Predictive geochemical mapping using environmental correlation |
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Affiliation: | 1. The University of Adelaide, School of Biological Sciences, Department of Molecular and Cellular Biology, Adelaide, South Australia 5005, Australia;2. CSIRO Land and Water, Environmental Contaminant Mitigation and Technologies, PMB2, Glen Osmond, South Australia 5064, Australia;3. Swedish University of Agricultural Sciences, Almas Allé 8, 750 07 Uppsala, Sweden;1. Department of Geography, University of Winnipeg, Winnipeg, MB R3B 2E9, Canada;2. Institute for Planetary Materials, Okayama University—Misasa, 827 Yamada, Misasa, Tottori 682-0193, Japan;3. Department of Earth and Environment, Franklin and Marshall College, Lancaster, PA 17604-2615, USA |
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Abstract: | The distribution of chemical elements at and near the Earth's surface, the so-called critical zone, is complex and reflects the geochemistry and mineralogy of the original substrate modified by environmental factors that include physical, chemical and biological processes over time.Geochemical data typically is illustrated in the form of plan view maps or vertical cross-sections, where the composition of regolith, soil, bedrock or any other material is represented. These are primarily point observations that frequently are interpolated to produce rasters of element distributions. Here we propose the application of environmental or covariate regression modelling to predict and better understand the controls on major and trace element geochemistry within the regolith. Available environmental covariate datasets (raster or vector) representing factors influencing regolith or soil composition are intersected with the geochemical point data in a spatial statistical correlation model to develop a system of multiple linear correlations. The spatial resolution of the environmental covariates, which typically is much finer (e.g. ∼90 m pixel) than that of geochemical surveys (e.g. 1 sample per 10-10,000 km2), carries over to the predictions. Therefore the derived predictive models of element concentrations take the form of continuous geochemical landscape representations that are potentially much more informative than geostatistical interpolations.Environmental correlation is applied to the Sir Samuel 1:250,000 scale map sheet in Western Australia to produce distribution models of individual elements describing the geochemical composition of the regolith and exposed bedrock. As an example we model the distribution of two elements – chromium and sodium. We show that the environmental correlation approach generates high resolution predictive maps that are statistically more accurate and effective than ordinary kriging and inverse distance weighting interpolation methods. Furthermore, insights can be gained into the landscape processes controlling element concentration, distribution and mobility from analysis of the covariates used in the model. This modelling approach can be extended to groups of elements (indices), element ratios, isotopes or mineralogy over a range of scales and in a variety of environments. |
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Keywords: | Geochemistry Critical zone Regolith Landscape processes Data mining Regression trees Yilgarn craton Australia |
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