Cambrian Stage 5
Stage 5 of the Cambrian is the first stage of the 3rd series of the Cambrian (or Middle Cambrian). Its lower boundary has not been formally defined by the ICS yet. The most promising definition is the first appearance of either the trilobite species Oryctocephalus indicus or Ovatoryctocara granulata which is currently estimated to be around ~509 million years ago. The end of Cambrian Stage 5 and the beginning of the Drumian stage is marked by the first appearance of the trilobite Ptychagnostus atavus around ~504.5 million years ago.
The International Commission on Stratigraphy has not officially named the 5th stage of the Cambrian. A likely candidate for the name is "Molodian", named after the river Molodo in Bulunsky District, Sakha Republic, Russia.
Three sections are currently discussed as GSSP candidates: the Wuliu-Zengjiayan section near Balang in Guizhou province (China), a section on Split Mountain in Nevada (USA) and the "Molodo river section" along the Molodo river. The Wuliu-Zengjiayan section is an outcrop of the Kaili Formation in the Wuliu quarry. The first candidate for the beginning of Stage 5 is the trilobite Oryctocephalus indicus, the second candidate is the trilobite Ovatoryctocara granulata. 
- 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: n/a–n/a. doi:10.1002/gj.1330.
- "GSSP Table - Paleozoic Era". Retrieved 15 November 2012.
- "The 13th International Field Conference of the Cambrian Stage Subdivision Working Group". Episodes 31 (4): 440–441.
- Sundberg, F.A.; Zhao, Y.L.; Yuan, J.L.; Lin, J.P. (22 September 2011). "Detailed trilobite biostratigraphy across the proposed GSSP for Stage 5 ("Middle Cambrian" boundary) at the Wuliu-Zengjiayan section, Guizhou, China". Bulletin of Geosciences: 423–464. doi:10.3140/bull.geosci.1211.
|Preceded by Proterozoic Eon||542 Ma - Phanerozoic Eon- Present|
|542 Ma - Paleozoic Era -251 Ma||251 Ma - Mesozoic Era - 66 Ma||66 Ma - Cenozoic Era - Present|