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.[1] Neither the upper nor lower boundary has yet been defined by the International Commission on Stratigraphy.[2] The preferred definitions for the lower boundary are the first appearance of the molluscs Watsonella crosbyi or Aldanella attleborensis around 529 million years ago.[3] The proposed upper boundary might be the first appearance of trilobites around 521 million years ago.[2]

Cambrian Stage 2
~529 – ~521 Ma
Chronology
Key events in the Cambrian
-540 —
-535 —
-530 —
-525 —
-520 —
-515 —
-510 —
-505 —
-500 —
-495 —
-490 —
-485 —
Orsten Fauna
Archaeocyatha extinction
SSF diversification, first brachiopods & archaeocyatha
Dresbachian extinction
Stratigraphic scale of the ICS subdivisions and Precambrian/Cambrian boundary.
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 candidatesFirst appearance of small shelly fauna or Archaeocyathids
Lower boundary GSSP candidate section(s)None
Upper boundary definitionNot formally defined
Upper boundary definition candidatesFAD 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.[4]

ReferencesEdit

  1. ^ 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.
  2. ^ a b "GSSP List ICS". ICS. Archived from the original on 15 November 2012. Retrieved 9 November 2012.
  3. ^ "International Commission on Stratigraphy".
  4. ^ 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.