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95-713: The basin started forming in the Early Jurassic, with the break-up of Pangea and the creation of the South Atlantic , when extensional tectonics , including rifting , formed several basins in eastern South America and southwestern Africa. The accommodation space in the Cañadón Asfalto Basin was filled by volcanic, fluvial and lacustrine deposits in various geologic formations, separated by unconformities related to transtensional and transpressional tectonic forces. The Cenozoic evolution of

190-500: A fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth 's crust result from the action of plate tectonic forces, with the largest forming the boundaries between the plates, such as the megathrust faults of subduction zones or transform faults . Energy release associated with rapid movement on active faults

285-405: A fault as oblique requires both dip and strike components to be measurable and significant. Some oblique faults occur within transtensional and transpressional regimes, and others occur where the direction of extension or shortening changes during the deformation but the earlier formed faults remain active. The hade angle is defined as the complement of the dip angle; it is the angle between

380-582: A fault hosting valuable porphyry copper deposits is northern Chile's Domeyko Fault with deposits at Chuquicamata , Collahuasi , El Abra , El Salvador , La Escondida and Potrerillos . Further south in Chile Los Bronces and El Teniente porphyry copper deposit lie each at the intersection of two fault systems. Faults may not always act as conduits to surface. It has been proposed that deep-seated "misoriented" faults may instead be zones where magmas forming porphyry copper stagnate achieving

475-489: A fault plane, where it becomes locked, are called asperities . Stress builds up when a fault is locked, and when it reaches a level that exceeds the strength threshold, the fault ruptures and the accumulated strain energy is released in part as seismic waves , forming an earthquake . Strain occurs accumulatively or instantaneously, depending on the liquid state of the rock; the ductile lower crust and mantle accumulate deformation gradually via shearing , whereas

570-408: A fault's age by studying soil features seen in shallow excavations and geomorphology seen in aerial photographs. Subsurface clues include shears and their relationships to carbonate nodules , eroded clay, and iron oxide mineralization, in the case of older soil, and lack of such signs in the case of younger soil. Radiocarbon dating of organic material buried next to or over a fault shear

665-427: A hanging wall or foot wall where a thrust fault formed along a relatively weak bedding plane is known as a flat and a section where the thrust fault cut upward through the stratigraphic sequence is known as a ramp . Typically, thrust faults move within formations by forming flats and climbing up sections with ramps. This results in the hanging wall flat (or a portion thereof) lying atop the foot wall ramp as shown in

760-484: A major fault. Synthetic faults dip in the same direction as the major fault while the antithetic faults dip in the opposite direction. These faults may be accompanied by rollover anticlines (e.g. the Niger Delta Structural Style). All faults have a measurable thickness, made up of deformed rock characteristic of the level in the crust where the faulting happened, of the rock types affected by

855-400: A manner that creates multiple listric faults. The fault panes of listric faults can further flatten and evolve into a horizontal or near-horizontal plane, where slip progresses horizontally along a decollement . Extensional decollements can grow to great dimensions and form detachment faults , which are low-angle normal faults with regional tectonic significance. Due to the curvature of

950-421: A non-vertical fault are known as the hanging wall and footwall . The hanging wall occurs above the fault plane and the footwall occurs below it. This terminology comes from mining: when working a tabular ore body, the miner stood with the footwall under his feet and with the hanging wall above him. These terms are important for distinguishing different dip-slip fault types: reverse faults and normal faults. In

1045-408: A northward direction, separating it from Antarctica and allowing complete oceanic circulation around Antarctica for the first time. This motion, together with decreasing atmospheric carbon dioxide concentrations, caused a rapid cooling of Antarctica and allowed glaciers to form. This glaciation eventually coalesced into the kilometers-thick ice sheets seen today. Other major events took place during

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1140-464: A reverse fault, the hanging wall displaces upward, while in a normal fault the hanging wall displaces downward. Distinguishing between these two fault types is important for determining the stress regime of the fault movement. Faults are mainly classified in terms of the angle that the fault plane makes with the Earth's surface, known as the dip , and the direction of slip along the fault plane. Based on

1235-612: A single chain, the Central Pangean Mountains . Fossil evidence for Pangaea includes the presence of similar and identical species on continents that are now great distances apart. For example, fossils of the therapsid Lystrosaurus have been found in South Africa , India and Antarctica , alongside members of the Glossopteris flora, whose distribution would have ranged from the polar circle to

1330-422: Is a horst . A sequence of grabens and horsts on the surface of the Earth produces a characteristic basin and range topography . Normal faults can evolve into listric faults, with their plane dip being steeper near the surface, then shallower with increased depth, with the fault plane curving into the Earth. They can also form where the hanging wall is absent (such as on a cliff), where the footwall may slump in

1425-423: Is a zone of folding close to a fault that likely arises from frictional resistance to movement on the fault. The direction and magnitude of heave and throw can be measured only by finding common intersection points on either side of the fault (called a piercing point ). In practice, it is usually only possible to find the slip direction of faults, and an approximation of the heave and throw vector. The two sides of

1520-711: Is currently on a collision course with eastern Asia . Both Australia and India are currently moving northeast at 5–6 centimeters (2–3 in) per year. Antarctica has been near or at the South Pole since the formation of Pangaea about 280 Ma. India started to collide with Asia beginning about 35 Ma, forming the Himalayan orogeny and closing the Tethys Ocean; this collision continues today. The African Plate started to change directions, from west to northwest toward Europe, and South America began to move in

1615-544: Is defined by the direction of movement of the ground as would be seen by an observer on the opposite side of the fault. A special class of strike-slip fault is the transform fault when it forms a plate boundary. This class is related to an offset in a spreading center , such as a mid-ocean ridge , or, less common, within continental lithosphere , such as the Dead Sea Transform in the Middle East or

1710-404: Is derived from Ancient Greek pan ( πᾶν , "all, entire, whole") and Gaia or Gaea ( Γαῖα , " Mother Earth , land"). The first to suggest that the continents were once joined and later separated may have been Abraham Ortelius in 1596. The concept that the continents once formed a contiguous land mass was hypothesised, with corroborating evidence, by Alfred Wegener , the originator of

1805-534: Is identical for all contemporaneous samples, can be subtracted, leaving the portion that shows continental drift and can be used to help reconstruct earlier continental latitudes and orientations. Pangaea is the most recent supercontinent reconstructed from the geologic record and therefore is by far the best understood. The formation of supercontinents and their breakup appears to be cyclical through Earth's history. There may have been several others before Pangaea. Paleomagnetic measurements help geologists determine

1900-543: Is often critical in distinguishing active from inactive faults. From such relationships, paleoseismologists can estimate the sizes of past earthquakes over the past several hundred years, and develop rough projections of future fault activity. Many ore deposits lie on or are associated with faults. This is because the fractured rock associated with fault zones allow for magma ascent or the circulation of mineral-bearing fluids. Intersections of near-vertical faults are often locations of significant ore deposits. An example of

1995-492: Is particularly clear in the case of detachment faults and major thrust faults . The main types of fault rock include: In geotechnical engineering , a fault often forms a discontinuity that may have a large influence on the mechanical behavior (strength, deformation, etc.) of soil and rock masses in, for example, tunnel , foundation , or slope construction. The level of a fault's activity can be critical for (1) locating buildings, tanks, and pipelines and (2) assessing

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2090-516: Is represented by the fluvial, marine and eolian Río Negro Formation , a formation extending into the Colorado Basin . The stratigraphy of the Cañadón Asfalto Basin covers the following units: The Cañadón Asfalto Basin has provided several fossils of various groups of flora and fauna. One of the largest dinosaurs known, the titanosaur Patagotitan mayorum , and one of the largest theropods , Tyrannotitan chubutensis , were found in

2185-425: Is the cause of most earthquakes . Faults may also displace slowly, by aseismic creep . A fault plane is the plane that represents the fracture surface of a fault. A fault trace or fault line is a place where the fault can be seen or mapped on the surface. A fault trace is also the line commonly plotted on geologic maps to represent a fault. A fault zone is a cluster of parallel faults. However,

2280-762: The Alpine Fault in New Zealand. Transform faults are also referred to as "conservative" plate boundaries since the lithosphere is neither created nor destroyed. Dip-slip faults can be either normal (" extensional ") or reverse . The terminology of "normal" and "reverse" comes from coal mining in England, where normal faults are the most common. With the passage of time, a regional reversal between tensional and compressional stresses (or vice-versa) might occur, and faults may be reactivated with their relative block movement inverted in opposite directions to

2375-741: The Caledonian orogeny . As Avalonia inched towards Laurentia, the seaway between them, a remnant of the Iapetus Ocean, was slowly shrinking. Meanwhile, southern Europe broke off from Gondwana and began to move towards Euramerica across the Rheic Ocean . It collided with southern Baltica in the Devonian. By the late Silurian, Annamia ( Indochina ) and the South China Craton split from Gondwana and moved northward, shrinking

2470-668: The Carboniferous covered the southern end of Pangaea. Glacial deposits, specifically till , of the same age and structure are found on many separate continents that would have been together in the continent of Pangaea. The continuity of mountain chains provides further evidence, such as the Appalachian Mountains chain extending from the southeastern United States to the Scandinavian Caledonides of Europe; these are now believed to have formed

2565-641: The Cenozoic . The Collón Curá Formation , that is also present in the southern Neuquén Basin , is the defining formation for the Colloncuran , used within the SALMA classification , the geochronology for the Cenozoic used in South America. The Cañadón Asfalto Basin was not defined as a separate sedimentary basin until the 1990s. Until then, the sediments deposited in the basin were considered part of

2660-631: The Cerro Barcino Formation . Fossils of Leonerasaurus taquetrensis , an early Sauropodomorph, were found in and named after the Las Leoneras Formation . The La Colonia Formation has provided fossils of a mammal; Argentodites coloniensis , and a nearly complete skeleton of the theropod Carnotaurus sastrei . Remains of the plesiosaur Aristonectes parvidens were found in the Maastrichtian section of

2755-749: The Colloncuran South American land mammal age , stretches across the Neuquén Basin to the northwest of the North Patagonian Massif and the western part of the Cañadón Asfalto Basin. The formation has provided many mammal, reptile and bird fossils, among which the largest terror bird Kelenken . Along the Chico River in the basin (localities 9 and 10 on the map), fossils of the sparassodont Patagosmilus goini , two new species of Protypotherium , and

2850-472: The Early Cretaceous . The opening of the Tethys Ocean also contributed to the warming of the climate. The very active mid-ocean ridges associated with the breakup of Pangaea raised sea levels to the highest in the geological record, flooding much of the continents. The expansion of the temperate climate zones that accompanied the breakup of Pangaea may have contributed to the diversification of

2945-711: The Huitrera Formation . In the Ñirihuau Basin, this sequence is covered by the Oligocene to Miocene Ventana Formation . During the Paleogene, in the Cañadón Asfalto Basin the volcaniclastic Laguna del Hunco Formation , and volcanic Sarmiento Group were deposited. The Neogene succession in the basin comprises the Early Miocene alluvial volcaniclastics of the La Pava Formation , and

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3040-527: The Iapetus Ocean and Paleoasian Ocean. Most of these landmasses coalesced again to form the relatively short-lived supercontinent Pannotia, which included large areas of land near the poles and a small strip connecting the polar masses near the equator. Pannotia lasted until 540  Ma , near the beginning of the Cambrian and then broke up, giving rise to the continents of Laurentia, Baltica, and

3135-896: The Jurassic , completely closing the Proto-Tethys Ocean. By the Early Permian , the Cimmerian plate split from Gondwana and moved towards Laurasia, thus closing the Paleo-Tethys Ocean and forming the Tethys Ocean in its southern end. Most of the landmasses were all in one. By the Triassic , Pangaea rotated a little, and the Cimmerian plate was still travelling across the shrinking Paleo-Tethys until

3230-803: The Lefipán Formation . Fossil flora ( pollen , spores , algae and macroflora) have been recovered from the Lonco Trapial Formation ( Cupressaceae ), and the Cañadón Asfalto Formation and comprise several families of plants, indicative of climatic conditions in the Late Jurassic; Osmundaceae , Caytoniaceae , Araucariaceae , Cheirolepidiaceae , Podocarpaceae , Botryococcaceae , Zygnemataceae , Prasinophyceae , Filicales and Taxodiaceae . The same formation also provided fossils of two species of

3325-759: The Middle Jurassic . By the Late Triassic , the Paleo-Tethys had closed from west to east, creating the Cimmerian Orogeny . Pangaea, which looked like a C , with the Tethys Ocean inside the C , had rifted by the Middle Jurassic. Pangaea existed as a supercontinent for 160 million years, from its assembly around 335 Ma (Early Carboniferous) to its breakup 175 Ma (Middle Jurassic). During this interval, important developments in

3420-571: The Triassic–Jurassic extinction event . These events resulted in disaster fauna showing little diversity and high cosmopolitanism, including Lystrosaurus , which opportunistically spread to every corner of Pangaea following the Permian–Triassic extinction event. On the other hand, there is evidence that many Pangaean species were provincial , with a limited geographical range, despite the absence of geographical barriers. This may be due to

3515-895: The Urkontinent . Wegener used the name "Pangaea" once in the 1920 edition of his book, referring to the ancient supercontinent as "the Pangaea of the Carboniferous". He used the Germanized form Pangäa , but the name entered German and English scientific literature (in 1922 and 1926, respectively) in the Latinized form Pangaea , especially during a symposium of the American Association of Petroleum Geologists in November 1926. Wegener originally proposed that

3610-640: The frog Notobatrachus , the turtle Condorchelys antiqua , the pterosaur Allkaruen koi , and several mammals. Fossil fish of Condorlepis groeberi were retrieved from the Cañadón Calcáreo Formation , and the crocodylomorphs Almadasuchus figarii (Cañadón Calcáreo Formation), and Barcinosuchus gradilis (Cerro Barcino Formation), come from the Mesozoic strata in the basin. Fossil leaves of Lefipania padillae and Araucaria lefipanensis come from and were named after

3705-609: The mantle . This succession is unconformably covered by lacustrine, fluvial and volcaniclastic rocks of the approximately 10 to 15 million year ranging Chubut Group comprising the older Los Adobes Formation and the younger Cerro Barcino Formation . The western side of the basin during the Late Cretaceous experienced a marine transgression of the Atlantic Ocean , depositing the fluvial and estuarine Paso del Sapo and Lefipán Formations . The marine sediments of

3800-477: The rodents Guiomys unica and Microcardiodon williensis were found. Pangea Pangaea or Pangea ( / p æ n ˈ dʒ iː ə / pan- JEE -ə ) was a supercontinent that existed during the late Paleozoic and early Mesozoic eras. It assembled from the earlier continental units of Gondwana , Euramerica and Siberia during the Carboniferous approximately 335 million years ago, and began to break apart about 200 million years ago, at

3895-456: The scientific theory of continental drift , in three 1912 academic journal articles written in German titled Die Entstehung der Kontinente ( The Origin of Continents ). He expanded upon his hypothesis in his 1915 book of the same title, in which he postulated that, before breaking up and drifting to their present locations, all the continents had formed a single supercontinent that he called

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3990-657: The seismic shaking and tsunami hazard to infrastructure and people in the vicinity. In California, for example, new building construction has been prohibited directly on or near faults that have moved within the Holocene Epoch (the last 11,700 years) of the Earth's geological history. Also, faults that have shown movement during the Holocene plus Pleistocene Epochs (the last 2.6 million years) may receive consideration, especially for critical structures such as power plants, dams, hospitals, and schools. Geologists assess

4085-680: The Cenozoic, including the opening of the Gulf of California , the uplift of the Alps , and the opening of the Sea of Japan . The break-up of Pangaea continues today in the Red Sea Rift and East African Rift . The breakup of Pangaea was accompanied by outgassing of large quantities of carbon dioxide from continental rifts. This produced a Mesozoic CO 2 high that contributed to the very warm climate of

4180-560: The Cretaceous when Laurasia started to rotate clockwise and moved northward with North America to the north, and Eurasia to the south. The clockwise motion of Laurasia led much later to the closing of the Tethys Ocean and the widening of the "Sinus Borealis", which later became the Arctic Ocean . Meanwhile, on the other side of Africa and along the adjacent margins of east Africa, Antarctica and Madagascar , rifts formed that led to

4275-663: The Early Cretaceous, Atlantica , today's South America and Africa, separated from eastern Gondwana. Then in the Middle Cretaceous, Gondwana fragmented to open up the South Atlantic Ocean as South America started to move westward away from Africa. The South Atlantic did not develop uniformly; rather, it rifted from south to north. Also, at the same time, Madagascar and Insular India began to separate from Antarctica and moved northward, opening up

4370-558: The Indian Ocean. Madagascar and India separated from each other 100–90 Ma in the Late Cretaceous. India continued to move northward toward Eurasia at 15 centimeters (6 in) per year (a plate tectonic record), closing the eastern Tethys Ocean, while Madagascar stopped and became locked to the African Plate . New Zealand , New Caledonia and the rest of Zealandia began to separate from Australia, moving eastward toward

4465-413: The Late Jurassic. During these phases, the basin went through an extensional tectonic regime, with transtensional movements. Several distinct tectonic reactivation cycles occurred, with block rotation due to transpressional forces. The geodynamic movements are noted in the stratigraphy by regional unconformities . The predominantly extensional movement was overprinted by a compressional setting, active since

4560-704: The Lefipán Formations have been correlated to the Salamanca Formation of the Golfo San Jorge Basin to the south and the Lefipán sediments were sourced from the North Patagonian Massif. To the west of the Cañadón Asfalto Basin, another basin started forming in these times, the Ñirihuau Basin , characterized by the deposition of the felsic to intermediate volcanic Don Juan Formation , the basaltic Tres Picos Prieto Formation and

4655-725: The Middle to Late Miocene volcaniclastic, fluvial, lacustrine and deltaic tuffs , sandstones and carbonates of the Collón Curá Formation . The Late Miocene to Quaternary succession comprises mostly the basaltic lava flows of the El Mirador Formation , the basalts of the Cráter Formation , and Quaternary alluvium . In the northern part of the basin, the Late Miocene and Early Pliocene

4750-421: The North Patagonian Massif. Homovc et al. (1991) and Figari & Courtade (1993) started defining the stratigraphic units in megasequences indicative of the evolution of a rift basin , resulting from the break-up of Pangea and Gondwana in particular. The basin has an irregular shape, comprising several depocenters defining sub-basins. The basin stretches from and partly covers the North Patagonian Massif in

4845-498: The Pacific and opening the Coral Sea and Tasman Sea . The third major and final phase of the break-up of Pangaea occurred in the early Cenozoic ( Paleocene to Oligocene ). Laurasia split when Laurentia broke from Eurasia, opening the Norwegian Sea about 60–55 Ma. The Atlantic and Indian Oceans continued to expand, closing the Tethys Ocean. Meanwhile, Australia split from Antarctica and moved quickly northward, just as India had done more than 40 million years before. Australia

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4940-473: The Proto-Tethys Ocean and opening the Paleo-Tethys Ocean to the south. In the Devonian Gondwana moved towards Euramerica, causing the Rheic Ocean to shrink. In the Early Carboniferous , northwest Africa had touched the southeastern coast of Euramerica, creating the southern portion of the Appalachian Mountains, the Meseta Mountains , and the Mauritanide Mountains , an event called the Variscan orogeny . South America moved northward to southern Euramerica, while

5035-420: The angiosperms. [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 Fault (geology) In geology ,

5130-421: The basin in the south in the Altar Valley . The Cañadón Asfalto Basin started forming in the earliest Jurassic on top of Permian basement constituted by the igneous - metamorphic Mamil Choique and Cushamen Formations . Two main phases of basin evolution are recognized; the Jurassic and Cretaceous megasequences. Figari et al. in 2015 describe two Jurassic megasequences, J1 in the Early Jurassic and J2 in

5225-410: The basin is mainly influenced by the Andean orogeny , producing folding and faulting in the basin. The basin is of paleontological significance as it hosts several fossiliferous stratigraphic units providing many fossils of dinosaurs , turtles , mammals , plesiosaurs , pterosaurs , crocodylomorphs , fish , amphibians and flora in the Mesozoic and mammals, amphibians, fish and flora in

5320-427: The breakup of Pangaea was caused by centripetal forces from Earth's rotation acting on the high continents. However, this mechanism was easily shown to be physically implausible, which delayed acceptance of the Pangaea hypothesis. Arthur Holmes proposed the more plausible mechanism of mantle convection , which, together with evidence provided by the mapping of the ocean floor following the Second World War , led to

5415-403: The brittle upper crust reacts by fracture – instantaneous stress release – resulting in motion along the fault. A fault in ductile rocks can also release instantaneously when the strain rate is too great. Slip is defined as the relative movement of geological features present on either side of a fault plane. A fault's sense of slip is defined as the relative motion of the rock on each side of

5510-474: The development and acceptance of the theory of plate tectonics . This theory provides the widely-accepted explanation for the existence and breakup of Pangaea. The geography of the continents bordering the Atlantic Ocean was the first evidence suggesting the existence of Pangaea. The seemingly close fit of the coastlines of North and South America with Europe and Africa was remarked on almost as soon as these coasts were charted. Careful reconstructions showed that

5605-436: The direction of slip, faults can be categorized as: In a strike-slip fault (also known as a wrench fault , tear fault or transcurrent fault ), the fault surface (plane) is usually near vertical, and the footwall moves laterally either left or right with very little vertical motion. Strike-slip faults with left-lateral motion are also known as sinistral faults and those with right-lateral motion as dextral faults. Each

5700-441: The early Cenozoic. This compressional phase is noted in folds and compressional faults present in the basin. The sedimentary infill of the Early and Middle Jurassic in the basin is characterized by fluvial and lacustrine sediments of the Las Leoneras , Cañadón Asfalto and Cañadón Calcáreo Formations covering the volcanic Lonco Trapial Formation , which comprises intermediate volcanic rocks sourced by magmas coming from

5795-415: The eastern portion of Gondwana ( India , Antarctica , and Australia ) headed toward the South Pole from the equator. North and South China were on independent continents. The Kazakhstania microcontinent had collided with Siberia. (Siberia had been a separate continent for millions of years since the breakup of Pannotia.) The Variscan orogeny raised the Central Pangaean Mountains, which were comparable to

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5890-406: The end of the Triassic and beginning of the Jurassic . Pangaea was C-shaped, with the bulk of its mass stretching between Earth 's northern and southern polar regions and surrounded by the superocean Panthalassa and the Paleo-Tethys and subsequent Tethys Oceans . Pangaea is the most recent supercontinent to have existed and the first to be reconstructed by geologists . The name "Pangaea"

5985-431: The equator if the continents had been in their present position; similarly, the freshwater reptile Mesosaurus has been found in only localized regions of the coasts of Brazil and West Africa . Geologists can also determine the movement of continental plates by examining the orientation of magnetic minerals in rocks . When rocks are formed, they take on the magnetic orientation of the Earth, showing which direction

6080-432: The equator. The assembly of Pangaea disrupted the Intertropical Convergence Zone and created an extreme monsoon climate that reduced the deposition of coal to its lowest level in the last 300 million years. During the Permian , coal deposition was largely restricted to the North and South China microcontinents, which were among the few areas of continental crust that had not joined with Pangaea. The extremes of climate in

6175-445: The evolution of life took place. The seas of the Early Carboniferous were dominated by rugose corals , brachiopods , bryozoans , sharks , and the first bony fish . Life on land was dominated by lycopsid forests inhabited by insects and other arthropods and the first tetrapods . By the time Pangaea broke up, in the Middle Jurassic, the seas swarmed with molluscs (particularly ammonites ), ichthyosaurs , sharks and rays, and

6270-456: The fault and of the presence and nature of any mineralising fluids . Fault rocks are classified by their textures and the implied mechanism of deformation. A fault that passes through different levels of the lithosphere will have many different types of fault rock developed along its surface. Continued dip-slip displacement tends to juxtapose fault rocks characteristic of different crustal levels, with varying degrees of overprinting. This effect

6365-402: The fault concerning the other side. In measuring the horizontal or vertical separation, the throw of the fault is the vertical component of the separation and the heave of the fault is the horizontal component, as in "Throw up and heave out". The vector of slip can be qualitatively assessed by studying any drag folding of strata, which may be visible on either side of the fault. Drag folding

6460-513: The fault plane and a vertical plane that strikes parallel to the fault. Ring faults , also known as caldera faults , are faults that occur within collapsed volcanic calderas and the sites of bolide strikes, such as the Chesapeake Bay impact crater . Ring faults are the result of a series of overlapping normal faults, forming a circular outline. Fractures created by ring faults may be filled by ring dikes . Synthetic and antithetic are terms used to describe minor faults associated with

6555-401: The fault plane, the horizontal extensional displacement on a listric fault implies a geometric "gap" between the hanging and footwalls of the fault forms when the slip motion occurs. To accommodate into the geometric gap, and depending on its rheology , the hanging wall might fold and slide downwards into the gap and produce rollover folding , or break into further faults and blocks which fil in

6650-427: The fault-bend fold diagram. Thrust faults form nappes and klippen in the large thrust belts. Subduction zones are a special class of thrusts that form the largest faults on Earth and give rise to the largest earthquakes. A fault which has a component of dip-slip and a component of strike-slip is termed an oblique-slip fault . Nearly all faults have some component of both dip-slip and strike-slip; hence, defining

6745-419: The few continental areas not merged with Pangaea, as a refugium. There were three major phases in the break-up of Pangaea. The Atlantic Ocean did not open uniformly; rifting began in the north-central Atlantic. The first breakup of Pangaea is proposed for the late Ladinian (230 Ma) with initial spreading in the opening central Atlantic. Then the rifting proceeded along the eastern margin of North America,

6840-445: The first ray-finned bony fishes, while life on land was dominated by forests of cycads and conifers in which dinosaurs flourished and in which the first true mammals had appeared. The evolution of life in this time reflected the conditions created by the assembly of Pangaea. The union of most of the continental crust into one landmass reduced the extent of sea coasts. Increased erosion from uplifted continental crust increased

6935-814: The formation of the Ural Mountains and Laurasia . This was the last step of the formation of Pangaea. Meanwhile, South America had collided with southern Laurentia, closing the Rheic Ocean and completing the Variscian orogeny with the formation the southernmost part of the Appalachians and Ouachita Mountains . By this time, Gondwana was positioned near the South Pole, and glaciers formed in Antarctica, India, Australia, southern Africa, and South America. The North China Craton collided with Siberia by

7030-424: The formation of the southwestern Indian Ocean in the Cretaceous. The second major phase in the break-up of Pangaea began in the Early Cretaceous (150–140 Ma), when Gondwana separated into multiple continents (Africa, South America, India, Antarctica, and Australia). The subduction at Tethyan Trench probably caused Africa, India and Australia to move northward, causing the opening of a "South Indian Ocean". In

7125-475: The gap. If faults form, imbrication fans or domino faulting may form. A reverse fault is the opposite of a normal fault—the hanging wall moves up relative to the footwall. Reverse faults indicate compressive shortening of the crust. A thrust fault has the same sense of motion as a reverse fault, but with the dip of the fault plane at less than 45°. Thrust faults typically form ramps, flats and fault-bend (hanging wall and footwall) folds. A section of

7220-497: The importance of floodplain and delta environments relative to shallow marine environments. Continental assembly and uplift also meant increasingly arid land climates, favoring the evolution of amniote animals and seed plants , whose eggs and seeds were better adapted to dry climates. The early drying trend was most pronounced in western Pangaea, which became a center of the evolution and geographical spread of amniotes. Coal swamps typically form in perpetually wet regions close to

7315-484: The interior of Pangaea are reflected in bone growth patterns of pareiasaurs and the growth patterns in gymnosperm forests. The lack of oceanic barriers is thought to have favored cosmopolitanism , in which successful species attain wide geographical distribution. Cosmopolitanism was also driven by mass extinctions , including the Permian–Triassic extinction event , the most severe in the fossil record, and also

7410-554: The later supercontinents, Pannotia and Pangaea. According to one reconstruction, when Rodinia broke up, it split into three pieces: proto- Laurasia , proto-Gondwana, and the smaller Congo Craton . Proto-Laurasia and proto-Gondwana were separated by the Proto-Tethys Ocean . Proto-Laurasia split apart to form the continents of Laurentia , Siberia , and Baltica . Baltica moved to the east of Laurentia, and Siberia moved northeast of Laurentia. The split created two oceans,

7505-519: The latest Maastrichtian within the Lefipán Formation. The Paleocene ( Tiupampan ) strata of the Lefipán Formation have provided fossils of the mammal Cocatherium lefipanum and fish Hypolophodon patagoniensis . The Early Eocene ( Casamayoran to Mustersan ) Laguna del Hunco Formation has provided fossils of the fish Bachmannia chubutensis , the frog Shelania pascuali , and fossil flora. The Collón Curá Formation , that defines

7600-438: The latitude and orientation of ancient continental blocks, and newer techniques may help determine longitudes. Paleontology helps determine ancient climates, confirming latitude estimates from paleomagnetic measurements, and the distribution of ancient forms of life provides clues on which continental blocks were close to each other at particular geological moments. However, reconstructions of continents prior to Pangaea, including

7695-409: The mismatch at the 500 fathoms (3,000 feet; 910 meters) contour was less than 130 km (81 mi), and it was argued that this was much too similar to be attributed to coincidence. Additional evidence for Pangaea is found in the geology of adjacent continents, including matching geological trends between the eastern coast of South America and the western coast of Africa . The polar ice cap of

7790-545: The modern Himalayas in scale. With Pangaea stretching from the South Pole across the equator and well into the Northern Hemisphere, an intense megamonsoon climate was established, except for a perpetually wet zone immediately around the central mountains. Western Kazakhstania collided with Baltica in the late Carboniferous, closing the Ural Ocean and the western Proto-Tethys ( Uralian orogeny ), causing

7885-600: The north and east towards the Cotricó High to the south of the Paso del Sapo Sub-basin, separating the Cañadón Asfalto Basin from the Golfo San Jorge Basin in the south. In the west, the basin is bound by uplifted areas with the small Ñirihuau Basin . The area of the basin is sparsely populated, with Gastre and Paso del Sapo representing some of the few villages in the basin. The Chubut River crosses

7980-573: The northern Appalachians. Siberia sat near Euramerica, with the Khanty Ocean between the two continents. While all this was happening, Gondwana drifted slowly towards the South Pole. This was the first step of the formation of Pangaea. The second step in the formation of Pangaea was the collision of Gondwana with Euramerica. By the middle of the Silurian , 430 Ma, Baltica had already collided with Laurentia, forming Euramerica, an event called

8075-692: The northwest African margin and the High , Saharan and Tunisian Atlas Mountains . Another phase began in the Early-Middle Jurassic (about 175 Ma), when Pangaea began to rift from the Tethys Ocean in the east to the Pacific Ocean in the west. The rifting that took place between North America and Africa produced multiple failed rifts . One rift resulted in the North Atlantic Ocean. The South Atlantic did not open until

8170-513: The number of islands that could have served as refugia for marine species. Species diversity may have already been reduced prior to mass extinction events due to mingling of species possible when formerly separate continents were merged. However, there is strong evidence that climate barriers continued to separate ecological communities in different parts of Pangaea. The eruptions of the Emeishan Traps may have eliminated South China, one of

8265-549: The ones in this section, remain partially speculative, and different reconstructions will differ in some details. The fourth-last supercontinent, called Columbia or Nuna, appears to have assembled in the period 2.0–1.8 billion years ago (Ga) . Columbia/Nuna broke up, and the next supercontinent, Rodinia , formed from the accretion and assembly of its fragments. Rodinia lasted from about 1.3 billion years ago until about 750 million years ago, but its configuration and geodynamic history are not nearly as well understood as those of

8360-500: The original movement (fault inversion). In such a way, a normal fault may therefore become a reverse fault and vice versa. In a normal fault, the hanging wall moves downward, relative to the footwall. The dip of most normal faults is at least 60 degrees but some normal faults dip at less than 45 degrees. A downthrown block between two normal faults dipping towards each other is a graben . A block stranded between two grabens, and therefore two normal faults dipping away from each other,

8455-403: The poles lie relative to the rock; this determines latitudes and orientations (though not longitudes). Magnetic differences between samples of sedimentary and intrusive igneous rock whose age varies by millions of years is due to a combination of magnetic polar wander (with a cycle of a few thousand years) and the drifting of continents over millions of years. The polar wander component, which

8550-420: The reduced area of continental shelf environments may have left marine species vulnerable to extinction. However, no evidence for a species-area effect has been found in more recent and better characterized portions of the geologic record. Another possibility is that reduced seafloor spreading associated with the formation of Pangaea, and the resulting cooling and subsidence of oceanic crust , may have reduced

8645-412: The right time for—and type of— igneous differentiation . At a given time differentiated magmas would burst violently out of the fault-traps and head to shallower places in the crust where porphyry copper deposits would be formed. As faults are zones of weakness, they facilitate the interaction of water with the surrounding rock and enhance chemical weathering . The enhanced chemical weathering increases

8740-463: The southern British Isles , and parts of Belgium , northern France , Nova Scotia , New England , South Iberia , and northwest Africa—broke free from Gondwana and began its journey to Laurentia. Baltica, Laurentia, and Avalonia all came together by the end of the Ordovician to form a landmass called Euramerica or Laurussia, closing the Iapetus Ocean. The collision resulted in the formation of

8835-617: The southern supercontinent Gondwana . In the Cambrian, Laurentia—which would later become North America —sat on the equator with three bordering oceans: the Panthalassic Ocean to the north and west, the Iapetus Ocean to the south, and the Khanty Ocean to the east. In the early Ordovician , around 480 Ma, the microcontinent Avalonia —a landmass incorporating fragments of what would become eastern Newfoundland ,

8930-512: The strong variations in climate by latitude and season produced by the extreme monsoon climate. For example, cold-adapted pteridosperms (early seed plants) of Gondwana were blocked from spreading throughout Pangaea by the equatorial climate, and northern pteridosperms ended up dominating Gondwana in the Triassic. The tectonics and geography of Pangaea may have worsened the Permian–Triassic extinction event or other mass extinctions. For example,

9025-468: The term is also used for the zone of crushed rock along a single fault. Prolonged motion along closely spaced faults can blur the distinction, as the rock between the faults is converted to fault-bound lenses of rock and then progressively crushed. Due to friction and the rigidity of the constituent rocks, the two sides of a fault cannot always glide or flow past each other easily, and so occasionally all movement stops. The regions of higher friction along

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