marinoan glaciation

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      The Marinoan glaciation, sometimes also known as the Varanger glaciation, was a period of worldwide glaciation.
      Its beginning is poorly constrained, but occurred no earlier than 654.5 Ma (million years ago).
      It ended approximately 632.3 ± 5.9 Ma
      during the Cryogenian period. This glaciation possibly covered the entire planet, in an event called the Snowball Earth. The end of the glaciation was caused by volcanic release of carbon dioxide and dissolution of gas hydrates
      and may have been hastened by the release of methane from equatorial permafrost.


      Origin of name and history of terminology


      The name is derived from the stratigraphic terminology of the Adelaide Geosyncline (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. The corresponding time period, referred to as the Marinoan Epoch, spanned from the middle Cryogenian to the top of the Ediacaran in modern terminology. Mawson recognised a glacial episode within the Marinoan Epoch which he referred to as the Elatina glaciation after the 'Elatina Tillite' (now Elatina Formation) where he found the evidence. However, the term Marinoan glaciation came into common usage because it was the glaciation that occurred during the Marinoan Epoch, as distinct from the earlier glaciation during the Sturtian Epoch (the time period of deposition of the older Sturtian Series).
      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.


      Cryogenian Snowball Earth



      Emerging evidence suggests that the Earth underwent a number of glaciations during the Neoproterozoic era. There were three (or possibly four) significant ice ages during the late Neoproterozoic. These periods of nearly complete glaciation of Earth are often referred to as "Snowball Earth", where it is hypothesized that at times the planet was covered by ice 1–2 km (0.62–1.24 mi) thick. Of these glaciations, the Sturtian glaciation was the most significant, whereas the Marinoan was a shorter, but still worldwide glaciation. Other Cryogenian glaciations were probably small and not global as compared to the Marinoan or Sturtian glaciations.
      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. Deglaciation likely started in the mid-latitudes, as in the tropics, the intense hydrological cycle replenished snow rapidly. As the mid-latitudes became ice free, dust was blown from them into other regions, lowering albedo and speeding up deglaciation.


      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 barite), and other unusual sedimentary structures. Two diamictite-rich layers in the top 1 km (0.62 mi) of the 7 km (4.3 mi) 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.


      See also


      Sturtian glaciation
      Adelaide Rift Complex
      Huronian glaciation


      Notes




      References

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    marinoan glaciation

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    Marinoan glaciation - Wikipedia

    The Marinoan glaciation, sometimes also known as the Varanger glaciation, [3] was a period of worldwide glaciation. [4] Its beginning is poorly constrained, but occurred no earlier than 654.5 Ma (million years ago). [5] It ended approximately 632.3 ± 5.9 Ma [4] during the Cryogenian period.

    Marinoan glaciation | geology | Britannica

    …and glaciers associated with the Marinoan (or Varanger-Marinoan) glaciation—which began near the end of the Cryogenian Period and ended approximately 635 million years ago—and declines in the carbon isotope composition of marine rocks. Oxygen levels rose in the atmosphere and in the oceans, and many scholars suggest that the change…

    Sturtian glaciation - Wikipedia

    The Sturtian glaciation is an informal, but commonly used name for the older of two worldwide glacial events (the other is known as the Marinoan/Elatina glaciation) preserved in Cryogenian rocks. [6]

    Glacial fluctuations in the Cryogenian Marinoan Snowball Earth

    The Marinoan glaciation represents the pinnacle of glacial severity in Earth’s geological history. Deep-water glacial deposits have revealed a complex interplay of at least two glacial advance-retreat cycles.

    Duration and nature of the end-Cryogenian (Marinoan) glaciation

    Aug 1, 2016 · The end-Cryogenian glaciation (Marinoan) is portrayed commonly as the archetype of snowball Earth, yet its duration and character remain uncertain. Here we report U-Pb zircon ages for two ash beds from widely separated localities of the Marinoan-equivalent Ghaub Formation in Namibia: 639.29 ± 0.26 Ma and 635.21 ± 0.59 Ma.

    Ocean oxygenation in the wake of the Marinoan glaciation

    Sep 26, 2012 · It has been suggested that an oxygenation event in the wake of the severe Marinoan glaciation was the driving factor behind this early diversification of metazoans and the shift in ecosystem ...

    Exploring climate variability during the Marinoan glaciation: A …

    Apr 1, 2024 · The Marinoan glaciation is the younger of the two extraordinary glaciations during the Cryogenian Period. It has been debated whether the glacial world was featured by a complete ice cover or if parts of the oceans remained ice free.

    Active methanogenesis during the melting of Marinoan snowball …

    Feb 11, 2021 · Geological evidence indicates that the deglaciation of Marinoan snowball Earth ice age (~635 Myr ago) was associated with intense continental weathering, recovery of primary productivity,...

    Three-stage formation of cap carbonates after Marinoan ... - Nature

    Aug 15, 2024 · Here, we present a global geologic carbon cycle model before, during, and after the second glaciation (i.e. the Marinoan) that explains cap carbonate characteristics.

    Marine redox fluctuations during the Marinoan glaciation

    Apr 1, 2024 · The dynamic Marinoan glaciation featured alternating marine red beds and diamictites in the Nantuo Formation. The scattered micro-hematite particles indicate the dehydration of iron (oxy)hydroxides, precipitating directly from the water column.