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Sturtian-Varangian

From Academic Kids

The Sturtian-Varangian (also known as the Cryogenian) is a late Precambrian world-wide glaciation episode ranging from 950Ma to 600Ma, represented by tillite deposits in Congo, Australia, China, North America, Sahara and Norway. It is generally considered to be divisible into at least two (Sturtian around 800Ma and Marinoan/Varanger 650Ma) or four significant glaciation extremes. The tillite deposits occurred also in what is believed to be low latitudes, which lead to the hypothesis of Snowball Earth

The population of acritarchs crashed during this glaciation and it is claimed that oxygen levels in the atmosphere increased after the glaciation. There are a number of enigmatic features with regard to this glaciation including indications of glaciation at very low latitudes and the presence of limestones -- normally warm water sediments above, below and intermixed with glacial deposits. Paleomagnetism seems to indicate very high continental drift rates leading some geologists to question whether some of the phenomena might be due to magnetic pole wandering rather than plate motion and low latitude glaciation. Evidence of the glaciation is found in various places and times: The Congo River basin from 950-750Ma and 620-600Ma. Australia from 800-780Ma and 690-680Ma. China 800-760Ma, 740-700Ma and 600Ma; Western North America 850-800Ma, Sahara 730-650Ma, Norway 650Ma. Spitsbergen 593-573Ma.

Other known world wide glaciations include the Huronian from 2400Ma to 2100Ma, Andean-Saharan from 450-420Ma, the Karoo glaciation from 360Ma to 260Ma, and the Cenozoic glaciation which started 30Ma in Antarctica and are not over.

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