Ambient pyrite grains in Precambrian cherts

Tyler, S. A.; Barghoorn, Elso S.

doi:10.2475/ajs.261.5.424

Cited by 67 publications

(35 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…The solid curve is a fit to the data (solid circles) using an exponential function with j 2p 5 100 mm. (2000) ,1 100 6 15 Filament U GSC 43592 2.3 6 0.2 14.7 6 1.0 18.4 6 2 behind minute (1-10 mm) pyrite grains migrating in the chert matrix (Tyler and Barghoorn 1963;Knoll and Barghoorn 1974). Examples of such trails do occur in our Gunflint specimens, but with a much smaller ratio of contour length to filament diameter than what is characteristic of the filaments we have selected for analysis.…”

Section: Microfossil Correlation Lengthsmentioning

confidence: 88%

Shape analysis of filamentous Precambrian microfossils and modern cyanobacteria

Boal¹,

Ng²

2010

Paleobiology

View full text Add to dashboard Cite

Variations in the orientation and cross-sectional shape of filamentous microfossils provide quantitative measures for characterizing them and probing their native mechanical structure. Here, we determine the tangent correlation length, which is the characteristic length scale for the variation in direction of a sinuous curve, for both a suite of Precambrian filamentous microfossils and six strains of modern filamentous cyanobacteria, all with diameters of a few microns. Among 1.9-2-Ga microfossils, Gunflintia grandis, Gunflintia minuta and Eomycetopsis filiformis possess, respectively, correlation lengths of 360 ± 40 μm, 670 ± 40 μm and 700 ±100 μm in two dimensions. Hundreds of times larger than the filament diameters, these values lie in the same range as the cyanobacteria Geitlerinema and Pseudanabaena, but are smaller than several strains of Oscillatoria. In contrast, the 2-Ga microfossil trichome Halythrix, is found to have a short correlation length of 29 ± 4 μm in two dimensions. Micron-wide pyritic replacement filaments observed in 3.23-Ga volcanogenic deposits also display a modest correlation length of 100 ± 15 μm in two dimensions. Sequences of species in two genera of our modern cyanobacteria possess tangent correlation lengths that rise as a power of the filament diameter D—D3.3 ± 1 for Oscillatoria and D5.1 ± 1 for Geitlerinema. These results can be compared with power-law scaling of D3 for hollow tubes and D4 for solid cylinders that is expected from continuum mechanics. Extrapolating the observed scaling behavior to smaller filament diameters, the measured correlation length of the pyrite filaments is consistent with modern Geitlerinema whereas that of Halythrix lies not far from modern Oscillatoria, suggesting that there may be structural similarities among these genera.

show abstract

Section: Microfossil Correlation Lengthsmentioning

confidence: 88%

Shape analysis of filamentous Precambrian microfossils and modern cyanobacteria

Boal¹,

Ng²

2010

Paleobiology

View full text Add to dashboard Cite

show abstract

“…As is well illustrated by the study of Knoll et al (1988), who coined the term "Archeanization" to refer to such marked diagenetic degradation, the state of preservation of organic-walled fossils, the geochemical maturity of the carbonaceous matter of which they are composed, is of prime importance to interpretation of their origin. Such difficulties have long been recognized-dating from at least as early as the 1960s (Tyler and Barghoorn, 1963), when active studies of Precambrian fossil microbes were first getting underway (Barghoorn and Schopf, 1965; Barghoorn and Tyler, 1965;Cloud, 1965;Schopf, 1968)-but questions regarding the biogenicity of ancient putative fossils continue to be raised (Brasier et al, 2002(Brasier et al, , 2004.…”

Section: Introductionmentioning

confidence: 97%

Raman Imagery: A New Approach to Assess the Geochemical Maturity and Biogenicity of Permineralized Precambrian Fossils

Schopf

Kudryavtsev²,

Agresti³

et al. 2005

Astrobiology

194

178

View full text Add to dashboard Cite

Laser-Raman imagery is a non-intrusive, non-destructive analytical technique, recently introduced to Precambrian paleobiology, that can be used to demonstrate a one-to-one spatial correlation between the optically discernible morphology and kerogenous composition of permineralized fossil microorganisms. Made possible by the submicron-scale resolution of the technique and its high sensitivity to the Raman signal of carbonaceous matter, such analyses can be used to determine the chemical-structural characteristics of organic-walled microfossils and associated sapropelic carbonaceous matter in acid-resistant residues and petrographic thin sections. Here we use this technique to analyze kerogenous microscopic fossils and associated carbonaceous sapropel permineralized in 22 unmetamorphosed or little-metamorphosed fine-grained chert units ranging from approximately 400 to approximately 2,100 Ma old. The lineshapes of the Raman spectra acquired vary systematically with five indices of organic geochemical maturation: (1) the mineral-based metamorphic grade of the fossil-bearing units; (2) the fidelity of preservation of the fossils studied; (3) the color of the organic matter analyzed; and both the (4) H/C and (5) N/C ratios measured in particulate kerogens isolated from bulk samples of the fossil-bearing cherts. Deconvolution of relevant spectra shows that those of relatively well-preserved permineralized kerogens analyzed in situ exhibit a distinctive set of Raman bands that are identifiable also in hydrated organic-walled microfossils and particulate carbonaceous matter freed from the cherts by acid maceration. These distinctive Raman bands, however, become indeterminate upon dehydration of such specimens. To compare quantitatively the variations observed among the spectra measured, we introduce the Raman Index of Preservation, an approximate measure of the geochemical maturity of the kerogens studied that is consistent both with the five indices of organic geochemical alteration and with spectra acquired from fossils experimentally heated under controlled laboratory conditions. The results reported provide new insight into the chemical-structural characteristics of ancient carbonaceous matter, the physicochemical changes that accompany organic geochemical maturation, and a new criterion to be added to the suite of evidence by which to evaluate the origin of minute fossil-like objects of possible but uncertain biogenicity.

show abstract

“…Putative microbial endoliths have recently been described from the margins of subaqueous basic pillow lavas in the ca 3.5 Gyr Hoogenoeg and Kromberg Formations of the Barberton . The challenge here is that the same kinds of morphological structure can be produced by ambient inclusion trails (AITs), especially those of pyrite (Tyler & Barghoorn 1963;Knoll & Barghoorn 1974), and an abiogenic origin needs to be falsified (Brasier et al 2004). Such AITs are considered to form when pyrite (or other inclusions) are impelled to migrate through silica under raised fluid/gas pressures, possibly generated by biological decay.…”

Section: Endoliths and The Warrawoona 'Microtubes'mentioning

confidence: 99%

“…These have been thought to form when metallic inclusions are propelled in some way through glassy silica or an organic mush (cf. Tyler & Barghoorn 1963;Knoll & Barghoorn 1974;Xiao & Knoll 1999) leaving behind a hollow tubular trail, which may remain empty or be infilled by a secondary mineral phase. They can be recognized by: (i) presence of a mineral grain (e.g.…”

Section: Endoliths and The Warrawoona 'Microtubes'mentioning

confidence: 99%

A fresh look at the fossil evidence for early Archaean cellular life

Brasier

McLoughlin

Green

et al. 2006

Phil. Trans. R. Soc. B

257

154

View full text Add to dashboard Cite

The rock record provides us with unique evidence for testing models as to when and where cellular life first appeared on Earth. Its study, however, requires caution. The biogenicity of stromatolites and 'microfossils' older than 3.0 Gyr should not be accepted without critical analysis of morphospace and context, using multiple modern techniques, plus rejection of alternative non-biological (null) hypotheses. The previous view that the co-occurrence of biology-like morphology and carbonaceous chemistry in ancient, microfossil-like objects is a presumptive indicator of biogenicity is not enough. As with the famous Martian microfossils, we need to ask not 'what do these structures remind us of ?', but 'what are these structures?' Earth's oldest putative 'microfossil' assemblages within 3.4-3.5 Gyr carbonaceous cherts, such as the Apex Chert, are likewise self-organizing structures that do not pass tests for biogenicity.There is a preservational paradox in the fossil record prior to ca 2.7 Gyr: suitable rocks (e.g. isotopically light carbonaceous cherts) are widely present, but signals of life are enigmatic and hard to decipher. One new approach includes detailed mapping of well-preserved sandstone grains in the ca 3.4 Gyr Strelley Pool Chert. These can contain endolithic microtubes showing syngenicity, grain selectivity and several levels of geochemical processing. Preliminary studies invite comparison with a class of ambient inclusion trails of putative microbial origin and with the activities of modern anaerobic proteobacteria and volcanic glass euendoliths.

show abstract

Ambient pyrite grains in Precambrian cherts

Cited by 67 publications

References 0 publications

Shape analysis of filamentous Precambrian microfossils and modern cyanobacteria

Shape analysis of filamentous Precambrian microfossils and modern cyanobacteria

Raman Imagery: A New Approach to Assess the Geochemical Maturity and Biogenicity of Permineralized Precambrian Fossils

A fresh look at the fossil evidence for early Archaean cellular life

Contact Info

Product

Resources

About