Editing Cambrian (section)

=== Stratigraphy {{anchor|Subdivisions}} ===
[[System (stratigraphy)|Systems]], [[Series (stratigraphy)|series]] and [[Stage (stratigraphy)|stages]] can be defined globally or regionally. For global stratigraphic correlation, the ICS ratify rock units based on a [[Global Boundary Stratotype Section and Point]] (GSSP) from a single [[Geological formation|formation]] (a [[stratotype]]) identifying the lower boundary of the unit. Currently the boundaries of the Cambrian System, three series and six stages are defined by global stratotype sections and points.<ref name="ICS" />

==== Ediacaran-Cambrian boundary ====
The lower boundary of the Cambrian was originally held to represent the first appearance of complex life, represented by [[trilobite]]s. The recognition of [[small shelly fossils]] before the first trilobites, and [[Ediacara biota]] substantially earlier, has led to calls for a more precisely defined base to the Cambrian Period.<ref name="Geyer-2016">{{Cite journal |last1=Geyer |first1=Gerd |last2=Landing |first2=Ed |year=2016 |title=The Precambrian–Phanerozoic and Ediacaran–Cambrian boundaries: A historical approach to a dilemma |journal=Geological Society, London, Special Publications |volume=448 |issue=1 |pages=311–349 |bibcode=2017GSLSP.448..311G |doi=10.1144/SP448.10 |s2cid=133538050}}</ref>

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]] was settled upon as a formal base of the Cambrian Period, which was to be correlated worldwide by the earliest appearance of ''[[Treptichnus pedum]]''.<ref name="Geyer-2016" /> 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.<ref name="Geyer-2016" /><ref>{{Cite journal |last1=Landing |first1=Ed |last2=Geyer |first2=Gerd |last3=Brasier |first3=Martin D. |last4=Bowring |first4=Samuel A. |year=2013 |title=Cambrian Evolutionary Radiation: Context, correlation, and chronostratigraphy—Overcoming deficiencies of the first appearance datum (FAD) concept |journal=Earth-Science Reviews |volume=123 |pages=133–172 |bibcode=2013ESRv..123..133L |doi=10.1016/j.earscirev.2013.03.008}}</ref>

This formal designation allowed radiometric dates to be obtained from samples across the globe that corresponded to the base of the Cambrian. An early date of 570 Ma quickly gained favour,<ref name="Geyer-2016" /> 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.<ref name="ICS" /> 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.<ref name="Geyer-2016" />
{| class="wikitable"
|+Approximate correlation of global and regional stages in Cambrian stratigraphy<ref name="Peng-2020">{{Citation |last1=Peng |first1=S.C. |title=The Cambrian Period |date=2020 |url=https://linkinghub.elsevier.com/retrieve/pii/B978012824360200019X |work=Geologic Time Scale 2020 |pages=565–629 |access-date=2023-06-08 |publisher=Elsevier |language=en |doi=10.1016/b978-0-12-824360-2.00019-x |isbn=978-0-12-824360-2 |last2=Babcock |first2=L.E. |last3=Ahlberg |first3=P.|s2cid=242177216 }}</ref>
!
!International Series
!International Stage
!Chinese
!Australian 
!Russian-Kazakhian
!North American
!European
|-
| rowspan="21" align="center" | '''C<br />a<br />m<br />b<br />r<br />i<br />a<br />n'''
| rowspan="5" align="center" | [[Furongian]] 
| rowspan="2" |"[[Cambrian Stage 10|Stage 10]]"
| rowspan="2" | Niuchehean|| Datsonian 
| rowspan="2" |Batyrbaian ||Skullrockian / Ibexian (part) 
| rowspan="6" |Merionethian
|-
| Payntonian
| rowspan="3" |Sunwaptan / [[Trempealeauan]]
|-
| rowspan="2" |[[Jiangshanian]]
| rowspan="2" |  Jiangshanian
| rowspan="2" | Iverian 
| Aksaian 
|-
| rowspan="2" | Sakian
|-
|[[Paibian]]
|  Paibian
|Idamean|| Steptoean / [[Franconian (stage)|Franconian]]
|-
| rowspan="6" align="center" |  [[Miaolingian]]
| rowspan="2" |[[Guzhangian]]|| rowspan="2" | Guzhangian || Mindyallan || Ayusokkanian 
| rowspan="4" |Marjuman / [[Dresbachian]]
|-
| Boomerangian 
| rowspan="3" |Mayan
| rowspan="5" |Acadian / St. David's
|-
| rowspan="2" |[[Drumian]]
| rowspan="2" | Wangcunian || Undillian 
|-
|Florian
|-
| rowspan="2" |[[Wuliuan]]
| rowspan="2" |  Wuliuan|| Templetonian || rowspan="3" |  Amgan / Amgaian||  Topazan
|-
| rowspan="3" |Ordian
| rowspan="3" | Delmaran 
|-
| rowspan="7" |[[Cambrian Series 2]]
| rowspan="4" |"[[Cambrian Stage 4|Stage 4]]"
| rowspan="4" |Duyunian
| rowspan="6" |Branchian / Comley (part)
|-
| rowspan="2" | Toyonian 
|-
| rowspan="8" |
| rowspan="3" |Dyeran
|-
| rowspan="2" |Botomian
|-
| rowspan="3" |"[[Cambrian Stage 3|Stage 3]]"
| rowspan="3" | Nangaoan 
|-
| rowspan="2" | Atdabanian 
| rowspan="2" |  Montezuman
|-
| rowspan="5" |Placentian / Comley (part)
|-
| rowspan="3" align="center" | [[Terreneuvian]]
| rowspan="2" |"[[Cambrian Stage 2|Stage 2]]"
|Meishucunian
|Tommotian*
| rowspan="3" |Begadean
|-
| rowspan="2" |Jinningian
| rowspan="2" |Nemakit-Daldynian*
|-
|[[Fortunian]]
|-
| colspan="2" align="center" | '''[[Ediacaran]]'''
| || Sinian 
| Adelaidean || Sakharan / Vendian
|  Hadrynian
|}
<nowiki>*</nowiki>Most Russian paleontologists define the lower boundary of the Cambrian at the base of the Tommotian Stage, characterized by diversification and global distribution of organisms with mineral skeletons and the appearance of the first [[Archaeocyatha|Archaeocyath]] bioherms.<ref name=Rozanov2008>{{cite journal
 |author1=A.Yu. Rozanov |author2=V.V. Khomentovsky |author3=Yu.Ya. Shabanov |author4=G.A. Karlova |author5=A.I. Varlamov |author6=V.A. Luchinina |author7=T.V. Pegel' |author8=Yu.E. Demidenko |author9=P.Yu. Parkhaev |author10=I.V. Korovnikov |author11=N.A. Skorlotova | year = 2008
 | title = To the problem of stage subdivision of the Lower Cambrian
 | journal = Stratigraphy and Geological Correlation
 | volume = 16
 | issue = 1
 | pages = 1–19
 | doi = 10.1007/s11506-008-1001-3
 | bibcode=2008SGC....16....1R
|s2cid=128128572 }}</ref><ref name=SokolovFedonkin1984>{{cite journal
 |author1     = B. S. Sokolov
 |author2     = M. A. Fedonkin
 |year        = 1984
 |title       = The Vendian as the Terminal System of the Precambrian
 |journal     = Episodes
 |volume      = 7
 |issue       = 1
 |pages       = 12–20
 |doi = 10.18814/epiiugs/1984/v7i1/004
 |doi-access = free
 }}</ref><ref name= Khomentovskii2005>{{cite journal
 | author1 = V. V. Khomentovskii
 | author2 = G. A. Karlova
 | year = 2005
 | title = The Tommotian Stage Base as the Cambrian Lower Boundary in Siberia
 | journal = Stratigraphy and Geological Correlation
 | volume = 13
 | issue = 1
 | pages = 21–34
 | url = http://www.maikonline.com/maik/showArticle.do?auid=VAE43XYML4
 | access-date = 15 March 2009
 | archive-url = https://web.archive.org/web/20110714022431/http://www.maikonline.com/maik/showArticle.do?auid=VAE43XYML4
 | archive-date = 14 July 2011
 | url-status = dead
 }}</ref>
[[File:Basal Cambrian GSSP.jpg|alt=Photograph of the layered rocks that make up the headland at Fortune Head GSSP|thumb|Ediacaran-Cambrian boundary section at Fortune Head, Newfoundland, GSSP|left]]

==== Terreneuvian ====
The [[Terreneuvian]] is the lowermost series/[[Geologic time scale|epoch]] of the Cambrian, lasting from 538.8 ± 0.6 Ma to c. 521 Ma. It is divided into two stages: the [[Fortunian]] stage, 538.8 ± 0.6 Ma to c. 529 Ma; and the unnamed Stage 2, c. 529 Ma to c. 521 Ma.<ref name="ICS" /> The name Terreneuvian was ratified by the [[International Union of Geological Sciences]] (IUGS) in 2007, replacing the previous "Cambrian Series 1". The GSSP defining its base is at Fortune Head on the Burin Peninsula, eastern Newfoundland, Canada (see Ediacaran - Cambrian boundary above). The Terreneuvian is the only series in the Cambrian to contain no trilobite fossils. Its lower part is characterised by complex, sediment-penetrating Phanerozoic-type [[trace fossil]]s, and its upper part by small shelly fossils.<ref name="Peng-2020" />

==== Cambrian Series 2 ====
The second series/epoch of the Cambrian is currently unnamed and known as [[Cambrian Series 2]]. It lasted from c. 521 Ma to c. 506.5 Ma. Its two stages are also unnamed and known as [[Cambrian Stage 3]], c. 521 Ma to c. 514.5 Ma, and [[Cambrian Stage 4]], c. 514.5 Ma to c. 506.5 Ma.<ref name="ICS" /> The base of Series 2 does not yet have a GSSP, but it is expected to be defined in [[Stratum|strata]] marking the first appearance of trilobites in [[Gondwana]]. There was a rapid diversification of [[Animal|metazoans]] during this epoch, but their restricted geographic distribution, particularly of the trilobites and [[Archaeocyatha|archaeocyaths]], have made global correlations difficult, hence ongoing efforts to establish a GSSP.<ref name="Peng-2020" />

==== Miaolingian ====
[[File:Diorama of the Burgess Shale Biota (Middle Cambrian) - sponges, arthropods (44691571505).jpg|thumb|250px|Diorama of the [[Paleobiota of the Burgess Shale|Burgess Shale Biota]]]]
The [[Miaolingian]] is the third series/epoch of the Cambrian, lasting from c. 506.5 Ma to c. 497 Ma, and roughly identical to the middle Cambrian in older literature.<ref>{{cite journal |url=https://www.tandfonline.com/doi/full/10.1080/11035897.2019.1621374 |last=Nielsen |first=Arne Thorshøj |title=The Miaolingian, a new name for the 'Middle' Cambrian (Cambrian Series 3): identification of lower and upper boundaries in Baltoscandia |journal=GFF |volume=141 |issue=2 |pages=162–173 |date=October 3, 2019 |doi=10.1080/11035897.2019.1621374 |bibcode=2019GFF...141..162N |access-date=January 2, 2025}}</ref> It is divided into three stages: the [[Wuliuan]] c. 506.5 Ma to 504.5 Ma; the [[Drumian]] c. 504.5 Ma to c. 500.5 Ma; and the Guzhangian c. 500.5 Ma to c. 497 Ma.<ref name="ICS" /> The name replaces Cambrian Series 3 and was ratified by the IUGS in 2018.<ref name="Zhao-2019">{{Cite journal |last1=Zhao |first1=Yuanlong |last2=Yuan |first2=Jinliang |last3=Babcock |first3=Loren E. |last4=Guo |first4=Qingjun |last5=Peng |first5=Jin |last6=Yin |first6=Leiming |last7=Yang |first7=Xinglian |last8=Peng |first8=Shanchi |last9=Wang |first9=Chunjiang |last10=Gaines |first10=Robert R. |last11=Esteve |first11=Jorge |last12=Tai |first12=Tongsu |last13=Yang |first13=Ruidong |last14=Wang |first14=Yue |last15=Sun |first15=Haijing |date=2019-06-01 |title=Global Standard Stratotype-Section and Point (GSSP) for the conterminous base of the Miaolingian Series and Wuliuan Stage (Cambrian) at Balang, Jianhe, Guizhou, China |journal=Episodes Journal of International Geoscience |language=en |volume=42 |issue=2 |pages=165–184 |doi=10.18814/epiiugs/2019/019013|doi-access=free }}</ref> It is named after the Miaoling Mountains in southeastern [[Guizhou|Guizhou Province]], South China, where the GSSP marking its base is found. This is defined by the first appearance of the [[Oryctocephalidae|oryctocephalid]] trilobite ''[[Oryctocephalus indicus]]''. Secondary markers for the base of the Miaolingian include the appearance of many [[acritarch]]s forms, a global [[marine transgression]], and the disappearance of the polymerid trilobites, ''Bathynotus'' or ''Ovatoryctocara.'' Unlike the Terreneuvian and Series 2, all the stages of the Miaolingian are defined by GSSPs''.''<ref name="Zhao-2019" />

The [[Olenelloidea|olenellids]], [[Eodiscidae|eodiscids]], and most [[Redlichiida|redlichiids]] trilobites went extinct at the boundary between Series 2 and the Miaolingian. This is considered the oldest mass extinction of trilobites.<ref name="Peng-2020" />

==== Furongian ====
The [[Furongian]], c. 497 Ma to 486.85 ± 1.5 Ma, is the fourth and uppermost series/epoch of the Cambrian. The name was ratified by the IUGS in 2003 and replaces Cambrian Series 4 and the traditional "Upper Cambrian". The GSSP for the base of the Furongian is in the [[Wuling Mountains]], in northwestern [[Hunan|Hunan Province]], China. It coincides with the first appearance of the agnostoid trilobite ''Glyptagnostus reticulatus'', and is near the beginning of a large positive [[Δ13C|δ<sup>13</sup>C]] isotopic excursion.<ref name="Peng-2020" />

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.<ref name="ICS" />

==== Cambrian–Ordovician boundary ====
The GSSP for the Cambrian–Ordovician boundary is at [[Green Point, Newfoundland and Labrador|Green Point]], western [[Newfoundland and Labrador|Newfoundland]], Canada, and is dated at 486.85 Ma. It is defined by the appearance of the [[conodont]] ''[[Iapetognathus fluctivagus]]''. Where these conodonts are not found the appearance of [[plankton]]ic [[graptolite]]s or the [[trilobite]] ''Jujuyaspis borealis'' can be used. The boundary also corresponds with the peak of the largest positive variation in the δ<sup>13</sup>C curve during the boundary time interval and with a global marine transgression.<ref>{{Citation |last1=Cooper |first1=R.A. |title=The Ordovician Period |date=2012 |work=The Geologic Time Scale |pages=489–523 |url=https://doi.org/10.1016/B978-0-444-59425-9.00020-2 |access-date=2024-05-12 |publisher=Elsevier |doi=10.1016/b978-0-444-59425-9.00020-2 |isbn=978-0-444-59425-9 |last2=Sadler |first2=P.M. |last3=Hammer |first3=O. |last4=Gradstein |first4=F.M.}}</ref>