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The study of hydrogeochemical data sets frequently calls for statistical dimension reducing techniques. It is well known that
hydrochemical parameters are compositions and, for this type of data, the direct application of classical statistical methods
based on the correlation matrix yield spurious results. But new results on compositional data analysis have identified the
sampling space, the simplex, with an Euclidean space, a fact that allows us to define a simplicial factor analysis strategy,
thus overcoming the problem. For illustration, we use samples from the Llobregat River and its tributaries (NE Spain). Three
unobservable or latent factorial components are extracted, which are identified with pristine waters, potash-mining influence
and urban sewage influence. These three factorial components or compositional factors are plotted in a factorial ternary diagram,
which reflects the relative influence of each one of these factors on each observation. 相似文献
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Water chemistry is commonly investigated to determine the suitability of water for various uses. With increased knowledge
of aqueous chemistry, it has become possible to interpret the evolutionary processes that determine water composition and
quality. This paper presents procedures for exploring and modeling the environment using compositional data from water analysis,
utilizing statistical tools in an appropriate sample space. Our procedures build on a methodology based on log-ratios initiated
by John Aitchison in the early 1980's. They are not only useful for interpreting the structure of the data, but also for characterizing
and modeling the influence of geochemical processes acting on the environment. The geochemistry of water samples collected
from wells on Vulcano Island (one of the Aeolian Islands of the Italian province of Sicily) will be used to illustrate the
techniques, although an exhaustive overview would require many different examples. Vulcano island is a quiescent volcanic
area where mobilization of chemical species by weathering of volcanic rocks and input of gaseous components from fumarolic
activity has produced environmental changes expressed in the composition of phreatic waters at the surface and in the shallow
subsurface. Changes in the chemical composition of waters in unconfined aquifers of the northwestern part of the island around
the active crater appear to be useful in understanding the natural processes at work. 相似文献
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The Devonian/Carboniferous (D/C) boundary is a critical interval in the Phanerozoic history, which is associated with vigorous climatic perturbations, continental glaciation, global sea-level fall and rapidly increased extinction rates in marine realms. In many sections world-wide, these global changes left a marked lithological signature, in particular the Hangenberg black shale (products of deep-shelf anoxia) and the overlying Hangenberg sandstone (sudden siliciclastic influx into predominantly carbonate depositional environments). Both layers bear a distinct geochemical signature. Even though either or both of these two lithologies are absent at many sections, their correlative counterparts can be indicated by subtle geochemical markers. We studied elemental geochemistry of fourteen D/C boundary sections in six key areas across Europe with the aim to select globally correlatable elemental proxy for the D/C boundary. Analysis of raw/log-transformed geochemical data (EDXRF, c.p.s. units), presenting the standard approach here, indicates that concentrations of terrigenous elements (Al, K, Rb, Ti and Zr) are mainly controlled by diluted Ca (carried by marine calcium carbonate) in limestone facies and, accordingly, their variations can be related to carbonate production in the sea rather than to terrigenous input from continent. Nevertheless, due to the relative nature of geochemical observations, reliance solely on statistical processing of raw data might lead to incomplete picture of multivariate data structure and/or biased interpretations. For this reason, the aim of this contribution is to discuss the logratio alternatives of the standard statistical methods, which may better reflect the relative nature of the data. For this purpose, principal component analysis was employed to reveal main geochemical patterns and while the geochemical signature of the D/C boundary was further analysed using Q-mode clustering that leads to predicative orthonormal logratio coordinates – balances. The comprehensive picture of the multivariate data structure provided by these statistical tools makes them a primary choice for exploratory compositional data analysis. At the same time, it turns out that the standard and compositional approaches have synergic effects. This fact can be extensively used in further geochemical studies. 相似文献
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J. A. Martín-Fernández C. Barceló-Vidal V. Pawlowsky-Glahn L. ó. Kovács G. P. Kovács 《Mathematical Geology》2005,37(7):729-752
Data selected from an extensive major element database of Cenozoic volcanic rocks (including calc-alkaline andesites, dacites,
rhyolites, and alkali basalts) of Hungary are used to illustrate the detection and modeling of subcompositional patterns using
a statistical analysis based on the assumption that relative differences between the observed values are more meaningful than
absolute ones. In particular, two roughly linear compositional patterns (associated one to the alkaline basalts, the other
to the calc-alkaline series) are revealed and evaluated, and it is shown how principal component analysis can be used to obtain
the estimated subcomposition of their incidental intersection point. 相似文献
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