The Neoproterozoic climatic paradox: Equatorial palaeolatitude for Marinoan glaciation near sea level in South Australia

Schmidt, P. W.; Williams, George E.

doi:10.1016/0012-821x(95)00106-m

Cited by 169 publications

(76 citation statements)

References 31 publications

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“…Unlike Paleozoic and younger glaciations, these two Precambrian deposits are closely associated with tropical rather than polar paleolatitude indicators such as carbonate rocks, red beds, and evaporites (1,2). These observations are supported by paleomagnetic results indicating that Neoproterozoic glaciogenic rocks occur within 5°of latitude of the equator (3)(4)(5), and two exposures of the Paleoproterozoic glaciation occur within Ϸ11°o f the equator (6,7). Climate models predict severe consequences of such lowlatitude glaciation: An ice-albedo feedback will drive a run-away glaciation (8) resulting in 500-1,500 m of global oceanic pack ice and average surface temperatures reaching Ϫ20 to Ϫ50°C (9,10).…”

mentioning

confidence: 74%

Paleoproterozoic snowball Earth: Extreme climatic and geochemical global change and its biological consequences

Kirschvink

Gaidos

Bertani

et al. 2000

Proc. Natl. Acad. Sci. U.S.A.

397

211

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mentioning

confidence: 74%

Paleoproterozoic snowball Earth: Extreme climatic and geochemical global change and its biological consequences

Kirschvink

Gaidos

Bertani

et al. 2000

Proc. Natl. Acad. Sci. U.S.A.

397

211

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“…In an effort to explain South Australian sand wedges and the wide-spread glacial deposits at the paleoequator, Williams (1975Williams ( , 2007 developed the prominent precursor to the snowball Earth hypothesis, the high-obliquity hypothesis (Schmidt and Williams, 1995;Williams et al, 1998;Williams, 2007Williams, , 1975. This hypothesis purported that during the Precambrian, Earth's obliquity (i.e., the angle between the Earth's axes of rotation and its axis of orbit around the sun) was greater than 54 • , as compared with about 23 • today, and this configuration allowed mean annual temperatures at the equator to drop below 0 • C. Importantly, this would have increased equatorial seasonality, thereby allowing sand wedge growth.…”

Section: Sand Wedge Formation and Models To Explain Low-latitude Sandmentioning

confidence: 99%

New constraints on equatorial temperatures during a Late Neoproterozoic snowball Earth glaciation

Ewing

Eisenman

Lamb

et al. 2014

Earth and Planetary Science Letters

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Intense glaciation during the end of Cryogenian time (∼635 million years ago) marks the coldest climate state in Earth history -a time when glacial deposits accumulated at low, tropical paleolatitudes. The leading idea to explain these deposits, the snowball Earth hypothesis, predicts globally frozen surface conditions and subfreezing temperatures, with global climate models placing surface temperatures in the tropics between −20 • C and −60 • C. However, precise paleosurface temperatures based upon geologic constraints have remained elusive and the global severity of the glaciation undetermined. Here we make new geologic observations of tropical periglacial, aeolian and fluvial sedimentary structures formed during the end-Cryogenian, Marinoan glaciation in South Australia; these observations allow us to constrain ancient surface temperatures. We find periglacial sand wedges and associated deformation suggest that ground temperatures were sufficiently warm to allow for ductile deformation of a sandy regolith. The wide range of deformation structures likely indicate the presence of a paleoactive layer that penetrated 2-4 m below the ground surface. These observations, paired with a model of ground temperature forced by solar insolation, constrain the local mean annual surface temperature to within a few degrees of freezing. This temperature constraint matches well with our observations of fluvial deposits, which require temperatures sufficiently warm for surface runoff. Although this estimate coincides with one of the coldest near sea-level tropical temperatures in Earth history, if these structures represent peak Marinaon glacial conditions, they do not support the persistent deep freeze of the snowball Earth hypothesis. Rather, surface temperatures near 0 • C allow for regions of seasonal surface melting, atmosphere-ocean coupling and possible tropical refugia for early metazoans. If instead these structures formed during glacial onset or deglaciation, then they have implications for the timescale and character for the transition into or out of a snowball state.

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“…A highlight has been the work on the south Australian Elatina Formation, a Marinoan glacigenic formation that also contains many sorted siliciclastic sediments including tidal rhythmites (Williams 2000). Through the work of Embleton & Williams (1986), Schmidt & Williams (1995) and Sohl et al (1999) progressively more diverse and rigorously tested data have been obtained to support low palaeolatitudes for glaciation. Sohl et al (1999) made a breakthrough in demonstrating repeated reversals of the palaeomagnetic field and hence deposition of the Elatina Formation over .10 5 10 7 years as well as estimating palaeolatitude at 8 AE 68 (95% confidence limits) at the onset of glaciation.…”

Section: Palaeomagnetism and Palaeogeographymentioning

confidence: 99%

Neoproterozoic glaciation in the Earth System

Fairchild

Kennedy

2007

JGS

215

116

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The Neoproterozoic contains severe glacial intervals (750–580 Ma) including two extending to low palaeomagnetic latitudes. Paucity of radiometric dates indicates the need for chronostratigraphic tools. Whereas the marine 87 Sr/ 86 Sr signatures show a steady rise, δ 13 C fluctuates, the most reproducible variations being negative signatures in carbonate caps to glacial units, but more diagenetic work is needed. Four conceptual models for the icehouse conditions are contrasted: Zipper-Rift Earth (diachronous glaciation related to continental rift margins), High-tilt Earth (high-obliquity and preferential low-latitude glaciation), Snowball Earth (extreme glaciation related to runaway ice–albedo feedback) and Slushball Earth (coexistence of unfrozen oceans and sea-level glaciers in the tropics). Climate models readily simulate runaway glaciation, but the Earth may not be able to recover from it. The Slushball state requires more extensive modelling. Biogeochemical models highlight the lack of CO 2 buffering in the Neoproterozoic and the likely transition from a methane- to a CO 2 -dominated climate system. Relevant processes include tropical weathering of volcanic provinces, and new land biotas stimulating both clay mineral formation and P delivery to the oceans, facilitating organic C burial. Hence a step change in the Earth System was probably both facilitated by organisms and responsible for moderating Phanerozoic climate.

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The Neoproterozoic climatic paradox: Equatorial palaeolatitude for Marinoan glaciation near sea level in South Australia

Cited by 169 publications

References 31 publications

Paleoproterozoic snowball Earth: Extreme climatic and geochemical global change and its biological consequences

Paleoproterozoic snowball Earth: Extreme climatic and geochemical global change and its biological consequences

New constraints on equatorial temperatures during a Late Neoproterozoic snowball Earth glaciation

Neoproterozoic glaciation in the Earth System

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