Geology of Sudan

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Rift basins of southern and eastern Sudan Central African Rifts.svg
Rift basins of southern and eastern Sudan

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.

Contents

Stratigraphy, tectonics & geologic history

The oldest rocks in Sudan are igneous and metamorphic inlier areas formed in the Precambrian and reactivated by the Pan-African orogeny. Examples include the Nuba mountains, Darfur block and the rocks beneath the Nubian and Bayuda deserts. In the two deserts, metasedimentary rocks were intruded by granitoids and turned to migmatite during the Pan-African orogeny. The Red Sea Hills preserve gneiss, metamorphosed to amphibolite grade in the sequence of metamorphic facies and metasediments together with ophiolite assemblages. Fragments of the East Saharan Craton form exotic terranes near Haya, southwest of Port Sudan in the Red Sea Hills. These rock units include quartzite and marble formed between 800 and 900 million years ago as a passive continental margin. [1]

Neoproterozoic: Pan-African Orogeny

Geologists have interpreted the metasedimentary belts between the East Sahara Craton and the Red Sea fold and thrust belt as a rifting zone, related to the formation of an ocean in the Neoproterozoic.

The Jebel Rahib Belt, situated in the northwest, contains deformed basic and ultrabasic igneous rocks and thick layers of carbonaceous metasediments, formed at the time of the Pan-African orogeny. This time constraint for deformation and low-grade metamorphism comes from granitoids formed after the orogeny, dated to 570 million years ago. Dense, mafic oceanic crust formed in the Jebel Rahib rift as evidenced by an ophiolite assemblage that includes ultramafic rocks, pyroxenite, gabbro, chert and pillow lava. Pan-African age rocks may have formed in the Nubian Shield outside the Red Sea fold and thrust belt.

The North Kordofan Belt is very similar to the Jebel Rahib rift and likely formed around the same time, although it lacks ophiolites. The belt contains tourmaline-bearing granites and granitoids, dated to 590 million years ago. Shear zones formed at the end of the orogeny were sealed with mica pegmatite by 560 million years ago. Similarly, intrusive granitoids in the Darfur Belt formed between 590 and 570 million years ago.

The low-grade volcanic and sedimentary rocks of the Nuba Mountains also include dismembered, remnant ophiolites, basic and acid plutons, metamorphosed 700 million years ago and affected by igneous activity 550 million years ago, after the orogeny ended. The eastern Nuba Mountains is younger Pan-African age crust, likely a klippe or a small ocean basin.

A strip of tonalite, granodiorite and peralkaline granites, formed from low-grade metasediments, metavolcanics and granitoids at the time of the Pan-African orogeny occur along the eastern bank of the Nile River. These rocks were intruded by granitoids twice, once 898 and again 678 million years ago. Between the Nile and Red Sea Hills, another area of metasedimentary rocks outcrops, including marbles intercalated with metaquartzite. [2]

Paleozoic-Mesozoic (541-66 million years ago)

Sudan experienced extensive pediplanation, a form of sheet flow erosion that scours away overlying sediments, leaving a gently inclined bedrock surface. Because of this, the country has hardly any unmetamorphosed rocks from the Paleozoic or early Mesozoic, with the exception of a few 530 million year old Early Cambrian rocks at Sabaloka.

Structural geologists believe that the Red Sea depression is not bounded by faults. Rather, it formed beginning in the Carboniferous as a subsidence zone and continued to develop in the Mesozoic as a depression between monocline flexures approximately marking the present African and Arabian coasts of the sea. [3]

Cenozoic (66 million years ago-present)

Rift-related faulting in the Oligocene through the Miocene in the Sudan monocline zone led to the deposition of 4.3 kilometers of sediment in the vicinity of what is now the Suakin Archipelago, filling the trough. By the Miocene, the region was an area of shallow lagoons, in which evaporites deposited.

A renewed period of intense faulting in the Pliocene and early Pleistocene formed a central trough and led to basic and ultrabasic volcanic dikes intruding the Red Sea area. The region stabilized by the Pleistocene, after the connection with the Mediterranean closed in the Pliocene. [3]

Hydrogeology

The 60 to 80 meter thick Quaternary Gezira, Atshan and Gash Formations are unconfined and unconsolidated aquifers, composed of alluvial sand, silt, clay and gravel with high quality water. The Gezira and Atshan aquifers are recharged by water leakage from the Blue and White Nile, while the Gezira is recharged from the Gezira River. The Um Ruwaba Formation, by contrast is also unconsolidated and sometimes several hundred meters thick, but recharges very slowly from rainwater, limiting its use to domestic production and livestock watering.

Fractured and weathered zones with Gedaref basalts and Jebel Mara volcanic rocks fresh groundwater close to the surface and brine deeper in the aquifers. Paleozoic sedimentary rocks in western Sudan and Red Sea littoral sediments exhibit a mix of intergranular and fracture flow. The Nubian Sandstone Aquifer and Gedaref Sandstone have significant intergranular flow and storage and range between 40 and 400 meters thick. Water from these formation is typically fresh, although high salinity affects some water at greater depths. A similar fresh to brackish range is seen in the five to 20 meter thick weathered zone—and fractures—associated with Precambrian basement rock. [4]

Natural resource geology

Sudan has extensive natural resources, even after the independence of South Sudan in 2011 reduced the oil reserves within its borders. Natural gas is found offshore of Port Sudan in the Red Sea and many mineral reserves are situated in the eastern highlands. Sudan has chromite, gold, gypsum, limestone and salt, although the combined production of chromite, salt and gold accounts for only one percent of the value of exports. [3]

Related Research Articles

The Pan-African orogeny was a series of major Neoproterozoic orogenic events which related to the formation of the supercontinents Gondwana and Pannotia about 600 million years ago. This orogeny is also known as the Pan-Gondwanan or Saldanian Orogeny. The Pan-African orogeny and the Grenville orogeny are the largest known systems of orogenies on Earth. The sum of the continental crust formed in the Pan-African orogeny and the Grenville orogeny makes the Neoproterozoic the period of Earth's history that has produced most continental crust.

Sveconorwegian orogeny

The Sveconorwegian orogeny was an orogenic system active 1140 to 960 million years ago and currently exposed as the Sveconorwegian orogenic belt in southwestern Sweden and southern Norway. In Norway the orogenic belt is exposed southeast of the front of the Caledonian nappe system and in nappe windows. The Sveconorwegian orogen is commonly grouped within the Grenvillian Mesoproterozoic orogens. Contrary to many other known orogenic belts the Sveconorwegian orogens eastern border does not have any known suture zone with ophiolites.

The geology of Central African Republic (CAR) is part of the broader geology of Africa. CAR occupies a swath of ancient rocks, dating back billions of years that record significant aspects of Earth history and yield minerals vital to the country's small economy.

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.

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 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.

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.

Geology of Somaliland

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.

Geology of South Sudan

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.

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.

The geology of Quebec involves several different geologic provinces, made up of ancient Precambrian crystalline igneous and metamorphic rock, overlain by younger sedimentary rocks and soils. Most of southern Quebec is dominated by the Grenville Province, while the vast north is divided between the large Superior Province and the Churchill Province to the east, near Labrador.

The geology of Brazil includes very ancient craton basement rock from the Precambrian overlain by sedimentary rocks and intruded by igneous activity, as well as impacted by the rifting of the Atlantic Ocean.

References

  1. Schlüter, Thomas (2008). Geological Atlas of Africa. Springer. p. 218–219.
  2. Schlüter 2008, p. 218.
  3. 1 2 3 Schlüter 2008, p. 220.
  4. "Hydrogeology of Sudan". British Geological Survey.