Cambrian Series 2
Cambrian Series 2 is the unnamed 2nd series of the Cambrian. It lies above the Terreneuvian series and below the Cambrian Series 3. Series 2 has not been formally defined by the International Commission on Stratigraphy, lacking a precise lower and upper 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. The upper boundary is proposed as the first appearance of either the trilobite species Oryctocephalus indicus or Ovatoryctocara granulata, currently estimated to be around 509 million years ago.
The International Commission on Stratigraphy has not named the 2nd stage of the Cambrian yet. The new name will replace the older terms "Lower Cambrian" and "Early Cambrian". The nomenclature used in Sibera uses the term "Yakutian" for this series.
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. The Siberian nomenclature distinguishes three stages (lowest first): Atdabanian, Botomian and Toyonian. In general most subdivisions of this series rely on biostratigraphy of trilobite zones.
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.
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.
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- Gozalo, Rodolfo; Álvarez, María Eugenia Dies; Vintaned, José Antonio Gámez; Zhuravlev, Andrey Yu.; Bauluz, Blanca; Subías, Ignacio; Chirivella Martorell, Juan B.; Mayoral, Eduardo; Gursky, Hans-Jürgen; Andrés, José Antonio; Liñán, Eladio (1 December 2011). "Proposal of a reference section and point for the Cambrian Series 2-3 boundary in the Mediterranean subprovince in Murero (NE Spain) and its intercontinental correlation". Geological Journal. 48: 142–155. doi:10.1002/gj.1330.
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- 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.
- 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. doi:10.1016/j.gr.2014.03.015.
|Preceded by Proterozoic Eon||Phanerozoic Eon|
|Paleozoic Era||Mesozoic Era||Cenozoic Era|