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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.[2][3] Neither the upper nor lower boundary has yet been defined by the International Commission on Stratigraphy.[4][5] The preferred definitions for the lower boundary are the first appearance of the molluscs Watsonella crosbyi or Aldanella attleborensis around 529 million years ago.[6][7] The correlation between the lowest occurrences of A. attleborensis and W. crosbyi with the Zhujiaqing positive carbon isotope excursion (ZHUCE) has led to the conclusion that the combination of these two markers are a reliable indicator of the boundary between the Fortunian and Stage 2.[8] The proposed upper boundary might be the first appearance of trilobites around 521 million years ago.[4]
| Cambrian Stage 2 | ||||||||||||||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Chronology | ||||||||||||||||||||||||||||||||||||||
| ||||||||||||||||||||||||||||||||||||||
| Etymology | ||||||||||||||||||||||||||||||||||||||
| Name formality | Informal | |||||||||||||||||||||||||||||||||||||
| Usage information | ||||||||||||||||||||||||||||||||||||||
| Celestial body | Earth | |||||||||||||||||||||||||||||||||||||
| Regional usage | Global (ICS) | |||||||||||||||||||||||||||||||||||||
| Time scale(s) used | ICS Time Scale | |||||||||||||||||||||||||||||||||||||
| Definition | ||||||||||||||||||||||||||||||||||||||
| Chronological unit | Age | |||||||||||||||||||||||||||||||||||||
| Stratigraphic unit | Stage | |||||||||||||||||||||||||||||||||||||
| 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 | |||||||||||||||||||||||||||||||||||||
Naming
The name "Laolinian" after the Laolin village in Yunnan, China, was proposed for the Stage 2 in 2012.[9]
Stratotype
Possible candidates for a GSSP include the first appearance of Watsonella crosbyi in the Zhujiaqing Formation (朱家庆组) in Yunnan, China or the Pestrotsvet Formation near the Aldan River on the Siberian Platform.[10]
References
External links
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