Cambrian Stage 2
Stage 2 of the Cambrian is the unnamed upper stage of the Terreneuvian series. It lies atop the Fortunian and below Stage 3 of the Cambrian. It is commonly referred to as the Tommotian, after the Cambrian stratigraphy of Siberia. Neither the upper nor lower boundary has yet been defined by the International Commission on Stratigraphy. The preferred definitions for the lower boundary are the first appearance of the molluscs Watsonella crosbyi or Aldanella attleborensis around 529 million years ago. The proposed upper boundary might be the first appearance of trilobites around 521 million years ago.
|Cambrian Stage 2|
|~529 – ~521 Ma|
|Regional Usage||Global (ICS)|
|Time scale(s) used||ICS Time Scale|
|Time span formality||Formal|
|Lower boundary definition||Not formally defined|
|Lower boundary definition candidates||First appearance of small shelly fauna or Archaeocyathids|
|Lower boundary GSSP candidate section(s)||None|
|Upper boundary definition||Not formally defined|
|Upper boundary definition candidates||FAD of Trilobites|
|Upper boundary GSSP candidate section(s)||None|
Possible candidates for a GSSP include the first appearance of Watsonella crosbyi in the Zhujiaqing Formation in Yunnan, China or the Pestrotsvet Formation near the Aldan River on the Siberian Platform.
- Kouchinsky, Artem; Bengtson, Stefan; Missarzhevsky, Vladimir V.; Pelechaty, Shane; Torssander, Peter; Val'kov, Anatolij K. (24 September 2001). "Carbon isotope stratigraphy and the problem of a pre-Tommotian stage in Siberia". Geological Magazine. 138 (4): 387–396. doi:10.1017/S0016756801005684.
- "GSSP List ICS". ICS. Archived from the original on 15 November 2012. Retrieved 9 November 2012.
- "International Commission on Stratigraphy".
- Li, Guoxiang; Zhao, Xin; Gubanov, Alexander; Zhu, Maoyan; Na, Lin (1 April 2011). "Early Cambrian Mollusc Watsonella crosbyi: A Potential GSSP Index Fossil for the Base of the Cambrian Stage 2". Acta Geologica Sinica - English Edition. 85 (2): 309–319. doi:10.1111/j.1755-6724.2011.00400.x.
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