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130-586: The CAMP volcanic eruptions occurred about 201 million years ago and split into four pulses lasting for over ~600,000 years. The resulting large igneous province is, in area covered, the most extensive on Earth. The volume of magma flow of between two and six million cubic kilometres makes it one of the most voluminous as well. This geologic event is associated with the Triassic–Jurassic extinction event . Although some connections among these basalts had long been recognized, in 1988 they were linked as constituting

260-465: A supercontinent . In 2013 the CAMP's connection to the end-Triassic extinction , with major extinctions that enabled dinosaur domination of land, became more firmly established. Until 2013, the uncertainties in the geochronologic dates had been too coarse to confirm that the volcanic eruptions were correlated with major climate changes. The work by Blackburn et al. demonstrated a tight synchroneity between

390-579: A CAMP–related (about 200 Ma) dike in North Carolina. Whiteside et al. (2007) suggest that reverse polarity intervals in this dike could be of post Triassic age and correlated with the same events in Morocco. The Tr-J boundary is not officially defined, but most workers recognise it in continental strata by the last appearance of index taxa such as Ovalipollis ovalis , Vallasporites ignatii and Patinasporites densus or, in marine sections, by

520-576: A biological turnover where modern groups of fish started to supplant earlier groups. Pycnodontiform fish were insignificantly affected. Conodonts , which were prominent index fossils throughout the Paleozoic and Triassic, finally became extinct at the T-J boundary following declining diversity. Like fish, marine reptiles experienced a substantial drop in diversity between the Middle Triassic and

650-518: A bolide impact have been found in the late Rhaetian, though not at the Triassic-Jurassic boundary itself; the discoverers of these trace metal anomalies purport that such a bolide impact could only have been an indirect cause of the TJME. The discovery of seismites two to four metres thick coeval with the carbon isotope fluctuations associated with the TJME has been interpreted as evidence of

780-539: A cause of extinction events were dismissed as catastrophism. Consequently, gradual environmental changes were favoured as the cause of the extinction. In the 1980s, Jack Sepkoski identified the Triassic-Jurassic boundary drop in biodiversity as one of the "Big 5" mass extinction events. After the discovery that the Cretaceous-Palaeogene extinction event was caused by a bolide impact, the TJME has also been suggested to have been caused by such an impact in

910-676: A certain correlation between the lower North American lava flows and the Lower Unit of the Moroccan CAMP, thus reinforcing the conclusion that the Moroccan basalts postdate the Tr-J boundary. Therefore, according to these data, CAMP basalts should not be included among the direct causes of the Tr-J mass extinction. Triassic%E2%80%93Jurassic extinction event The Triassic–Jurassic ( Tr-J ) extinction event ( TJME ), often called

1040-547: A clear trend towards increased aridification towards the end of the Triassic. Although high-latitude areas like Greenland and Australia actually became wetter, most of the world experienced more drastic changes in climate as indicated by geological evidence. This evidence includes an increase in carbonate and evaporite deposits (which are most abundant in dry climates) and a decrease in coal deposits (which primarily form in humid environments such as coal forests ). In addition,

1170-504: A collapse in the reef community, which was likely driven by ocean acidification resulting from CO 2 supplied to the atmosphere by the CAMP eruptions. Most evidence points to a relatively fast recovery from the mass extinction. Benthic ecosystems recovered far more rapidly after the TJME than they did after the PTME. British Early Jurassic benthic marine environments display a relatively rapid recovery that began almost immediately after

1300-618: A completely reliable constraint. CAMP lava flows of North America can be geochemically separated in three units: the older ones are classified as high titanium quartz normative (HTQ) basalts (TiO 2 = 1.0-1.3 wt%); these are followed by lava flows classified as low titanium quartz normative (LTQ) basalts (TiO 2 = ca. 0.8-1.3 wt%); and then by the youngest lava flow unit classified as high titanium iron quartz normative (HTIQ) basalts (TiO 2 = 1.4-1.6 wt%). According to Whiteside et al. (2007) , geochemical analyses based upon titanium, magnesium and silicon contents show

1430-459: A few sites, the TJME was associated with fully oxygenated waters. Positive δ N excursions have also been interpreted as evidence of anoxia concomitant with increased denitrification in marine sediments in the TJME's aftermath. In northeastern Panthalassa, episodes of anoxia and euxinia were already occurring during the Rhaetian before the TJME, making its marine ecosystems unstable even before

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1560-412: A great lateral extension and a maximum thickness up to 1 km. The basaltic flows occur on top of continental fluvial and lacustrine sedimentary units of Triassic age. Ar/Ar data (on plagioclase) indicate for these basaltic units an absolute age of 198–200 Ma bringing this magmatic event undoubtedly close to the Triassic-Jurassic (Tr-J) boundary. Thus it is necessary to determine whether it straddles

1690-595: A palynologic turnover, interpreted as the Tr-J boundary. In Morocco, two reversals have been detected in two lava flow sequences. Two distinct correlations between the Moroccan and the Newark magnetostratigraphy have been proposed. Marzoli et al. (2004) suggest that the Tr-J boundary is located above the lower reverse polarity level which is positioned more or less at the base of the Intermediate basalt unit of Morocco. These two levels can be correlated with chron E23r of

1820-503: A play is likely in a given trap. Changes in sedimentation rate revealed by magnetostratigraphy are often related to either climatic factors or to tectonic developments in nearby or distant mountain ranges. Evidence to strengthen this interpretation can often be found by looking for subtle changes in the composition of the rocks in the section. Changes in sandstone composition are often used for this type of interpretation. The Siwalik fluvial sequence (~6000 m thick, ~20 to 0.5 Ma) represents

1950-441: A positive feedback resulting from warming, which has been suggested as one possible cause of the PTME, the largest mass extinction of all time, may have exacerbated greenhouse conditions, although others suggest that methane hydrate release was temporally mismatched with the TJME and thus not a cause of it. Besides the carbon dioxide-driven long-term global warming, CAMP volcanism had shorter term cooling effects resulting from

2080-513: A possible bolide impact, although no definitive link between these seismites and any impact event has been found. On the other hand, the dissimilarity between the isotopic perturbations characterising the TJME and those characterising the end-Cretaceous mass extinction makes an extraterrestrial impact highly unlikely to have been the cause of the TJME, according to many researchers. Various trace metal ratios, including palladium/iridium, platinum/iridium, and platinum/rhodium, in rocks deposited during

2210-487: A pronounced negative δ U excursion, indicating a major decrease in marine oxygen availability. Isorenieratane concentration increase reveals that populations of green sulphur bacteria , which photosynthesise using hydrogen sulphide instead of water, grew significantly across the Triassic-Jurassic boundary; these findings indicate that euxinia , a form of anoxia defined by not just the absence of dissolved oxygen but high concentrations of hydrogen sulphide , also developed in

2340-522: A role in the ecological crisis. Geological formations in Europe and the Middle East seem to indicate a drop in sea levels at the end of the Triassic associated with the TJME. Although falling sea levels have sometimes been considered a culprit for marine extinctions, evidence is inconclusive since many sea level drops in geological history are not correlated with increased extinctions. However, there

2470-494: A sharp, very rapid decline followed by an adaptive radiation, a more gradual turnover in both fossil plants and spores with several intermediate stages is observed over the course of the extinction event. Extinction of plant species can in part be explained by the suspected increased carbon dioxide in the atmosphere as a result of CAMP volcanic activity, which would have created photoinhibition and decreased transpiration levels among species with low photosynthetic plasticity, such as

2600-491: A significant decrease of seawater pH known as ocean acidification , which is discussed as a relevant driver of marine extinction. Evidence for ocean acidification as an extinction mechanism comes from the preferential extinction of marine organisms with thick aragonitic skeletons and little biotic control of biocalcification (e.g., corals, hypercalcifying sponges), which resulted in a coral reef collapse and an early Hettangian "coral gap". The decline of megalodontoid bivalves

2730-420: A single major flood basalt province . The basaltic sills of similar age (near 200 Ma, or earliest Jurassic) and composition (intermediate-Ti quartz tholeiite) which occur across the vast Amazon River basin of Brazil were linked to the province in 1999. Remnants of CAMP have been identified on four continents (Africa, Europe, North America and South America) and consist of tholeiitic basalts formed during

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2860-511: A site are then compared and their average magnetic polarity is determined with directional statistics , most commonly Fisher statistics or bootstrapping . The statistical significance of each average is evaluated. The latitudes of the Virtual Geomagnetic Poles from those sites determined to be statistically significant are plotted against the stratigraphic level at which they were collected. These data are then abstracted to

2990-594: A widespread effect on the planet; a 214-million-year-old ejecta blanket of shocked quartz has been found in rock layers as far away as England and Japan. There is still a possibility that the Manicouagan impact was responsible for a small extinction midway through the Late Triassic at the Carnian–Norian boundary, although the disputed age of this boundary (and whether an extinction actually occurred in

3120-424: Is also attributed to increased seawater acidity. Extensive fossil remains of malformed calcareous nannoplankton, a common sign of significant drops in pH, have also been extensively reported from the Triassic-Jurassic boundary. Global interruption of carbonate deposition at the Triassic-Jurassic boundary has been cited as additional evidence for catastrophic ocean acidification. Upwardly developing aragonite fans in

3250-513: Is believed to have resulted in increased storminess and lightning activity as a consequence of the more humid climate. The uptick in lightning activity is in turn implicated as a cause of an increase in wildfire activity. The combined presence of charcoal fragments and heightened levels of pyrolytic polycyclic aromatic hydrocarbons in Polish sedimentary facies straddling the Triassic-Jurassic boundary indicates wildfires were extremely commonplace during

3380-509: Is complex) is challenging, as each new discovery has to be inserted (or if not validated, removed). The two standardised marine magnetic anomalies sequences are the "C-sequence" and "M-sequence" and cover from the Middle Jurassic to date. Accordingly the main C polarity chrons series extend backwards from the current C1n, commonly termed Brunhes, with the most recent transition at C1r, commonly termed Matuyama, at 0.773  Ma which

3510-424: Is composed by a smaller number of lava flows (i.e., a lower volume) than the preceding one. These data suggest that they were created by five short magma pulses and eruption events, each one possibly <400 (?) years long. All lava flow sequences are characterized by normal polarity, except for a brief paleomagnetic reversal yielded by one lava flow and by a localized interlayered limestone in two distinct section of

3640-579: Is difficult, as the last stage of the Triassic, the Rhaetian, and the first stage of the Jurassic, the Hettangian , each have few records of large land animals; some paleontologists have considered only phytosaurs and procolophonids to have become extinct at the Triassic–Jurassic boundary, with other groups having become extinct earlier. However, it is likely that many other groups survived up until

3770-443: Is not universally accepted that even this local diversity drop was caused by sea level fall. A pronounced sea level change in latest Triassic records from Lake Williston in northeastern British Columbia , which was then the northeastern margin of Panthalassa, resulted in an extinction event of infaunal (sediment-dwelling) bivalves, though not epifaunal ones. Some have hypothesized that an impact from an asteroid or comet caused

3900-556: Is often obtained from layers of volcanic ash . Failing that, one can tie a polarity to a biostratigraphic event that has been correlated elsewhere with isotopic ages. With the aid of the independent isotopic age or ages, the local magnetostratigraphic column is correlated with the Global Magnetic Polarity Time Scale (GMPTS). Because the age of each reversal shown on the GMPTS is relatively well known,

4030-480: Is still some evidence that marine life was affected by secondary processes related to falling sea levels, such as decreased oxygenation (caused by sluggish circulation), or increased acidification. These processes do not seem to have been worldwide, with the sea level fall observed in European sediments believed to be not global but regional, but they may explain local extinctions in European marine fauna. However, it

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4160-670: Is the Brunhes–Matuyama reversal . The C (for Cenozoic) sequence ends in the Cretaceous Normal Superchron termed C34n which on age calibration occurred at 120.964 Ma and lasted to Chron C33r at 83.650  Ma that defined the Santonian geologic age. The M series is defined from M0, with full label M0r, at 121.400 Ma, which is the beginning of the Aptian to M44n.2r which is before 171.533 Ma in

4290-451: Is to determine the rate at which the sediment accumulated. This is accomplished by plotting the age of each reversal (in millions of years ago) vs. the stratigraphic level at which the reversal is found (in meters). This provides the rate in meters per million years which is usually rewritten in terms of millimeters per year (which is the same as kilometers per million years). These data are also used to model basin subsidence rates . Knowing

4420-532: The Aalenian . Subdivisions in the sequencies also have specific nomenclature so C8n.2n is the second oldest normal polarity subchron comprising normal-polarity Chron C8n and the youngest cryptochron, the Emperor cryptochron, is named C1n-1. Certain terms in the literature such as M-1r to describe a postulated brief reversal at about 118 Ma are provisional. Oriented paleomagnetic samples are collected in

4550-605: The Central Atlantic Magmatic Province (CAMP), the largest known large igneous province by area, and one of the most voluminous, with its flood basalts extending across parts of southwestern Europe, northwestern Africa, northeastern South America, and southeastern North America. The coincidence and synchrony of CAMP activity and the TJME is indicated by uranium-lead dating , argon-argon dating , and palaeomagnetism . The isotopic composition of fossil soils and marine sediments near

4680-618: The Central Atlantic Magmatic Province (CAMP), which released large amounts of carbon dioxide into the Earth's atmosphere, causing profound global warming along with ocean acidification . Older hypotheses have proposed that gradual climate or sea level change may be the culprit, or perhaps one or more asteroid strikes. The earliest research on the TJME was conducted in the mid-20th century, when events in earth history where widely assumed to have been gradual (a paradigm known as uniformitarianism ) and comparatively rapid cataclysms as

4810-479: The Industrial Revolution . The degassing rate of the first pulse of CAMP volcanism is estimated to have been around half of the rate of modern anthropogenic emissions. Palaeontologists studying the TJME and its impacts warn that a major reduction in humanity's carbon dioxide emissions to slow down climate change is of critical importance for preventing a catastrophe similar to the TJME from befalling

4940-548: The Middle Triassic . Though this may have been due to falling sea levels or the Carnian Pluvial Event , it may instead be a result of sampling bias considering that Middle Triassic fish have been more extensively studied than Late Triassic fish. Despite the apparent drop in diversity, neopterygiians (which include most modern bony fish) suffered less than more "primitive" actinopterygiians, indicating

5070-828: The Sichuan Basin , relatively cool mixed forests in the late Rhaetian were replaced by hot, arid fernlands during the Triassic–Jurassic transition, which in turn later gave way to a cheirolepid-dominated flora in the Hettangian and Sinemurian. The abundance of ferns in China that were resistant to high levels of aridity increased significantly across the Triassic–Jurassic boundary, though ferns better adapted for moist, humid environments declined, indicating that plants experienced major environmental stress, albeit not an outright mass extinction. In some regions, however, major floral extinctions did occur, with some researchers challenging

5200-530: The end-Triassic extinction , marks the boundary between the Triassic and Jurassic periods, 201.4  million years ago . It is one of five major extinction events , profoundly affecting life on land and in the oceans. In the seas, about 23–34% of marine genera disappeared. On land, all archosauromorph reptiles other than crocodylomorphs (the lineage leading to modern crocodilians), dinosaurs , and pterosaurs (flying reptiles) became extinct; some of

5330-493: The 1980s and 1990s. The theory that the TJME was caused by massive volcanism in the Central Atlantic Magmatic Province (CAMP) first emerged in the 1990s after similar research examining the Permian-Triassic extinction event found it to have been caused by volcanic activity. Despite some early objections, this paradigm remains the scientific consensus in the present day. The Triassic-Jurassic extinction completed

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5460-413: The 21st century. In addition, the flood basalts intruded through sediments that were rich in organic matter and combusted it, which led to the degassing of volatiles that further enhanced volcanic warming of the climate. Thermogenic carbon release through such contact metamorphism of carbon-rich deposits has been found to be a sensible hypothesis providing a coherent explanation for the magnitude of

5590-579: The 9 km (6 mi) wide Red Wing Creek structure in North Dakota . Spray et al. (1998) noted an interesting phenomenon, that being how the Manicouagan, Rochechouart, and Saint Martin craters all seem to be at the same latitude, and that the Obolon' and Red Wing craters form parallel arcs with the Rochechouart and Saint Martin craters, respectively. Spray and his colleagues hypothesized that

5720-592: The Central High Atlas: Lower, Intermediate, Upper and Recurrent basalts. The Lower and Intermediate units are constituted by basaltic andesites , whereas the Upper and Recurrent units have basaltic composition. From Lower to Recurrent unit, we observe: Ages were determined by Ar/Ar analysis on plagioclase . These data show indistinguishable ages (199.5±0.5 Ma) from Lower to Upper lava flows, from central to northern Morocco. Therefore, CAMP

5850-613: The Eiberg Basin of the Northern Calcareous Alps , there was a very rapid palynomorph turnover. The palynological and palaeobotanical succession in Queensland shows a Classopolis bloom after the TJME. Polyploidy may have been an important factor that mitigated a conifer species' risk of going extinct. The leading and best evidenced explanation for the TJME is massive volcanic eruptions, specifically from

5980-473: The Eiberg Basin. The persistence of anoxia into the Hettangian age may have helped delay the recovery of marine life in the extinction's aftermath, and recurrent hydrogen sulphide poisoning likely had the same retarding effect on biotic rediversification. Research on the role of ozone shield deterioration during the Permian-Triassic mass extinction has suggested that it may have been a factor in

6110-619: The High Atlas CAMP. Palynological data from sedimentary layers samples at the base of four lava flow sequences constrain the onset of the CAMP, since there is no evidence of depositional hiatus or tectonic deformation at the bottom of the lava flow piles. The palynological assemblage observed in these basal layers is typical of Late Triassic age, similar to that of the uppermost Triassic sedimentary rocks of eastern North America. Samples from interlayered limestone in lava flows provided unreliable palynological data. One limestone bed from

6240-516: The Jurassic. However, their extinction rate at the Triassic–Jurassic boundary was not elevated. The highest extinction rates experienced by Mesozoic marine reptiles actually occurred at the end of the Ladinian stage, which corresponds to the end of the Middle Triassic. The only marine reptile families which became extinct at or slightly before the Triassic–Jurassic boundary were the placochelyids (the last family of placodonts ), making plesiosaurs

6370-475: The Manicouagan and Rochechouart craters were formed in eras of different magnetic polarity, and radiometric dating of the individual craters has shown that the impacts occurred millions of years apart. Shocked quartz has been found in Rhaetian deposits from the Northern Apennines of Italy, providing possible evidence of an end-Triassic extraterrestrial impact. Certain trace metals indicative of

6500-454: The Manicouagan reservoir. The eroded Rochechouart impact structure in France has most recently been dated to 201 ± 2 million years ago, but at 25 km (16 mi) across (possibly up to 50 km (30 mi) across originally), it appears to be too small to have affected the ecosystem, although it has been speculated to have played a role in an alleged much smaller extinction event at

6630-921: The Newark Basin, therefore the North American CAMP Basalts postdate the Tr–J boundary whereas part of the Moroccan CAMP was erupted within the Triassic. Contrarily, Whiteside et al. (2007) propose that these two levels could be earliest Jurassic intervals of reverse polarity not sampled in the Newark Basin Sequence (many more lava flows are present in the Moroccan Succession than in the Newark Basin), but observed in Early Jurassic sedimentary sequences of

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6760-522: The Norian and suffered further losses in the TJME. Conulariids seemingly completely died out at the end of the Triassic. Around 96% of coral genera died out, with integrated corals being especially devastated. Corals practically disappeared from the Tethys Ocean at the end of the Triassic except for its northernmost reaches, resulting in an early Hettangian "coral gap". There is good evidence for

6890-687: The Norian-Rhaetian boundary. The 40 km (25 mi) wide Saint Martin crater in Manitoba has been proposed as a candidate for a possible TJME-causing impact, but its has since been dated to be Carnian. Other putative or confirmed Triassic craters include the 80 km (50 mi) wide Puchezh-Katunki crater in Eastern Russia (though it may be Jurassic in age), the 15 km (9 mi) wide Obolon' crater in Ukraine , and

7020-710: The Paris Basin of France. Reverse polarity intervals in America could be present within North Mountain (Fundy basin, Nova Scotia) which are poorly sampled even if previous magnetostratigraphy analysis in this sequence showed only normal polarity, or in the Scots Bay Member of the Fundy basin which have never been sampled. There is only one outcrop in the CAMP of America where reverse polarity is observable:

7150-409: The TJME as well. A spike in the abundance of unseparated tetrads of Kraeuselisporites reissingerii has been interpreted as evidence of increased ultraviolet radiation flux resulting from ozone layer damage caused by volcanic aerosols. The extinctions at the end of the Triassic were initially attributed to gradually changing environments. Within his 1958 study recognizing biological turnover between

7280-547: The TJME coincides with mercury anomalies and is thus believed by researchers to have been caused by mercury poisoning . δ Hg and Δ Hg evidence suggests that volcanism caused the mercury loading directly at the Triassic-Jurassic boundary, but that there were later bouts of elevated mercury in the environment during the Early Jurassic caused by eccentricity-forced enhancement of hydrological cycling and erosion that resulted in remobilisation of volcanically injected mercury that had been deposited in wetlands. The intense, rapid warming

7410-541: The TJME have numerical values very different from what would be expected in an extraterrestrial impact scenario, providing further evidence against this hypothesis. The Triassic-Jurassic boundary furthermore lacks a fern spore spike akin to that observed at the terminus of the Cretaceous, inconsistent with an asteroid impact. The extremely rapid, centuries-long timescale of carbon emissions and global warming caused by pulses of CAMP volcanism has drawn comparisons between

7540-549: The TJME, mobile bivalve taxa outnumbered stationary bivalve taxa. Gastropod diversity was barely affected at the Triassic-Jurassic boundary, although gastropods gradually suffered numerous losses over the late Norian and Rhaetian, during the leadup to the TJME. Brachiopods declined in diversity at the end of the Triassic before rediversifying in the Sinemurian and Pliensbachian . Bryozoans , particularly taxa that lived in offshore settings, had already been in decline since

7670-657: The Tr-J boundary climatic and biotic crisis that led to the mass-extinction . The North American portion of the CAMP lava flows crop out in various sections in the basins of Newark, Culpeper, Hartford, Deerfield, i.e. the Newark Supergroup in New England (USA), and in the Fundy Basin in Nova Scotia (Canada). The CAMP is here constituted by rare olivine - and common quartz-normative basalts showing

7800-463: The Triassic and Jurassic, Edwin H. Colbert 's proposal was that this extinction was a result of geological processes decreasing the diversity of land biomes. He considered the Triassic period to be an era of the world experiencing a variety of environments, from towering highlands to arid deserts to tropical marshes. In contrast, the Jurassic period was much more uniform both in climate and elevation due to excursions by shallow seas. Later studies noted

7930-408: The Triassic experienced a "multiple impact event", a large fragmented asteroid or comet which broke up and impacted the earth in several places at the same time. Such an impact has been observed in the present day, when Comet Shoemaker-Levy 9 broke up and hit Jupiter in 1992. However, the "multiple impact event" hypothesis for Triassic impact craters has not been well-supported; Kent (1998) noted that

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8060-425: The Triassic, or instead more gradual. During the Triassic, amphibians were mainly represented by large, crocodile-like members of the order Temnospondyli . Although the earliest lissamphibians (modern amphibians like frogs and salamanders ) did appear during the Triassic, they would become more common in the Jurassic while the temnospondyls diminished in diversity past the Triassic–Jurassic boundary. Although

8190-652: The Triassic-Jurassic extinction and were nearly wiped out. Ceratitidans , the most prominent group of ammonites in the Triassic, became extinct at the end of the Rhaetian after having their diversity reduced significantly in the Norian , while other ammonite groups such as the Ammonitina , Lytoceratina , and Phylloceratina diversified from the Early Jurassic onward. Bivalves suffered heavy losses, although

8320-550: The Triassic-Jurassic mass extinction and anthropogenic global warming , currently causing the Holocene extinction . The current rate of carbon dioxide emissions is around 50 gigatonnes per year, hundreds of times faster than during the latest Triassic, although the lack of extremely detailed stratigraphic resolution and pulsed nature of CAMP volcanism means that individual pulses of greenhouse gas emissions likely occurred on comparable timescales to human release of warming gases since

8450-488: The Triassic–Jurassic boundary. The boundary between the Adamanian and Revueltian land vertebrate faunal zones, which involved extinctions and faunal changes in tetrapods and plants, was possibly also caused by the Manicouagan impact, although discrepancies between magnetochronological and isotopic dating lead to some uncertainty. Other Triassic craters are closer to the Triassic–Jurassic boundary but also much smaller than

8580-593: The Triassic–Jurassic extinction, similar to the extraterrestrial object which was the main factor in the Cretaceous–Paleogene extinction about 66 million years ago, as evidenced by the Chicxulub crater in Mexico. However, so far no impact crater of sufficient size has been dated to precisely coincide with the Triassic–Jurassic boundary. Nevertheless, the Late Triassic did experience several impacts, including

8710-543: The abruptness of this transition and the relative abundances of given spore types both before and after the boundary are highly variable from one region to another, pointing to a global ecological restructuring rather than a mass extinction of plants. Overall, plants suffered minor diversity losses on a global scale as a result of the extinction, but species turnover rates were high and substantial changes occurred in terms of relative abundance and growth distribution among taxa. Evidence from Central Europe suggests that rather than

8840-462: The amount of carbon dioxide emitted was only around 250 ppm, not enough to generate a mass extinction. In addition, at some sites, changes in carbon isotope ratios have been attributed to diagenesis and not any primary environmental changes. The flood basalts of the CAMP released gigantic quantities of carbon dioxide , a potent greenhouse gas causing intense global warming. Before the TJME, carbon dioxide levels were around 1,000 ppm as measured by

8970-433: The basis for related but different kinds of stratigraphic units known collectively as magnetostratigraphic units (magnetozones) . The magnetic property most useful in stratigraphic work is the change in the direction of the remanent magnetization of the rocks, caused by reversals in the polarity of the Earth's magnetic field . The direction of the remnant magnetic polarity recorded in the stratigraphic sequence can be used as

9100-639: The basis for the subdivision of the sequence into units characterized by their magnetic polarity. Such units are called "magnetostratigraphic polarity units" or chrons. If the ancient magnetic field was oriented similar to today's field ( North Magnetic Pole near the Geographic North Pole ) the strata retains a normal polarity. If the data indicates that the North Magnetic Pole was near the Geographic South Pole ,

9230-433: The boundary according to British fissure deposits from the Rhaetian. Aetosaurs, kuehneosaurids , drepanosaurs, thecodontosaurids , "saltoposuchids" (like Terrestrisuchus ), trilophosaurids, and various non- crocodylomorph pseudosuchians are all examples of Rhaetian reptiles which may have become extinct at the Triassic–Jurassic boundary. In the TJME's aftermath, dinosaurs experienced a major radiation, filling some of

9360-402: The boundary between the Late Triassic and Early Jurassic has been tied to a large negative δ C excursion, with values as low as -2.8%. Carbon isotopes of hydrocarbons ( n -alkanes ) derived from leaf wax and lignin , and total organic carbon from two sections of lake sediments interbedded with the CAMP in eastern North America have shown carbon isotope excursions similar to those found in

9490-529: The boundary or not: if not, then the CAMP could not be a cause of the Late Triassic extinction event . For example, according to Whiteside et al. (2007) there are palynological, geochemical, and magnetostratigraphic evidences that the CAMP postdates the Tr-J boundary. In the Newark Basin , a magnetic reversal (E23r) is observed just below the oldest basalts and more or less in the same position as

9620-600: The broad leaved Ginkgoales which declined to near extinction across the Tr–J boundary. Ferns and other species with dissected leaves displayed greater adaptability to atmosphere conditions of the extinction event, and in some instances were able to proliferate across the boundary and into the Jurassic. In the Jiyuan Basin of North China, Classopolis content increased drastically in concordance with warming, drying, wildfire activity, enrichments in isotopically light carbon, and an overall reduction in floral diversity. In

9750-458: The carbon cycle was so disrupted that it did not stabilise until the Sinemurian . Mercury anomalies from deposits in various parts of the world have further bolstered the volcanic cause hypothesis, as have anomalies from various platinum-group elements. Nickel enrichments are also observed at the Triassic-Jurassic boundary coevally with light carbon enrichments, providing yet more evidence of massive volcanism. Some scientists initially rejected

9880-508: The carbon isotopic excursions are shown in the same places, making the case for a volcanic cause of a mass extinction. The observed negative carbon isotope excursion is lower in some sites that correspond to what was then eastern Panthalassa because of the extreme aridity of western Pangaea limiting weathering and erosion there. The negative δ C excursion associated with CAMP volcanism lasted for approximately 20,000 to 40,000 years, or about one or two of Earth's axial precession cycles, although

10010-460: The climate may have become much more seasonal, with long droughts interrupted by severe monsoons . The world gradually got warmer over this time as well; from the late Norian to the Rhaetian, mean annual temperatures rose by 7 to 9 °C. The site of Hochalm in Austria preserves evidence of carbon cycle perturbations during the Rhaetian preceding the Triassic-Jurassic boundary, potentially having

10140-413: The correlation establishes numerous time lines through the stratigraphic section. These ages provide relatively precise dates for features in the rocks such as fossils , changes in sedimentary rock composition, changes in depositional environment, etc. They also constrain the ages of cross-cutting features such as faults , dikes , and unconformities . Perhaps the most powerful application of these data

10270-462: The decline of temnospondyls did send shockwaves through freshwater ecosystems, it was probably not as abrupt as some authors have suggested. Brachyopoids , for example, survived until the Cretaceous according to new discoveries in the 1990s. Several temnospondyl groups did become extinct near the end of the Triassic despite earlier abundance, but it is uncertain how close their extinctions were to

10400-413: The depth of a hydrocarbon source rock beneath the basin-filling strata allows calculation of the age at which the source rock passed through the generation window and hydrocarbon migration began. Because the ages of cross-cutting trapping structures can usually be determined from magnetostratigraphic data, a comparison of these ages will assist reservoir geologists in their determination of whether or not

10530-712: The earliest Jurassic, immediately after the Triassic-Jurassic transition. Elevated wildfire activity is also known from the Junggar Basin . In the Jiyuan Basin, two distinct pulses of drastically elevated wildfire activity are known: the first mainly affected canopies and occurred amidst relatively humid conditions while the second predominantly affected ground cover and was associated with aridity. Frequent wildfires, combined with increased seismic activity from CAMP emplacement, led to apocalyptic soil degradation . In addition to these climatic effects, oceanic uptake of volcanogenic carbon and sulphur dioxide would have led to

10660-459: The earliest volcanism and extinction of large populations using zircon uranium-lead (U-Pb) dating. They further demonstrated that the magmatic eruptions as well as the accompanying atmospheric changes were split into four pulses lasting for over ~600,000 years. Before that integration, two hypotheses were in debate. One hypothesis was based especially on studies on Triassic-Jurassic basins from Morocco where CAMP lava flows are outcropping, whereas

10790-571: The emission of sulphur dioxide aerosols. A 2022 study shows that high latitudes had colder climates with evidence of mild glaciation. The authors propose that cold periods ("ice ages") induced by volcanic ejecta clouding the atmosphere might have favoured endothermic animals, with dinosaurs, pterosaurs, and mammals being more capable at enduring these conditions than large pseudosuchians due to insulation. CAMP volcanism released enormous amounts of toxic mercury . The appearance of high rates of mutaganesis of varying severity in fossil spores during

10920-413: The end of the Triassic, with both dominant herbivorous subgroups (such as aetosaurs ) and carnivorous ones ( rauisuchids ) having died out. Phytosaurs, drepanosaurs , trilophosaurids , tanystropheids , and procolophonids , which were other common reptiles in the Late Triassic, had also become extinct by the start of the Jurassic. However, pinpointing the extinction of these different land reptile groups

11050-569: The end of the Triassic. The last known metoposaurids (" Apachesaurus ") were from the Redonda Formation , which may have been early Rhaetian or late Norian . Gerrothorax , the last known plagiosaurid , has been found in rocks which are probably (but not certainly) Rhaetian, while a capitosaur humerus was found in Rhaetian-age deposits in 2018. Therefore, plagiosaurids and capitosaurs were likely victims of an extinction at

11180-494: The end of the mass extinction despite numerous relapses into anoxic conditions during the earliest Jurassic. In the Neuquén Basin , recovery began in the late early Hettangian and lasted until a new biodiversity equilibrium in the late Hettangian. Also despite recurrent anoxic episodes, large bivalves began to reappear shortly after the extinction event. Siliceous sponges dominated the immediate aftermath interval thanks to

11310-434: The enormous influx of silica into the oceans from the weathering of the CAMP's aerially extensive basalts. Some clades recovered more slowly than others, however, as exemplified by corals and their disappearance in the early Hettangian. Fish did not suffer a mass extinction at the end of the Triassic. The Late Triassic in general did experience a gradual drop in actinopterygiian diversity after an evolutionary explosion in

11440-530: The extinction was highly selective, with some bivalve clades escaping substantial diversity losses. The Lilliput effect affected megalodontid bivalves, whereas file shell bivalves experienced the Brobdingnag effect, the reverse of the Lilliput effect, as a result of the mass extinction event. There is some evidence of a bivalve cosmopolitanism event during the mass extinction. Additionally, following

11570-608: The extinction. The site of St. Audrie's Bay displays a shift from diverse gymnosperm-dominated forests to Cheirolepidiaceae-dominated monocultures. The Danish Basin saw 34% of its Rhaetian spore-pollen assemblage, including Cingulizonates rhaeticus , Limbosporites lundbladiae , Polypodiisporites polymicroforatus , and Ricciisporites tuberculatus , disappear, with the post-extinction plant community being dominated by pinacean conifers such as Pinuspollenites minimus and tree ferns such as Deltoidospora , with ginkgos, cycads, cypresses, and corystospermous seed ferns also represented. Along

11700-430: The field using a rock core drill, or as hand samples (chunks broken off the rock face). To average out sampling errors, a minimum of three samples is taken from each sample site. Spacing of the sample sites within a stratigraphic section depends on the rate of deposition and the age of the section. In sedimentary layers, the preferred lithologies are mudstones , claystones , and very fine-grained siltstones because

11830-520: The first appearance of the ammonite Psiloceras planorbis . In the Newark basin the palynological turnover event (hence the Tr-J boundary mass extinction) occurs below the oldest CAMP lava flows. The same can be said for the Fundy, Hartford and Deerfield Basins. In the investigated Moroccan CAMP sections (Central High Atlas Basin), sedimentary layers sampled immediately below the oldest basaltic lava flows, apparently contain Triassic taxa (e.g., P. densus ), and were thus defined as Triassic in age as at least

11960-445: The first place) makes it difficult to correlate the impact with extinction. Onoue et al. (2016) alternatively proposed that the Manicouagan impact was responsible for a marine extinction in the middle of the Norian which affected radiolarians, sponges, conodonts, and Triassic ammonoids. Thus, the Manicouagan impact may have been partially responsible for the gradual decline in the latter two groups which culminated in their extinction at

12090-399: The floristic turnover by exploiting newly abundant plants. Odonates suffered highly selective losses, and their morphospace was heavily restructured as a result. The extinction event marks a floral turnover as well, with estimates of the percentage of Rhaetian pre-extinction plants being lost ranging from 17% to 73%. Though spore turnovers are observed across the Triassic-Jurassic boundary,

12220-411: The groups which died out were previously abundant, such as aetosaurs , phytosaurs , and rauisuchids . Plants , crocodylomorphs, dinosaurs, pterosaurs and mammals were left largely untouched, allowing the dinosaurs, pterosaurs, and crocodylomorphs to become the dominant land animals for the next 135 million years. The cause of the Tr-J extinction event may have been extensive volcanic eruptions in

12350-499: The hypothesis of there being no significant floral mass extinction on this basis. In the Newark Supergroup of the United States East Coast , about 60% of the diverse monosaccate and bisaccate pollen assemblages disappear at the Tr–J boundary, indicating a major extinction of plant genera. Early Jurassic pollen assemblages are dominated by Corollina , a new genus that took advantage of the empty niches left by

12480-422: The largest province by volume, the CAMP certainly encompasses the greatest area known, roughly 11,000,000 square kilometres (4,200,000 sq mi), of any continental large igneous province . Nearly all CAMP rocks are tholeiitic in composition, with widely separated areas where basalt flows are preserved, as well as large groups of diabase (dolerite) sills or sheets, small lopoliths , and dikes throughout

12610-460: The lowest lava flows . Still, a different interpretation is suggested by Whiteside et al. (2007) : the sampled sedimentary strata are quite deformed and this can mean that some sedimentary units could be lacking (eroded or structurally omitted). With respect to the Triassic pollens found in some sedimentary units above the Upper Unit basalts, they could have been reworked, so they don’t represent

12740-404: The magnetic grains are finer and more likely to orient with the ambient field during deposition. Samples are first analyzed in their natural state to obtain their natural remanent magnetization (NRM). The NRM is then stripped away in a stepwise manner using thermal or alternating field demagnetization techniques to reveal the stable magnetic component. Magnetic orientations of all samples from

12870-575: The main crisis began. This early phase of environmental degradation in eastern Panthalassa may have been caused by an early phase of CAMP activity. Anoxic, reducing conditions were likewise present in western Panthalassa off the coast of what is now Japan for about a million years prior to the TJME. During the TJME, the rapid warming and increase in continental weathering led to the stagnation of ocean circulation and deoxygenation of seawater in many ocean regions, causing catastrophic marine environmental effects in conjunction with ocean acidification, which

13000-626: The margins of the European Epicontinental Sea and the European shores of the Tethys, coastal and near-coastal mires fell victim to an abrupt sea level rise. These mires were replaced by a pioneering opportunistic flora after an abrupt sea level fall, although its heyday was short lived and it died out shortly after its rise. The opportunists that established themselves along the Tethyan coastline were primarily spore-producers. In

13130-430: The modern biosphere. If human-induced climate change persists as is, predictions can be made as to how various aspects of the biosphere will respond based on records of the TJME. For example, current conditions such the increased carbon dioxide levels, ocean acidification , and ocean deoxygenation create a similar climate to that of the Triassic-Jurassic boundary for marine life, so it is the common assumption that should

13260-423: The mostly marine St. Audrie's Bay section, Somerset, England; the correlation suggests that the TJME began at the same time in marine and terrestrial environments, slightly before the oldest basalts in eastern North America but simultaneous with the eruption of the oldest flows in Morocco, with both a critical CO 2 greenhouse and a marine biocalcification crisis. Contemporaneous CAMP eruptions, mass extinction, and

13390-457: The negative carbon isotope excursions at the terminus of the Triassic. Global temperatures rose sharply by 3 to 4 °C. In some regions, the temperature rise was as great as 10 °C. Kaolinite-dominated clay mineral spectra reflect the extremely hot and humid greenhouse conditions engendered by the CAMP. Soil erosion occurred as the hydrological cycle was accelerated by the extreme global heat. The catastrophic dissociation of gas hydrates as

13520-408: The niches of more ancient groups of amphibians and reptiles which were extinct by the start of the Jurassic. Olsen (1987) estimated that 42% of all terrestrial tetrapods became extinct at the end of the Triassic, based on his studies of faunal changes in the Newark Supergroup of eastern North America. More modern studies have debated whether the turnover in Triassic tetrapods was abrupt at the end of

13650-463: The niches vacated by the victims of the extinction. Crocodylomorphs likewise underwent a very rapid and major adaptive radiation. Surviving non-mammalian synapsid clades similarly played a role in the post-TJME adaptive radiation during the Early Jurassic. Herbivorous insects were minimally affected by the TJME; evidence from the Sichuan Basin shows they were overall able to quickly adapt to

13780-399: The oceans. A meteoric shift towards positive sulphur isotope ratios in reduced sulphur species indicates a complete utilisation of sulphate by sulphate reducing bacteria. Evidence of anoxia has been discovered at the Triassic-Jurassic boundary across the world's oceans; the western Tethys, eastern Tethys, and Panthalassa were all affected by a precipitous drop in seawater oxygen, although at

13910-484: The only surviving sauropterygians , and giant ichthyosaurs such as shastasaurids . Nevertheless, some authors have argued that the end of the Triassic acted as a genetic " bottleneck " for ichthyosaurs, which never regained the level of anatomical diversity and disparity which they possessed during the Triassic. The high diversity of rhomaelosaurids immediately after the TJME points to a gradual extinction of marine reptiles rather than an abrupt one. Terrestrial fauna

14040-612: The opening of the Atlantic Ocean basin during the breakup of the Pangean supercontinent. The province has been described as extending within Pangaea from present-day central Brazil northeastward about 5,000 kilometres (3,100 mi) across western Africa , Iberia , and northwestern France , and from the interior of western Africa westward for 2,500 kilometres (1,600 mi) through eastern and southern North America . If not

14170-671: The other was based on end-Triassic extinction data from eastern North American basins and lava flows showing an extremely large turnover in fossil pollen, spores (sporomorphs), and vertebrates, respectively. The thickest lava flow sequences of the African CAMP are in Morocco, where there are basaltic lava piles more than 300 metres thick. The most-studied area is Central High Atlas , where the best preserved and most complete basaltic lava piles are exposed. According to geochemical, petrographic and isotopic data four distinct tholeiitic basaltic units were recognized and can be placed throughout

14300-403: The past. As well as a number, each chron is divided into two parts, labelled "n" and "r", thereby showing the position of the field's polarity. Chrons are also referred by a capital letter of a reference sequence such as "C". A chron is the time equivalent to a chronozone or a polarity zone. It was called a "polarity subchron" when the interval is less than 200,000 years long, although the term

14430-494: The province. Dikes occur in very large individual swarms with particular compositions and orientations. CAMP activity is apparently related to the rifting and breakup of Pangaea during the Late Triassic through Early Jurassic periods, and the enormous province size, varieties of basalt, and brief time span of CAMP magmatism invite speculation about mantle processes that could produce such a magmatic event as well as rift

14560-676: The second-largest confirmed impact in the Mesozoic. The Manicouagan Reservoir in Quebec is one of the most visible large impact craters on Earth, and at 100 km (62 mi) in diameter it is tied with the Eocene Popigai impact structure in Siberia as the fourth-largest impact crater on Earth. Olsen et al. (1987) were the first scientists to link the Manicouagan crater to the Triassic–Jurassic extinction, citing its age which at

14690-399: The section. The samples are analyzed to determine their characteristic remanent magnetization (ChRM), that is, the polarity of Earth's magnetic field at the time a stratum was deposited. This is possible because volcanic flows acquire a thermoremanent magnetization and sediments acquire a depositional remanent magnetization , both of which reflect the direction of the Earth's field at

14820-409: The shallow subseafloor may also reflect decreased pH, these structures being speculated to have precipitated concomitantly with acidification. In some studied sections, the TJME biocalcification crisis is masked by emersion of carbonate platforms induced by marine regression. Anoxia was another mechanism of extinction; the end-Triassic extinction was coeval with an uptick in black shale deposition and

14950-558: The standard black and white magnetostratigraphic columns in which black indicates normal polarity and white is reversed polarity. Because the polarity of a stratum can only be normal or reversed, variations in the rate at which the sediment accumulated can cause the thickness of a given polarity zone to vary from one area to another. This presents the problem of how to correlate zones of like polarities between different stratigraphic sections. To avoid confusion at least one isotopic age needs to be collected from each section. In sediments, this

15080-403: The stomatal index of Lepidopteris ottonis , but this quantity jumped to 1,300 ppm at the onset of the extinction event. During the TJME, carbon dioxide concentrations increased fourfold. The record of CAMP degassing shows several distinct pulses of carbon dioxide immediately following each major pulse of magmatism, at least two of which amount to a doubling of atmospheric CO 2 . Carbon dioxide

15210-470: The strata exhibits reversed polarity. A polarity chron , or in context chron , is the time interval between polarity reversals of Earth's magnetic field . It is the time interval represented by a magnetostratigraphic polarity unit. It represents a certain time period in geologic history where the Earth's magnetic field was in predominantly a "normal" or "reversed" position. Chrons are numbered in order starting from today and increasing in number into

15340-476: The time of formation. This technique is typically used to date sequences that generally lack fossils or interbedded igneous rock. It is particularly useful in high-resolution correlation of deep marine stratigraphy where it allowed the validation of the Vine–Matthews–Morley hypothesis related to the theory of plate tectonics . When measurable magnetic properties of rocks vary stratigraphically they may be

15470-412: The time was roughly considered to be Late Triassic. More precise radiometric dating by Hodych & Dunning (1992) has shown that the Manicouagan impact occurred about 214 million years ago, about 13 million years before the Triassic–Jurassic boundary. Therefore, it could not have been responsible for an extinction precisely at the Triassic–Jurassic boundary. Nevertheless, the Manicouagan impact did have

15600-555: The top to the central High Atlas upper basalts yielded a Late Triassic palynological assemblage. However, the observed sporomorphs in this sample are rare and poorly preserved. All of these data indicate that the basaltic lava flows of the Central Atlantic magmatic province in Morocco were erupted at c. 200 Ma and spanned the Tr - J boundary. Thus, it is very possible that there is a connection between this magmatic event and

15730-628: The transition from the Palaeozoic evolutionary fauna to the Modern evolutionary fauna, a change that began in the aftermath of the end-Guadalupian extinction and continued following the Permian-Triassic extinction event (PTME). Between 23% and 34.1% of marine genera went extinct. Plankton diversity dropped suddenly, but it was relatively mildly impacted at the Triassic-Jurassic boundary, although extinction rates among radiolarians rose significantly. Ammonites were affected substantially by

15860-502: The trends continue, modern reef-building taxa and skeletal benthic organisms will be preferentially impacted. The end-Triassic reef crisis has been specifically cited as a possible analogue for the fate of present coral reefs should anthropogenic global warming continue. Magnetostratigraphy Magnetostratigraphy is a geophysical correlation technique used to date sedimentary and volcanic sequences. The method works by collecting oriented samples at measured intervals throughout

15990-570: The very end of the Triassic, while most other temnospondyls were already extinct. Terrestrial reptile faunas were dominated by archosauromorphs during the Triassic, particularly phytosaurs and members of Pseudosuchia (the reptile lineage which leads to modern crocodilians ). In the Early Jurassic and onwards, dinosaurs and pterosaurs became the most common land reptiles, while small reptiles were mostly represented by lepidosauromorphs (such as lizards and tuatara relatives). Among pseudosuchians, only small crocodylomorphs did not become extinct by

16120-415: The volcanic eruption theory because the Newark Supergroup , a section of rock in eastern North America that records the Triassic–Jurassic boundary, contains no ash-fall horizons and because its oldest basalt flows were estimated to lie around 10 m above the transition zone, which they estimated to have occurred 610 kyr after the TJME. Also among their objections was that the Triassic-Jurassic boundary

16250-514: Was affected by the TJME much more severely than marine fauna. One of the earliest pieces of evidence for a Late Triassic extinction was a major turnover in terrestrial tetrapods such as amphibians, reptiles, and synapsids. Edwin H. Colbert drew parallels between the system of extinction and adaptation between the Triassic–Jurassic and Cretaceous–Paleogene boundaries. He recognized how dinosaurs, lepidosaurs ( lizards and their relatives), and crocodyliforms ( crocodilians and their relatives) filled

16380-518: Was an intense, short magmatic event. Basalts of the Recurrent unit are slightly younger (mean age: 197±1 Ma) and represent a late event. Consistently, the Upper and Recurrent basalts are separated by a sedimentary layer that locally reaches a thickness of circa 80 m. According to magnetostratigraphic data, the Moroccan CAMP events were divided into five groups, differing in paleomagnetic orientations (declination and inclination). Each group

16510-412: Was emitted quickly and in enormous quantities compared to other periods of Earth's history, rate of carbon dioxide emissions was one of the most meteoric rises in carbon dioxide levels in Earth's entire history. It is estimated that a single volcanic pulse from the large igneous province would have emitted an amount of carbon dioxide roughly equivalent to projected anthropogenic carbon dioxide emissions for

16640-645: Was enhanced and exacerbated by widespread photic zone euxinia through organic matter respiration and carbon dioxide release. Off the shores of the Wrangellia Terrane, the onset of photic zone euxinia was preceded by an interval of limited nitrogen availability and increased nitrogen fixation in surface waters while euxinia developed in bottom waters. In what is now northwestern Europe, shallow seas became salinity stratified, enabling easy development of anoxia. Reduced salinity, in conjunction with increased influx of terrestrial organic matter, enkindled anoxia in

16770-530: Was poorly defined and the CAMP eruptions poorly constrained temporally. However, updated dating protocol and wider sampling has confirmed that the CAMP eruptions started in Morocco only a few thousand years before the extinction, preceding their onset in Nova Scotia and New Jersey , and that they continued in several more pulses for the next 600,000 years. Volcanic global warming has also been criticised as an explanation because some estimates have found that

16900-504: Was redefined in 2020 to an approximate duration between 10,000 to 100,000 years and polarity chron for an approximate duration between 100,000 years and a million years. Other terms used are Megachron for a duration between 10 and 10 years, Superchron for a duration between 10 and 10 years and Crytochron for a duration less than 3×10 years. The nomenclature for the succession of polarity intervals, especially when changes are of short durations, or not universal (the earth's magnetic field

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