Elemental composition sandstones

Kraishan G. M., Rezaee M. R., and Worden R. H. (2000) Significance of trace element composition of quartz cement as a key to reveal the origin of sihca in sandstones an example from the Cretaceous of the Barrow Sub-basin, Western Australia. In Quartz Cementation in Sandstones (eds. R. H. Worden and S. Morad). International Association of Sedimentologists, Oxford, vol. 29, pp. 317-331. 

Figures 2-4 summarize the currently available information on the stoichiometry and minor or trace element concentration of saddle dolomite in carbonates, sandstones and carbonate-sandstone mixtures. Saddle dolomite shows a variable elemental composition, from near-stoichiometric to calcian dolomite and/or ankerite. The bulk of published major, minor and trace element data on saddle dolomite are based on electron microprobe analyses, although some authors used powder X-ray diffraction analysis to determine the dolomite stoichiometry. Others used spectrometric techniques (e.g. atomic absorption) to analyse for trace elements. We found it difficult to evaluate this published information because some authors report bulk analyses of several crystals, whereas others report intracrystalline elemental variations. Moreover, analyses are often incomplete (e.g. wt% Fe and Mn no data on Ca and Mg) and cannot be directly recalculated in terms of mol%. Further, some authors report a single measurement whereas others list hundreds of data points.

Although the number of samples analyzed is limited, the inescapable conclusion to be drawn from our data is that some of the Nile silt formations can be differentiated on the basis of trace element contents and REE distribution patterns. In addition, we conclude that the Early Predynastic (Amratian) pottery was made from clays found in the immediate vicinity of the kiln. Older shales that are found layered with the much earlier sandstone deposits that were cut by the Great Wadi were also analyzed. The REE patterns as well as the scandium, chromium, and iron concentrations are different enough to suggest that these materials were not used to produce pottery (21), In a previous paper, we discussed the possibility that some of this shale, or the white salt found associated with it (anhydrite-CaSOj, was mixed with the local clay to produce the finer, harder plum red ware (21). This addition could account for the slight difference in the average composition of the sherds from localities 11, 39, and 59 and the Masmas silt. 

Carbonate cements are often among the dominant components of diagenesis and hence are of decisive importance in determining the reservoir quality of sandstone sequences. Despite this, the timing, the geochemical conditions of precipitation and dissolution, as well as the source and fate of these cements are not fully understood. In continental and near-shore sediments, cements commonly precipitate as calcretes and dolocretes in the vadose and phreatic zones, and attain a variety of mineral-ogical, textural and distribution patterns as well as elemental and isotopic compositions. These cements form lenses and layers of densely cemented... 

There is no systematic difference in elemental concentrations or covariation, either within or between concretions, that can be correlated with either age or tectonic setting of the sandstone. In Fig. 12 both foreland and piggy-back basin samples occur across the compositional ranges identified with relatively early and relatively late calcite pre-... 

The values of Fe and Mn reported for saddle dolomite are presented together in Fig. 3 because the geochemical properties of these elements are similar. Fe -i- Mn concentrations in saddle dolomite show wide variability, from <10 ppm to 30 mol% (Fig. 3), reflecting in part the compositional zoning in the saddle dolomite structure. In sandstones. 

Almost any of the chemical elements may be found in soils, at least in traces, but actually most of the inorganic portion consists of a comparatively small number of these elements. This is because soils are formed chiefly from igneous rocks, shales and sandstones, 98% of which on the average consist of less than ten elements. In Table 2.11 is shown the approximate composition, expressed as oxides of the elements, of the earth s crust and also the mean composition of the A-horizon of 18 representative soils. These data of Byers et al. (1938) emphasize the extent to which weathering removes the bases... 

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