Projects per year
Abstract
Single component geochemical maps are the most basic representation of spatial elemental distributions and commonly used in environmental and exploration geochemistry. However, the compositional nature of geochemical data imposes several limitations on how the data should be presented. The problems relate to the constant sum problem (closure), and the inherently multivariate relative information conveyed by compositional data. Well known is, for instance, the tendency of all heavy metals to show lower values in soils with significant contributions of diluting elements (e.g., the quartz dilution effect); or the contrary effect, apparent enrichment in many elements due to removal of potassium during weathering. The validity of classical single component maps is thus investigated, and reasonable alternatives that honour the compositional character of geochemical concentrations are presented. The first recommended such method relies on knowledgedriven logratios, chosen to highlight certain geochemical relations or to filter known artefacts (e.g. dilution with SiO2 or volatiles). This is similar to the classical normalisation approach to a single element. The second approach uses the (so called) logcontrasts, that employ suitable statistical methods (such as classification techniques, regression analysis, principal component analysis, clustering of variables, etc.) to extract potentially interesting geochemical summaries. The caution from this work is that if a compositional approach is not used, it becomes difficult to guarantee that any identified pattern, trend or anomaly is not an artefact of the constant sum constraint. In summary the authors recommend a chain of enquiry that involves searching for the appropriate statistical method that can answer the required geological or geochemical question whilst maintaining the integrity of the compositional nature of the data. The required logratio transformations should be applied followed by the chosen statistical method. Interpreting the results may require a closer working relationship between statisticians, data analysts and geochemists.
Original language  English 

Pages (fromto)  1628 
Number of pages  13 
Journal  Journal of Geochemical Exploration 
Volume  162 
DOIs  
Publication status  Published  01 Mar 2016 
Event  GeoMap Workshop  Olomouc, Czech Republic Duration: 17 Jun 2014 → 20 Jun 2014 
Keywords
 soil geochemistry
 compositional data analysis, logratios, mapping
Fingerprint Dive into the research topics of 'The single component geochemical map: Fact or fiction?'. Together they form a unique fingerprint.
Projects
 1 Active
Activities

Using compositional geochemical ground survey data as predictors for geogenic radon potential
Jennifer McKinley (Speaker)
09 Nov 2015 → 12 Nov 2015Activity: Consultancy types › Contribution to the work of national or international committees and working groups

Invited keynote lecture presentation: Investigating potentially harmful trace elements in soils and their bioaccessibility: a compositional data analysis approach at the first GeoMap Workshop (held in Olomouc, Czech Republic, 1720 June 2014)
Jennifer McKinley (Speaker)
17 Jun 2014 → 20 Jun 2014Activity: Talk or presentation types › Invited talk