Primary features in cherty iron-formations

Gross, G A

doi:10.1016/0037-0738(72)90024-3

Cited by 58 publications

(17 citation statements)

References 8 publications

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“…1E and 5E). Although the distribution of iron within granules is slightly heterogeneous, it does not defi ne concentric laminations as in oolitic iron granules that occur in some granular iron formations (Beukes and Klein, 1990;Dimroth and Chauvel, 1973;Goode et al, 1983;Gross, 1972;Simonson, 1987Simonson, , 2003. This indicates the coprecipitation of silica and iron phases, rather than alternating deposition of silica and iron layers.…”

Section: Petrography and Environmental Distributionmentioning

confidence: 98%

“…Some granular iron formations contain oolitic grains with concentric layering, although non-oolitic iron granules are much more common (Bekker et al, 2010;Beukes and Klein, 1990;Dimroth and Chauvel, 1973;Goode et al, 1983;Gross, 1972;Simonson, 1987Simonson, , 2003. Although granular iron formations are rich in SiO 2 (~50 wt%), they also contain a signifi cant amount of iron (>15 wt%, but commonly ~30 wt%) in the form of iron oxides or iron silicates (Bekker et al, 2010(Bekker et al, , 2014Klein, 2005;Simonson, 2003;Trendall, 2002).…”

Section: Relationship To Granular Iron Formationmentioning

confidence: 98%

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Sedimentology and geochemistry of Archean silica granules

Stefurak

Lowe

Zentner

et al. 2015

Geological Society of America Bulletin

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The production of biogenic silica has dominated the marine silica cycle since early Paleozoic time, drawing down the concentration of dissolved silica in modern seawater to a few parts per million (ppm). Prior to the biological innovation of the fi rst silica biomineralizing organisms in late Proterozoic time, inputs of silica into Precambrian seawater were balanced by strictly chemical silica and silicate precipitation processes, although the mechanics of this abiotic marine silica cycle remain poorly understood. Cherty sedimentary rocks are abundant in Archean sequences, and many previous authors have suggested that primary precipitation of amorphous silica could have occurred in Archean seawater. The recent discovery that many pure chert layers in early Archean rocks formed as sedimentary beds of sandsized, subspherical silica granules has provided direct evidence for primary silica deposition. Here, we provide further sedimentological and geochemical analyses of early Archean silica granules in order to gain a better understanding of the mechanisms of granule formation. Silica granules are common components of sedimentary cherts from a variety of depositional settings and water depths. The abundance and widespread distribution of silica granules in Archean rocks suggest that they represented a signifi cant primary silica depositional mode and that most formed by precipitation in the upper part of the water column. The regular occurrence of silica granules as centimeterscale layers within banded chert alternating with layers of black or ferruginous chert containing few granules indicates episodic granule sedimentation. Contrasting silicon iso topic compositions of granules from different depo sitional environments indicate that isotopic signatures were modifi ed during early diagenesis. Looking to modern siliceous sinters for insight into silica precipitation, we suggest that silica granules may have formed via multiple stages of aggregation of silica nanospheres and microspheres. Consistent with this hypothesis, Archean ocean chemistry would have favored particle aggregation over gelling. Granule formation would have been most favorable under conditions promoting rapid silica polymerization, including high salinity and/or high concentrations of dissolved silica. Our observations suggest that granule sedimentation was often episodic, suggesting that granule formation may have also been episodic, perhaps linked to variations in these key parameters.

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Section: Petrography and Environmental Distributionmentioning

confidence: 98%

Section: Relationship To Granular Iron Formationmentioning

confidence: 98%

Sedimentology and geochemistry of Archean silica granules

Stefurak

Lowe

Zentner

et al. 2015

Geological Society of America Bulletin

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“…A similarly widespread Archaean iron-formation in the Yilgarn Block ( Fig. 1) led Gole & Klein (1981) to conclude that Archaean and Proterozoic iron-formations display more similarities than differences, as has previously been proposed (Gross, 1972).…”

Section: Basinal Type Iron-formationmentioning

confidence: 82%

“…Iron-formations of the older Archaean terrains in South Africa and this type are conventionally referred to as Algoman Western Australia. The purpose of this paper is to (Gross, 1972). Specific reference to the occurrence document the occurrences and propose environments and depositional environments of these orthochemical of deposition and controls on formation of these sediments has been made by Dunbar & McCall orthochemical sediments.…”

Section: Introductionmentioning

confidence: 99%

“…the Yilgarn Block in Australia. This group comprises Whereas the modes of occurrence of the first three iron-formations and jaspillite, with minor chert and groups of orthochemical sediments are well-doculimestone, and is associated with intercalated vol-mented, this is not so for iron-formation, jaspillite and canics and volcaniclastic sediments (e.g., Goodwin, chert within the terrigenous sedimentary intervals of 1962; Gross, 1972;Lowe, 1982). Iron-formations of the older Archaean terrains in South Africa and this type are conventionally referred to as Algoman Western Australia.…”

Section: Introductionmentioning

confidence: 99%

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Siliciclastic‐hosted iron‐formations in the early Archaean Barberton and Pilbara sequences

Eriksson¹

1983

Journal of the Geological Society of Australia

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Banded Iron Formations and The Early Atmosphere

Simonson¹,

Kaufman²

Encyclopedia of Earth Sciences Series

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IRON FORMATIONS, a class of chemical sediments comparable to evaporites or phosphorites, occur on all continental cratons and represent the largest repositories of iron ever precipitated from Earth's hydrosphere (Trendall and Morris, 1983; Clout and Simonson, 2005). Iron formations reveal much about the composition of the atmosphere because of the redox sensitivity of iron in solution, and because of the dramatic change in the way iron was deposited through geologic time. The first-order observations are that Precambrian iron-rich sediments (known as iron formations) are generally cherty, thinly laminated (or banded), and widespread, whereas Phanerozoic iron-rich sediments (known as IRONSTONES) generally lack chert and are richer in aluminum (reflecting clastic contamination), not laminated, and smaller in areal extent. In order to make correct inferences about temporal changes in Earth's atmosphere, iron formations must first be understood as chemical sediments.

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Primary features in cherty iron-formations

Cited by 58 publications

References 8 publications

Sedimentology and geochemistry of Archean silica granules

Sedimentology and geochemistry of Archean silica granules

Siliciclastic‐hosted iron‐formations in the early Archaean Barberton and Pilbara sequences

Banded Iron Formations and The Early Atmosphere

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