Session 3: On geologyhttp://hdl.handle.net/10256/6412017-11-22T20:27:32Z2017-11-22T20:27:32ZApplication of compositional data analysis to geochemical data of marine sedimentsBurger, H.Kuhn, T.http://hdl.handle.net/10256/7312012-06-28T12:30:36Z2008-05-28T00:00:00ZApplication of compositional data analysis to geochemical data of marine sediments
Burger, H.; Kuhn, T.
Daunis i Estadella, Josep; Martín Fernández, Josep Antoni
In an earlier investigation (Burger et al., 2000) five sediment cores near the Rodrigues
Triple Junction in the Indian Ocean were studied applying classical statistical methods
(fuzzy c-means clustering, linear mixing model, principal component analysis) for the
extraction of endmembers and evaluating the spatial and temporal variation of
geochemical signals. Three main factors of sedimentation were expected by the marine
geologists: a volcano-genetic, a hydro-hydrothermal and an ultra-basic factor. The
display of fuzzy membership values and/or factor scores versus depth provided
consistent results for two factors only; the ultra-basic component could not be
identified. The reason for this may be that only traditional statistical methods were
applied, i.e. the untransformed components were used and the cosine-theta coefficient as
similarity measure.
During the last decade considerable progress in compositional data analysis was made
and many case studies were published using new tools for exploratory analysis of these
data. Therefore it makes sense to check if the application of suitable data transformations,
reduction of the D-part simplex to two or three factors and visual
interpretation of the factor scores would lead to a revision of earlier results and to
answers to open questions . In this paper we follow the lines of a paper of R. Tolosana-
Delgado et al. (2005) starting with a problem-oriented interpretation of the biplot
scattergram, extracting compositional factors, ilr-transformation of the components and
visualization of the factor scores in a spatial context: The compositional factors will be
plotted versus depth (time) of the core samples in order to facilitate the identification of
the expected sources of the sedimentary process.
Kew words: compositional data analysis, biplot, deep sea sediments
2008-05-28T00:00:00ZStudies in stoichiometry with compositional dataGrunsky, Eric C.Kjarsgaard, Bruce A.Egozcue, Juan JoséPawlowsky-Glahn, VeraThió i Fernández de Henestrosa, Santiagohttp://hdl.handle.net/10256/7302012-11-27T11:00:05Z2008-05-28T00:00:00ZStudies in stoichiometry with compositional data
Grunsky, Eric C.; Kjarsgaard, Bruce A.; Egozcue, Juan José; Pawlowsky-Glahn, Vera; Thió i Fernández de Henestrosa, Santiago
Daunis i Estadella, Josep; Martín Fernández, Josep Antoni
Geochemical data that is derived from the whole or partial analysis of various geologic materials
represent a composition of mineralogies or solute species. Minerals are composed of structured
relationships between cations and anions which, through atomic and molecular forces, keep the elements
bound in specific configurations. The chemical compositions of minerals have specific relationships that
are governed by these molecular controls. In the case of olivine, there is a well-defined relationship
between Mn-Fe-Mg with Si. Balances between the principal elements defining olivine composition and
other significant constituents in the composition (Al, Ti) have been defined, resulting in a near-linear
relationship between the logarithmic relative proportion of Si versus (MgMnFe) and Mg versus (MnFe),
which is typically described but poorly illustrated in the simplex.
The present contribution corresponds to ongoing research, which attempts to relate stoichiometry and
geochemical data using compositional geometry. We describe here the approach by which stoichiometric
relationships based on mineralogical constraints can be accounted for in the space of simplicial
coordinates using olivines as an example. Further examples for other mineral types (plagioclases and
more complex minerals such as clays) are needed. Issues that remain to be dealt with include the
reduction of a bulk chemical composition of a rock comprised of several minerals from which appropriate
balances can be used to describe the composition in a realistic mineralogical framework. The overall
objective of our research is to answer the question: In the cases where the mineralogy is unknown, are
there suitable proxies that can be substituted?
Kew words: Aitchison geometry, balances, mineral composition, oxides
2008-05-28T00:00:00ZStatistical evidences of cyclic changes in volcanic gas chemistry composition by inverse modellingBuccianti, AntonellaTassi, FrancoVaselli, OrlandoMontegrossi, Giordanohttp://hdl.handle.net/10256/7292012-12-03T08:19:51Z2008-05-28T00:00:00ZStatistical evidences of cyclic changes in volcanic gas chemistry composition by inverse modelling
Buccianti, Antonella; Tassi, Franco; Vaselli, Orlando; Montegrossi, Giordano
Daunis i Estadella, Josep; Martín Fernández, Josep Antoni
The identification of compositional changes in fumarolic gases of active and quiescent volcanoes is one of the most
important targets in monitoring programs. From a general point of view, many systematic (often cyclic) and random
processes control the chemistry of gas discharges, making difficult to produce a convincing mathematical-statistical
modelling.
Changes in the chemical composition of volcanic gases sampled at Vulcano Island (Aeolian Arc, Sicily, Italy) from
eight different fumaroles located in the northern sector of the summit crater (La Fossa) have been analysed by
considering their dependence from time in the period 2000-2007. Each intermediate chemical composition has been
considered as potentially derived from the contribution of the two temporal extremes represented by the 2000 and 2007
samples, respectively, by using inverse modelling methodologies for compositional data. Data pertaining to fumaroles
F5 and F27, located on the rim and in the inner part of La Fossa crater, respectively, have been used to achieve the
proposed aim. The statistical approach has allowed us to highlight the presence of random and not random fluctuations,
features useful to understand how the volcanic system works, opening new perspectives in sampling strategies and in
the evaluation of the natural risk related to a quiescent volcano
2008-05-28T00:00:00ZAn alternative method for dating unknown tephras based on a segmented regression modelLee, Bik-waBacon Shone, Johnhttp://hdl.handle.net/10256/7282012-11-29T08:11:28Z2008-05-28T00:00:00ZAn alternative method for dating unknown tephras based on a segmented regression model
Lee, Bik-wa; Bacon Shone, John
Daunis i Estadella, Josep; Martín Fernández, Josep Antoni
In CoDaWork’05, we presented an application of discriminant function analysis (DFA) to 4 different
compositional datasets and modelled the first canonical variable using a segmented regression model
solely based on an observation about the scatter plots. In this paper, multiple linear regressions are
applied to different datasets to confirm the validity of our proposed model. In addition to dating the
unknown tephras by calibration as discussed previously, another method of mapping the unknown tephras
into samples of the reference set or missing samples in between consecutive reference samples is
proposed. The application of these methodologies is demonstrated with both simulated and real datasets.
This new proposed methodology provides an alternative, more acceptable approach for geologists as their
focus is on mapping the unknown tephra with relevant eruptive events rather than estimating the age of
unknown tephra.
Kew words: Tephrochronology; Segmented regression
2008-05-28T00:00:00Z