Marinoan glaciation

Origin of name and history of terminology

The name is derived from the stratigraphic terminology of the Adelaide Superbasin (Adelaide Rift Complex) in South Australia and is taken from the Adelaide suburb of Marino. The term Marinoan Series was first used in a 1950 paper by Douglas Mawson and Reg Sprigg to subdivide the Neoproterozoic rocks of the Adelaide area, and encompassed all strata from the top of the Brighton Limestone to the base of the Cambrian.{{cite journal| author = Mawson, D.|author2=Sprigg, R.C.| year = 1950| title = Subdivision of the Adelaide System| journal = Australian Journal of Science| volume = 13| pages = 69–72

The term Marinoan glaciation was later applied globally to any glaciogenic formations assumed (directly or indirectly) to correlate with Mawson's original Elatina glaciation in South Australia. Recently, there has been a move to return to the term Elatina glaciation in South Australia because of uncertainties regarding global correlation and because an Ediacaran glacial episode (Gaskiers) also occurs within the wide-ranging Marinoan Epoch.{{cite journal

Cryogenian Snowball Earth

Emerging evidence suggests that the Earth underwent a number of glaciations during the Neoproterozoic era.{{cite journal

During the Marinoan glaciation, characteristic glacial deposits indicate that Earth suffered one of the most severe ice ages in its history. Glaciers extended and contracted in a series of rhythmic pulses, possibly reaching as far as the equator.

The Earth may not have been fully covered in ice, as some computer simulations show an extreme slowdown of the hydrological cycle that inhibited new glacial formation before the Earth was fully ice-covered.

The melting of the Snowball Earth is associated with greenhouse warming due to the accumulation of high levels of carbon dioxide in the atmosphere.{{cite journal

Evidence

Even though much evidence has been lost through geological changes, field investigations show evidence of the Marinoan glaciation in China, Svalbard archipelago and South Australia. In Guizhou Province, China, glacial rocks were found to be underlying and overlying a layer of volcanic ashes which contained zircon minerals, which could be dated through radioisotopes. Glacial deposits in South Australia are approximately the same age (about 630 Ma), confirmed by similar stable carbon isotopes, mineral deposits (including sedimentary baryte), and other unusual sedimentary structures. Two diamictite-rich layers in the top 1 km of the 7 km Neoproterozoic strata of the northeastern Svalbard archipelago represent the first and final phases of the Marinoan glaciation. In Uruguay, evidence of the Marinoan glaciation is known from dropstones, diamictites, rhythmites, clast layers, and varve-like deposits.

According to Eyles and Young, the Marinoan is a second episode of Neoproterozoic glaciation (680–690 Ma) occurring in the Adelaide Geosyncline. According to them, "It is separated from the Sturtian by a thick succession of sedimentary rocks containing no evidence of glaciation. This glacial phase could correspond to the recently described Ice Brooke formation in the northern Cordillera."

Effects on life

The survival of benthic macroalgae indicates that there remained areas of suitable habitat for them in the photic zone along the coasts of mid-latitude continents during the Marinoan glaciation.

Notes

References

References

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