Concept information
Terme préférentiel
Cryogenian
Définition
- The Cryogenian (from Ancient Greekromanized: krýos, meaning "cold" and romanized: génesis, meaning "birth") is a geologic period that lasted from 720 to 635 million years ago. It forms the second geologic period of the Neoproterozoic Era, preceded by the Tonian Period and followed by the Ediacaran. The Cryogenian was a time of drastic biosphere changes. After the previous Boring Billion years of stability, at the beginning of Cryogenian the severe Sturtian glaciation began, freezing the entire Earth in a planetary state known as a Snowball Earth. After 70 million years it ended, but was quickly followed by the Marinoan glaciation, which was also a global event. These events are the subject of much scientific controversy specifically over whether these glaciations covered the entire planet or a band of open sea survived near the equator (termed "slushball Earth"). The name of the geologic period refers to the very cold global climate of the Cryogenian. Characteristic glacial deposits indicate that Earth suffered the most severe ice ages in its history during this period (Sturtian and Marinoan). According to Eyles and Young, "Late Proterozoic glaciogenic deposits are known from all the continents. They provide evidence of the most widespread and long-ranging glaciation on Earth." Several glacial periods are evident, interspersed with periods of relatively warm climate, with glaciers reaching sea level in low paleolatitudes. Glaciers extended and contracted in a series of rhythmic pulses, possibly reaching as far as the equator. Diamictite of the Elatina Formation in South Australia, formed during the Marinoan glaciation of the late Cryogenian. The Cryogenian is generally considered to be divisible into at least two major worldwide glaciations. The Sturtian glaciation persisted from 720 to 660 million years ago, and the Marinoan glaciation which ended approximately 635 Ma, at the end of the Cryogenian. The deposits of glacial tillite also occur in places that were at low latitudes during the Cryogenian, a phenomenon which led to the hypothesis of deeply frozen planetary oceans called "Snowball Earth". Between the Sturtian and Marinoan glaciations was a so-called "Cryogenian interglacial period" marked by relatively warm climate and anoxic oceans, along with marine transgression. (Adapted from: https://en.wikipedia.org/wiki/Cryogenian)
Concept générique
Traductions
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français
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glaciation Varanger
URI
http://data.loterre.fr/ark:/67375/QX8-D87X9G1P-H
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