Size, shape and orientation of grains in sands and sandstones—image analysis applied to rock thin-sections

Schäfer, Andreas; Teyssen, Thomas

doi:10.1016/0037-0738(87)90064-9

Cited by 44 publications

(16 citation statements)

References 19 publications

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“…For aggregates of granules, individual granules were measured rather than the dimension of aggregates. Apparent grain sizes were corrected using a Matlab script based on the work of Schäfer and Teyssen (1987) to estimate the true grain sizes from observations of spherical segment diameters in thin section cuts through grains. Grains were approximated as oblate spheres.…”

Section: Methodsmentioning

confidence: 99%

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: Methodsmentioning

confidence: 99%

Sedimentology and geochemistry of Archean silica granules

Stefurak

Lowe

Zentner

et al. 2015

Geological Society of America Bulletin

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“…Image analysis is familiar to geologists who have extensively explored the possibilities of this method (Schafer and Teyssen 1987; Allard and Sotin 1988). But quantitative petrographic analysis of ceramic pastes has not been used very often.…”

Section: The Methods Used For the Quantification Of The Petrographic Datamentioning

confidence: 99%

Amphorae From Lyons: Petrographic and Chemical Arguments*

Schmitt¹

1998

Archaeometry

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This paper briefly presents a method for the interpretation of quantitative petrographic data and chemical composition data from amphorae found in Lyons with the aim of determining whether or not the amphorae are of local production. We will try to define the exact place of each argument in our reasoning about the attribution of the origin of these ceramics, while insisting on the zones of uncertainty for each method. It is important to emphasize here that in assigning the origin of the Lyons amphorae all the arguments must be used conjointly. The presence of rhyolite in the temper is not enough to determine the Lyons origin of an amphora, and the geochemical arguments are ofen insuflcient to make a decision. It is a reasoned application of petrographic, geochemical and archaeological arguments which enables us to pronounce an attribution.

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“…However, grain size distributions of fractions which are derived from thin sections are generally biased due to individual grains being cut randomly so that the two-dimensional sections of the grains mostly do not indicate the maximum or minimum cross section, the latter being measured by sieving (Schäfer and Teyssen, 1987;Heilbronner and Keulen, 2006). Furthermore, the circularity measurement can distinguish a circle (i.e.…”

Section: Quartzmentioning

confidence: 99%

“…Many of the workers who have used image analysis to measure the shape and size of particles (Schäfer and Teyssen, 1987;Francus, 1998;Persson, 1998;Mertens and Elsen, 2006) have concluded that image analysis results provide two-dimensional parameters that show a close correlation with the results of three-dimensional parameter methods (sieving) (Mertens and Elsen, 2006). However, grain size distributions of fractions which are derived from thin sections are generally biased due to individual grains being cut randomly so that the two-dimensional sections of the grains mostly do not indicate the maximum or minimum cross section, the latter being measured by sieving (Schäfer and Teyssen, 1987;Heilbronner and Keulen, 2006).…”

Section: Quartzmentioning

confidence: 99%