Furongian

The Furongian is the fourth and final epoch and series of the Cambrian. It lasted from 497 to 486.85 million years ago. It succeeds the Miaolingian series of the Cambrian and precedes the Lower Ordovician Tremadocian Stage. It is subdivided into three stages: the Paibian, Jiangshanian and the unnamed 10th stage of the Cambrian.

The Furongian was also known as the Cambrian Series 4, and the name replaced the older term Upper Cambrian and equivalent to the local term Hunanian. The present name was ratified by the International Commission on Stratigraphy in 2003. Fúróng (芙蓉) means 'lotus' in Mandarin and refers to Hunan which is known as the "lotus state".

The lower boundary is defined in the same way as the GSSP of the Paibian Stage. Both begin with the first appearance of the trilobite Glyptagnostus reticulatus around 497 million years ago. The upper boundary is the lower boundary and GSSP of the Tremadocian Stage which is the first appearance of the conodont Iapetognathus fluctivagus around 486.85 million years ago.

The following table shows the subdivisions of the Furongian series/epoch:

The base of two of three stages of the Furongian are defined as the first appearance of a trilobite. The base of the Paibian is the first appearance of Glyptagnostus reticulatus and the base of the Jiangshanian is the first appearance of Agnostotes orientalis. The still unnamed Cambrian Stage 10 might be defined as the first appearance of Lotagnostus americanus or the conodont Eoconodontus notchpeakensis.

The Furongian can be divided into a number of trilobite zones:

At the beginning of the Furongian epoch, the Guzhangian–Paibian extinction ended. Species diversity, which had decreased by 45%, returned to its previous level at the very beginning of the Jiangshanian age. The ensuing Jiangshanian extinction reduced species diversity by 55.2% and was followed by an interval of relatively small fluctuations in species richness, which ended shortly after the beginning of the Ordovician.

Steptoean positive carbon isotope excursion (SPICE) occurred in close proximity in time to the Miaolingian–Furongian boundary (and, accordingly, the Guzhangian–Paibian boundary). This event is recorded on almost all Cambrian paleocontinents, but its exact causes are not fully understood. It is assumed that it may be associated with the Sauk megasequence, which in turn is associated with sea level changes; decrease in oxygen or occurrence of euxinic conditions in ocean waters; or the trilobite biomere turnover.