The Paibian is the lowest stage of the Furongian 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 ...

System A system is a group of interacting or interrelated elements that act according to a set of rules to form a unified whole. A system, surrounded and influenced by its open system (systems theory), environment, is described by its boundaries, str ...

. The Paibian is also the first age of the Furongian

Epoch In chronology and periodization, an epoch or reference epoch is an instant in time chosen as the origin of a particular calendar era. The "epoch" serves as a reference point from which time is measured. The moment of epoch is usually decided b ...

of the Cambrian Period. It follows the Guzhangian ( Miaolingian series of the Cambrian) and is succeeded by the Jiangshanian Stage. The base is defined as the first appearance of the trilobite '' Glyptagnostus reticulatus'' around million years ago. The top, or the base of the Jiangshanian is defined as the first appearance of the trilobite '' Agnostotes orientalis'' around million years ago.

GSSP

The name is derived from Paibi, a village in

Hunan Hunan is an inland Provinces of China, province in Central China. Located in the middle reaches of the Yangtze watershed, it borders the Administrative divisions of China, province-level divisions of Hubei to the north, Jiangxi to the east, Gu ...

, China. The GSSP is defined in the "Paibi section" ( Wuling Mountains, Huayuan County), an outcrop of the Huaqiao Formation (花桥组). The base is the first occurrence of '' Glyptagnostus reticulatus'' which is 396 m above the base of the Huaqiao Formation at the type locality ().

Major events

At the turn of the Guzhangian and Paibian ages, an extinction event occurred that reduced the species richness by 45%. This event coincided with Marjuman extinction that can be traced to trilobite and

brachiopod Brachiopods (), phylum (biology), phylum Brachiopoda, are a phylum of animals that have hard "valves" (shells) on the upper and lower surfaces, unlike the left and right arrangement in bivalve molluscs. Brachiopod valves are hinged at the rear e ...

assemblages in Laurentia. Two phases of extinction can be traced in the sediments of South China: the first, with a slight decline in species, lasted in Guzhangian, about 1.8 million years; the second, with a sharper decline in richness, lasted 1.2 million years, more in the Paibian. After the extinction, species diversity returned to its previous level. Steptoean positive carbon isotope excursion (SPICE) began around the Guzhangian-Paibian boundary. This event is associated with a global carbon-cycle perturbation. The driving mechanism of this change are not fully understood, but it is believed to be caused by the expansion of anoxic deep water into shallow regions. SPICE event had a noticeable impact on trilobites. A decrease in their diversity is observed at the beginning and at the termination of its interval, which coincides with the Laurentian End-Marjuman Biomere Extinction (EMBE) and the End-Steptoean Biomere Extinction (ESBE), respectively. The SPICE event was accompanied by cooling, which contributed to the recovery of ecosystems after its onset, but the further warming disrupted the circulation of ocean waters and triggered new redox changes that precipitated the ESBE.

Paleontology

Agnostoid genera, including ''Glyptagnostus'', '' Homagnostus'', '' Pseudagnostus'' and '' Acmarhachis'', are known from the Paibian deposits.

References

External links

* * * Cambrian geochronology Geological ages {{cambrian-stub