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A new rock-based definition for the Cryogenian Period (circa 720 - 635 Ma)

Shields-Zhou, GA; Porter, S; Halverson, GP; (2016) A new rock-based definition for the Cryogenian Period (circa 720 - 635 Ma). Episodes , 39 (1) pp. 3-8. 10.18814/epiiugs/2016/v39i1/89231. Green open access

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Abstract

The Cryogenian Period was first established in 1988 along with other Precambrian eon, era and period-level subdivisions that were defined numerically by Global Standard Stratigraphic Ages (GSSAs). As absolute age constraints have improved, some of these time intervals no longer bracket adequately the geological event(s), for which they were named. For example, the age discrepancy between the basal Cryogenian GSSA at 850 Ma and the onset of widespread glaciation ca. 717 Ma has rendered the 850 Ma boundary obsolete. The International Commission on Stratigraphy has now formally approved the removal of the Cryogenian GSSA from its International Chronostratigraphic Chart and supports its replacement with a rock-based Global Stratotype Section and Point (GSSP). The new Cryogenian GSSP will be placed at a globally correlative level that lies stratigraphically beneath the first appearance of widespread glaciation and is assigned in the interim a 'calibrated age' of circa 720 Ma. This new definition for the Tonian/Cryogenian boundary should be used in future publications until a formal Cryogenian GSSP can be ratified. The change marks progress towards establishment of a 'natural' (rock-based) scale for Precambrian time.

Type: Article
Title: A new rock-based definition for the Cryogenian Period (circa 720 - 635 Ma)
Open access status: An open access version is available from UCL Discovery
DOI: 10.18814/epiiugs/2016/v39i1/89231
Publisher version: http://dx.doi.org/10.18814/epiiugs/2016/v39i1/8923...
Language: English
Additional information: Copyright © International Union of Geological Sciences.
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Earth Sciences
URI: https://discovery.ucl.ac.uk/id/eprint/1496826
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