Cambrian Series 2
~521 – ~509 Ma
Name formalityInformal
Usage information
Celestial bodyEarth
Regional usageGlobal (ICS)
Time scale(s) usedICS Time Scale
Chronological unitEpoch
Stratigraphic unitSeries
Time span formalityFormal
Lower boundary definitionNot formally defined
Lower boundary definition candidatesFAD of Trilobites
Lower boundary GSSP candidate section(s)None
Upper boundary definitionFAD of Oryctocephalus indicus.
Upper boundary GSSPWuliu-Zengjiayan, Guizhou, China
26°04′51″N 108°24′50″E / 26.0807°N 108.4138°E / 26.0807; 108.4138
Upper GSSP ratified2018[2]

Cambrian Series 2 is the unnamed 2nd series of the Cambrian. It lies above the Terreneuvian series and below the Miaolingian. Series 2 has not been formally defined by the International Commission on Stratigraphy, lacking a precise lower boundary and subdivision into stages. The proposed lower boundary is the first appearance of trilobites which is estimated to be around 521 million years ago.[3][4]


The International Commission on Stratigraphy has not named the 2nd series of the Cambrian yet.[3] In part the new name will replace the older terms "Lower Cambrian" and "Early Cambrian". The nomenclature used in Siberia uses the term "Yakutian" for this series.[5]


The 2nd series is currently subdivided by the ICS into two stages: Cambrian Stage 3 and Cambrian Stage 4. Both of these stages also lack formal definition.[3] The Siberian nomenclature distinguishes three stages (lowest first): Atdabanian, Botomian and Toyonian.[5] In general most subdivisions of this series rely on biostratigraphy of trilobite zones.[6]


The beginning of the 2nd series of the Cambrian is marked by the appearance of trilobites. Correlating this event on different continents has proven difficult and resolving this is essential for the definition of the lower boundary of this series. Currently the oldest trilobite known is Lemdadella which marks the beginning of the Fallotaspis zone.[6]

The end of the 2nd series of the Cambrian is marked by the first major biotic extinction of the Paleozoic. Changes in ocean chemistry and the marine environment are posited as the most likely cause of these extinctions.[7]


  1. ^ "Chart/Time Scale". International Commission on Stratigraphy.
  2. ^ Zhao; et al. (June 2019). "Global Standard Stratotype-Section and Point (GSSP) for the conterminous base of the Miaolingian Series and Wuliuan Stage (Cambrian) at Balang, Jianhe, Guizhou, China" (PDF). Episodes. 42: 165–184. Retrieved 8 December 2020.
  3. ^ a b c "GSSP Table - Paleozoic Era". Retrieved 18 November 2012.
  4. ^ Wu, Tong; Yang, Ruidong; Gao, Junbo; Li, Jun (1 January 2021). "Age of the lower Cambrian Vanadium deposit, East Guizhou, South China: Evidences from age of tuff and carbon isotope analysis along the Bagong section". Open Geosciences. 13 (1): 999–1012. doi:10.1515/geo-2020-0287. ISSN 2391-5447.
  5. ^ a b "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 2012-11-23.
  6. ^ a b 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.
  7. ^ Zhang, Wenhao; et al. (2014). "Mass-occurrence of oncoids at the Cambrian Series 2–Series 3 transition: Implications for microbial resurgence following an Early Cambrian extinction". Gondwana Research. 28: 432–450. doi:10.1016/