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105-613: The Pelotas Basin is one of the basins that formed on the present-day South Atlantic margins of South America and Africa due to the break-up of Gondwana in the Early Cretaceous . The sedimentary succession started as the other Brazilian marginal basins with a series of basalts, younger than the Paraná and Etendeka traps exposed in the Paraná Basin to the west, followed by shallow to deeper marine carbonate and clastic sediments. Other than

210-617: A complex series of orogenic events assembled the eastern parts of Gondwana (eastern Africa, Arabian-Nubian Shield, Seychelles, Madagascar, India, Sri Lanka, East Antarctica, and Australia) c. 750 to 530 Ma . First, the Arabian-Nubian Shield collided with eastern Africa (in the Kenya-Tanzania region) in the East African Orogeny c. 750 to 620 Ma . Then Australia and East Antarctica were merged with

315-585: A continuous arc chain, the direction of subduction was different between the Australian-Tasmanian and New Zealand-Antarctica arc segments. Many terranes were accreted to Eurasia during Gondwana's existence, but the Cambrian or Precambrian origin of many of these terranes remains uncertain. For example, some Palaeozoic terranes and microcontinents that now make up Central Asia, often called the "Kazakh" and "Mongolian terranes", were progressively amalgamated into

420-715: A diversified assemblage of true insects. In Gondwana, in contrast, ice and, in Australia, volcanism decimated the Devonian flora to a low-diversity seed fern flora – the pteridophytes were increasingly replaced by the gymnosperms which were to dominate until the Mid-Cretaceous. Australia, however, was still located near the Equator during the Early Carboniferous, and during this period, temnospondyl and lepospondyl amphibians and

525-472: A few million years, reached its peak at c. 200 Ma , and coincided with the Triassic–Jurassic extinction event . The reformed Gondwanan continent was not precisely the same as that which had existed before Pangaea formed; for example, most of Florida and southern Georgia and Alabama is underlain by rocks that were originally part of Gondwana, but this region stayed attached to North America when

630-589: A gradual decline during the Triassic while ferns, though never dominant, managed to diversify. The brief period of icehouse conditions during the Triassic–Jurassic extinction event had a dramatic impact on dinosaurs but left plants largely unaffected. The Jurassic was mostly one of hot-house conditions and, while vertebrates managed to diversify in this environment, plants have left little evidence of such development, apart from Cheiroleidiacean conifers and Caytoniales and other groups of seed ferns. In terms of biomass,

735-807: A high-density igneous crust-mantle interface intruded by the Tristan da Cunha plume . The central onshore boundary of the basin is formed by the Neoproterozoic Pelotas Batholith . The stratigraphy of the Pelotas Basin and the Punta del Este Basin to the south had a different history due to the Polônio paleohigh until the Late Maastrichtian . The basinal sequence starts with the Imbituba Formation,

840-561: A layer immediately beneath it. Continental crust is produced and (far less often) destroyed mostly by plate tectonic processes, especially at convergent plate boundaries . Additionally, continental crustal material is transferred to oceanic crust by sedimentation. New material can be added to the continents by the partial melting of oceanic crust at subduction zones, causing the lighter material to rise as magma, forming volcanoes. Also, material can be accreted horizontally when volcanic island arcs , seamounts or similar structures collide with

945-456: A lower density compared to the oceanic crust , called sima which is richer in magnesium silicate (Mg-Si) minerals. Changes in seismic wave velocities have shown that at a certain depth (the Conrad discontinuity ), there is a reasonably sharp contrast between the more felsic upper continental crust and the lower continental crust, which is more mafic in character. Most continental crust

1050-473: A much older supercontinent, Rodinia , to amalgamate. One of those orogenic belts, the Mozambique Belt , formed 800 to 650 Ma and was originally interpreted as the suture between East (India, Madagascar, Antarctica, and Australia) and West Gondwana (Africa and South America). Three orogenies were recognised during the 1990s as a result of data sets compiled on behalf of oil and mining companies:

1155-514: A north-east motion about 90 million years ago. While subduction direction changed, it remained oblique (and not perpendicular) to the coast of South America, and the direction change affected several subduction zone -parallel faults including Atacama , Domeyko and Liquiñe-Ofqui . Insular India began to collide with Asia circa 70 Ma , forming the Indian subcontinent , since which more than 1,400 km (870 mi) of crust has been absorbed by

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1260-623: A number of species related to those of the laurissilva of Valdivia, through the connection of the Antarctic flora . These include gymnosperms and the deciduous species of Nothofagus , as well as the New Zealand laurel, Corynocarpus laevigatus , and Laurelia novae-zelandiae . New Caledonia and New Zealand became separated from Australia by continental drift 85 million years ago. The islands still retain plants that originated in Gondwana and spread to

1365-531: A pattern that reflects the Jurassic break-up of Pangaea. The Cretaceous saw the arrival of the angiosperms , or flowering plants, a group that probably evolved in western Gondwana (South America–Africa). From there the angiosperms diversified in two stages: the monocots and magnoliids evolved in the Early Cretaceous, followed by the hammamelid dicots . By the Mid-Cretaceous, angiosperms constituted half of

1470-514: A peak in biodiversity – the end-Permian extinction was enormous and so was the radiation that followed. Two families of conifers, Podocarpaceae and Araucariaceae , dominated Gondwana in the Early Triassic, but Dicroidium , an extinct genus of fork-leaved seed ferns, dominated woodlands and forests of Gondwana during most of the Triassic. Conifers evolved and radiated during the period, with six of eight extant families already present before

1575-808: A series of events severally restricted the Proto-ACC: change to shallow marine conditions along the North Scotia Ridge; closure of the Fuegan Seaway, the deep sea that existed in Tierra del Fuego; and uplift of the Patagonian Cordillera. This, together with the reactivated Iceland plume , contributed to global warming. During the Miocene, the Drake Passage began to widen, and as water flow between South America and

1680-681: A single jaw from Australia. The closure of the Rheic Ocean and the formation of Pangaea in the Carboniferous resulted in the rerouting of ocean currents that initiated an Ice House period. As Gondwana began to rotate clockwise, Australia shifted south to more temperate latitudes. An ice cap initially covered most of southern Africa and South America but spread to eventually cover most of the supercontinent, save for northernmost Africa-South America and eastern Australia. Giant lycopod and horsetail forests continued to evolve in tropical Laurasia together with

1785-439: A steady-state hypothesis argue that the total volume of continental crust has remained more or less the same after early rapid planetary differentiation of Earth and that presently found age distribution is just the result of the processes leading to the formation of cratons (the parts of the crust clustered in cratons being less likely to be reworked by plate tectonics). However, this is not generally accepted. In contrast to

1890-497: A unit consisting of basaltic volcanic rocks. Parts of these rocks have been dated at ages between 125 ± 0.7 Ma and 118 ± 1.9 Ma, more recent than the flood basaltic Serra Geral Formation of the Paraná and Etendeka traps to the west in the Paraná Basin . The basalts are exposed in the Serra Geral National Park as a 700-metre-high (2,300 ft) cliff. The volcanic deposits form seaward dipping reflectors (SDR) in

1995-539: Is dry land above sea level. However, 94% of the Zealandia continental crust region is submerged beneath the Pacific Ocean , with New Zealand constituting 93% of the above-water portion. The continental crust consists of various layers, with a bulk composition that is intermediate (SiO 2 wt% = 60.6). The average density of the continental crust is about, 2.83 g/cm (0.102 lb/cu in), less dense than

2100-453: Is interrupted by the presence of various Paleogene hiatuses, that appear also in the regressive Miocene to recent beds. The unconformities have been analysed in detail using Sr/Sr ratios . The Pelotas Basin is relatively underexplored. The Brazilian part of the basin had a total of twenty exploration wells drilled until 2017. The first eight wells were drilled in the onshore section in the 1950s and 1960s. After acquiring seismic survey in

2205-409: Is little evidence of continental crust prior to 3.5 Ga . About 20% of the continental crust's current volume was formed by 3.0 Ga. There was relatively rapid development on shield areas consisting of continental crust between 3.0 and 2.5 Ga. During this time interval, about 60% of the continental crust's current volume was formed. The remaining 20% has formed during the last 2.5 Ga. Proponents of

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2310-771: Is now the Transantarctic Mountains ): the Antarctic Peninsula , Marie Byrd Land , Zealandia , and Thurston Island ; the Falkland Islands and Ellsworth–Whitmore Mountains (in Antarctica) were rotated 90° in opposite directions; and South America south of the Gastre Fault (often referred to as Patagonia ) was pushed westward. The history of the Africa-Antarctica break-up can be studied in great detail in

2415-566: Is now the southern Weddell Sea where initial break-up occurred during the Jurassic c. 180 to 160 Ma . Gondwana began to break up in the early Jurassic following the extensive and fast emplacement of the Karoo-Ferrar flood basalts c. 184 Ma . Before the Karoo plume initiated rifting between Africa and Antarctica , it separated a series of smaller continental blocks from Gondwana's southern, Proto-Pacific margin (along what

2520-537: Is presumed to have been linked to the subduction of cold oceanic lithosphere . During the mid to Late Cretaceous ( c.  90 million years ago ), the Andean orogeny changed significantly in character. Warmer and younger oceanic lithosphere is believed to have started to be subducted beneath South America around this time. Such kind of subduction is held responsible not only for the intense contractional deformation that different lithologies were subject to, but also

2625-755: The Antarctic Peninsula increased, the renewed ACC resulted in cooler global climate. Since the Eocene, the northward movement of the Australian Plate has resulted in an arc-continent collision with the Philippine and Caroline plates and the uplift of the New Guinea Highlands . From the Oligocene to the late Miocene, the climate in Australia, dominated by warm and humid rainforests before this collision, began to alternate between open forest and rainforest before

2730-850: The Antongil Block in far eastern Madagascar, the Seychelles , and the Napier and Rayner Complexes in East Antarctica ). The Azania continent (much of central Madagascar , the Horn of Africa and parts of Yemen and Arabia) was an island in the Mozambique Ocean. The continent Australia/ Mawson was still separated from India, eastern Africa, and Kalahari by c. 600 Ma , when most of western Gondwana had already been amalgamated. By c. 550 Ma, India had reached its Gondwanan position, which initiated

2835-456: The Atlantic Ocean , for example) are termed passive margins . The high temperatures and pressures at depth, often combined with a long history of complex distortion, cause much of the lower continental crust to be metamorphic – the main exception to this being recent igneous intrusions . Igneous rock may also be "underplated" to the underside of the crust, i.e. adding to the crust by forming

2940-1006: The Australian Plate are now separated by the Capricorn Plate and its diffuse boundaries. During the opening of the Indian Ocean, the Kerguelen hotspot first formed the Kerguelen Plateau on the Antarctic Plate c. 118 to 95 Ma and then the Ninety East Ridge on the Indian Plate at c. 100 Ma . The Kerguelen Plateau and the Broken Ridge , the southern end of the Ninety East Ridge, are now separated by

3045-540: The Cambrian explosion . All continental crust is ultimately derived from mantle-derived melts (mainly basalt ) through fractional differentiation of basaltic melt and the assimilation (remelting) of pre-existing continental crust. The relative contributions of these two processes in creating continental crust are debated, but fractional differentiation is thought to play the dominant role. These processes occur primarily at magmatic arcs associated with subduction . There

3150-827: The Campbell Plateau , Chatham Rise , Lord Howe Rise , Norfolk Ridge , and New Caledonia , from West Antarctica c. 84 Ma . The opening of the South Atlantic Ocean divided West Gondwana (South America and Africa), but there is considerable debate over the exact timing of this break-up. Rifting propagated from south to north along Triassic–Early Jurassic lineaments, but intra-continental rifts also began to develop within both continents in Jurassic–Cretaceous sedimentary basins, subdividing each continent into three sub-plates. Rifting began c. 190 Ma at Falkland latitudes, forcing Patagonia to move relative to

3255-590: The Central Atlantic opened . Antarctica, the centre of the supercontinent, shared boundaries with all other Gondwana continents and the fragmentation of Gondwana propagated clockwise around it. The break-up was the result of the eruption of the Karoo-Ferrar igneous province , one of the Earth's most extensive large igneous provinces (LIP) c. 200 to 170 Ma , but the oldest magnetic anomalies between South America, Africa, and Antarctica are found in what

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3360-795: The Drake Passage and the deepening of the Tasman Gateway. The oldest oceanic crust in the Drake Passage, however, is 34 to 29 Ma -old which indicates that the spreading between the Antarctic and South American plates began near the Eocene/Oligocene boundary. Deep sea environments in Tierra del Fuego and the North Scotia Ridge during the Eocene and Oligocene indicate a "Proto-ACC" opened during this period. Later, 26 to 14 Ma ,

3465-575: The East African Orogeny ( 650 to 800 Ma ) and Kuunga orogeny (including the Malagasy Orogeny in southern Madagascar) ( 550 Ma ), the collision between East Gondwana and East Africa in two steps, and the Brasiliano orogeny ( 660 to 530 Ma ), the successive collision between South American and African cratons . The last stages of Gondwanan assembly overlapped with

3570-551: The East African Orogeny , the collision of India and Madagascar with East Africa, and culminating in c.   600 to 530 Ma with the overlapping Brasiliano and Kuunga orogenies, the collision of South America with Africa, and the addition of Australia and Antarctica, respectively. Eventually, Gondwana became the largest piece of continental crust of the Palaeozoic Era, covering an area of some 100,000,000 km (39,000,000 sq mi), about one-fifth of

3675-720: The Great American Interchange . The break-up of Gondwana can be said to continue in eastern Africa at the Afar Triple Junction , which separates the Arabian , Nubian , and Somali plates, resulting in rifting in the Red Sea and East African Rift . In the Early Cenozoic , Australia was still connected to Antarctica c. 35–40° south of its current location and both continents were largely unglaciated. A rift between

3780-765: The Himalayan - Tibetan orogen. During the Cenozoic, the orogen resulted in the construction of the Tibetan Plateau between the Tethyan Himalayas in the south and the Kunlun and Qilian mountains in the north. Later, South America was connected to North America via the Isthmus of Panama , cutting off a circulation of warm water and thereby making the Arctic colder, as well as allowing

3885-425: The Mediterranean Sea at about 340 Ma. Continental crust and the rock layers that lie on and within it are thus the best archive of Earth's history. The height of mountain ranges is usually related to the thickness of crust. This results from the isostasy associated with orogeny (mountain formation). The crust is thickened by the compressive forces related to subduction or continental collision. The buoyancy of

3990-481: The Ordovician . This is the Cuyania or Precordillera terrane of the Famatinian orogeny in northwest Argentina which may have continued the line of the Appalachians southwards. Chilenia terrane accreted later against Cuyania. The collision of the Patagonian terrane with the southwestern Gondwanan occurred in the late Paleozoic. Subduction-related igneous rocks from beneath the North Patagonian Massif have been dated at 320–330 million years old, indicating that

4095-456: The Paleogene (from around 66 to 23 million years ago (Ma)). Gondwana was not considered a supercontinent by the earliest definition, since the landmasses of Baltica , Laurentia , and Siberia were separated from it. To differentiate it from the Indian region of the same name (see § Name ), it is also commonly called Gondwanaland . Regions that were part of Gondwana shared floral and zoological elements that persist to

4200-481: The Pangaea supercontinent during the Carboniferous. Pangaea began to break up in the Mid-Jurassic when the Central Atlantic opened . In the western end of Pangaea, the collision between Gondwana and Laurasia closed the Rheic and Palaeo-Tethys oceans. The obliquity of this closure resulted in the docking of some northern terranes in the Marathon , Ouachita , Alleghanian , and Variscan orogenies, respectively. Southern terranes, such as Chortis and Oaxaca , on

4305-436: The Polônio High in the south, forming the border with the Punta del Este Basin . The coastal ranges Serras de Sudeste in Brazil and Cuchilla Grande in Uruguay form the western boundary, underlain by the Sierra Ballena Shear Zone . The onshore part of the basin is from north to south crossed by the Urussanga , Araranguá , Mampituba , Jacuí , Guaíba , Camaquã , Jaguarão/Yaguarón and Cebollatí Rivers . The basins of

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4410-499: The Southeast Indian Ridge . Separation between Australia and East Antarctica began c. 132 Ma with seafloor spreading occurring c. 96 Ma . A shallow seaway developed over the South Tasman Rise during the Early Cenozoic and as oceanic crust started to separate the continents during the Eocene c. 35.5 Ma global ocean temperature dropped significantly. A dramatic shift from arc- to rift magmatism c. 100 Ma separated Zealandia , including New Zealand ,

4515-442: The Uralian orogeny and Laurasia . Pangaea was finally amalgamated in the Late Carboniferous-Early Permian, but the oblique forces continued until Pangaea began to rift in the Triassic. In the eastern end, collisions occurred slightly later. The North China , South China , and Indochina blocks rifted from Gondwana during the middle Paleozoic and opened the Proto-Tethys Ocean . North China docked with Mongolia and Siberia during

4620-422: The Variscan orogeny close to the Carboniferous–Permian boundary. South-east Asia was made of Gondwanan and Cathaysian continental fragments that were assembled during the Mid-Palaeozoic and Cenozoic. This process can be divided into three phases of rifting along Gondwana's northern margin: first, in the Devonian, North and South China , together with Tarim and Quidam (north-western China) rifted, opening

4725-403: The uplift and erosion known to have occurred from the Late Cretaceous onward. Plate tectonic reorganisation since the mid-Cretaceous might also have been linked to the opening of the South Atlantic Ocean . Another change related to mid-Cretaceous plate tectonic rearrangement was the change of subduction direction of the oceanic lithosphere that went from having south-east motion to having

4830-400: The 1970s, seven more wells were drilled in the shallow offshore part. Five other offshore wells were drilled between 1995 and 2001. The first and hitherto only well drilled in the Uruguayan part of the basin was drilled in 2016. Hydrocarbon accumulations have yet to be discovered in Pelotas Basin. An exploration area of approximately 15,000 square kilometres (5,800 sq mi) was offered in

4935-502: The Brazil Bidding Round of 2017.       De Santa Ana, Héctor; Goso Aguilar, César; Montaño, Jorge; Piñeiro, Graciela; Muzio, Rossana; Rossello, Eduardo; Perea, Daniel; Ucha, Nelson (2004). Cuencas sedimentarias de Uruguay - geología, paleontología y recursos naturales - Mesozóico (PDF) . División Relaciones y Actividades Culturales de Facultad de Ciencias . pp. 1–219 . Retrieved 2017-09-11 . Gondwana Gondwana ( / ɡ ɒ n d ˈ w ɑː n ə / )

5040-406: The Brazilian continental margin, the Late Turonian is marked by a regional unconformity . The Late Cretaceous to recent sequence is subdivided into the proximal Cidreira Formation, related to the fluvial progradation of the Rio Grande, and a distal part known as the Imbé Formation, consisting of shales , intercalated with sporadic siltstones and fine-grained sandstones . The transgressive series

5145-502: The Carboniferous–Permian, followed by South China. The Cimmerian blocks then rifted from Gondwana to form the Palaeo-Thethys and Neo-Tethys oceans in the Late Carboniferous, and docked with Asia during the Triassic and Jurassic. Western Pangaea began to rift while the eastern end was still being assembled. The formation of Pangaea and its mountains had a tremendous impact on global climate and sea levels, which resulted in glaciations and continent-wide sedimentation. In North America,

5250-405: The Early Cretaceous, and West Burma and Woyla during the Late Cretaceous. Gondwana's long, northern margin remained a mostly passive margin throughout the Palaeozoic. The Early Permian opening of the Neo-Tethys Ocean along this margin produced a long series of terranes, many of which were and still are being deformed in the Himalaya Orogeny . These terranes are, from Turkey to north-eastern India:

5355-403: The Earth's surface. It fused with Euramerica during the Carboniferous to form Pangea . It began to separate from northern Pangea ( Laurasia ) during the Triassic , and started to fragment during the Early Jurassic (around 180 million years ago). The final stages of break-up, involving the separation of Antarctica from South America (forming the Drake Passage ) and Australia, occurred during

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5460-448: The Equator during this period and remained a lifeless and barren landscape. West Gondwana drifted north during the Devonian , bringing Gondwana and Laurasia close together. Global cooling contributed to the Late Devonian extinction (19% of marine families and 50% of genera went extinct) and glaciation occurred in South America. Before Pangaea had formed, terrestrial plants, such as pteridophytes , began to diversify rapidly resulting in

5565-400: The Equator on landmasses then limited to Laurasia and, in Gondwana, to Australia. In the late Silurian, two distinctive lineages, zosterophylls and rhyniophytes , had colonised the tropics. The former evolved into the lycopods that were to dominate the Gondwanan vegetation over a long period, whilst the latter evolved into horsetails and gymnosperms . Most of Gondwana was located far from

5670-446: The Jurassic flora was dominated by conifer families and other gymnosperms that had evolved during the Triassic. The Pteridophytes that had dominated during the Palaeozoic were now marginalised, except for ferns. In contrast to Laurentia, very few insect fossils have been found in Gondwana, to a considerable extent because of widespread deserts and volcanism. While plants had a cosmopolitan distribution, dinosaurs evolved and diversified in

5775-406: The Kuunga orogeny (also known as the Pinjarra orogeny). Meanwhile, on the other side of the newly forming Africa, Kalahari collided with Congo and Rio de la Plata which closed the Adamastor Ocean . c. 540–530 Ma, the closure of the Mozambique Ocean brought India next to Australia–East Antarctica, and both North and South China were in proximity to Australia. As the rest of Gondwana formed,

5880-422: The Late Permian, many known from South Africa and Australia. Beetles and cockroaches remained minor elements in this fauna. Tetrapod fossils from the Early Permian have only been found in Laurasia but they became common in Gondwana later during the Permian. The arrival of the therapsids resulted in the first plant-vertebrate-insect ecosystem. During the Mid- to Late Triassic, hot-house conditions coincided with

5985-405: The Miocene, a warm and humid climate developed with pockets of rainforests in central Australia, but before the end of the period, colder and drier climate severely reduced this rainforest. A brief period of increased rainfall in the Pliocene was followed by drier climate which favoured grassland. Since then, the fluctuation between wet interglacial periods and dry glacial periods has developed into

6090-443: The Neoproterozoic to Palaeozoic phase of the Terra Australis Orogen , a series of terranes were rafted from the proto-Andean margin when the Iapteus Ocean opened, to be added back to Gondwana during the closure of that ocean. During the Paleozoic, some blocks which helped to form parts of the Southern Cone of South America, include a piece transferred from Laurentia when the west edge of Gondwana scraped against southeast Laurentia in

6195-441: The Palaeo-Tethys behind them. These terranes accreted to Asia during Late Devonian and Permian. Second, in the Late Carboniferous to Early Permian, Cimmerian terranes opened Meso-Tethys Ocean; Sibumasu and Qiangtang were added to south-east Asia during Late Permian and Early Jurassic. Third, in the Late Triassic to Late Jurassic, Lhasa , West Burma , Woyla terranes opened the Neo-Tethys Ocean; Lhasa collided with Asia during

6300-407: The Pelotas Basin. The sedimentary succession of the Pelotas Basin is underlain by an extremely deformed (highly stretched, thinned and faulted) continental crust , covered by grabens that can achieve thicknesses of more than 20 kilometres (66,000 ft). The nature of the lower crust below the Pelotas Basin remains uncertain, but by analogy with the Namibian conjugate margin, it may correspond to

6405-446: The Santos Basin to the north in the Barremian . Seafloor spreading continued northwards to the Campos Basin in the Early Albian , at approximately 112 Ma. Five tectonic stages have been identified in the Brazilian basins: While the basins to the north of Pelotas Basin, the Santos , Campos and Espírito Santo Basins , are characterised by a thick sequence of salt and an accompanying pre-salt layer , evaporites are almost absent in

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6510-456: The South Atlantic (Brazil and Cameroon ) dating to around 120  million years ago , suggesting that some form of land connection still existed between Africa and South America as recently as the early Aptian . The first phases of Andean orogeny in the Jurassic and Early Cretaceous were characterised by extensional tectonics , rifting , the development of back-arc basins and the emplacement of large batholiths . This development

6615-414: The South Atlantic margin started forming in the Early Cretaceous with the break-up of Gondwana , the southern part of the former supercontinent Pangea . This tectonic movement resulted in a sequence of rift basins bordering the present-day South Atlantic on the Brazilian and southwestern African sides. The Pelotas-Namibia spreading commenced in the Hauterivian , around 133 million years ago, and reached

6720-437: The Southern Hemisphere continents later. [REDACTED] Africa Continental crust Continental crust is the layer of igneous , metamorphic , and sedimentary rocks that forms the geological continents and the areas of shallow seabed close to their shores, known as continental shelves . This layer is sometimes called sial because its bulk composition is richer in aluminium silicates (Al-Si) and has

6825-465: The Southern Hemisphere, has a "Gondwanan distribution" and is often described as an archaic, or relict , lineage. The distributions in the Proteaceae is, nevertheless, the result of both Gondwanan rafting and later oceanic dispersal. During the Silurian, Gondwana extended from the Equator (Australia) to the South Pole (North Africa and South America) whilst Laurasia was located on the Equator opposite to Australia. A short-lived Late Ordovician glaciation

6930-408: The Taurides in southern Turkey; the Lesser Caucasus Terrane in Georgia; the Sanand, Alborz, and Lut terranes in Iran; the Mangysglak or Kopetdag Terrane in the Caspian Sea; the Afghan Terrane; the Karakorum Terrane in northern Pakistan; and the Lhasa and Qiangtang terranes in Tibet. The Permian–Triassic widening of the Neo-Tethys pushed all these terranes across the Equator and over to Eurasia. During

7035-429: The Uruguayan side in 2016. No hydrocarbon accumulations have been proven in the basin thus far. The basin is named after the city of Pelotas , the hometown of Rodi Ávila Medeiros, the geologist who studied the area. The Pelotas Basin is an approximately 346,000-square-kilometre-large (134,000 sq mi), mostly offshore sedimentary basin, located in the South Atlantic offshore Brazil and Uruguay . It covers

7140-550: The base of the Absaroka sequence coincides with the Alleghanian and Ouachita orogenies and are indicative of a large-scale change in the mode of deposition far away from the Pangaean orogenies. Ultimately, these changes contributed to the Permian–Triassic extinction event and left large deposits of hydrocarbons, coal, evaporite, and metals. The breakup of Pangaea began with the Central Atlantic magmatic province (CAMP) between South America, Africa, North America, and Europe. CAMP covered more than seven million square kilometres over

7245-414: The colonisation of Gondwana. The Baragwanathia Flora, found only in the Yea Beds of Victoria, Australia, occurs in two strata separated by 1,700 m (5,600 ft) or 30 Ma; the upper assemblage is more diverse and includes Baragwanathia, the first primitive herbaceous lycopod to evolve from the zosterophylls. During the Devonian, giant club mosses replaced the Baragwanathia Flora, introducing

7350-492: The continent Kazakhstania in the late Silurian . Whether these blocks originated on the shores of Gondwana is not known. In the Early Palaeozoic, the Armorican terrane , which today form large parts of France, was part of either Peri-Gondwana or core Gondwana; the Rheic Ocean closed in front of it and the Palaeo-Tethys Ocean opened behind it. Precambrian rocks from the Iberian Peninsula suggest that it, too, formed part of core Gondwana before its detachment as an orocline in

7455-424: The continent became the arid or semiarid landscape it is today. The adjective "Gondwanan" is in common use in biogeography when referring to patterns of distribution of living organisms, typically when the organisms are restricted to two or more of the now-discontinuous regions that were once part of Gondwana, including the Antarctic flora . For example, the plant family Proteaceae , known from all continents in

7560-432: The crust forces it upwards, the forces of the collisional stress balanced by gravity and erosion. This forms a keel or mountain root beneath the mountain range, which is where the thickest crust is found. The thinnest continental crust is found in rift zones, where the crust is thinned by detachment faulting and eventually severed, replaced by oceanic crust. The edges of continental fragments formed this way (both sides of

7665-800: The development of rifts systems on both continents, including the Central African Rift System and the Central African Shear Zone which lasted until c. 85 Ma . At Brazilian latitudes spreading is more difficult to assess because of the lack of palaeo-magnetic data, but rifting occurred in Nigeria at the Benue Trough c. 118 Ma . North of the Equator the rifting began after 120.4 Ma and continued until c. 100 to 96 Ma . Dinosaur footprints representing identical species assemblages are known from opposite sides of

7770-419: The dominant mode of continental crust formation and destruction. It is a matter of debate whether the amount of continental crust has been increasing, decreasing, or remaining constant over geological time. One model indicates that at prior to 3.7 Ga ago continental crust constituted less than 10% of the present amount. By 3.0 Ga ago the amount was about 25%, and following a period of rapid crustal evolution it

7875-544: The end of it. Bennettitales and Pentoxylales , two now extinct orders of gymnospermous plants, evolved in the Late Triassic and became important in the Jurassic and Cretaceous. It is possible that gymnosperm biodiversity surpassed later angiosperm biodiversity and that the evolution of angiosperms began during the Triassic but, if so, in Laurasia rather than in Gondwana. Two Gondwanan classes, lycophytes and sphenophytes , saw

7980-916: The eruption of the Deccan basalts , whose eruption site may survive as the Réunion hotspot . The Seychelles and the Maldives are now separated by the Central Indian Ridge . During the initial break-up in the Early Jurassic a marine transgression swept over the Horn of Africa covering Triassic planation surfaces with sandstone , limestone , shale , marls and evaporites . East Gondwana, comprising Antarctica, Madagascar, India, and Australia, began to separate from Africa. East Gondwana then began to break up c. 132.5 to 96 Ma when India moved northwest from Australia-Antarctica. The Indian Plate and

8085-550: The evolution of Voltziales , one of the few plant orders to survive the end-Permian extinction (57% of marine families and 83% of genera went extinct) and which came to dominate in the Late Permian and from whom true conifers evolved. Tall lycopods and horsetails dominated the wetlands of Gondwana in the Early Permian. Insects co-evolved with glossopterids across Gondwana and diversified with more than 200 species in 21 orders by

8190-554: The first amniote reptilians evolved, all closely related to the Laurasian fauna, but spreading ice eventually drove these animals away from Gondwana entirely. The Gondwana ice sheet melted, and sea levels dropped during the Permian and Triassic global warming. During this period, the extinct glossopterids colonised Gondwana and reached peak diversity in the Late Permian when coal-forming forests covered much of Gondwana. The period also saw

8295-510: The first trees, and by the Late Devonian this first forest was accompanied by the progymnosperms , including the first large trees Archaeopteris . The Late Devonian extinction probably also resulted in osteolepiform fishes evolving into the amphibian tetrapods , the earliest land vertebrates, in Greenland and Russia. The only traces of this evolution in Gondwana are amphibian footprints and

8400-518: The flora in northeastern Australia. There is, however, no obvious connection between this spectacular angiosperm radiation and any known extinction event nor with vertebrate/insect evolution. Insect orders associated with pollination, such as beetles , flies , butterflies and moths , and wasps, bees, and ants , radiated continuously from the Permian-Triassic, long before the arrival of the angiosperms. Well-preserved insect fossils have been found in

8505-618: The fracture zones and magnetic anomalies flanking the Southwest Indian Ridge . The Madagascar block and the Mascarene Plateau , stretching from the Seychelles to Réunion , were broken off India, causing Madagascar and Insular India to be separate landmasses : elements of this break-up nearly coincide with the Cretaceous–Paleogene extinction event . The India–Madagascar–Seychelles separations appear to coincide with

8610-833: The lake deposits of the Santana Formation in Brazil, the Koonwarra Lake fauna in Australia, and the Orapa diamond mine in Botswana. Dinosaurs continued to prosper but, as the angiosperm diversified, conifers, bennettitaleans and pentoxylaleans disappeared from Gondwana c. 115 Ma together with the specialised herbivorous ornithischians , whilst generalist browsers, such as several families of sauropodomorph Saurischia , prevailed. The Cretaceous–Paleogene extinction event killed off all dinosaurs except birds, but plant evolution in Gondwana

8715-705: The northern area of Pelotas Basin of the Ariri Formation , the evaporites that form the salt layer in the Santos Basin to the north. The rapid subsidence from the Albian to Turonian created a wide marine platform with in the north elevated areas due to the doming of the Curumim Formation. On this platform, the marine limestones and siliciclastics of the Porto Belo Formation were deposited. Shales comprise

8820-525: The northern neighbours Santos and Campos Basins , the Pelotas Basin lacks a thick layer of salt and the pre-salt layer pinches out just in the north of the Pelotas Basin stratigraphy. Within the Brazilian Atlantic margin, the Pelotas Basin is relatively underexplored. Twenty exploration wells have been drilled in the Brazilian portion of the basin with one ultra-deepwater exploration well drilled on

8925-615: The oldest rocks on Earth are within the cratons or cores of the continents, rather than in repeatedly recycled oceanic crust ; the oldest intact crustal fragment is the Acasta Gneiss at 4.01 Ga , whereas the oldest large-scale oceanic crust (located on the Pacific plate offshore of the Kamchatka Peninsula ) is from the Jurassic (≈180 Ma ), although there might be small older remnants in

9030-626: The opening of the Iapetus Ocean between Laurentia and western Gondwana. During this interval, the Cambrian explosion occurred. Laurentia was docked against the western shores of a united Gondwana for a brief period near the Precambrian/Cambrian boundary, forming the short-lived and still disputed supercontinent Pannotia . The Mozambique Ocean separated the Congo – Tanzania – Bangweulu Block of central Africa from Neoproterozoic India (India,

9135-587: The other hand, remained largely unaffected by the collision along the southern shores of Laurentia. Some Peri-Gondwanan terranes, such as Yucatán and Florida , were buffered from collisions by major promontories. Other terranes, such as Carolina and Meguma , were directly involved in the collision. The final collision resulted in the Variscan- Appalachian Mountains , stretching from present-day Mexico to southern Europe. Meanwhile, Baltica collided with Siberia and Kazakhstania which resulted in

9240-543: The outer marine deposition of this stratigraphic unit, considered as a potential source rock . Overlying the Porto Belo Formation are the proximal Tramandaí and the distal Atlántida Formations , composed of coarse-grained fluvial to alluvial clastics, intercalated with siltstones and shales. This phase is characteristic of a large-scale prolonged transgression that lasted until the Oligocene . As in other areas of

9345-466: The persistence of continental crust, the size, shape, and number of continents are constantly changing through geologic time. Different tracts rift apart, collide and recoalesce as part of a grand supercontinent cycle . There are currently about 7 billion cubic kilometres (1.7 billion cubic miles) of continental crust, but this quantity varies because of the nature of the forces involved. The relative permanence of continental crust contrasts with

9450-542: The present arid regime. Australia has thus experienced various climate changes over a 15-million-year period with a gradual decrease in precipitation. The Tasman Gateway between Australia and Antarctica began to open c. 40 to 30 Ma . Palaeontological evidence indicates the Antarctic Circumpolar Current (ACC) was established in the Late Oligocene c. 23 Ma with the full opening of

9555-521: The present day. The continent of Gondwana was named by the Austrian scientist Eduard Suess , after the region in central India of the same name , which is derived from Sanskrit for "forest of the Gonds ". The name had been previously used in a geological context, first by H. B. Medlicott in 1872, from which the Gondwana sedimentary sequences ( Permian - Triassic ) are also described. Some scientists prefer

9660-746: The remaining Gondwana c. 570 to 530 Ma in the Kuunga Orogeny. The later Malagasy orogeny at about 550–515 Mya affected Madagascar, eastern East Africa and southern India. In it, Neoproterozoic India collided with the already combined Azania and Congo–Tanzania–Bangweulu Block, suturing along the Mozambique Belt. The 18,000 km-long (11,000 mi) Terra Australis Orogen developed along Gondwana's western, southern, and eastern margins. Proto-Gondwanan Cambrian arc belts from this margin have been found in eastern Australia, Tasmania, New Zealand, and Antarctica. Though these belts formed

9765-582: The seismic surveys of the basin. The conglomerates , siltstones and diamictites of the Cassino Formation represent the top of the Gondwana break-up unconformity, dates to the Middle Aptian . The depositional environment has been interpreted as fluvio - deltaic to lacustrine . The formation is followed by the volcanics of the Curumim Formation , dated at 113 ± 0.1 Ma, and small incursions in

9870-521: The short life of oceanic crust. Because continental crust is less dense than oceanic crust, when active margins of the two meet in subduction zones, the oceanic crust is typically subducted back into the mantle. Continental crust is rarely subducted (this may occur where continental crustal blocks collide and overthicken, causing deep melting under mountain belts such as the Himalayas or the Alps ). For this reason

9975-494: The side of the continent as a result of plate tectonic movements. Continental crust is also lost through erosion and sediment subduction, tectonic erosion of forearcs, delamination, and deep subduction of continental crust in collision zones. Many theories of crustal growth are controversial, including rates of crustal growth and recycling, whether the lower crust is recycled differently from the upper crust, and over how much of Earth history plate tectonics has operated and so could be

10080-626: The southern Brazilian states of Santa Catarina and Rio Grande do Sul and the Uruguayan departments Cerro Largo , Rocha and Treinta y Tres . About 40,900 square kilometres (15,800 sq mi) of the basin is onshore. The onshore part of the basin in Uruguay is locally called Merín Basin. The basin is bound by the Florianópolis High , separating it from the Santos Basin in the north and

10185-601: The still static remainder of South America and Africa, and this westward movement lasted until the Early Cretaceous 126.7 Ma . From there rifting propagated northward during the Late Jurassic c. 150 Ma or Early Cretaceous c. 140 Ma most likely forcing dextral movements between sub-plates on either side. South of the Walvis Ridge and Rio Grande Rise the Paraná and Etendeka magmatics resulted in further ocean-floor spreading c. 130 to 135 Ma and

10290-399: The subduction process initiated in the early Carboniferous. This was relatively short-lived (lasting about 20 million years), and initial contact of the two landmasses occurred in the mid-Carboniferous, with broader collision during the early Permian. In the Devonian, an island arc named Chaitenia accreted to Patagonia in what is now south-central Chile. Gondwana and Laurasia formed

10395-512: The term "Gondwanaland" for the supercontinent to make a clear distinction between the region and the supercontinent. The assembly of Gondwana was a protracted process during the Neoproterozoic and Paleozoic , which remains incompletely understood because of the lack of paleo-magnetic data. Several orogenies , collectively known as the Pan-African orogeny , caused the continental fragments of

10500-613: The two developed but remained an embayment until the Eocene-Oligocene boundary when the Circumpolar Current developed and the glaciation of Antarctica began. Australia was warm and wet during the Palaeocene and dominated by rainforest. The opening of the Tasman Gateway at the Eocene-Oligocene boundary ( 33 Ma ) resulted in abrupt cooling but the Oligocene became a period of high rainfall with swamps in southeast Australia. During

10605-500: The ultramafic material that makes up the mantle , which has a density of around 3.3 g/cm (0.12 lb/cu in). Continental crust is also less dense than oceanic crust, whose density is about 2.9 g/cm (0.10 lb/cu in). At 25 to 70 km (16 to 43 mi) in thickness, continental crust is considerably thicker than oceanic crust, which has an average thickness of around 7 to 10 km (4.3 to 6.2 mi). Approximately 41% of Earth's surface area and about 70% of

10710-405: The volume of Earth's crust are continental crust. Because the surface of continental crust mainly lies above sea level, its existence allowed land life to evolve from marine life. Its existence also provides broad expanses of shallow water known as epeiric seas and continental shelves where complex metazoan life could become established during early Paleozoic time, in what is now called

10815-490: Was a large landmass, sometimes referred to as a supercontinent . The remnants of Gondwana make up around two-thirds of today's continental area, including South America , Africa , Antarctica , Australia , Zealandia , Arabia , and the Indian Subcontinent . Gondwana was formed by the accretion of several cratons (large stable blocks of the Earth's crust), beginning c.   800 to 650 Ma with

10920-477: Was followed by a Silurian Hot House period. The End-Ordovician extinction , which resulted in 27% of marine invertebrate families and 57% of genera going extinct, occurred during this shift from Ice House to Hot House. By the end of the Ordovician, Cooksonia , a slender, ground-covering plant, became the first known vascular plant to establish itself on land. This first colonisation occurred exclusively around

11025-533: Was hardly affected. Gondwanatheria is an extinct group of non- therian mammals with a Gondwanan distribution (South America, Africa, Madagascar, India, Zealandia and Antarctica) during the Late Cretaceous and Palaeogene. Xenarthra and Afrotheria , two placental clades, are of Gondwanan origin and probably began to evolve separately c. 105 Ma when Africa and South America separated. The laurel forests of Australia, New Caledonia, and New Zealand have

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