better researched than former Italian Somaliland. Somaliland is built on more than 700 million year old igneous and metamorphic crystalline basement rock.. 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 South Sudan is founded on Precambrian igneous and metamorphic rocks, that cover 40 percent of the country's surface and underlie other rock units. The region was affected by the Pan-African orogeny in the Neoproterozoic and extensional tectonics in the Mesozoic that deposited very thick oil-bearing sedimentary sequences in rift basins. Younger basalts, sandstones and sediments formed in the last 66 million years of the Cenozoic. The discovery of oil in 1975 was a major factor in the Second Sudanese Civil War, leading up to independence in 2011. The country also has gold, copper, cobalt, zinc, iron, marble, limestone and dolomite.
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.
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 Libya formed on top of deep and poorly understood Precambrian igneous and metamorphic crystalline basement rock. Most of the country is intra-craton basins, filled with thick layers of sediment. The region experienced long-running subsidence and terrestrial sedimentation during the Paleozoic, followed by phases of volcanism and intense folding in some areas, and widespread flooding in the Mesozoic and Cenozoic due to a long marine transgression. Libya has the largest hydrocarbon reserves in Africa, as well as deposits of evaporites.
The geology of Sudan formed primarily in the Precambrian, as igneous and metamorphic crystalline basement rock. Ancient terranes and inliers were intruded with granites, granitoids as well as volcanic rocks. Units of all types were deformed, reactivated, intruded and metamorphosed during the Proterozoic Pan-African orogeny. Dramatic sheet flow erosion prevented almost any sedimentary rocks from forming during the Paleozoic and Mesozoic. From the Mesozoic into the Cenozoic the formation of the Red Sea depression and complex faulting led to massive sediment deposition in some locations and regional volcanism. Sudan has petroleum, chromite, salt, gold, limestone and other natural resources.
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.
The geology of North Carolina includes ancient Proterozoic rocks belonging to the Grenville Province in the Blue Ridge. The region experienced igneous activity and the addition of new terranes and orogeny mountain building events throughout the Paleozoic, followed by the rifting of the Atlantic Ocean and the deposition of thick sediments in the Coastal Plain and offshore waters.
{{cite journal}}
: CS1 maint: multiple names: authors list (link)