Earliest part of Earth's stratigraphic record: A reappraisal of the &gt;3.7 Ga Isua (Greenland) supracrustal sequence

Rosing, Minik T.; Rose, Nicholas M.; Bridgwater, D.; Thomsen, Heidi S.

doi:10.1130/0091-7613(1996)024<0043:epoess>2.3.co;2

Cited by 209 publications

(92 citation statements)

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“…Sedimentary strata contain a powerful record of this interplay and house information of planetary history 1,2 including the origin and evolution of life 3 , oxygenation of the Earth's atmosphere 4 , global climate change 5 and the great wetting and drying of Mars 6 . Quantitative reconstructions of environmental conditions from the sedimentary record are vital, especially under present climatic changes, as they provide a pre-anthropogenic baseline to guide future landscape and climate management.…”

mentioning

confidence: 99%

Quantitative bounds on morphodynamics and implications for reading the sedimentary record

2014

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Sedimentary rocks are the archives of environmental conditions and ancient planetary surface processes that led to their formation. Reconstructions of Earth's past surface behaviour from the physical sedimentary record remain controversial, however, in part because we lack a quantitative framework to deconvolve internal dynamics of sediment-transport systems from environmental signal preservation. Internal dynamics of landscapes-a consequence of the coupling between bed topography, sediment transport and flow dynamics (morphodynamics)-result in regular and quasiperiodic landforms that abound on the Earth and other planets. Here, using theory and a data compilation of morphodynamic landforms that span a wide range of terrestrial, marine and planetary depositional systems, we show that the advection length for settling sediment sets bounds on the scales over which internal landscape dynamics operate. These bounds provide a universal palaeohydraulic reconstruction tool on planetary surfaces and allow for quantitative identification of depositional systems that may preserve tectonic, climatic and anthropogenic signals.

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confidence: 99%

Quantitative bounds on morphodynamics and implications for reading the sedimentary record

2014

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“…However, the intra-zircon magmatic petrology plus a few rare low-strain domains in the rocks indicate that they are clearly not derived by metasomatism of tonalites or mafic rocks (as was proposed by Rosing et al, 1996 andMyers, 2001). Instead, they are interpreted to be of volcanic origin, possibly including some ignimbritic units (e.g.…”

Section: Protolith Of the Isua 3806 Ma Felsic Schistsmentioning

confidence: 74%

“…In this paper we refer to these structures in a non-genetic sense as 'nodules'. The unit was re-evaluated again by Rosing et al (1996) who concluded that it represents a strongly metasomatised, carbonated tonalite sheet intruded into the belt. Myers (2001) reinterpreted the unit as a strongly metasomatised series of mafic volcanic rocks.…”

Section: Previous Studiesmentioning

confidence: 99%

“…The two commonest interpretations of these rocks are that (a) they are altered, metamorphosed felsic volcanic rocks (Allaart, 1976;Nutman et al, 1983Nutman et al, , 1984 or (b) they are mylonitised and metasomatised tonalites (Rosing et al, 1996). There are key petrographic features that support the former volcanic interpretation, and negate the latter mylonitised tonalite interpretation.…”

Section: Whole-rock Petrographymentioning

confidence: 99%

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3806Ma Isua rhyolites and dacites affected by low temperature Eoarchaean surficial alteration: Earth's earliest weathering

Nutman

Bennett

Chivas

et al. 2015

Precambrian Research

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This paper reports evidence for Earth's oldest-recognised low temperature alteration, at ∼3800 Ma. Potassic felsic schists with a protolith age of 3806 ± 2 Ma form a ∼30 km long unit in the amphibolite facies, deformed, Isua supracrustal belt (West Greenland). At a single locality, boudinaged layers (nodules) within the schists are low strain zones: they are fine-grained, weakly feldspar-phyric, contain quartz amygdules and have fiammelike structures, all supporting a volcanic protolith. The nodules and surrounding schistose matrix contain abundant, 100-50 μm, euhedral, oscillatory zoned 3806 Ma zircons. The rare earth patterns of the zircons indicate crystallisation was magmatic. Some zircons contain axial lobate voids indicating that they grew at low pressure as the magma exsolved a fluid. Ti-in-zircon thermometry indicates crystallisation temperatures of 750-650 °C. Taken together, these zircon features indicates growth at eutectic temperatures in a hypabyssal chamber as the magma was exsolving a fluid phase. The magmatic zircons have ɛHf initial values of ∼0 and δ18OVSMOW of +5.0‰ ( Hiess et al., 2009), showing that the source of the volcanic rocks was devoid of assimilated markedly older or weathered crustal material, and probably essentially juvenile. In contrast, the whole rock δ18OVSMOW values are elevated at +14.7 to +16.2‰, indicative of superimposed lowtemperature alteration processes. The nodules and matrix schists have non-igneous bulk compositions, exemplified by strong enrichment in K2O and depletion in Na2O. They are depleted in Sr, have no negative Eu anomalies, but have high Rb/Sr, with an Rb-Sr age of 3760 ± 140 Ma ( Jacobsen and Dymek, 1988). This indicates that the alteration involving strong degradation of plagioclase occurred in the Eoarchaean. Trace element compositions and establishment of alteration vectors suggest the protoliths were likely rhyolitic and dacitic in composition. The strongest-modified matrix schist compositions contain biotite ± calcite ± dolomite with increase in MgO relative to the nodules, which indicates early magnesian carbonate growth. The whole-rock chemistry, decoupling of the igneous zircon and whole-rock oxygen isotope signatures and the Rb-Sr dating indicate that after eruption, the 3806 Ma felsic volcanic rocks underwent Eoarchaean lowtemperature potassic alteration with weathering and groundwater circulation the most likely process. The geochemistry of the Isua felsic schists is compared with that of better-preserved volcanic rocks where the alteration conditions are known. This suggests a subaerial environment. The carbonatisation of the Isua felsic schists demonstrates drawdown of atmospheric CO2 into rocks made porous by the weathering.

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“…Todavia, até há cerca de 4 mil Ma, impactos meteoríticos ocasionais provocavam aquecimento dos oceanos então existentes, esterilizando-os (Nisbet & Sleep, 2001). As mais antigas rochas sedimentares marinhas encontradas até agora (e que, portanto, conseguiram sobreviver aos intensos episódios tectónicos e metamórficos por que passaram) são as de Akilia, na Groenlândia Ocidental, datada de há uns 3,86 mil Ma (Nutman et al, 1996), e de Isua, no Sudoeste da Groenlândia, com 3,7 mil Ma (Rosing et al, 1996). Embora se considere que a vida na Terra existe desde antes de 3,8 mil Ma (e.g., Nisbet & Sleep, 2001;Schidlowski, 1988), a escassa biosfera então existente seria constituída por extremófilos, possivelmente hipertermófilos (e.g., Schidlowski, 1988;Rothschild & Mancinelli, 2001), que talvez vivessem junto a exsudações hidrotermais oceânicas e que, por vezes, seriam destruídos devido a impactos meteoríticos.…”

Section: Das Dinâmicas Naturaisunclassified

Alterações Climáticas, Perceções e Racionalidades

Viegas

Azeiteiro

Dias

et al. 2014

RGCI

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RESUMOConsiderando que as Alterações Climáticas (AC) -uma das cinco áreas-guia da Estratégia 2020 da Comissão Europeia -são um problema global que requer respostas locais articuladas aos níveis macro, meso e micro; e que a sua compreensão implica a identificação das relações reciprocamente influentes entre a Natureza, a Sociedade e a Cultura; qualquer intervenção -seja no sentido da mitigação das AC, seja no sentido da adaptação às AC -envolve necessariamente essa mesma sociedade, em toda a complexidade das suas dimensões socioculturais e ambientais. Neste artigo, enquadrado pelas teorias compreensivas, refletimos brevemente sobre algumas das inter-relações entre os sistemas climáticos, ambientais e socioculturais e defendemos que as racionalidades leigas, por se enraizarem em tipos e fontes de saber plurais, são um dos pilares para melhor se compreender e lidar com o fenómeno das AC. Palavras

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Earliest part of Earth's stratigraphic record: A reappraisal of the >3.7 Ga Isua (Greenland) supracrustal sequence

Cited by 209 publications

References 0 publications

Quantitative bounds on morphodynamics and implications for reading the sedimentary record

Quantitative bounds on morphodynamics and implications for reading the sedimentary record

3806Ma Isua rhyolites and dacites affected by low temperature Eoarchaean surficial alteration: Earth's earliest weathering

Alterações Climáticas, Perceções e Racionalidades

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