Cherts of the Barberton Greenstone Belt Interpreted as Products of Submarine Exhalative Activity

Paris, I. A.; Stanistreet, Ian G.; Hughes, Martin J.

doi:10.1086/628935

Cited by 121 publications

(37 citation statements)

References 21 publications

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“…The usual explanation for the poor fossil record of early Earth, especially in the case of the Archean cherts, is that these cherts must have been secondarily silicified (Paris et al, 1985). This would mean that primary calcification destroyed the morphological record of early life and left only unidentifiable carbonaceous traces for subsequent silicification (chertification).…”

Section: Implication For the Early Fossil Recordmentioning

confidence: 99%

Calcification and Silicification: Fossilization Potential of Cyanobacteria from Stromatolites of Niuafo‘ou's Caldera Lakes (Tonga) and Implications for the Early Fossil Record

et al. 2012

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Calcification and silicification processes of cyanobacterial mats that form stromatolites in two caldera lakes of Niuafo'ou Island (Vai Lahi and Vai Si'i) were evaluated, and their importance as analogues for interpreting the early fossil record are discussed. It has been shown that the potential for morphological preservation of Niuafo'ou cyanobacteria is highly dependent on the timing and type of mineral phase involved in the fossilization process. Four main modes of mineralization of cyanobacteria organic parts have been recognized: (i) primary early postmortem calcification by aragonite nanograins that transform quickly into larger needle-like crystals and almost totally destroy the cellular structures, (ii) primary early postmortem silicification of almost intact cyanobacterial cells that leave a record of spectacularly well-preserved cellular structures, (iii) replacement by silica of primary aragonite that has already recrystallized and obliterated the cellular structures, (iv) occasional replacement of primary aragonite precipitated in the mucopolysaccharide sheaths and extracellular polymeric substances by Al-Mg-Fe silicates. These observations suggest that the extremely scarce earliest fossil record may, in part, be the result of (a) secondary replacement by silica of primary carbonate minerals (aragonite, calcite, siderite), which, due to recrystallization, had already annihilated the cellular morphology of the mineralized microbiota or (b) relatively late primary silicification of already highly degraded and no longer morphologically identifiable microbial remains.

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Section: Implication For the Early Fossil Recordmentioning

confidence: 99%

Calcification and Silicification: Fossilization Potential of Cyanobacteria from Stromatolites of Niuafo‘ou's Caldera Lakes (Tonga) and Implications for the Early Fossil Record

et al. 2012

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“…The Precambrian cherts have often been considered as chemical precipitates from a warm and silica-saturated Archean ocean [Siever, 1992]. However, an increasing number of studies have provided evidence that the cherts are, in fact, ''replacement cherts,'' that is, sediments (often volcanoclastic) that have been post-depositionally silicified by pervasive hydrothermal or diagenetic fluids [de Wit et al, 1982;Paris et al, 1985;Sugitani, 1992;Kato and Nakamura, 2003;Hofmann, 2005;Orberger et al, 2006c; see also Perry and Lefticariu, 2003]. Post-depositional alteration [Rouchon et al, 2004], and metamorphism [Boyd and Philippot, 1998] of these cherts can also alter their primary biogenic N (and C) isotopic signature [Dauphas and Marty, 2004;.…”

Section: Introductionmentioning

confidence: 99%

Biogenic nitrogen and carbon in Fe‐Mn‐oxyhydroxides from an Archean chert, Marble Bar, Western Australia

Pinti

Hashizume

Orberger

et al. 2007

Geochem Geophys Geosyst

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[1] To quantify and localize nitrogen (N) and carbon (C) in Archean rocks from the Marble Bar formation, Western Australia, and to gain insights on their origin and potential biogenicity, we conducted nuclear reaction analyses (NRA) and carbon and nitrogen isotope ratio measurements on various samples from the 3460-Myr-old Fe-rich Marble Bar chert. The Marble Bar chert formed during the alteration of basaltic volcanoclastic rocks with Fe-and Si-rich hydrothermal fluids, and the subsequent precipitation of magnetite, carbonates, massive silica, and, locally, sulfides. At a later stage, the magnetite, sulfides, and carbonates were replaced by Fe-Mn-oxyhydroxides. Nuclear reaction analyses indicate that most of the N and C resides within these Fe-Mn-oxyhydroxides, but a minor fraction is found in K-feldspars and Ba-mica dispersed in the silica matrix. The N and C isotopic composition of Fe-oxides suggests the presence of a unique biogenic source with d 15 N AIR values from +6.0 ± 0.5% to 7.3 ± 1.1% and a d 13 C PDB value of À19.9 ± 0.1%. The C and N isotope ratios are similar to those observed in Proterozoic and Phanerozoic organic matter. Diffusion-controlled fractionation of N and C released during high combustion temperatures indicates that these two elements are firmly embedded within the iron oxides, with activation energies of 18.7 ± 3.7 kJ/mol for N and 13.0 ± 3.8 kJ/mol for C. We propose that N and C were chemisorbed on iron and were subsequently embedded in the crystals during iron oxidation and crystal growth. The Fe-isotopic composition of the Marble Bar chert (d 56 Fe = À0.38 ± 0.02%) is similar to that measured in iron oxides formed by direct precipitation of iron from hydrothermal plumes in contact G 3

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“…This carbonate precipitation occurred by the reaction between bicarbonate ions in the circulating seawater and Ca, Mg, Fe, and Mn in the oceanic crust Kato, 2000, 2001). Such carbonatized greenstone has been commonly recognized in the Early Archean greenstone belts other than the Warrawoona Group (e.g., Knauth and Lowe, 1978;Paris et al, 1985;Barley and Groves, 1987), indicating that seafloor hydrothermal carbonatization was a common and major process of the carbonate precipitation in the Early Archean. The question arises when the carbonate precipitation changed from the Early Archean style to modern one.…”

Section: Carbonate Precipitation On the Early Archean Earthmentioning

confidence: 93%

Carbonate Minerals in the Warrawoona Group, Pilbara Craton: Implications for Continental Crust, Life, and Global Carbon Cycle in the Early Archean

Nakamura¹,

Kato²

2002

Resource Geology

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Abstract:The occurrences of the Early Archean carbonate minerals are compiled and their precipitation processes are investigated for the Warrawoona Group, Pilbara Craton. Sedimentary carbonate rocks such as limestone and dolostone are very rare, and only a small amount of sedimentary carbonate minerals are sometimes contained in the hydrothermal bedded chert, implying that a sink of CO 2 was minor in the Early Archean sediments. Moreover, it is very likely that the activity of cyanobacteria forming stromatolites was considerably low in the Early Archean. Microfossils and carbonaceous matter in the hydrothermal cherts are probably derived from a non-photosynthetic microorganisms related to the seafloor hydrothermal activity. Their preservation in sediments may play a very minor role in carbon sink of the Earth's surface.On the other hand, carbonatized volcanic rocks subjected to seafloor hydrothermal alteration occur ubiquitously in the Early Archean greenstone belts such as the Warrawoona Group, suggesting that the hydrothermally altered oceanic crust had large amounts of CO 2 as carbonate minerals. Global carbon cycle in the Early Archean is considered to have been controlled by the intense seafloor hydrothermal alteration. Large amounts of CO 2 were sunk into the oceanic crust by the alteration. The carbonatized oceanic crust was partly accreted to the continents and/or island-arcs, and partly subducted into the mantle without decomposition. Significant amounts of carbonate minerals in the carbonatized oceanic crust were very likely to store in the accretionary prisms and mantle, consequently giving rise to a decrease of atmospheric and oceanic CO 2 .Keywords: hydrothermal, carbonatization, carbonate, carbon dioxide, oceanic crust, stromatolite, global carbon cycle, Early Archean, Warrawoona Group carbonate displaying a stromatolite texture deposited in the ocean (Fig. 2b;Walter and Heys, 1985;Awramik, 1992;Semikhatov and Raaben, 1996). This geological evidence suggests that biological activity of cyanobacteria was mostly responsible for carbonate precipitation in the Proterozoic (Grotzinger and Knoll, 1999;Riding, 2000). In contrast, sedimentary carbonates were much less in the Archean than the Proterozoic and Phanerozoic (Fig. 2a;Ronov, 1964;Veizer et al., 1989a). Although more than 20 of stromatolite occurrences are now known worldwide in the Archean (Martin et al., 1980;Walter, 1983;Beukes and Lowe, 1989), the true fossil record such as a stromatolite texture and microfossils is sparse in the Archean compared to the Proterozoic (Hofmann, 1999). In particular, the occurrences of the stromatolites older than 3.2 Ga are rare ( Fig. 2b; Hofmann, 1999), and the biogenesis of the stromatolite-like textures has been questioned (Walter et al., 1980;Lowe, 1980bLowe, , 1994Lowe, , 1995Buick et al., 1995). It is assured that the carbonate sediment was significantly minor in the Archean. However, several researchers have believed that the carbonate precipitation is essentially the same throughout the Earth's history ...

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Cherts of the Barberton Greenstone Belt Interpreted as Products of Submarine Exhalative Activity

Cited by 121 publications

References 21 publications

Calcification and Silicification: Fossilization Potential of Cyanobacteria from Stromatolites of Niuafo‘ou's Caldera Lakes (Tonga) and Implications for the Early Fossil Record

Calcification and Silicification: Fossilization Potential of Cyanobacteria from Stromatolites of Niuafo‘ou's Caldera Lakes (Tonga) and Implications for the Early Fossil Record

Biogenic nitrogen and carbon in Fe‐Mn‐oxyhydroxides from an Archean chert, Marble Bar, Western Australia

Carbonate Minerals in the Warrawoona Group, Pilbara Craton: Implications for Continental Crust, Life, and Global Carbon Cycle in the Early Archean

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