An iron shuttle for deepwater silica in Late Archean and early Paleoproterozoic iron formation

Fischer, Woodward W.; Knoll, Andrew H.

doi:10.1130/b26328.1

Cited by 86 publications

(129 citation statements)

References 140 publications

(176 reference statements)

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“…However, this hypothesis requires that chemical precipitation of silica does not fractionate Ge from Si and that the Ge/Si ratio of continental and hydrothermal sources has remained constant over time. This does not appear to be the case (Hammond et al, 2000;Anders et al, 2003;Pokrovsky et al, 2006;Fischer and Knoll, 2009). In addition, it is not clear how the Ge/Si ratio is affected by diagenesis (Hamade et al, 2003).…”

Section: Silica Fluxes To the Precambrian Oceans And Their Isotopic Cmentioning

confidence: 95%

“…However, it is clear from the sedimentary geology and petrography that these materials vary in mode of formation and environmental setting, raising the question of whether long term trends might principally reflect the succession in sample dominance from hydrothermal cherts in the Early Archean, to iron formation in late Archean and Paleoproterozoic basins, to pertidal cherts in younger Proterozoic basins (e.g. Fischer and Knoll, 2009;van den Boorn et al, 2010). Added to this is the potentially complicating issue that isotope fractionation accompanies silica adsorption onto iron oxides, with the lighter isotope preferentially enriched in the precipitate Opfergelt et al, 2009).…”

Section: Samplesmentioning

confidence: 99%

“…Added to this is the potentially complicating issue that isotope fractionation accompanies silica adsorption onto iron oxides, with the lighter isotope preferentially enriched in the precipitate Opfergelt et al, 2009). Thus, we analyzed 12 chert samples from the late Archean Transvaal Supergroup, South Africa (Knoll and Beukes, 2009), a collection that includes peritidal cherts in carbonates, deep Knoll et al 1989Knoll et al , 1991(2) Allison and Awramik, 1989;Macdonald et al, , 2011(3) Green et al, 1989;(4) Knoll, 1984;(5) Sergeev et al 1997;(6) Strother et al, 1983; (7) Kah and Knoll, 1996;(8) Sergeev et al, 1995;(9) Walter et al, 1976;Tobin, 1990;(10) Wilson et al, 2010;(11) Barghoorn and Tyler 1965;(12) Brotton et al, 2007;(13) Yi-Liang et al, 2011;(14) Fischer and Knoll, 2009;Knoll and Beukes, 2009 (14) water chert nodules and basinal iron formation. This allows us to ask whether the basinal sedimentation of silica adsorbed onto iron ferrihydroxides (e.g.…”

Section: Samplesmentioning

confidence: 99%

“…This allows us to ask whether the basinal sedimentation of silica adsorbed onto iron ferrihydroxides (e.g. Fischer and Knoll, 2009) imparts a detectable environmental variation onto cherts from this basin. Building on this, we also analyzed a pair of samples from the Late Archean Hamersley Supergroup, Australia (Yi-Liang et al, 2011), and eight samples from several 1800-1990 Ma successions that include late Paleoproterozoic iron formation (Barghoorn and Tyler, 1965;Tobin, 1990;Brotton et al, 2007;Wilson et al, 2010 and references therein).…”

Section: Samplesmentioning

confidence: 99%

“…While seasonal fluctuations in saturation state might drive silica precipitation in shallow water, it is not clear that this mechanism would work in the open marine settings where Archean iron formations actually accumulated. Alternatively, silica may have been transported to deeper water BIFs via the 'iron shuttle' (Fischer and Knoll, 2009) by adsorption on Fe-oxide/hydroxide particles and accompanying Si isotope fractionation (c.f. Delstanche et al, 2009) leading to the progressive enrichment of heavy Si isotopes in the ambient water.…”

Section: Silica Cycling and Si Isotopes In Precambrian Oceansmentioning

confidence: 99%

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Si isotope variability in Proterozoic cherts

Chakrabarti

Knoll

Jacobsen

et al. 2012

Geochimica et Cosmochimica Acta

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We report Si-isotopic compositions of 75 sedimentologically and petrographically characterized chert samples with ages ranging from $2600 to 750 Ma using multi-collector inductively coupled plasma mass spectrometry. d 30 Si values of the cherts analyzed in this study show a $7& range, from À4.29 to +2.85. This variability can be explained in part by (1) simple mixing of silica derived from continental (higher d 30 Si) and hydrothermal (lower d 30 Si) sources, (2) multiple mechanisms of silica precipitation and (3) Rayleigh-type fractionations within pore waters of individual basins.We observe $3& variation in peritidal cherts from a single Neoproterozoic sedimentary basin (Spitsbergen). This variation can be explained by Rayleigh-type fractionation during precipitation from silica-saturated porewaters. In some samples, postdissolution and reprecipitation of silica could have added to this effect. Our data also indicate that peritidal cherts are enriched in the heavier isotopes of Si whereas basinal cherts associated with banded iron formations (BIF) show lower d 30 Si. This difference could partly be due to Si being derived from hydrothermal sources in BIFs. We postulate that the difference in d 30 Si between non-BIF and BIF cherts is consistent with the contrasting genesis of these deposits. Low d 30 Si in BIF is consistent with laboratory experiments showing that silica adsorbed onto Fe-hydroxide particles preferentially incorporates lighter Si isotopes.Despite large intrabasinal variation and environmental differences, the data show a clear pattern of secular variation. Low d 30 Si in Archean cherts is consistent with a dominantly hydrothermal source of silica to the oceans at that time. The monotonically increasing d 30 Si from 3.8 to 1.5 Ga appears to reflect a general increase in continental versus hydrothermal sources of Si in seawater, as well as the preferential removal of lighter Si isotopes during silica precipitation in iron-associated cherts from silica-saturated seawater. The highest d 30 Si values are observed in 1.5 Ga peritidal cherts; in part, these enriched values could reflect increasing sequestration of light silica during soil-forming processes, thus, delivering relatively heavy dissolved silica to the oceans from continental sources. The causes behind the reversal in trend towards lower d 30 Si in cherts younger than 1.5 Ga old are less clear. Cherts deposited 1800-1900 Ma are especially low d 30 Si, a possible indication of transiently strong hydrothermal input at this time.

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Section: Silica Fluxes To the Precambrian Oceans And Their Isotopic Cmentioning

confidence: 95%

Section: Samplesmentioning

confidence: 99%

Section: Samplesmentioning

confidence: 99%

Section: Samplesmentioning

confidence: 99%

Section: Silica Cycling and Si Isotopes In Precambrian Oceansmentioning

confidence: 99%

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Si isotope variability in Proterozoic cherts

Chakrabarti

Knoll

Jacobsen

et al. 2012

Geochimica et Cosmochimica Acta

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High manganese concentrations in rocks at Gale crater, Mars

Lanza

Fischer

Wiens

et al. 2014

Geophysical Research Letters

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The surface of Mars has long been considered a relatively oxidizing environment, an idea supported by the abundance of ferric iron phases observed there. However, compared to iron, manganese is sensitive only to high redox potential oxidants, and when concentrated in rocks, it provides a more specific redox indicator of aqueous environments. Observations from the ChemCam instrument on the Curiosity rover indicate abundances of manganese in and on some rock targets that are 1-2 orders of magnitude higher than previously observed on Mars, suggesting the presence of an as-yet unidentified manganese-rich phase. These results show that the Martian surface has at some point in time hosted much more highly oxidizing conditions than has previously been recognized.

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Diagenetic silica enrichment and late‐stage groundwater activity in Gale crater, Mars

Frydenvang

Gasda

Hurowitz

et al. 2017

Geophysical Research Letters

102

155

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Diagenetic silica enrichment in fracture‐associated halos that crosscut lacustrine and unconformably overlying aeolian sedimentary bedrock is observed on the lower north slope of Aeolis Mons in Gale crater, Mars. The diagenetic silica enrichment is colocated with detrital silica enrichment observed in the lacustrine bedrock yet extends into a considerably younger, unconformably draping aeolian sandstone, implying that diagenetic silica enrichment postdates the detrital silica enrichment. A causal connection between the detrital and diagenetic silica enrichment implies that water was present in the subsurface of Gale crater long after deposition of the lacustrine sediments and that it mobilized detrital amorphous silica and precipitated it along fractures in the overlying bedrock. Although absolute timing is uncertain, the observed diagenesis likely represents some of the most recent groundwater activity in Gale crater and suggests that the timescale of potential habitability extended considerably beyond the time that the lacustrine sediments of Aeolis Mons were deposited.

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An iron shuttle for deepwater silica in Late Archean and early Paleoproterozoic iron formation

Cited by 86 publications

References 140 publications

Si isotope variability in Proterozoic cherts

Si isotope variability in Proterozoic cherts

High manganese concentrations in rocks at Gale crater, Mars

Diagenetic silica enrichment and late‐stage groundwater activity in Gale crater, Mars

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