The Experts below are selected from a list of 201930 Experts worldwide ranked by ideXlab platform
Loïc Villier - One of the best experts on this subject based on the ideXlab platform.
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Phanerozoic trends in skeletal Mineralogy driven by mass extinctions
Nature Geoscience, 2008Co-Authors: Wolfgang Kiessling, Martin Aberhan, Loïc VillierAbstract:Changes in ocean chemistry that favoured the precipitation of aragonite or calcite are thought to have influenced the skeletal Mineralogy of marine calcifyers. An investigation of the original skeletal Mineralogy of large numbers of marine taxa suggests that the selective recovery of marine organisms from mass extinctions has a much greater influence on the overall percentage of aragonitic organisms than the Mg/Ca ratio of the oceans. Marine calcifying organisms that produce sediments and build reefs generally have skeletons and shells that are composed of either aragonite or calcite. Long-term changes in the estimated Mg/Ca ratios of sea water tend to correspond to changes in the prevailing Mineralogy of these creatures^ 1 , 2 . High Mg/Ca ratios are expected to favour the spread of aragonitic organisms, whereas calcitic taxa are thought to benefit from low Mg/Ca ratios^ 3 , 4 , 5 , 6 . Here we test these patterns throughout the Phanerozoic eon and assess the relative impacts of changing ocean chemistry and mass extinctions on the evolutionary success of calcifying organisms. We find that mass extinctions are more important in regulating long-term patterns of skeletal Mineralogy than the Mg/Ca ratios of the global oceans. Furthermore, selective recovery from mass extinctions is usually more important than selective extinction, in driving the Phanerozoic pattern of skeletal Mineralogy. But even in the recovery phase there is no clear connection between changes in the dominance of aragonite or calcite and the Mg/Ca ratio of the oceans, thus providing further evidence for the complexity of biotic recoveries^ 7 .
Cecilia Akselsson - One of the best experts on this subject based on the ideXlab platform.
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comparison of measured xrpd and modeled a2m soil mineralogies a study of some swedish forest soils in the context of weathering rate predictions
Geoderma, 2018Co-Authors: Sophie Casetougustafson, Cecilia Akselsson, Magnus Simonsson, Johan Stendahl, Stephen Hillier, Bengt A OlssonAbstract:Abstract Quantitative soil Mineralogy has been identified as a key factor influencing PROFILE weathering estimates, and is often calculated with normative methods, such as the “Analysis to Mineralogy” (‘A2M’) model. In Sweden and other countries, there is a large request for accurate base cation weathering estimates in order to establish how sustainable harvest of biomass should be performed in the future. However, there is a lack of knowledge around the accuracy of the arithmetic mean output of A2M estimates, the most common A2M solution used in weathering studies. To our knowledge, a thorough investigation of how A2M input data affect the arithmetic mean output (center of gravity of the A2M solution space) is missing. In this study, the indirect geochemical normative method (A2M) was compared with a direct x-ray powder diffraction method (XRPD) to quantify soil Mineralogy at two sites and 8 soil profiles, at a 10 cm depth interval. We explored the hypothesis that normative calculations performed with A2M produce an output in closer agreement with the Mineralogy obtained from XRPD, if site specific mineralogical input data are used rather than regional data. Site-specific mineralogical input data consisted of mineral stoichiometry data measured by electron microprobe analysis (EMPA) and mineral identity determined by XRPD, whereas regional mineral input data were based on previously reported data on mineral stoichiometry and mineral identity, derived from three geological regions in Sweden. The results from this comparison showed that the site-specific approach yielded relatively low average biases and root mean square errors (RMSE) for most minerals, with the exception of quartz (Average bias of − 4.8 wt%, RMSE of 5.3 wt%) at the Asa site. The regional approach yielded deviating results for K-feldspar and dioctahedral mica, with high average biases and RMSE for dioctahedral mica (Asa: 7.8 wt%, 9.0 wt%; Flakaliden: 12.8 wt%, 15.5 wt%) and for K-feldspar (Asa: − 5.2 wt%, 6.1 wt%; Flakaliden: − 5.6 wt%, 6.7 wt%). The results from this study were supported by a close agreement between measured geochemistry and normalized geochemistry derived from a back calculation of the XRPD Mineralogy (i.e. mineral budgeting). In conclusion, our findings suggest that A2M results in combination with site-specific mineralogical input data are improved independent of study site and soil profile. However, for future weathering studies it might be beneficial to find constraints of how to select a solution from the entire A2M solution space which is in better agreement with the XRPD Mineralogy.
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Relations between elemental content in till, Mineralogy of till and bedrock Mineralogy in the province of Småland, southern Sweden
Geoderma, 2006Co-Authors: Cecilia Akselsson, Johan Holmqvist, Daniel Kurz, Harald SverdrupAbstract:Information on soil Mineralogy is essential for weathering rate calculations. Quantitative mineralogical analyses are expensive and time-consuming, and thus indirect methods of determining the mineralogical composition are important, for example estimating the composition based on the elemental content in till (total concentrations), or based on information about the underlying bedrock. The mineralogical composition and the elemental content in till were analysed in two areas in southern Sweden, at 10 sites in each area. There were significant differences between the areas regarding both elemental content and optically determined Mineralogy. The content of calcium was significantly higher in one area, 5ESV, and there were tendencies in this direction also for magnesium and iron. The potassium content was significantly higher in the other area, 6FNV. The variation in soil chemistry between the areas can be explained by higher contents of the minerals biotite, hornblende and epidote in the first area (5ESV) and higher contents of K-feldspar in the second (6FNV). Normative Mineralogy was determined based on the elemental content. A comparison between the normative Mineralogy and the optically determined Mineralogy showed great similarities which indicates that there is good potential for using elemental content for estimating the mineralogical composition. The difference in till composition between the areas could not be explained by the underlying bedrock, which indicates that the information available on the bedrock is not sufficient for estimation of the till mineralogical composition.
Claire Chenu - One of the best experts on this subject based on the ideXlab platform.
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does phyllosilicate Mineralogy explain organic matter stabilization in different particle size fractions in a 19 year c3 c4 chronosequence in a temperate cambisol
Geoderma, 2016Co-Authors: Oihane Fernandezugalde, Pierre Barre, Inigo Virto, Fabien Hubert, Daniel Billiou, Claire ChenuAbstract:Finely divided minerals play a key role on the stabilization of soil organic matter (SOM). Among them, phyllosilicates are known to be particularly efficient due to their surface properties. However, how the wide variety of phyllosilicates with contrasted surface properties results in differing abilities to stabilize SUM is still unclear. In this study, we used a C-3/C-4 chronosequence established in a temperate Cambisol to compare the quantity of organic C and the incorporation of maize-derived C associated to various particle-size fractions with contrasting phyllosilicate Mineralogy. We separated sand, silt and clay fractions in samples from 0-20-cm and 45-60-cm horizons. In each fraction, we measured organic C, total N and C isotope signatures. Phyllosilicate Mineralogy of fine-silt, coarse-clay, medium-clay, and fine-clay fractions (2-20 mu m, 0.2-2 mu m, 0.2-0.05 mu m, <0.05 mu m) was determined using X-ray diffraction. Although phyllosilicate Mineralogy differed between fractions, no clear relation was observed between Mineralogy and organic C among the various particle-size fractions in any horizon. Interestingly, coarse-clay fractions providing a lower specific surface area had the greatest content of organic C and the lowest incorporation of fresh maize-C This supported the hypothesis that a significant part of organic C stabilized in these fractions is due to the presence of very stable clay-size aggregates (resistant to sonication) that encapsulate organic C. The differing ability of the various phyllosilicates to stabilize organic C should therefore be evaluated according to both their ability to adsorb organic C and to form stable clay-size aggregates. This may prevent from finding simple relationships between phyllosilicate Mineralogy and organic C stabilization.
Wolfgang Kiessling - One of the best experts on this subject based on the ideXlab platform.
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Phanerozoic trends in skeletal Mineralogy driven by mass extinctions
Nature Geoscience, 2008Co-Authors: Wolfgang Kiessling, Martin Aberhan, Loïc VillierAbstract:Changes in ocean chemistry that favoured the precipitation of aragonite or calcite are thought to have influenced the skeletal Mineralogy of marine calcifyers. An investigation of the original skeletal Mineralogy of large numbers of marine taxa suggests that the selective recovery of marine organisms from mass extinctions has a much greater influence on the overall percentage of aragonitic organisms than the Mg/Ca ratio of the oceans. Marine calcifying organisms that produce sediments and build reefs generally have skeletons and shells that are composed of either aragonite or calcite. Long-term changes in the estimated Mg/Ca ratios of sea water tend to correspond to changes in the prevailing Mineralogy of these creatures^ 1 , 2 . High Mg/Ca ratios are expected to favour the spread of aragonitic organisms, whereas calcitic taxa are thought to benefit from low Mg/Ca ratios^ 3 , 4 , 5 , 6 . Here we test these patterns throughout the Phanerozoic eon and assess the relative impacts of changing ocean chemistry and mass extinctions on the evolutionary success of calcifying organisms. We find that mass extinctions are more important in regulating long-term patterns of skeletal Mineralogy than the Mg/Ca ratios of the global oceans. Furthermore, selective recovery from mass extinctions is usually more important than selective extinction, in driving the Phanerozoic pattern of skeletal Mineralogy. But even in the recovery phase there is no clear connection between changes in the dominance of aragonite or calcite and the Mg/Ca ratio of the oceans, thus providing further evidence for the complexity of biotic recoveries^ 7 .
Oihane Fernandezugalde - One of the best experts on this subject based on the ideXlab platform.
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does phyllosilicate Mineralogy explain organic matter stabilization in different particle size fractions in a 19 year c3 c4 chronosequence in a temperate cambisol
Geoderma, 2016Co-Authors: Oihane Fernandezugalde, Pierre Barre, Inigo Virto, Fabien Hubert, Daniel Billiou, Claire ChenuAbstract:Finely divided minerals play a key role on the stabilization of soil organic matter (SOM). Among them, phyllosilicates are known to be particularly efficient due to their surface properties. However, how the wide variety of phyllosilicates with contrasted surface properties results in differing abilities to stabilize SUM is still unclear. In this study, we used a C-3/C-4 chronosequence established in a temperate Cambisol to compare the quantity of organic C and the incorporation of maize-derived C associated to various particle-size fractions with contrasting phyllosilicate Mineralogy. We separated sand, silt and clay fractions in samples from 0-20-cm and 45-60-cm horizons. In each fraction, we measured organic C, total N and C isotope signatures. Phyllosilicate Mineralogy of fine-silt, coarse-clay, medium-clay, and fine-clay fractions (2-20 mu m, 0.2-2 mu m, 0.2-0.05 mu m, <0.05 mu m) was determined using X-ray diffraction. Although phyllosilicate Mineralogy differed between fractions, no clear relation was observed between Mineralogy and organic C among the various particle-size fractions in any horizon. Interestingly, coarse-clay fractions providing a lower specific surface area had the greatest content of organic C and the lowest incorporation of fresh maize-C This supported the hypothesis that a significant part of organic C stabilized in these fractions is due to the presence of very stable clay-size aggregates (resistant to sonication) that encapsulate organic C. The differing ability of the various phyllosilicates to stabilize organic C should therefore be evaluated according to both their ability to adsorb organic C and to form stable clay-size aggregates. This may prevent from finding simple relationships between phyllosilicate Mineralogy and organic C stabilization.
