Editing Cambrian (section)

==== 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]]