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]

Key events in the Cambrian

-540 —

–

-535 —

–

-530 —

–

-525 —

–

-520 —

–

-515 —

–

-510 —

–

-505 —

–

-500 —

–

-495 —

–

-490 —

–

-485 —

–

N
P
Z

P
a
l
e
o
z
o
i
c

Ediacaran

C
a
m
b
r
i
a
n

Ordovician

T
e
r
r
e
n
e
u
v
i
a
n

S
e
r
i
e
s

2

M
i
a
o
l
i
n
g
i
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n

F
u
r
o
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g
i
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n

Fortunian

"Stage 2"

"Stage 3"

"Stage 4"

Wuliuan

Drumian

Guzhangian

Paibian

Jiangshanian

"Stage 10"

 

 

 

 

 

 

 

 

 

 

←

Orsten Fauna

←

Burgess Shale

←

Kaili biota

←

Archaeocyatha extinction

←

Emu Bay Shale

←

Sirius Passet biota

←

Chengjiang biota

←

First Trilobites

←

SSF diversification, first brachiopods & archaeocyatha

←

First halkieriids, mollusсs, hyoliths SSF

←

Treptichnus pedum trace
Large negative peak δ 13C_carb excursion

←

Baykonurian glaciation

 Major Glacial period

Stratigraphic scale of the ICS subdivisions and Precambrian/Cambrian boundary.

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]

References

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. "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.