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The Cambrian ( ) is the first geological period of the Paleozoic Era, and the Phanerozoic Eon. The Cambrian lasted 51.95 million years from the end of the preceding Ediacaran period 538.8 Ma (million years ago) to the beginning of the Ordovician Period 486.85 Ma.
Most of the continents were located in the southern hemisphere surrounded by the vast Panthalassa. The assembly of Gondwana during the Ediacaran and early Cambrian led to the development of new convergent plate boundaries and Volcanic arc along its margins that helped drive up global temperatures. Laurentia lay across the equator, separated from Gondwana by the opening Iapetus Ocean.
The Cambrian marked a profound change in Life; prior to the Period, the majority of living organisms were small, unicellular and poorly preserved. Complex, multicellular organisms gradually became more common during the Ediacaran, but it was not until the Cambrian that fossil diversity seems to rapidly increase, known as the Cambrian explosion, produced the first representatives of most modern animal Phylum. The Period is also unique in its unusually high proportion of lagerstätte deposits, sites of exceptional preservation where "soft" parts of organisms are preserved as well as their more resistant shells.
This early agreement did not last. Due to the scarcity of fossils, Sedgwick used rock types to identify Cambrian strata. He was also slow in publishing further work. The clear fossil record of the Silurian, however, allowed Murchison to correlate rocks of a similar age across Europe and Russia, and on these he published extensively. As increasing numbers of fossils were identified in older rocks, he extended the base of the Silurian downwards into the Sedgwick's "Upper Cambrian", claiming all fossilised strata for "his" Silurian series. Matters were complicated further when, in 1852, fieldwork carried out by Sedgwick and others revealed an unconformity within the Silurian, with a clear difference in fauna between the two. This allowed Sedgwick to now claim a large section of the Silurian for "his" Cambrian and gave the Cambrian an identifiable fossil record. The dispute between the two geologists and their supporters, over the boundary between the Cambrian and Silurian, would extend beyond the life times of both Sedgwick and Murchison. It was not resolved until 1879, when Charles Lapworth proposed the disputed strata belong to its own system, which he named the Ordovician.
The term Cambrian for the oldest period of the Paleozoic was officially agreed in 1960, at the 21st International Geological Congress. It only includes Sedgwick's "Lower Cambrian series", but its base has been extended into much older rocks.
Despite the long recognition of its distinction from younger Ordovician rocks and older Precambrian rocks, it was not until 1994 that the Cambrian system/period was internationally ratified. After decades of careful consideration, a continuous sedimentary sequence at Fortune Head, Newfoundland, Canada, was settled upon as a formal base of the Cambrian Period, which was to be correlated worldwide by the earliest appearance of Treptichnus pedum. Discovery of this fossil a few metres below the GSSP led to the refinement of this statement, and it is the T. pedum ichnofossil assemblage that is now formally used to correlate the base of the Cambrian.
This formal designation allowed to be obtained from samples across the globe that corresponded to the base of the Cambrian. An early date of 570 Megaannum quickly gained favour, though the methods used to obtain this number are now considered to be unsuitable and inaccurate. A more precise analysis using modern radiometric dating yields a date of 538.8 ± 0.6 Ma. The ash horizon in Oman from which this date was recovered corresponds to a marked fall in the abundance of carbon-13 that correlates to equivalent excursions elsewhere in the world, and to the disappearance of distinctive Ediacaran fossils ( Namacalathus, Cloudina). Nevertheless, there are arguments that the dated horizon in Oman does not correspond to the Ediacaran-Cambrian boundary, but represents a facies change from marine to evaporite-dominated strata – which would mean that dates from other sections, ranging from 544 to 542 Ma, are more suitable.
| +Approximate correlation of global and regional stages in Cambrian stratigraphy ! !International Series !International Stage !Chinese !Australian !Russian-Kazakhian !North American !European | |||||
| C a m b r i a n | Furongian | "Stage 10" | Datsonian | Skullrockian / Ibexian (part) | Merionethian |
| Payntonian | Sunwaptan / Trempealeauan | ||||
| Jiangshanian | Jiangshanian | Iverian | Aksaian | ||
| Sakian | |||||
| Paibian | Paibian | Steptoean / Franconian | |||
| Miaolingian | Ayusokkanian | Marjuman / Dresbachian | |||
| Boomerangian | Mayan | Acadian / St. David's | |||
| Drumian | Undillian | ||||
| Florian | |||||
| Wuliuan | Topazan | ||||
| Ordian | Delmaran | ||||
| Cambrian Series 2 | "Stage 4" | Duyunian | Branchian / Comley (part) | ||
| Toyonian | |||||
| Dyeran | |||||
| Botomian | |||||
| "Stage 3" | Nangaoan | ||||
| Atdabanian | Montezuman | ||||
| Placentian / Comley (part) | |||||
| Terreneuvian | "Stage 2" | Meishucunian | Tommotian* | Begadean | |
| Jinningian | Nemakit-Daldynian* | ||||
| Fortunian | |||||
| Ediacaran | Sinian | Sakharan / Vendian | Hadrynian | ||
The Olenelloidea, Eodiscidae, and most Redlichiida trilobites went extinct at the boundary between Series 2 and the Miaolingian. This is considered the oldest mass extinction of trilobites.
The Furongian is divided into three stages: the Paibian, c. 497 Ma to c. 494 Ma, and the Jiangshanian c. 494.2 Ma to c. 491 Ma, which have defined GSSPs; and the unnamed Cambrian Stage 10, c. 491 Ma to 486.85 ± 1.5 Ma.
Most models show Gondwana stretching from the south polar region to north of the equator. (2025). 9781107105324, Cambridge University Press. ISBN 9781107105324 Early in the Cambrian, the south pole corresponded with the western South American sector and as Gondwana rotated anti-clockwise, by the middle of the Cambrian, the south pole lay in the northwest African region.
Laurentia lay across the equator, separated from Gondwana by the Iapetus Ocean. Proponents of Pannotia have Laurentia and Baltica close to the Amazonia region of Gondwana with a narrow Iapetus Ocean that only began to open once Gondwana was fully assembled c. 520 Ma. Those not in favour of the existence of Pannotia show the Iapetus opening during the Late Neoproterozoic, with up to c. 6,500 km (c. 4038 miles) between Laurentia and West Gondwana at the beginning of the Cambrian.
Of the smaller continents, Baltica lay between Laurentia and Gondwana, the Ran Ocean (an arm of the Iapetus) opening between it and Gondwana. Siberia lay close to the western margin of Gondwana and to the north of Baltica. Annamia and South China formed a single continent situated off north central Gondwana. The location of North China is unclear. It may have lain along the northeast Indian sector of Gondwana or already have been a separate continent.
After the Late Neoproterozoic (or mid-Cambrian) of Laurentia from Gondwana and the subsequent opening of the Iapetus Ocean, Laurentia was largely surrounded by with much of the continent covered by shallow seas.
As Laurentia separated from Gondwana, a sliver of continental terrane rifted from Laurentia with the narrow Taconic orogeny opening between them. The remains of this terrane are now found in southern Scotland, Ireland, and Newfoundland. Intra-oceanic subduction either to the southeast of this terrane in the Iapetus, or to its northwest in the Taconic seaway, resulted in the formation of an island arc. This accreted to the terrane in the late Cambrian, triggering southeast-dipping subduction beneath the terrane itself and consequent closure of the marginal seaway. The terrane collided with Laurentia in the Early Ordovician.
Towards the end of the early Cambrian, rifting along Laurentia's southeastern margin led to the separation of Cuyania (now part of Argentina) from the Ouachita embayment with a new ocean established that continued to widen through the Cambrian and Early Ordovician.
The that formed Gondwana came together during the Neoproterozoic to early Cambrian. A narrow ocean separated Amazonian craton from Gondwana until c. 530 Ma and the Arequipa-Antofalla block united with the sector of Gondwana in the early Cambrian. The Kuunga orogeny between northern (Congo craton, Madagascar and India) and southern Gondwana (Kalahari craton and East Antarctica), which began c. 570 Ma, continued with parts of northern Gondwana over-riding southern Gondwana and was accompanied by metamorphism and the intrusion of .
Subduction, active since the Neoproterozoic, extended around much of Gondwana's margins, from northwest Africa southwards round South America, South Africa, East Antarctica, and the eastern edge of West Australia. Shorter subduction zones existed north of Arabia and India.
The Famatinian continental arc stretched from central Peru in the north to central Argentina in the south. Subduction beneath this proto-Andean orogeny margin began by the late Cambrian.
Along the northern margin of Gondwana, between northern Africa and the Armorican Terranes of southern Europe, the continental arc of the Cadomian Orogeny continued from the Neoproterozoic in response to the oblique subduction of the Iapetus Ocean. This subduction extended west along the Gondwanan margin and by c. 530 Ma may have evolved into a major transform fault system.
At c. 511 Ma the Flood basalt of the Kalkarindji large igneous province (LIP) began to erupt. These covered an area of > 2.1 million km2 across northern, central and Western Australia regions of Gondwana making it one of the largest, as well as the earliest, LIPs of the Phanerozoic. The timing of the eruptions suggests they played a role in the early to middle Cambrian Extinction event.
Baltica lay at mid-to-high southerly latitudes, separated from Laurentia by the Iapetus and from Gondwana by the Ran Ocean. It was composed of two continents, Baltic Shield and Sarmatian craton, separated by shallow seas. The deposited in these Unconformity overlay Precambrian basement rocks. The lack of coarse-grained sediments indicates low lying topography across the centre of the craton.
Along Baltica's northeastern margin subduction and arc magmatism associated with the Ediacaran Timanide Orogen was coming to an end. In this region the early to middle Cambrian was a time of non-deposition and followed by late Cambrian rifting and sedimentation.
Its southeastern margin was also a convergent boundary, with the accretion of island arcs and microcontinents to the craton, although the details are unclear.
From the Late Neoproterozoic to the Ordovician, a series of island arcs accreted to Siberia's then northeastern margin, accompanied by extensive arc and Back-arc region volcanism. These now form the Altai-Sayan terranes. Some models show a convergent plate margin extending from Greater Avalonia, through the Timanide margin of Baltica, forming the Kipchak island arc offshore of southeastern Siberia and curving round to become part of the Altai-Sayan convergent margin.
Along the then western margin, Late Neoproterozoic to early Cambrian rifting was followed by the development of a passive margin.
To the then north, Siberia was separated from the Central Mongolian terrane by the narrow and slowly opening Mongol-Okhotsk Ocean. The Central Mongolian terrane's northern margin with the Panthalassa was convergent, whilst its southern margin facing the Mongol-Okhotsk Ocean was passive.
To the south of these the Tarim microcontinent lay between Gondwana and Siberia. Its northern margin was passive for much of the Paleozoic, with thick sequences of platform carbonates and fluvial to marine sediments resting unconformably on Precambrian basement. Along its southeast margin was the Altyn-Tagh Cambro–Ordovician accretionary complex, whilst to the southwest a subduction zone was closing the narrow seaway between the North West Kunlun Mountains region of Tarim and the South West Kunlun terrane.
Northern North China was a passive margin until the onset of subduction and the development of the Bainaimiao arc in the late Cambrian. To its south was a convergent margin with a southwest dipping subduction zone, beyond which lay the North Qinling terrane (now part of the Qinling Orogenic Belt), together with Qilian-Qaidam, Altyn belts, and South West Kunlun terranes.
The northern margin South China, including the South Qinling block, was a passive margin.
Along the southeastern margin, lower Cambrian volcanics indicate the accretion of an island arc along the Song Ma suture zone. Also, early in the Cambrian, the eastern margin of South China changed from passive to active, with the development of oceanic volcanic island arcs that now form part of the Japanese terrane.
Calculations of global average temperatures (GAT) vary depending on which techniques are used. Whilst some measurements show GAT over c. models that combine multiple sources give GAT of c. in the Terreneuvian increasing to c. for the rest of the Cambrian. The warm climate was linked to elevated atmospheric carbon dioxide levels. Assembly of Gondwana led to the reorganisation of the tectonic plates with the development of new convergent plate margins and continental-margin arc magmatism that helped drive climatic warming. The eruptions of the Kalkarindji LIP during Stage 4 and into the early Miaolingian, also released large quantities of carbon dioxide, methane and Sulfur dioxide into the atmosphere leading to rapid climatic changes and elevated sea surface temperatures.
There is uncertainty around the maximum sea surface temperatures. These are calculated using δ18O values from marine rocks, and there is an ongoing debate about the levels δ18O in Cambrian seawater relative to the rest of the Phanerozoic. Estimates for tropical sea surface temperatures vary from c. , to c. . Modern average tropical sea surface temperatures are .
Atmospheric oxygen levels rose steadily rising from the Neoproterozoic due to the increase in organisms. Cambrian levels varied between c. 3% and 14% (present day levels are c. 21%). Low levels of atmospheric oxygen and the warm climate resulted in lower dissolved oxygen concentrations in marine waters and widespread Anoxic waters in deep ocean waters.
There is a complex relationship between oxygen levels, the biogeochemistry of ocean waters, and the evolution of life. Newly evolved burrowing organisms exposed anoxic sediments to the overlying oxygenated seawater. This bioturbation decreased the burial rates of organic carbon and Sulfur, which over time reduced atmospheric and oceanic oxygen levels, leading to widespread anoxic conditions. Periods of higher rates of continental weathering led to increased delivery of nutrients to the oceans, boosting productivity of phytoplankton and stimulating metazoan evolution. However, rapid increases in nutrient supply led to eutrophication, where rapid growth in phytoplankton numbers result in the depletion of oxygen in the surrounding waters.
Pulses of increased oxygen levels are linked to increased biodiversity; raised oxygen levels supported the increasing Metabolism demands of organisms, and increased by expanding habitable areas of seafloor. Conversely, incursions of oxygen-deficient water, due to changes in sea level, ocean circulation, upwellings from deeper waters and/or biological productivity, produced anoxic conditions that limited habitable areas, reduced ecological niches and resulted in extinction events both regional and global.
Overall, these dynamic, fluctuating environments, with global and regional anoxic incursions resulting in extinction events, and periods of increased oceanic oxygenation stimulating biodiversity, drove evolutionary innovation.
The base of the Miaolingian is marked by the Redlichiid–Olenellid extinction carbon isotope event (ROECE), which coincides with the main phase of Kalkarindji volcanism.
During the Miaolingian, orogenic events along the Australian-Antarctic margin of Gondwana led to an increase in weathering and an influx of nutrients into the ocean, raising the level of productivity and organic carbon burial. These can be seen in the steady increase in 87Sr/86Sr and δ13C.
87Sr/86Sr fell sharply near the top of the Jiangshanian Stage, and through Stage 10 as the Gondwanan mountains were eroded down and rates of weathering decreased.
During the late Ediacaran to early Cambrian increasing oxygen levels led to a decrease in ocean acidity and an increase in the concentration of calcium in sea water. However, there was not a simple transition from aragonite to calcite seas, rather a protracted and variable change through the Cambrian. Aragonite and high-magnesium precipitation continued from the Ediacaran into Cambrian Stage 2. Low-magnesium calcite skeletal hard parts appear in Cambrian Age 2, but inorganic precipitation of aragonite also occurred at this time. Mixed aragonite–calcite seas continued through the middle and late Cambrian, with fully calcite seas not established until the early Ordovician.
These variations and slow decrease in Mg2+/Ca2+ of seawater were due to low oxygen levels, high continental weathering rates and the geochemistry of the Cambrian seas. In conditions of low oxygen and high iron levels, iron substitutes for magnesium in Authigenesis deposited on the ocean floor, slowing the removal rates of magnesium from seawater. The enrichment of ocean waters in silica, prior to the radiation of siliceous organisms, and the limited bioturbation of the anoxic ocean floor increased the rates of deposition, relative to the rest of the Phanerozoic, of these clays. This, together with the high input of magnesium into the oceans via enhanced continental weathering, delayed the reduction in Mg2+/Ca2+ and facilitated continued aragonite precipitation.
The conditions that favoured the deposition of authigenic clays were also ideal for the formation of lagerstätten, with the minerals in the clays replacing the soft body parts of Cambrian organisms.
No land plant (embryophyte) fossils are known from the Cambrian. However, biofilms and microbial mats were well developed on Cambrian tidal flats and beaches 500 mya, and microbes forming microbial Earth , comparable with modern soil crust of desert regions, contributing to soil formation. Although molecular clock estimates suggest Embryophyta may have first emerged during the Middle or Late Cambrian, the consequent large-scale removal of the greenhouse gas CO2 from the atmosphere through sequestration did not begin until the Ordovician.
Land plants may have emerged during the Cambrian, but the evidence for this is fragmentary and contested and the oldest unamibiguous evidence for land plants is from the following Ordovician. Molecular clock estimates have also led some authors to suggest that arthropods colonised land during the Cambrian, but again the earliest physical evidence of this is during the following Ordovician.
The period marked a steep change in the diversity and composition of Earth's biosphere. The Ediacaran biota suffered a mass extinction at the start of the Cambrian Period, which corresponded with an increase in the abundance and complexity of burrowing behaviour. This behaviour had a profound and irreversible effect on the substrate which transformed the seabed ecosystems. Before the Cambrian, the sea floor was covered by . By the end of the Cambrian, burrowing animals had destroyed the mats in many areas through bioturbation. As a consequence, many of those organisms that were dependent on the mats became extinct, while the other species adapted to the changed environment that now offered new ecological niches. Around the same time there was a seemingly rapid appearance of representatives of all the mineralized phylum, including the Bryozoa, which were once thought to have only appeared in the Lower Ordovician. However, many of those phyla were represented only by stem-group forms; and since mineralized phyla generally have a benthic origin, they may not be a good proxy for (more abundant) non-mineralized phyla.
While the early Cambrian showed such diversification that it has been named the Cambrian Explosion, this changed later in the period, when there occurred a sharp drop in biodiversity. About 515 Ma, the number of species going extinct exceeded the number of new species appearing. Five million years later, the number of genera had dropped from an earlier peak of about 600 to just 450. Also, the speciation rate in many groups was reduced to between a fifth and a third of previous levels. 500 Ma, oxygen levels fell dramatically in the oceans, leading to hypoxia, while the level of poisonous hydrogen sulfide simultaneously increased, causing another extinction. The later half of Cambrian was surprisingly barren and showed evidence of several rapid extinction events; the which had been replaced by reef building sponges known as Archaeocyatha, returned once more as the archaeocyathids became extinct. This declining trend did not change until the Great Ordovician Biodiversification Event.
Marine life lived under low and fluctuating levels of oxygen in the ocean. During upwellings of Anoxic waters deep ocean waters into shallow marine environments could push organisms over the edge into mass extinctions, leading ultimately to increased biodiversity.
Some Cambrian organisms ventured onto land, producing the trace fossils Protichnites and Climactichnites. Fossil evidence suggests that , an extinct group of arthropods, produced at least some of the Protichnites. Fossils of the track-maker of Climactichnites have not been found; however, fossil trackways and resting traces suggest a large, slug-like mollusc.
In contrast to later periods, the Cambrian fauna was somewhat restricted; free-floating organisms were rare, with the majority living on or close to the sea floor; and mineralizing animals were rarer than in future periods, in part due to the unfavourable ocean chemistry.
Many modes of preservation are unique to the Cambrian, and some preserve soft body parts, resulting in an abundance of Lagerstätten. These include Sirius Passet, the Sinsk Algal Lens, the Maotianshan Shales, the Emu Bay Shale, and the Burgess Shale.
Symbol
The United States Federal Geographic Data Committee uses a "barred capital C" character to represent the Cambrian Period.
The Unicode character is . Unicode Character 'LATIN CAPITAL LETTER C WITH BAR' (U+A792). fileformat.info. Retrieved 15 June 2015
Gallery
See also
Further reading
(2025). 9780444528599, Elsevier. ISBN 9780444528599
External links
target="_blank" rel="nofollow"> Chronostratigraphy scale v.2018/08 | Cambrian
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