| Cambrian Series 2 | ||||||||||||||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| ~521 – ~506.5Ma | ||||||||||||||||||||||||||||||||||||||
 A map of Earth 515 million years ago during the Cambrian's 2nd series, Stage 3 | ||||||||||||||||||||||||||||||||||||||
| Chronology | ||||||||||||||||||||||||||||||||||||||
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| Etymology | ||||||||||||||||||||||||||||||||||||||
| Name formality | Informal | |||||||||||||||||||||||||||||||||||||
| Usage information | ||||||||||||||||||||||||||||||||||||||
| Celestial body | Earth | |||||||||||||||||||||||||||||||||||||
| Regional usage | Global (ICS) | |||||||||||||||||||||||||||||||||||||
| Time scale(s) used | ICS Time Scale | |||||||||||||||||||||||||||||||||||||
| Definition | ||||||||||||||||||||||||||||||||||||||
| Chronological unit | Epoch | |||||||||||||||||||||||||||||||||||||
| Stratigraphic unit | Series | |||||||||||||||||||||||||||||||||||||
| Time span formality | Formal | |||||||||||||||||||||||||||||||||||||
| Lower boundary definition | Not formally defined | |||||||||||||||||||||||||||||||||||||
| Lower boundary definition candidates | FAD ofTrilobites | |||||||||||||||||||||||||||||||||||||
| Lower boundary GSSP candidate section(s) | None | |||||||||||||||||||||||||||||||||||||
| Lower GSSP ratified | Not formally defined | |||||||||||||||||||||||||||||||||||||
| Upper boundary definition | FAD ofOryctocephalus indicus. | |||||||||||||||||||||||||||||||||||||
| Upper boundary GSSP | Wuliu-Zengjiayan,Guizhou,China 26°04′51″N108°24′50″E / 26.0807°N 108.4138°E /26.0807; 108.4138 | |||||||||||||||||||||||||||||||||||||
| Upper GSSP ratified | June 25, 2018[2] | |||||||||||||||||||||||||||||||||||||
Cambrian Series 2 is the unnamed 2nd series of theCambrian. It lies above theTerreneuvian series and below theMiaolingian. Series 2 has not been formally defined by theInternational Commission on Stratigraphy, lacking a precise lower boundary and subdivision into stages. The proposed lower boundary is thefirst appearance oftrilobites which is estimated to be around 521 million years ago.[3][4]
TheInternational Commission on Stratigraphy has not named the 2nd series of theCambrian yet.[3] In part the new name will replace the older terms "Lower Cambrian" and "Early Cambrian". The nomenclature used in Siberia uses the term "Yakutian" for this series.[5]
The 2nd series is currently subdivided by theICS into two stages:Cambrian Stage 3 andCambrian Stage 4. Both of these stages also lack formal definition.[3] The Siberian nomenclature distinguishes three stages (lowest first):Atdabanian,Botomian andToyonian.[5] In general most subdivisions of this series rely on biostratigraphy oftrilobite zones.[6]
The Ordian stage, which is use in Australian chronostratigraphical scale, was originally supposed to be the lowest stage of the Miaolingian, but may belong to upper Series 2. As of 2024, the base of the Ordian is not defined yet.[7]
The beginning of the 2nd series of the Cambrian is marked by the appearance oftrilobites. Correlating this event on different continents has proven difficult and resolving this is essential for the definition of the lower boundary of this series. Currently the oldest trilobite known isLemdadella which marks the beginning of theFallotaspis zone.[6]
The end of the 2nd series of the Cambrian is marked by the first major biotic extinction of thePaleozoic. Changes inocean chemistry and the marine environment are posited as the most likely cause of this extinction.[8] At the Series 2–Miaolingian boundary, the first major trilobite extinction, known as theOlenellid Biomere boundary, occurred. In particular, trilobites of the familiesOlenellidae andRedlichiidae have been extinct inLaurentia and South China, respectively.[9] The firstO. indicus appear after this global extinction, and in areas whereO. indicus fossils are absent, the Series 2–Miaolingian boundary is determined bychemostratigraphic data.[10]
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