Oued Guir is an intermittent river or wadi that flows through the Drâa-Tafilalet and Oriental regions in southeastern Morocco and Béchar Province in western Algeria .
54-591: The Oued Guir originates high in the Atlas Mountains 22 kilometres (14 mi) northeast of the town of Gourrama , Drâa-Tafilalet , then flows south to Boudenib and turns east, crossing into Oriental Region. Here it meets the Beni Yal and Oued Zelmou and turns south to the border with Algeria . After entering Algeria, the river enters the Djorf Torba dam, the continues past Abadla to Igli , where it merges with
108-887: A mountain range in the Maghreb in North Africa . It separates the Sahara Desert from the Mediterranean Sea and the Atlantic Ocean ; the name "Atlantic" is derived from the mountain range, which stretches around 2,500 km (1,600 mi) through Morocco , Algeria and Tunisia . The range's highest peak is Toubkal , which is in central Morocco, with an elevation of 4,167 metres (13,671 ft). The Atlas Mountains are primarily inhabited by Berber populations. The terms for 'mountain' are Adrar and adras in some Berber languages , and these terms are believed to be cognates of
162-422: A convergent plate tectonic boundary in the gap between an active volcanic arc and the associated trench , thus above the subducting oceanic plate. The formation of a forearc basin is often created by the vertical growth of an accretionary wedge that acts as a linear dam, parallel to the volcanic arc, creating a depression in which sediments can accumulate. Trench basins are deep linear depressions formed where
216-509: A high probability of preservation. In contrast, sedimentary basins formed on oceanic crust are likely to be destroyed by subduction . Continental margins formed when new ocean basins like the Atlantic are created as continents rift apart are likely to have lifespans of hundreds of millions of years, but may be only partially preserved when those ocean basins close as continents collide. Sedimentary basins are of great economic importance. Almost all
270-445: A load is placed on the lithosphere, it will tend to flex in the manner of an elastic plate. The magnitude of the lithospheric flexure is a function of the imposed load and the flexural rigidity of the lithosphere, and the wavelength of flexure is a function of flexural rigidity of the lithospheric plate. Flexural rigidity is in itself, a function of the lithospheric mineral composition, thermal regime, and effective elastic thickness of
324-606: A million, and their sedimentary fills range from one to almost twenty kilometers in thickness. A dozen or so common types of sedimentary basins are widely recognized and several classification schemes are proposed, however no single classification scheme is recognized as the standard. Most sedimentary basin classification schemes are based on one or more of these interrelated criteria: Although no one basin classification scheme has been widely adopted, several common types of sedimentary basins are widely accepted and well understood as distinct types. Over its complete lifespan
378-665: A result of isostasy . The long-term preserved geologic record of a sedimentary basin is a large scale contiguous three-dimensional package of sedimentary rocks created during a particular period of geologic time, a 'stratigraphic succession', that geologists continue to refer to as a sedimentary basin even if it is no longer a bathymetric or topographic depression. The Williston Basin , Molasse basin and Magallanes Basin are examples of sedimentary basins that are no longer depressions. Basins formed in different tectonic regimes vary in their preservation potential . Intracratonic basins, which form on highly-stable continental interiors, have
432-650: A result of the closing of a major ocean through continental collision resulting from plate tectonics. As a result the sedimentary record of inactive passive margins often are found as thick sedimentary sequences in mountain belts. For example the passive margins of the ancient Tethys Ocean are found in the mountain belts of the Alps and Himalayas that formed when the Tethys closed. Many authors recognize two subtypes of foreland basins: Peripheral foreland basins Retroarc foreland basins A sedimentary basin formed in association with
486-575: A single sedimentary basin can go through multiple phases and evolve from one of these types to another, such as a rift process going to completion to form a passive margin. In this case the sedimentary rocks of the rift basin phase are overlain by those rocks deposited during the passive margin phase. Hybrid basins where a single regional basin results from the processes that are characteristic of multiple of these types are also possible. Terrestrial rift valleys Proto-oceanic rift troughs Passive margins are long-lived and generally become inactive only as
540-404: A subducting oceanic plate descends into the mantle, beneath the overriding continental (Andean type) or oceanic plate (Mariana type). Trenches form in the deep ocean but, particularly where the overriding plate is continental crust they can accumulate thick sequences of sediments from eroding coastal mountains. Smaller 'trench slope basins' can form in association with a trench can form directly atop
594-419: A thick sequence of sediments have accumulated to form a large three-dimensional body of sedimentary rock . They form when long-term subsidence creates a regional depression that provides accommodation space for accumulation of sediments. Over millions or tens or hundreds of millions of years the deposition of sediment , primarily gravity-driven transportation of water-borne eroded material, acts to fill
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#1732858536627648-527: A widespread extension of the Earth's crust that rifted and separated the continents mentioned above. This extension was responsible for the formation of many thick intracontinental sedimentary basins including the present Atlas. Most of the rocks forming the surface of the present High Atlas were deposited under the ocean at that time. In the Paleogene and Neogene Periods (~66 million to ~1.8 million years ago),
702-516: Is a piece of rubber, which thins in the middle when stretched.) An example of a basin caused by lithospheric stretching is the North Sea – also an important location for significant hydrocarbon reserves. Another such feature is the Basin and Range Province which covers most of Nevada, forming a series of horst and graben structures. Tectonic extension at divergent boundaries where continental rifting
756-572: Is large enough and long-lived enough to create a sedimentary basin often called a pull-apart basin or strike-slip basin. These basins are often roughly rhombohedral in shape and may be called a rhombochasm . A classic rhombochasm is illustrated by the Dead Sea rift, where northward movement of the Arabian Plate relative to the Anatolian Plate has created a strike slip basin. The opposite effect
810-540: Is occurring can create a nascent ocean basin leading to either an ocean or the failure of the rift zone . Another expression of lithospheric stretching results in the formation of ocean basins with central ridges. The Red Sea is in fact an incipient ocean, in a plate tectonic context. The mouth of the Red Sea is also a tectonic triple junction where the Indian Ocean Ridge, Red Sea Rift and East African Rift meet. This
864-458: Is particularly measurable and observable with oceanic crust, as there is a well-established correlation between the age of the underlying crust and depth of the ocean . As newly-formed oceanic crust cools over a period of tens of millions of years. This is an important contribution to subsidence in rift basins, backarc basins and passive margins where they are underlain by newly-formed oceanic crust. In strike-slip tectonic settings, deformation of
918-535: Is that of transpression , where converging movement of a curved fault plane causes collision of the opposing sides of the fault. An example is the San Bernardino Mountains north of Los Angeles, which result from convergence along a curve in the San Andreas Fault system. The Northridge earthquake was caused by vertical movement along local thrust and reverse faults "bunching up" against the bend in
972-416: Is the only place on the planet where such a triple junction in oceanic crust is exposed subaerially . This is due to a high thermal buoyancy ( thermal subsidence ) of the junction, and also to a local crumpled zone of seafloor crust acting as a dam against the Red Sea. Lithospheric flexure is another geodynamic mechanism that can cause regional subsidence resulting in the creation of a sedimentary basin. If
1026-466: Is thus an important area of study for purely scientific and academic reasons. There are however important economic incentives as well for understanding the processes of sedimentary basin formation and evolution because almost all of the world's fossil fuel reserves were formed in sedimentary basins. All of these perspectives on the history of a particular region are based on the study of a large three-dimensional body of sedimentary rocks that resulted from
1080-691: The Alleghenian orogeny . These mountains were formed when Africa and America collided and were once a chain rivaling today's Himalayas . Today, the remains of this chain can be seen in the Fall Line region in the Eastern United States . Some remnants can also be found in the later formed Appalachians in North America. A second phase took place during the Mesozoic Era (before ~66 My). It consisted of
1134-559: The Atlantic Ocean in the southwest of Morocco toward the northeast to the heights of Ouarzazate and further east to the city of Tafilalt (altogether a distance of approximately 500 kilometres or 300 miles). In the south it borders the Sahara . The easternmost point of the anti-Atlas is the Jbel Saghro range and its northern boundary is flanked by sections of the High Atlas range . It includes
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#17328585366271188-846: The Mediterranean coast and joins with the Saharan Atlas in Eastern Algeria and Tunisia. The highest summit of the Tell Atlas is the 2,308 m (7,572 ft) Lalla Khadidja in the Djurdjura range of Kabylia . The western end of the Tell Atlas merges with the Middle Atlas range in Morocco. The area immediately to the south of the Tell Atlas is the high plateau of the Hautes Plaines , with lakes in
1242-563: The Oued Zouzfana to form the Oued Saoura . 31°44′N 2°48′W / 31.733°N 2.800°W / 31.733; -2.800 This article related to a river in Morocco is a stub . You can help Misplaced Pages by expanding it . This article related to a river in Algeria is a stub . You can help Misplaced Pages by expanding it . Atlas Mountains The Atlas Mountains are
1296-576: The toponym Atlas . The mountains are home to a number of animals and plants which are mostly found within Africa but some of which can be found in Europe. Many of these species are endangered and a few are already extinct . The weather is generally cool but summers are sunny, and the average temperature there is 25 °C. The Atlas Mountains have earned a reputation as a trekkers’ den, attracting adventurers year-round. The basement rock of most of Africa
1350-849: The Atlas mountain range. It covers parts of Algeria and Tunisia . The Aurès natural region is named after the range. Flora in the mountains include the Atlas cedar , evergreen oak and many semi-evergreen oaks such as the Algerian oak . Animals that live in the area include the Barbary macaque (misnamed as the Barbary ape), Barbary leopard , Barbary stag , Barbary sheep , Atlas Mountain badger , Cuvier's gazelle , North African boar , striped hyena , Red fox , northern bald ibis , Algerian nuthatch , dipper , and Atlas mountain viper . Many animals used to inhabit
1404-502: The Atlas mountains such as the Atlas bear , North African elephant , North African aurochs , bubal hartebeest and Atlas wild ass , but these subspecies are all extinct. Barbary lions are currently extinct in the wild, but descendants exist in captivity. Sedimentary basin Sedimentary basins are region-scale depressions of the Earth's crust where subsidence has occurred and
1458-619: The Djebel Siroua, a massif of volcanic origin with the highest summit of the range at 3,304 m. The Jebel Bani is a much lower range running along the southern side of the Anti Atlas. The High Atlas in central Morocco rises in the west at the Atlantic coast and stretches in an eastern direction to the Moroccan-Algerian border. It has several peaks over 4,000 m (13,000 ft), including
1512-606: The High Atlas, crossing Algeria from the Moroccan border and into Tunisia. The Aures Mountains are often presented as being the easternmost part of the Saharan Atlas. Though not as high as the High Atlas, they reach similar altitudes as the Tell Atlas range that runs to the north of them and closer to the coast. The highest peak in the range, outside of the Aures Mountains, is the 2,236 m (7,336 ft) high Djebel Aissa. They mark
1566-603: The area are Ouarzazate , Tahannaout , Amizmiz , Imlil , Tin Mal and Ijoukak . The Middle Atlas is completely in Morocco and is the northernmost of its three main Atlas ranges. The range lies north of the High Atlas, separated by the Moulouya and Oum Er-Rbia rivers, and south of the Rif mountains, separated by the Sebou River . To the west are the main coastal plains of Morocco with many of
1620-482: The associated accretionary prism as it grows and changes shape creating ponded basins. Pull-apart basins is are created along major strike-slip faults where a bend in the fault geometry or the splitting of the fault into two or more faults creates tensional forces that cause crustal thinning or stretching due to extension, creating a regional depression. Frequently, the basins are rhombic, S-like or Z-like in shape. A broad comparatively shallow basin formed far from
1674-645: The case of the Africa-Europe collision, it is clear that tectonic convergence is partially responsible for the formation of the High Atlas , as well as for the closure of the Strait of Gibraltar and the formation of the Alps and the Pyrenees . However, there is a lack of evidence for the nature of the subduction in the Atlas region, or for the thickening of the Earth's crust generally associated with continental collisions. One of
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1728-443: The depression. As the sediments are buried, they are subject to increasing pressure and begin the processes of compaction and lithification that transform them into sedimentary rock . Sedimentary basins are created by deformation of Earth's lithosphere in diverse geological settings, usually as a result of plate tectonic activity. Mechanisms of crustal deformation that lead to subsidence and sedimentary basin formation include
1782-401: The earth's surface over time. Regional study of these rocks can be used as the primary record for different kinds of scientific investigation aimed at understanding and reconstructing the earth's past plate tectonics (paleotectonics), geography ( paleogeography , climate ( paleoclimatology ), oceans ( paleoceanography ), habitats ( paleoecology and paleobiogeography ). Sedimentary basin analysis
1836-425: The edge of a continental craton as a result of prolonged, broadly distributed but slow subsidence of the continental lithosphere relative to the surrounding area. They are sometimes referred to as intracratonic sag basins. They tend to be subcircular in shape and are commonly filled with shallow water marine or terrestrial sedimentary rocks that remain flat-lying and relatively undeformed over long periods of time due to
1890-439: The effect is believed to be twofold. The lower, hotter part of the lithosphere will "flow" slowly away from the main area being stretched, whilst the upper, cooler and more brittle crust will tend to fault (crack) and fracture. The combined effect of these two mechanisms is for Earth's surface in the area of extension to subside, creating a geographical depression which is then often infilled with water and/or sediments. (An analogy
1944-405: The fill of one or more sedimentary basins over time. The scientific studies of stratigraphy and in recent decades sequence stratigraphy are focused on understanding the three-dimensional architecture, packaging and layering of this body of sedimentary rocks as a record resulting from sedimentary processes acting over time, influenced by global sea level change and regional plate tectonics. Where
1998-527: The highest summit in North Africa, Toubkal (4,167 m or 13,671 ft), and further east Ighil m'Goun (4,071 m or 13,356 ft), the second major summit of the range. At the Atlantic and to the southwest, the range drops abruptly and makes a transition to the coast and the Anti-Atlas range. To the north, in the direction of Marrakesh , the range descends less abruptly. On the heights of Ouarzazate
2052-425: The lithosphere occurs primarily in the plane of Earth as a result of near horizontal maximum and minimum principal stresses . Faults associated with these plate boundaries are primarily vertical. Wherever these vertical fault planes encounter bends, movement along the fault can create local areas of compression or tension. When the curve in the fault plane moves apart, a region of transtension occurs and sometimes
2106-405: The lithosphere. Plate tectonic processes that can create sufficient loads on the lithosphere to induce basin-forming processes include: After any kind of sedimentary basin has begun to form, the load created by the water and sediments filling the basin creates additional load, thus causing additional lithospheric flexure and amplifying the original subsidence that created the basin, regardless of
2160-478: The long-lived tectonic stability of the underlying craton. The geodynamic forces that create them remain poorly understood. Sedimentary basins form as a result of regional subsidence of the lithosphere, mostly as a result of a few geodynamic processes. If the lithosphere is caused to stretch horizontally, by mechanisms such as rifting (which is associated with divergent plate boundaries) or ridge-push or trench-pull (associated with convergent boundaries),
2214-501: The major cities and, to the east, the high barren plateau that lies between the Saharan and Tell Atlas. The high point of the range is the jbel Bou Naceur (3340 m). The Middle Atlas experiences more rain than the ranges to the south, making it an important water catchment for the coastal plains and important for biodiversity. It is home to the majority of the world's population of Barbary macaque . The Saharan Atlas of Algeria runs east of
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2268-515: The massif is cut through by the Draa Valley which opens southward. It is mainly inhabited by Berber people, who live in small villages and cultivate the high plains of the Ourika Valley . Near Barrage Cavagnac there is a hydroelectric dam that has created the artificial lake Lalla Takerkoust . The lake serves also as a source for fish for the local fishermen. The largest villages and towns of
2322-670: The most striking features of the Atlas to geologists is the relative small amount of crustal thickening and tectonic shortening despite the important altitude of the mountain range. Recent studies suggest that deep processes rooted in the Earth's mantle may have contributed to the uplift of the High and Middle Atlas. The Atlas are rich in natural resources . There are deposits of iron ore , lead ore , copper , silver , mercury , rock salt , phosphate , marble , anthracite coal and natural gas among other resources. The range can be divided into four general regions: The Anti-Atlas extends from
2376-466: The mountain chains that today constitute the Atlas were uplifted, as the land masses of Europe and Africa collided at the southern end of the Iberian Peninsula . Such convergent tectonic boundaries occur where two plates slide towards each other forming a subduction zone (if one plate moves underneath the other), and/or a continental collision (when the two plates contain continental crust ). In
2430-482: The northern edge of the Sahara Desert . The mountains see some rainfall and are better suited to agriculture than the plateau region to the north. Today, most of the population of the region are Berbers ( Imazighen ). The Tell Atlas is a mountain chain over 1,500 kilometres (900 mi) in length, belonging to the Atlas mountain ranges and stretching from Eastern Morocco to Tunisia, and through Algeria. It parallels
2484-471: The original cause of basin inception. Cooling of a lithospheric plate, particularly young oceanic crust or recently stretched continental crust, causes thermal subsidence . As the plate cools it shrinks and becomes denser through thermal contraction . Analogous to a solid floating in a liquid, as the lithospheric plate gets denser it sinks because it displaces more of the underlying mantle through an equilibrium process known as isostasy . Thermal subsidence
2538-413: The otherwise strike-slip fault environment. The study of sedimentary basins as entities unto themselves is often referred to as sedimentary basin analysis . Study involving quantitative modeling of the dynamic geologic processes by which they evolved is called basin modelling . The sedimentary rocks comprising the fill of sedimentary basins hold the most complete historical record of the evolution of
2592-429: The rocks directly and also very importantly allow paleontologists to study the microfossils they contain ( micropaleontology ). At the time they are being drilled, boreholes are also surveyed by pulling electronic instruments along the length of the borehole in a process known as well logging . Well logging, which is sometimes appropriately called borehole geophysics , uses electromagnetic and radioactive properties of
2646-486: The sedimentary rocks comprising a sedimentary basin's fill are exposed at the earth's surface, traditional field geology and aerial photography techniques as well as satellite imagery can be used in the study of sedimentary basins. Much of a sedimentary basin's fill often remains buried below the surface, often submerged in the ocean, and thus cannot be studied directly. Acoustic imaging using seismic reflection acquired through seismic data acquisition and studied through
2700-400: The specific sub-discipline of seismic stratigraphy is the primary means of understanding the three-dimensional architecture of the basin's fill through remote sensing . Direct sampling of the rocks themselves is accomplished via the drilling of boreholes and the retrieval of rock samples in the form of both core samples and drill cuttings . These allow geologists to study small samples of
2754-402: The thinning of underlying crust; depression of the crust by sedimentary, tectonic or volcanic loading; or changes in the thickness or density of underlying or adjacent lithosphere . Once the process of basin formation has begun, the weight of the sediments being deposited in the basin adds a further load on the underlying crust that accentuates subsidence and thus amplifies basin development as
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#17328585366272808-511: The wet season and salt flats in the dry. The eastern half of the Tell Atlas has the most humid climate of North Africa, with annual precipitation reaching well above 1,000 mm (39 in), and sometimes over 1,500 mm (59 in) like in the Collo Peninsula or near Ain Draham . An important amount of snow falls on the summits in winter. The Aurès Mountains are the easternmost portion of
2862-546: The world's natural gas and petroleum and all of its coal are found in sedimentary rock. Many metal ores are found in sedimentary rocks formed in particular sedimentary environments. Sedimentary basins are also important from a purely scientific perspective because their sedimentary fill provides a record of Earth's history during the time in which the basin was actively receiving sediment. More than six hundred sedimentary basins have been identified worldwide. They range in areal size from tens of square kilometers to well over
2916-739: Was formed during the Precambrian supereon and is much older than the Atlas Mountains lying on the continent. The Atlas was formed during three subsequent phases of Earth's geology. The first tectonic deformation phase involves only the Anti-Atlas , which was formed in the Paleozoic Era (~300 million years ago) as the result of continental collisions . North America , Europe and Africa were connected millions of years ago. The Anti-Atlas Mountains are believed to have originally been formed as part of
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