Cambrian

Cambrian Period
541–485.4 million years ago
Mean atmospheric 2 content over period durationc. 12.5 vol %[1][2]
(63 % of modern level)
Mean atmospheric 2 content over period durationc. 4500 ppm[3]
(16 times pre-industrial level)
Mean surface temperature over period durationc. 21 °C[4]
(7 °C above modern level)
Sea level (above present day)Rising steadily from 30m to 90m[5]
Key events in the Cambrian
view •  • 
-550 —
-540 —
-530 —
-520 —
-510 —
-500 —
-490 —
 
 
 
 
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Orsten Fauna
Archaeocyatha extinction
SSF diversification, first brachiopods & archaeocyatha
Treptichnus pedum trace
Large negative peak δ 13Ccarb excursion
First Cloudina & Namacalathus mineral tubular fossils
Stratigraphic scale of the ICS subdivisions and Precambrian/Cambrian boundary.

The Cambrian Period ( n/ or n/) was the first geological period of the Paleozoic Era, and of the Phanerozoic Eon.[6] The Cambrian lasted 55.6 million years from the end of the preceding Ediacaran Period 541 million years ago (mya) to the beginning of the Ordovician Period 485.4 mya.[7] Its subdivisions, and its base, are somewhat in flux. The period was established (as “Cambrian series”) by Adam Sedgwick,[6] who named it after Cambria, the Latinised form of Cymru, the Welsh name for Wales, where Britain's Cambrian rocks are best exposed.[8][9][10] The Cambrian is unique in its unusually high proportion of lagerstätte sedimentary deposits, sites of exceptional preservation where "soft" parts of organisms are preserved as well as their more resistant shells. As a result, our understanding of the Cambrian biology surpasses that of some later periods.[11]

The Cambrian marked a profound change in life on Earth; prior to the Cambrian, the majority of living organisms on the whole were small, unicellular and simple; the Precambrian Charnia being exceptional. Complex, multicellular organisms gradually became more common in the millions of years immediately preceding the Cambrian, but it was not until this period that mineralized—hence readily fossilized—organisms became common.[12] The rapid diversification of lifeforms in the Cambrian, known as the Cambrian explosion, produced the first representatives of all modern animal phyla. Phylogenetic analysis has supported the view that during the Cambrian radiation, metazoa (animals) evolved monophyletically from a single common ancestor: flagellated colonial protists similar to modern choanoflagellates.

Although diverse life forms prospered in the oceans, the land is thought to have been comparatively barren—with nothing more complex than a microbial soil crust[13] and a few molluscs that emerged to browse on the microbial biofilm known to have been present.[14] Most of the continents were probably dry and rocky due to a lack of vegetation. Shallow seas flanked the margins of several continents created during the breakup of the supercontinent Pannotia. The seas were relatively warm, and polar ice was absent for much of the period.

Stratigraphy

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. The base of the Cambrian lies atop a complex assemblage of trace fossils known as the Treptichnus pedum assemblage.[15] The use of Treptichnus pedum, a reference ichnofossil to mark the lower boundary of the Cambrian, is difficult as the occurrence of very similar trace fossils belonging to the Treptichnids group are found well below the T. pedum in Namibia, Spain and Newfoundland, and possibly, in the western USA. The stratigraphic range of T. pedum overlaps the range of the Ediacaran fossils in Namibia, and probably in Spain.[16][17]

Subdivisions

The Cambrian Period followed the Ediacaran Period and was followed by the Ordovician Period. The Cambrian is divided into four epochs (series) and ten ages (stages). Currently only three series and six stages are named and have a GSSP (an internationally agreed-upon stratigraphic reference point).

Because the international stratigraphic subdivision is not yet complete, many local subdivisions are still widely used. In some of these subdivisions the Cambrian is divided into three series (epochs) with locally differing names – the Early Cambrian (Caerfai or Waucoban, 541 ± 1.0 to 509 ± 1.7 mya), 497 ± 1.7 mya) and 485.4 ± 1.7 mya; also known as Late Cambrian, Merioneth or Croixan). Rocks of these epochs are referred to as belonging to the Lower, Middle, or Upper Cambrian.

Trilobite zones allow biostratigraphic correlation in the Cambrian.

Each of the local series is divided into several stages. The Cambrian is divided into several regional faunal stages of which the Russian-Kazakhian system is most used in international parlance:

Chinese North American Russian-Kazakhian Australian Regional
C
a
m
b
r
i
a
n
Furongian Ibexian (part) Ayusokkanian Datsonian Dolgellian (Trempealeauan, Fengshanian)
Payntonian
Sunwaptan Sakian Iverian Ffestiniogian (Franconian, Changshanian)
Steptoan Aksayan Idamean Maentwrogian (Dresbachian)
Marjuman Batyrbayan Mindyallan
Miaolingian Maozhangian Mayan Boomerangian
Zuzhuangian Delamaran Amgan Undillian
Zhungxian Florian
Templetonian
  Dyeran Ordian
Cambrian Series 2 Longwangmioan Toyonian Lenian
Changlangpuan Montezuman Botomian
Qungzusian Atdabanian
Terreneuvian
Meishuchuan
Jinningian
Placentian Tommotian
Nemakit-Daldynian*
Cordubian
Precambrian Sinian Hadrynian Nemakit-Daldynian*
Sakharan
Adeladean

*In Russian scientific thought the lower boundary of the Cambrian is suggested to be defined at the base of the Tommotian Stage which is characterized by diversification and global distribution of organisms with mineral skeletons and the appearance of the first Archaeocyath bioherms.[18][19][20]

Dating the Cambrian

The International Commission on Stratigraphy list the Cambrian period as beginning at 541 million years ago and ending at 485.4 million years ago.

The lower boundary of the Cambrian was originally held to represent the first appearance of complex life, represented by trilobites. The recognition of small shelly fossils before the first trilobites, and Ediacara biota substantially earlier, led to calls for a more precisely defined base to the Cambrian period.[21]

After decades of careful consideration, a continuous sedimentary sequence at Fortune Head, Newfoundland was settled upon as a formal base of the Cambrian period, which was to be correlated worldwide by the earliest appearance of Treptichnus pedum.[21] 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.[21][22]

This formal designation allowed radiometric dates to be obtained from samples across the globe that corresponded to the base of the Cambrian. Early dates of 570 million years ago quickly gained favour,[21] though the methods used to obtain this number are now considered to be unsuitable and inaccurate. A more precise date using modern radiometric dating yield a date of 541 ± 0.3 million years ago.[23] 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, more suitable sections, ranging from 544 or 542 Ma, are more suitable.[21]

Other Languages
Afrikaans: Kambrium
Alemannisch: Kambrium
asturianu: Cambrianu
Bahasa Banjar: Kambrium
Bân-lâm-gú: Cambria-kí
беларуская: Кембрыйскі перыяд
беларуская (тарашкевіца)‎: Кембр
български: Камбрий
brezhoneg: Kambrian
català: Cambrià
čeština: Kambrium
Cymraeg: Cambriaidd
dansk: Kambrium
Deutsch: Kambrium
eesti: Kambrium
español: Cámbrico
Esperanto: Kambrio
euskara: Kanbriar
فارسی: کامبرین
français: Cambrien
Gaeilge: Caimbriach
galego: Cámbrico
한국어: 캄브리아기
hrvatski: Kambrij
Bahasa Indonesia: Kambrium
italiano: Cambriano
עברית: קמבריון
Basa Jawa: Kambriyum
Latina: Cambrium
latviešu: Kembrijs
Lëtzebuergesch: Kambrium
lietuvių: Kambras
Limburgs: Cambrium
magyar: Kambrium
македонски: Камбриум
مازِرونی: کامبرین
Bahasa Melayu: Kambria
Mìng-dĕ̤ng-ngṳ̄: Cambrian
Nederlands: Cambrium
Nordfriisk: Kambrium
norsk: Kambrium
norsk nynorsk: Kambrium
occitan: Cambrian
oʻzbekcha/ўзбекча: Kembriy sistemasi
پنجابی: کیمبرین
Piemontèis: Cambrian
polski: Kambr
português: Cambriano
română: Cambrian
саха тыла: Кембрий
Scots: Cambrian
Simple English: Cambrian
slovenčina: Kambrium
slovenščina: Kambrij
српски / srpski: Камбријум
srpskohrvatski / српскохрватски: Kambrij
svenska: Kambrium
Tagalog: Cambrian
Tiếng Việt: Kỷ Cambri
Volapük: Kambrium
文言: 寒武紀
Winaray: Cambrian
粵語: 寒武紀
中文: 寒武纪