Chapter 18 - The Ediacaran Period

Abstract

The Ediacaran Period (635–538Ma) has the longest duration among all stratigraphically defined geological periods. The basal boundary of the Ediacaran System is defined by a horizon near the base of the Nuccaleena Formation overlying the Cryogenian diamictite of the Elatina Formation at the Enorama Creek section in South Australia. Most Ediacaran fossils represent soft-bodied organisms and their preservation is affected by taphonomic biases. Thus the Phanerozoic approach of defining stratigraphic boundaries using the first appearance datum of widely distributed, rapidly evolving, easily recognizable, and readily preservable species would have limited success in the Ediacaran System. The subdivision and correlation of the Ediacaran System must therefore be founded on a holistic approach integrating biostratigraphic, chemostratigraphic, paleoclimatic and geochronometric data, particularly carbon and strontium isotopes, glacial diamictites, acanthomorphic acritarchs, Ediacara-type megafossils, and certain tubular fossils. Our preferred scheme is to divide the Ediacaran System into two series separated by the 580Ma Gaskiers glaciation. Stage-level subdivisions at the bottom and top of the Ediacaran System, including the definition of the second Ediacaran stage (SES) and the terminal Ediacaran stage (TES), are feasible in the near future. Additional Ediacaran stages between the SES and TES can be envisioned, but formal definition of these stages are not possible until various stratigraphic markers are thoroughly tested and calibrated at both regional and global scales.