Cambrian Stage 3

Cambrian Stage 3 is the still unnamed third stage of the Cambrian. It succeeds Cambrian Stage 2 and precedes Cambrian Stage 4, although neither its base nor top have been formally defined. The plan is for its lower boundary to correspond approximately to the first appearance of trilobites, about 521 million years ago,[2] though the globally asynchronous appearance of trilobites warrants the use of a separate, globally synchronous marker to define the base.[3] The upper boundary and beginning of Cambrian Stage 4 is informally defined as the first appearance of the trilobite genera Olenellus or Redlichia around 514 million years ago.[4]

Cambrian Stage 3
Chronology
Etymology
Name formalityInformal
Usage information
Celestial bodyEarth
Regional usageGlobal (ICS)
Time scale(s) usedICS Time Scale
Definition
Chronological unitAge
Stratigraphic unitStage
Time span formalityFormal
Lower boundary definitionNot formally defined
Lower boundary definition candidatesFAD of Trilobites
Lower boundary GSSP candidate section(s)None
Upper boundary definitionNot formally defined
Upper boundary definition candidatesFAD of the Trilobites Olenellus or Redlichia
Upper boundary GSSP candidate section(s)None

Naming

The International Commission on Stratigraphy has not officially named the 3rd stage of the Cambrian. The stage approximately corresponds to the "Atdabanian", which is used by geologists working in Siberia.[5]

Biostratigraphy

The oldest trilobite known is Lemdadella which appears at the beginning of the Fallotaspis zone.[6] The Cambrian radiation of animal phyla ends here, after the diversification and origination of arthropods, molluscs, lophophorates, chordates (including vertebrates) among others.

References
  • Zhang (2017). "Challenges in defining the base of Cambrian Series 2 and Stage 3". Earth-Science Reviews. 172: 124–139. Bibcode:2017ESRv..172..124Z. doi:10.1016/j.earscirev.2017.07.017.
  1. "Chart/Time Scale". stratigraphy.org. International Commission on Stratigraphy.
  2. Ahlberg, Per; Babcock, Loren E. "Subcommission on Cambrian Stratigraphy Annual Report 2017" (PDF). International Commission on Stratigraphy. Retrieved 14 March 2022.
  3. "International Commission on Stratigraphy".
  4. "GSSP Table - Paleozoic Era". Retrieved 18 November 2012.
  5. "The 13th International Field Conference of the Cambrian Stage Subdivision Working Group" (PDF). Episodes. 31 (4): 440–441. Archived from the original (PDF) on 2014-11-05. Retrieved 2012-11-18.
  6. Yuan, J.L.; Zhu, X.J.; Lin, J.P.; Zhu, M.Y. (22 September 2011). "Tentative correlation of Cambrian Series 2 between South China and other continents" (PDF). Bulletin of Geosciences: 397–404. doi:10.3140/bull.geosci.1274. Retrieved 23 November 2012.
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