Abstract
The geological time scale before 720 Ma uses rounded absolute ages rather than specific events recorded in rocks to subdivide time. This has led increasingly to mismatches between subdivisions
and the features for which they were named. Here we review the formal processes that led to the current time scale, outline rock-based concepts that could be used to subdivide pre-Cryogenian time
and propose revisions. An appraisal of the Precambrian rock record confirms that purely chronostratigraphic subdivision would require only modest deviation from current chronometric boundaries, removal of which could be expedited by establishing event-based concepts and provisional, approximate ages for eon-, era- and period-level subdivisions. Our review leads to the following conclusions: 1) the current informal four-fold Archean subdivision should be simplified to a tripartite scheme, pending more detailed analysis, and 2) an improved rock-based Proterozoic Eon
might comprise a Paleoproterozoic Era with three periods (early Paleoproterozoic or Skourian, Rhyacian, Orosirian), Mesoproterozoic Era with four periods (Statherian, Calymmian, Ectasian, Stenian) and a Neoproterozoic Era with four periods (pre-Tonian or Kleisian, Tonian, Cryogenian and Ediacaran). These proposals stem from a wide community and could be used to guide future development of the pre-Cryogenian timescale by international bodies.
and the features for which they were named. Here we review the formal processes that led to the current time scale, outline rock-based concepts that could be used to subdivide pre-Cryogenian time
and propose revisions. An appraisal of the Precambrian rock record confirms that purely chronostratigraphic subdivision would require only modest deviation from current chronometric boundaries, removal of which could be expedited by establishing event-based concepts and provisional, approximate ages for eon-, era- and period-level subdivisions. Our review leads to the following conclusions: 1) the current informal four-fold Archean subdivision should be simplified to a tripartite scheme, pending more detailed analysis, and 2) an improved rock-based Proterozoic Eon
might comprise a Paleoproterozoic Era with three periods (early Paleoproterozoic or Skourian, Rhyacian, Orosirian), Mesoproterozoic Era with four periods (Statherian, Calymmian, Ectasian, Stenian) and a Neoproterozoic Era with four periods (pre-Tonian or Kleisian, Tonian, Cryogenian and Ediacaran). These proposals stem from a wide community and could be used to guide future development of the pre-Cryogenian timescale by international bodies.
| Original language | English |
|---|---|
| Article number | jgs2020-222 |
| Number of pages | 22 |
| Journal | Journal of the Geological Society |
| Volume | 179 |
| Issue number | 1 |
| Early online date | 7 Jun 2021 |
| DOIs | |
| Publication status | Published - 1 Jan 2022 |
Bibliographical note
AcknowledgementsThe authors represent an international working group of the International Commission on Stratigraphy on pre-Cryogenian chronostratigraphic subdivision. We are greatly indebted to many people who have provided comments, encouragement and helpful advice on various drafts of this article from its early green paper stage, including the ICS executive officers David Harper, Brian
Huber, Phil Gibbard and Shuzhong Shen, the IUGS general secretary Stan Finney, and the following people who commented on various draft versions Phil Donoghue, A.K. Jain, Vivek Kale, Mihir Deb, M.
Jayananda, Jyotiranjan Ray, Aivo Lepland, Peter Haines, Thomas Vandyk and Martin Whitehouse. New period names were suggested by A. Bekker (Scourian/Skourian), D. Evans (Kleisian, Syndian) and G. Shields (Kratian). We thank Peter Cawood, Damian Nance for detailed review comments and Deta Gasser for helpful editorial advice that greatly improved the final manuscript