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Neoproterozoic Glaciation—Snowball Earth Hypothesis

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... During the Cryogenian Period, Earth experienced global glacial events where the whole Earth was covered by ice (Snowball hypothesis, Hoffman and Schrag, 2002) followed by postglacial greenhouse eras. Three glacial events are recorded; Gaskiers, 585-582 Ma, Marinoan, ~650-640-635 Ma and Sturtian, 717-660 Ma (Condon et al., 2005;Hoffman et al., 1998;Hoffman and Schrag, 2002;Rooney et al., 2015;Stern and Miller, 2019). Only the Sturtian and Marinoan events were global (Rooney et al., 2015). ...
... Age constrains of UZF and age of metamorphism suggest that sedimentation commenced at 825 Ma and lasted until 659 Ma (Eyal et al., 2014;Moghazi et al., 2012). In this time span, Earth witnessed an affirmed snowball earth event i.e., Sturtian (717-660 Ma) (Condon et al., 2005;Hoffman et al., 1998;Hoffman and Schrag, 2002;Rooney et al., 2015;Stern and Miller, 2019). Age wise, UZF could have been deposited during this snowball event, however, features characteristic of the glaciation event are only noted in the uppermost part of the UZF, i.e., around 660 Ma. ...
Article
Despite the vast extent of the Arabian Nubian Shield (ANS) and its growth during the renowned Neoproterzoic dramatic climatic changes (Snowball Earth Events), only few records of snowball events are identified among its rocks. Here we present geological and geochemical evidence that the northern part of the Arabian Nubian Shield (Um Zariq Formation (UZF), southeast Sinai, Egypt) witnessed global snowball event(s). The UZF was deposited in a convergent plate margin during Cryogenian and comprises metapelitic schists and cap-carbonates on top. The whole succession underwent amphibolite facies metamorphism around 660 Ma ago. In the upper most part of the metapelitic schists, intercalations of conglomeritic, poorly sorted components and large pebbles show many features comparable to metamorphosed diamictites and dropstones. The arsenic (As) contents of metapelites are 1–3 orders of magnitude higher than average phyllites. The high As contents and the presence, cap carbonates, diamictites and dropstones at UZF point toward deposition under glacial -postglacial conditions apparently during the Sturtian (717-660 Ma) snowball event.
... Here, we update what we know about ANS successions that contain evidence of Neoproterozoic climate and oxygenation events or whose deposition may have been contemporaneous with Neoproterozoic glaciations but have not been systematically studied for glacigenic influences ( Fig. 7.2). For background on evidence supporting Neoproterozoic glacigenic activity (i.e., glacial deposits such as diamictites and dropstones, regional-scale unconformities, cap carbonates, sedimentary iron formation, and globally synchronous low paleolatitude glaciation and deglaciation), the reader is referred to Stern et al. (2006), Hoffman et al. (2017, and Stern and Miller (2019). For background on triggering mechanisms of NSE episodes, the reader is referred to the synthesis in Stern and Miller (2018). ...
Chapter
Neoproterozoic evolution of the Arabian-Nubian Shield (ANS) and East African Orogen (EAO), 870–541 Ma, spanned revolutionary changes in Earth Systems, including a supercontinent cycle (Rodinia break-up, opening/closing of the Mozambique Ocean, Gondwana assembly), extreme climate fluctuations between long-lived glacial episodes as postulated by the Snowball Earth Hypothesis (1992–2002), marked increases in oceanic and atmospheric oxygen levels, and expansion of the biosphere from simple microbial life to the inclusion of larger and more diverse multicellular organisms. Understanding of these Earth System transitions has advanced tremendously over the past two decades through the integration of global studies of Neoproterozoic sedimentary successions with refined geochronologic techniques. This approach applied to Neoproterozoic Snowball Earth (NSE) localities now indicates that Neoproterozoic glaciations included two global-scale (panglacial) episodes, the ~717–659 Ma Sturtian and ~650–640 to 635 Ma Marinoan glaciations—which together comprise the Cryogenian Period, and more regional episodes during the Ediacaran Period and possibly, albeit controversially, during the earlier Tonian Period. Recent geochronologic, geochemical, and sedimentologic studies of low metamorphic grade ANS successions substantially contribute to the global Neoproterozoic dataset and, along with recently revised age constraints for the Cryogenian Period, facilitate an updated assessment of how Neoproterozoic glaciations may have influenced the sedimentary record of the ANS during its development. Tonian and Sturtian glaciations would have occurred following Rodinian break-up and major phases of juvenile crust formation in arc/island arc settings of the Mozambique Ocean (870–690 Ma), while latent terrane accretion and magmatism were still active. Paleogeographic reconstructions for these intervals generally place the ANS at tropical latitudes, where chemical weathering rates of juvenile crust terranes would have been high. Evidence supporting Tonian glaciation in the ANS is unresolved, with banded iron formation (BIF) and possible glacial diamictite scattered over the Central Eastern Desert (CED) of Egypt, NW Arabia, and possible correlative units in NE Sudan, as strongest candidates based on available age control (~780–740 Ma) and lithologic compatibility with NSE episodes. New age constraints for some of these localities (i.e., Atud diamictite and Um Nar, El-Hadid, Um Ghamis, and Wadi Kareim BIF localities in the CED) now demonstrate that deposition coincided with the Sturtian panglacial interval. Strong evidence of Sturtian glaciation in the ANS also occurs at the top of the Tonian-early Cryogenian Tambien Group in Northern Ethiopia, where polymict diamictite (<719.7 ± 0.5 Ma) bearing clasts consistent with glacial transport transitionally overlies limestone with pre-Sturtian ⁸⁷Sr/⁸⁶Sr values of 0.7066. Diamictite clast compositions similar to lower Tambien Group units suggest derivation from Tambien Group source terranes within the ANS, such as may have developed during early structural emergence of the EAO and/or associated eustatic sea-level fall. Carbonate units preserving negative carbon isotope excursions correlated to the ~800 Ma Bitter Springs anomaly, ~737 Ma Islay anomaly, and ~720 Ma pre-Sturtian transition, demonstrate that the Tambien Group is an important archive for studying the Tonian transition to extreme climates of the Cryogenian. The Marinoan (~645–635 Ma) glaciation overlapped with incipient development of the EAO, resulting from convergence, uplift, and structural deformation of earlier formed arc and accreted arc terranes, as the Mozambique Ocean closed between cratonic fragments of West and East Gondwana. Because most of the ANS was likely elevated above sea level, the ANS/EAO had few depocenters capable of preserving Marinoan sedimentation. Some peripheral margin basins, such as Murdama and Furayh basins in Arabia, overlapped with the Marinoan glaciation, but their sedimentary records have not been systematically studied for glacigenic characteristics. The onset of sedimentation in some post-amalgamation basins of the northern ANS (e.g., Jibalah Group of NW Arabia and possible equivalents in Jordan and Israel) may have overlapped with the Marinoan glaciation or Marinoan sediments could have been subsequently reworked in alluvial systems and redeposited during early basin formation. Following continental collision (~630–600 Ma), Ediacaran glaciations would have coincided with continued shortening and orogenic uplift (~600–540 Ma), when vast alluvial fan systems transported sediments away from EAO highlands. Ediacaran paleogeographic reconstructions generally place the ANS at higher tropical or temperate latitudes in the S. Hemisphere that may have supported regional scale glaciation. Within post-amalgamation basins of the northern Arabian Shield, the Jibalah Group sedimentary record includes polymict conglomerate, matrix-supported diamictite, and occasional dropstones that could be glacigenic. Regional deposition, constrained between underlying shield rocks (likely ≤605 ± 5 Ma) and the overlying Lower Cambrian basal unconformity (~540–520 Ma) and confirmed by U–Pb zircon dating of volcanic intervals within several basins, would have spanned the ~580 Ma Gaskiers glaciation, the ~575–567 Ma Shuram negative carbon isotope excursion, and younger Ediacaran glaciations. Although highly variable, sedimentary fill in many basins begins as polymict conglomerate with increasing limestone abundance in the higher succession, possibly consistent with a marine transgression. Carbonate δ¹³C values in combination with detrital zircon ages indicate that the basal conglomerate units pre-date the Shuram anomaly and could correlate with the ~580 Ma Gaskiers glaciation. Post-glacial supersequences may have been similarly deposited throughout northern Gondwana (Israel, Jordan, Saudi Arabia, Oman). Metazoan trace and probable body fossils are documented in Dhaiqa and Jifn basins above conglomeratic strata (Mataar Fm and Jifn Polymictic Conglomerate) that have been prospectively correlated with the Gaskiers glaciation. The lowest fossil horizons are no younger than 577 ± 5 Ma (Jifn) and 569 ± 3 Ma (Dhaiqa), similar to the Newfoundland record, where Ediacaran fauna appear ~9.5 myr after the ~580 Ma Gaskiers glaciation (Pu et al. in Geology 44:955–958, 2016). Follow-up studies are needed to assess the timing and glacigenic affinity of conglomerate and diamictite units, and to establish if and when marine deposition occurred within the Jibalah Group. A conspicuous stratigraphic feature of the northern Gondwanan margin is the widespread occurrence of an erosional unconformity throughout North Africa and Arabia separating Neoproterozoic basement from Cambro-Ordovician age sandstone that was principally sourced from erosion of the EAO. Although EAO erosion would have initiated as soon as regional uplift began, the exceptional power of Marinoan and Ediacaran ice sheets acting on a Himalaya-scale orogen may have contributed to ~650–540 Ma beveling of the Afro-Arabian Peneplain.
... The dug well sections observed in the annular moat of the Dhala structure comprise various sedimentary units (sandstone, pebbly sandstone, siltstone, sandy shale, and shale) that contain dropstones, convolute bedding, and related soft-sediment deformation structures (Pati, Reimold, et al., 2008;Pati et al., 2010Pati et al., , 2019. The occurrence of dropstones is the best evidence for glacial activity in the area (Stern & Miller, 2021). where late seismic activity has been observed at terrestrial impact structures (Poag et al., 2004;Baird et al., 2009). ...
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The ~450 million years of Neoproterozoic time (1000–542 Ma) was a remarkable episode of change in the Earth system and the biosphere. Here we develop and explore the hypothesis that explosive volcanism was at least partly responsible for Neoproterozoic climate change, synopsized as the “Volcanic winter to snowball Earth” (VW2SE) hypothesis. We review how climate cools as a result of sulfuric acid aerosols injected into the stratosphere by violent volcanic eruptions. A protracted increase in explosive volcanism could disrupt Earth’s radiative balance by continuously injecting sulfur aerosols into the stratosphere, causing cooling that could lead to glaciation. This mechanism would be especially effective when acting in concert with other agents for cooling. We show that the global Neoproterozoic magmatic flux was intense, so that explosive volcanism episodicly had a major effect on climate. Neoproterozoic volcanism and glacial activity happened about the same times in the Cryogenian and Ediacaran periods with no glaciation and reduced igneous activity in the Tonian Period. Glaciation followed soon after igneous activity increased as the supercontinent Rodinia broke apart, suggesting a causal relationship. The tectonic setting of climate-controlling explosive volcanism changed systematically over the Neoproterozoic supercontinent cycle, from extension-related early to arc-related late. Marinoan (~635 Ma) glaciation in particular corresponds to a peak time of subduction-related igneous activity in the Arabian-Nubian Shield and the East African Orogen. Isotopic chemostratigraphies are generally consistent with VW2SE hypothesis. These observations cumulatively support the VW2SE hypothesis as a viable explanation for what solid Earth processes caused Neoproterozoic climate oscillations.
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New stratigraphic, geochronological and palaeomagnetic constraints allow updates to be made to a synthesis of Neoproterozoic glacial palaeolatitudes, including modifications to some reliability estimates. The overall pattern of a Neoproterozoic climatic paradox persists: there is an abundance of tropical palaeolatitudes and near to complete absence of glaciogenic deposits demonstrably laid down between latitudes of 60° and 90°. In addition to 12 units with palaeolatitude estimates that are somewhat reliable, estimates with moderate to high reliability now include Konnarock (less than 10° from the palaeo-equator), Elatina, Rapitan, Mechum River, Grand Conglomerat (10-20°), Upper Tindir, Puga (20-30°), Nantuo, Gaskiers (30-40°) and Walsh (40-50°). Among these, Elatina, Upper Tindir and Nantuo are considered to have the highest reliability, all with estimates of low to moderate palaeolatitude. The Elatina result stems from sedimentary rocks with quantitative correction of inclination-shallowing effects, and the Upper Tindir result stems from data collected from igneous rocks that are precisely coeval with the glacial deposits. Despite continuing debate on the global character of Neoproterozoic ice ages, their pan-glacial extent (ice extending to low latitude in a low-obliquity world) is well demonstrated.
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A relatively simple numerical model of the energy balance of the earth-atmosphere is set up and applied. The dependent variable is the average annual sea level temperature in 10° latitude belts. This is expressed basically as a function of the solar constant, the planetary albedo, the transparency of the atmosphere to infrared radiation, and the turbulent exchange coefficients for the atmosphere and the oceans. The major conclusions of the analysis are that removing the arctic ice cap would increase annual average polar temperatures by no more than 7C, that a decrease of the solar constant by 2–5% might be sufficient to initiate another ice age, and that man's increasing industrial activities may eventually lead to a global climate much warmer than today.
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In its motion through the Milky Way galaxy, the solar system encounters an average -density (≥330 H atoms cm−3) giant molecular cloud (GMC) approximately every 108 years, a dense (∼2 × 103 H atoms cm−3) GMC every ∼109 years and will inevitably encounter them in the future [Talbot and Newman, 1977]. However, there have been no studies linking such events with severe (snowball) glaciations in Earth history. Here we show that dramatic climate change can be caused by interstellar dust accumulating in Earth's atmosphere during the solar system's immersion into a dense (∼2 × 103 H atoms cm−3) GMC. The stratospheric dust layer from such interstellar particles could provide enough radiative forcing to trigger the runaway ice-albedo feedback that results in global snowball glaciations. We also demonstrate that more frequent collisions with less dense GMCs could cause moderate ice ages.
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The late Precambrian Vendian Glaciation may have been triggered by a worldwide fall of temperature following the locking up of carbon dioxide in Upper Riphean Dolomites. In this "anti-greenhouse" mechanism, the Vendian case appears to differ from Gondwana and Pleistocene events which are restricted to the poles and not worldwide in extent. In the Vendian, but not in the Gondwana or Pleistocene glaciations, thick dolomite deposits almost always precede the tillites. And dolomite stones in those tillites indicate even more extensive Upper Riphean dolomite sedimentation than outcrops preserved today. Immediately after the glaciation, dolomite sedimentation generally became less important than before. Attention is given to the geochemical problems relating to atmospheric carbon dioxide balance. The synchroneity of glaciations is discussed, with regard to their central importance in Precambrian stratigraphy. The need to consider glaciations individually and not generalize from one to the other is stressed.
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A fundamental question of earth history concerns the nature of the Late Proterozoic glaciogenic sequences that are known from almost all of the major cratonic areas, including North America, the Gondwana continents, and the Baltic Platform. A major controversy involves the probable latitude of formation for these deposits- were they formed at relatively high latitudes, as were those of the Permian and our modern glacial deposits, or were many of them formed much closer to the equator? Arguments supporting a low depositional latitude for many of these units have been discussed extensively for the past 30 years (e.g., Harland 1964), beginning with the field observations that some of the diamictites had a peculiar abundance of carbonate fragments, as if the ice had moved over carbonate platforms. Indeed, many of these units, such as the Rapitan Group of the Canadian Cordillera, are bounded above and below by thick carbonate sequences which, at least for the past 100 Ma, are only known to have been formed in the tropical belt within about 33° of the equator (Ziegler et al. 1984). Other anomalies include dropstones and varves in the carbonates, as well as evaporites (for a complete review, see Williams 1975). Either the earth was radically different during the late Precambrian glacial episode(s), or the major continental land masses spent an extraordinary amount of time traversing back and forth between the tropics and the poles.
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Sheet-crack cements and coextensive intrastratal folds and breccias occur in a stratigraphically controlled, meter-thick zone, near the base of Marinoan (635 Ma) cap dolostones in slope settings. We demonstrate that sheet-crack cements on the margins of the Congo and Kalahari cratons are localized at a turbidite-to-grainstone transition, which records a transient fall in relative sea-level, preceding the larger glacioeustatic transgression. Sheet-cracks opened vertically, implying that pore-fluid pressure exceeded lithostatic pressure. When the margin of an ice-sheet retreats from a coast, a net fall in sea-level occurs in the vicinity, because of the weakened gravitational attraction between the ice-sheet and the nearby ocean. Augmented by glacioisostatic adjustment (postglacial rebound), the early regional fall in relative sea-level can mask the simultaneous rise in global mean sea-level caused by the addition of meltwater. We propose that sheet-cracks and related structures in Marinoan cap dolostones manifest pore-fluid overpressures resulting from rapid sea-level falls in the vicinity of vanishing ice-sheets.
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The gradual discovery that late Neoproterozoic ice sheets extended to sea level near the equator poses a palaeoenvironmental conundrum. Was the Earth's orbital obliquity > 60° (making the tropics colder than the poles) for 4.0 billion years following the lunar-forming impact, or did climate cool globally for some reason to the point at which runaway ice-albedo feedback created a `snowball' Earth? The high-obliquity hypothesis does not account for major features of the Neoproterozoic glacial record such as the abrupt onsets and terminations of discrete glacial events, their close association with large (> 10‰) negative δ13C shifts in seawater proxies, the deposition of strange carbonate layers (`cap carbonates') globally during post-glacial sea-level rise, and the return of large sedimentary iron formations, after a 1.1 billion year hiatus, exclusively during glacial events. A snowball event, on the other hand, should begin and end abruptly, particularly at lower latitudes. It should last for millions of years, because outgassing must amass an intense greenhouse in order to overcome the ice albedo. A largely ice-covered ocean should become anoxic and reduced iron should be widely transported in solution and precipitated as iron formation wherever oxygenic photosynthesis occurred, or upon deglaciation. The intense greenhouse ensures a transient post-glacial regime of enhanced carbonate and silicate weathering, which should drive a flux of alkalinity that could quantitatively account for the world-wide occurrence of cap carbonates. The resulting high rates of carbonate sedimentation, coupled with the kinetic isotope effect of transferring the CO2 burden to the ocean, should drive down the δ13C of seawater, as is observed. If cap carbonates are the `smoke' of a snowball Earth, what was the `gun'? In proposing the original Neoproterozoic snowball Earth hypothesis, Joe Kirschvink postulated that an unusual preponderance of land masses in the middle and low latitudes, consistent with palaeomagnetic evidence, set the stage for snowball events by raising the planetary albedo. Others had pointed out that silicate weathering would most likely be enhanced if many continents were in the tropics, resulting in lower atmospheric CO2 and a colder climate. Negative δ13C shifts of 10–20‰ precede glaciation in many regions, giving rise to speculation that the climate was destabilized by a growing dependency on greenhouse methane, stemming ultimately from the same unusual continental distribution. Given the existing palaeomagnetic, geochemical and geological evidence for late Neoproterozoic climatic shocks without parallel in the Phanerozoic, it seems inevitable that the history of life was impacted, perhaps profoundly so.
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New Sr and C isotopic data, both obtained on the same samples of marine carbonates, provide a relatively detailed record of isotopic variation in seawater through the latest Proterozoic and allow, for the first time, direct correlation of these isotopic changes in the Vendian (∼ 540–610 Ma). The strong isotope variations determined in this study record significant environmental and tectonic changes. Together with a fairly poorly constrained Nd isotopic record, the Sr and C isotopic records can be used to constrain rates of erosion, hydrothermal alteration and organic C burial. Further, comparison of these records with those of the Cenozoic permit investigation of the general relationship between global tectonics and continental glaciation. In particular, results of this study show a very large change in the 87Sr/86Sr of marine carbonates from low pre-Vendian ( > 610 Ma) values ( ∼ 0.7066) to high Middle Cambrian values ( ∼ 0.7090). This change is greater in magnitude than the significant increase in seawater 87Sr/86Sr through the Cenozoic. Both changes are attributed to high erosion rates associated with continent-continent collisions (Pan-African and Himalayan-Tibetan). In the latest Proterozoic these high erosion rates, probably coupled with high organic productivity and anoxic bottom-water conditions, contributed to a significant increase in the burial rate of organic C. Ice ages mark both the Neoproterozoic and Cenozoic, but different stratigraphic relationships between the Sr isotopic increase and continental glaciation indicate that uplift-driven models proposed to explain Cenozoic climatic change cannot account for the latest Proterozoic ice ages.
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We report here new geochronological and paleomagnetic data from the 802±10 Ma Xiaofeng dykes in South China. Together with existing data, these results suggest that Rodinia probably spread from the equator to the polar region at ca. 800 Ma, followed by a rapid ca. 90° rotation around an axis near Greenland that brought the entire supercontinent to a low-latitude position by ca. 750 Ma. We propose that it was the initiation of a mantle superplume under the polar end of Rodinia that triggered an episode of true polar wander (TPW) which brought the entire supercontinent into equatorial latitudes. An unusually extensive emerged land area at the equator increased both atmospheric CO2 drawdown and global albedo, which, along with waning plume volcanism led directly to the low-latitude Sturtian glaciation at ca. 750–720 Ma.
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The ‘Snowball Earth’ model of Hoffman et al. [Science 281 (1998) 1342] has stimulated renewed interest in the causes of glaciation in Earth history and the sedimentary, stratigraphic and geochemical response. The model invokes catastrophic global Neoproterozoic refrigerations when oceans froze, ice sheets covered the tropics and global temperatures plummeted to −50 °C. Each event is argued to be recorded by tillites and have lasted up to 10 million years. Planetary biological activity was arrested only to resume in the aftermath of abrupt and brutal volcanically generated ‘greenhouse’ deglaciations when global temperatures reached +50 °C. The ‘Cambrian explosion’ is regarded by some as a consequence of post-Snowball glacioeustatic flooding of continental shelves. We shall show by a systematic review of the model that it is based on many long standing assumptions of the character and origin of the Neoproterozoic glacial record, in particular, ‘tillites’, that are no longer valid.
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The roughly 25 percent increase in luminosity over the life of the sun shared by many different solar models is shown to be a very general result, independent of the uncertainties suggested by the solar neutrino experiment. Superficially, this leads to a conflict with the climatic history of the earth, and if basic concepts of stellar evolution are not fundamentally in error, compensating effects must have occurred, as first pointed out by Sagan and Mullen. One possible interpretation supported by recent detailed models of the earth's atmosphere is that the greenhouse effect was substantially more important than at present even as recently as 1 billion to 2 billion years ago.
Evidence of late Precambrian glaciation and its significance
  • W B Harland
Harland WB (1964) Evidence of late Precambrian glaciation and its significance. In: Nairn AEM (ed.) Problems in Palaeoclimatology, pp. 119-149. London: Interscience.
  • P F Hoffman
  • A J Kaufman
  • G P Halverson
  • D P Schrag
Hoffman PF, Kaufman AJ, Halverson GP, and Schrag DP (1998) A Neoproterozoic snowball Earth. Science 281: 1343-1346.