Pocatello Formation and overlying strata, southeastern Idaho: Snowball Earth diamictites, cap carbonates, and Neoproterozoic isotopic profiles

2005 ◽  
pp. 251-259 ◽  
Author(s):  
Paul Karl Link ◽  
Frank A. Corsetti ◽  
Nathaniel J. Lorentz
Keyword(s):  
Snowball Earth ◽  
Cap Carbonates ◽  
Overlying Strata

scholarly journals A geochemical modelling study of the evolution of the chemical composition of seawater linked to a "snowball" glaciation

2008 ◽  
Vol 5 (1) ◽  
pp. 253-267 ◽  
Author(s):  
G. Le Hir ◽  
Y. Goddéris ◽  
Y. Donnadieu ◽  
G. Ramstein
Keyword(s):  
Environmental Changes ◽  
Snowball Earth ◽  
Large Shift ◽  
Environmental Perturbations ◽  
Seawater Ph ◽  
Oceanic Surface ◽  
Cap Carbonates ◽  
Evolution Of Life ◽  
Global Cycles ◽  
Modelling Study

Abstract. The Snowball Earth theory initially proposed by Kirschvink (1992) to explain the Neoproterozoic glacial episodes, suggested that the Earth was fully ice-covered at 720 Ma (Sturtian episode) and 640 Ma (Marinoan episode). This succession of extreme climatic crises induced environmental perturbations which are considered as a strong selective pressure on the evolution of life (Hoffman et al., 1998). Using a numerical model of carbon-alkalinity global cycles, we quantify environmental stresses caused by a global glaciation. According to our results, we suggest that during global glaciations, the ocean becomes acidic (pH~6), and undersaturated with respect to carbonate minerals. Moreover the quick transition from ice-house to greenhouse conditions implies an abrupt and large shift of the oceanic surface temperature which causes an extended hypoxia. The intense continental weathering, in the aftermath of the glaciation, deeply affects the seawater composition inducing rapid changes in terms of pH and alkalinity. We also propose a new timing for post glacial perturbations and for the cap carbonates deposition, ~2 Myr instead of 200 kyr as suggested in a previous modelling study. In terms of Precambrian life sustainability, seawater pH modifications appear drastic all along the glaciation, but we suggest that the buffering action of the oceanic crust dissolution avoids a total collapse of biological productivity. But short-lived and large post-glacial perturbations are more critical and may have played the role of an environmental filter proposed in the classic snowball Earth theory. Although the link between environmental changes and life sustainability cannot be modelled accurately, we suggest that only a permissive life (Knoll, 2003) may explain the relative continuity in microfossils diversity observed before, during and after Neoproterozoic glaciation events.

scholarly journals A geochemical modelling study of the evolution of the chemical composition of seawater linked to a global glaciation: implications for life sustainability

2007 ◽  
Vol 4 (3) ◽  
pp. 1839-1876
Author(s):  
G. Le Hir ◽  
Y. Goddéris ◽  
Y. Donnadieu ◽  
G. Ramstein
Keyword(s):  
Snowball Earth ◽  
Large Shift ◽  
Apparent Paradox ◽  
Seawater Ph ◽  
Oceanic Surface ◽  
Cap Carbonates ◽  
Before And After ◽  
Global Cycles ◽  
Global Glaciation ◽  
Modelling Study

Abstract. The Snowball Earth theory initially proposed by Kirschvink (Kirschvink, 1992) to explain the Neoproterozoic glacial episodes, suggested that the Earth was fully ice-covered at 720 My (Sturtian episode) and 640 My (Marinoan episode). This succession of extreme climatic crises induced a stress which is considered as a strong selective pressure on the evolution of life (Hoffman et al., 1998). However recent biological records (Corsetti, 2006) do not support this theory as little change is observed in the diversity of microfossils outcrops before and after the Marinoan glacial interval. In this contribution we address this apparent paradox. Using a numerical model of carbon-alkalinity global cycles, we quantify several environmental stresses caused by a global glaciation. We suggest that during global glaciations, the ocean becomes acidic (pH~6), and unsaturated with respect to carbonate minerals. Moreover the quick transition from ice-house to greenhouse conditions implies an abrupt and large shift of the oceanic surface temperature which causes an extended hypoxia. The intense continental weathering, in the aftermath of the glaciation, deeply affects the seawater composition inducing rapid changes in terms of pH and alkalinity. We also propose a new timing for post glacial perturbations and for the cap carbonates deposition, ~2 Myr instead of 200 kyr as suggested in a previous modelling study. In terms of Precambrian life sustainability, seawater pH modifications appear drastic all along the glaciation, but we show that the buffering action of the oceanic crust dissolution processes avoids a total collapse of biological productivity. In opposite short-lived and large post-glacial perturbations are more critical and may have played a role of environmental filter suggested in the classic snowball Earth theory. Only a permissive life (prokaryotes or simple eukaryotes) may explain the relative continuity in microfossils diversity observed before, during and after Neoproterozoic glaciation events.

U-Pb and Re-Os geochronology tracks stratigraphic condensation in the Sturtian snowball Earth aftermath

Geology ◽  
2020 ◽  
Vol 48 (6) ◽  
pp. 625-629 ◽  
Author(s):  
Alan D. Rooney ◽  
Chuan Yang ◽  
Daniel J. Condon ◽  
Maoyan Zhu ◽  
Francis A. Macdonald
Keyword(s):  
South China ◽  
Snowball Earth ◽  
Ionization Mass ◽  
Rift Basins ◽  
Authigenic Carbonates ◽  
Ice Volume ◽  
Accommodation Space ◽  
Cap Carbonates ◽  
Minimum Age ◽  
Os Isotope

Abstract The snowball Earth hypothesis predicts a strong hysteresis resulting in discrete multi-million-year glaciations followed by globally synchronous deglaciation. Here we present new U-Pb zircon and Re-Os sedimentary rock geochronology and Os isotope chemostratigraphy from post-Sturtian sequences in south China to test the synchroneity of deglaciation. High-precision chemical abrasion–isotope dilution–thermal ionization mass spectrometry (CA-ID-TIMS) U-Pb zircon dates refine the minimum age of deglaciation to 660.98 ± 0.74 Ma, which is ∼2 m.y. older than previously reported. We also provide a new maximum age constraint on the onset of the Marinoan glaciation of 657.17 ± 0.78 Ma. A global compilation of new Os isotope chemostratigraphy reveals a large and systematic trend to unradiogenic values over <1 m of stratigraphy. Together, these data indicate that the Mn-carbonates in south China are not cap carbonates that formed as a response to post-snowball alkalinity, but are authigenic carbonates that formed millions of years after deglaciation. Sturtian cap carbonates tend to be absent or more condensed than their younger Marinoan counterparts. We suggest that this reflects a combination of enhanced accommodation space in early Cryogenian underfilled rift basins, stronger hysteresis, larger ice volume, and/or higher CO2 levels needed for deglaciation of the longer Sturtian glaciation. Further, our findings indicate that the apparent diachroneity of deglaciation can be explained readily as a consequence of stratigraphic condensation, itself due to the large post-Sturtian glacioeustatic transgressive sequence that outpaced shallow-water carbonate deposition.

scholarly journals Episode of intense chemical weathering during the termination of the 635 Ma Marinoan glaciation

2016 ◽  
Vol 113 (52) ◽  
pp. 14904-14909 ◽  
Author(s):  
Kang-Jun Huang ◽  
Fang-Zhen Teng ◽  
Bing Shen ◽  
Shuhai Xiao ◽  
Xianguo Lang ◽  
...  
Keyword(s):  
South China ◽  
Chemical Weathering ◽  
Snowball Earth ◽  
Carbonate Precipitation ◽  
Isotopic Data ◽  
Low Intensity ◽  
Cap Carbonates ◽  
Cap Carbonate ◽  
Carbonate Deposition ◽  
Global Precipitation

Cryogenian (∼720–635 Ma) global glaciations (the snowball Earth) represent the most extreme ice ages in Earth’s history. The termination of these snowball Earth glaciations is marked by the global precipitation of cap carbonates, which are interpreted to have been driven by intense chemical weathering on continents. However, direct geochemical evidence for the intense chemical weathering in the aftermath of snowball glaciations is lacking. Here, we report Mg isotopic data from the terminal Cryogenian or Marinoan-age Nantuo Formation and the overlying cap carbonate of the basal Doushantuo Formation in South China. A positive excursion of extremely high δ26Mg values (+0.56 to +0.95)—indicative of an episode of intense chemical weathering—occurs in the top Nantuo Formation, whereas the siliciclastic component of the overlying Doushantuo cap carbonate has significantly lower δ26Mg values (<+0.40), suggesting moderate to low intensity of chemical weathering during cap carbonate deposition. These observations suggest that cap carbonate deposition postdates the climax of chemical weathering, probably because of the suppression of carbonate precipitation in an acidified ocean when atmospheric CO2 concentration was high. Cap carbonate deposition did not occur until chemical weathering had consumed substantial amounts of atmospheric CO2 and accumulated high levels of oceanic alkalinity. Our finding confirms intense chemical weathering at the onset of deglaciation but indicates that the maximum weathering predated cap carbonate deposition.

Aragonite Crystal Fans In Neoproterozoic Cap Carbonates: A Case Study From Brazil and Implications For the Post-Snowball Earth Coastal Environment

2015 ◽  
Vol 85 (3) ◽  
pp. 285-300 ◽  
Author(s):  
L. C. Vieira ◽  
A. Nedelec ◽  
S. Fabre ◽  
R. I. F. Trindade ◽  
R. P. de Almeida
Keyword(s):  
Coastal Environment ◽  
Snowball Earth ◽  
Aragonite Crystal ◽  
Cap Carbonates

scholarly journals Orbital forcing of ice sheets during snowball Earth

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Ross N. Mitchell ◽  
Thomas M. Gernon ◽  
Grant M. Cox ◽  
Adam R. Nordsvan ◽  
Uwe Kirscher ◽  
...  
Keyword(s):  
Climate Models ◽  
Ice Sheets ◽  
Snowball Earth ◽  
Iron Formation ◽  
Orbital Forcing ◽  
Banded Iron Formation ◽  
Cap Carbonates ◽  
Recent Climate ◽  
Sedimentary Dynamics ◽  
Milankovitch Orbital

AbstractThe snowball Earth hypothesis—that a runaway ice-albedo feedback can cause global glaciation—seeks to explain low-latitude glacial deposits, as well as geological anomalies including the re-emergence of banded iron formation and “cap” carbonates. One of the most significant challenges to snowball Earth has been sedimentological cyclicity that has been taken to imply more climate dynamics than expected when the ocean is completely covered in ice. However, recent climate models suggest that as atmospheric CO2 accumulates, the snowball climate system becomes sensitive to orbital forcing. Here we show the presence of nearly all Milankovitch (orbital) cycles preserved in stratified banded iron formation deposited during the Sturtian snowball Earth. These results provide evidence for orbitally forced cyclicity of global ice sheets that resulted in periodic oxidation of ferrous iron. Orbital glacial advance and retreat cycles provide a simple mechanism to reconcile both the sedimentary dynamics and the enigmatic survival of multicellular life during snowball Earth.

How Should Snowball Earth Deglaciation Start

2020 ◽  
Author(s):  
Jiacheng Wu ◽  
Yonggang Liu ◽  
Zhouqiao Zhao
Keyword(s):  
Snowball Earth
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