The Pongola glaciation is a glacial episode that occurred in the
Mesoarchean, 2.9
Ga ago for about 150 Ma. It is the oldest known glaciation on the planet.
Geology
The oldest known traces of glaciation date from the
Mesoarchean. They correspond to the
diamictite of the Pongola supergroup[1] (more precisely to the Mozaan formation,[2]) in
KwaZulu-Natal and in
Eswatini.[3]
Climate
Even if the climate of the Archean is not well known, the study of the
oxygen isotopes in the
cherts of the time seem to show that the climate of the
Archean was warm or, at least, temperate,[4] in particular due to high levels of methane and carbon dioxide in the atmosphere; a glaciation around 2.9 Ga is therefore likely to have been caused by a drop in the rate of these greenhouse gases.[5][6] The Pongola glaciation is also associated with changes in sulfur isotopes (δ34S), suggesting that this may also involve early and short-lived oxygenation of the Earth's atmosphere.[7][8]
Extension
The extension of the glaciation is not determined with certainty.[9][8] Some authors argue that the glacial deposits were formed at low latitudes, below 30° N,[10] therefore close to the tropics, which would imply extensive glaciation, while others argue that the area was located at mid-latitude[note 1] or even high latitude, closer to the pole, where a polar glacier could have formed, like the current situation.[11][12]
Regarding its duration, the corresponding glacial deposits fall within the interval 2985 ± 1 and 2837 ± 5 Ma.[8][13]
Notes & references
Notes
^The oldest known midlatitude glaciation, recorded in the Pongola Supergroup diamictite, occurred at 2.9 Ga.[1]
Young, Grant M.; von Brunn, Victor; Gold, Digby J. C.; Minter, W. E. L. (1998). "Earth's Oldest Reported Glaciation: Physical and Chemical Evidence from the Archean Mozaan Group (~2.9 Ga) of South Africa". The Journal of Geology. 106 (5): 523-538.
doi:
10.1086/516039.
S2CID129717765.
Gold, D.J.C.; Johnson, M.R.; Anhaeusser, C.R.; Thomas, Bob (2006). "The Pongola Supergroup. The geology of South Africa". Geol. Soc. South Afr.: 135-148.