Cambrian Series 2 is the unnamed 2nd series of the

Cambrian The Cambrian ( ) is the first geological period of the Paleozoic Era, and the Phanerozoic Eon. The Cambrian lasted 51.95 million years from the end of the preceding Ediacaran period 538.8 Ma (million years ago) to the beginning of the Ordov ...

. It lies above the

Terreneuvian The Terreneuvian is the lowermost and oldest Series (stratigraphy), series of the Cambrian geological System (stratigraphy), system. Its base is defined by the first appearance datum of the trace fossil ''Treptichnus pedum'' around million years ...

series and below the Miaolingian. Series 2 has not been formally defined by the

International Commission on Stratigraphy The International Commission on Stratigraphy (ICS), sometimes unofficially referred to as the International Stratigraphic Commission, is a daughter or major subcommittee grade scientific organization that concerns itself with stratigraphy, strati ...

, lacking a precise lower boundary and subdivision into stages. The proposed lower boundary is the

first appearance In comic books and other stories with a long history, first appearance refers to the first issue to feature a fictional character. These issues are often highly valued by collectors due to their rarity and iconic status. Reader interest in fir ...

trilobites Trilobites (; meaning "three-lobed entities") are extinct marine arthropods that form the class Trilobita. One of the earliest groups of arthropods to appear in the fossil record, trilobites were among the most successful of all early animals, ...

which is estimated to be around million years ago.

Naming

The

has not named the 2nd series of the

yet. 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.

Subdivisions

The 2nd series is currently subdivided by the ICS into two stages:

Cambrian Stage 3 Cambrian Stage 3 is the still unnamed third stage of the Cambrian. It succeeds Cambrian Stage 2 and precedes Cambrian Stage 4, although neither its base nor top have been formally defined. The plan is for its lower boundary to correspond approxima ...

and Cambrian Stage 4. Both of these stages also lack formal definition. The Siberian nomenclature distinguishes three stages (lowest first): Atdabanian, Botomian and Toyonian. In general most subdivisions of this series rely on biostratigraphy of trilobite zones. 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.

Biostratigraphy

The beginning of the 2nd series of the Cambrian is marked by the appearance of

. 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 is '' Lemdadella'' which marks the beginning of the ''Fallotaspis'' zone. The end of the 2nd series of the Cambrian is marked by the first major biotic extinction of the

Paleozoic The Paleozoic ( , , ; or Palaeozoic) Era is the first of three Era (geology), geological eras of the Phanerozoic Eon. Beginning 538.8 million years ago (Ma), it succeeds the Neoproterozoic (the last era of the Proterozoic Eon) and ends 251.9 Ma a ...

. Changes in ocean chemistry and the marine environment are posited as the most likely cause of this extinction. At the Series 2–Miaolingian boundary, the first major trilobite extinction, known as the Olenellid Biomere boundary, occurred. In particular, trilobites of the families Olenellidae and Redlichiidae have been extinct in

Laurentia Laurentia or the North American craton is a large continental craton that forms the Geology of North America, ancient geological core of North America. Many times in its past, Laurentia has been a separate continent, as it is now in the form of ...

and South China, respectively. The first ''O. indicus'' appear after this global extinction, and in areas where ''O. indicus'' fossils are absent, the Series 2–Miaolingian boundary is determined by chemostratigraphic data.

References

External links

* * {{Geological history, p, p, state=collapsed *02 Geological epochs