Separating anthropogenic from natural anomalies in environmental geochemistry

Environmental geochemistry has attracted increasing interest during the last decade. In Sweden, geochemical mapping is carried out with methods that allow the data to be used in environmental research, including sampling plant roots and mosses from streams, soils and bedrock. These three sample types form an integrated strategy in environmental research, as well as in geochemical exploration. However, one problem that becomes prominent in geochemical mapping is to distinguish the signals derived from natural sources from those derived from anthropogenic sources. So far, this has mostly been done by using different types of samples, for example, different soil horizons. This is both expensive and time-consuming.We are currently developing alternative statistical solutions to this problem. The method used here is PLSR (partial least squares regression analysis). In this paper, we present an initial discussion on the applicability of PLSR in differentiating anthropogenic anomalies from natural contents.PLSR performs a simultaneous, interdependent principal component analysis decomposition in both X- and Y-matrices, in such a way that the information in the Y-matrix is used directly as a guide for optimal decomposition of the X-matrix. PLSR thus performs a generalized multivariate regression of Y on X overcoming the multicollinearity problem of correlated X-variables. The advantage of PLSR is that it gives optimal prediction ability in a strict statistical sense.Bedrock geochemistry from different lithologies in the mapping area in southern Sweden (Y-matrix) is analyzed together with stream or soil data (X-matrix). By modelling the PLS-regression between these two data sets, separate multivariate geochemical models based on the different bedrock types were developed. This step is called the training or modelling stage of the multivariate calibration. These calibrated models are subsequently used for predicting new (X) geochemical samples and estimating the corresponding Y-variable values. Information is obtained on how much of the metal contents in each new geochemical sample correlate with the different modelled bedrock types.By computing the appropriate X-residuals, we obtain information on the anthropogenic impact that is also carried by these new samples. In this way, it is possible from one single geochemical survey to derive both conventional geochemical background data and anthropogenic data, both of which can be readily displayed as maps.The present study concerns development of data analysis methods. Examples of the applications of the methodology are presented using Pb and U. The results show the share of these contents in different sampling media that is derived from bedrock on the one hand, and from anthropogenic sources, on the other.     

An evaluation of proposed platinum group element contents in the parental magmas of the Bushveld complex

Samples collected by the authors and representing three proposed parental magmas of the Bushveld complex were analyzed for their platinum group element (PGE) contents by three different laboratories. Results differ strongly between laboratories, but imply that the parental magmas may have had flatter chondrite normalized patterns and an overall lower content than previously reported. It seems, however, that the Bushveld magmas were enriched in PGE's relative to average mafic rocks. A clear difference between the three magma types could not be substantiated. At present the PGE content of proposed parental melts of the Bushveld complex must be considered to be insufficiently known to warrant any quantitative models.     

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Geophysical results in Austria with special regard to telluric measurements

Summary The paper treats the results of telluric measurements in the Austrian Molasse-Zone and in the Vienna Basin, supplemented with data of other geophysical methods and deep-wells. The analysis of the results shows that the telluric method supplies not only a picture with good reconnaissance proceeding from which further, especially seismic research can be planned more expediently, but can render good services in solving detailed problems too. The hypothesis concerning the anisotropy of sediments resp. its effect is verified by the results of modelexperiments too.

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Zusammenfassung Die Arbeit behandelt die Ergebnisse der Tellurischen Forschungen in der österreichischen Molasse-Zone und im Wiener Becken unter Einbeziehung von Angaben anderer geophysikalischen Messungen und Tiefbohrungen. Die Analyse der Ergebnisse zeigt, dass die tellurische Methode nicht bloss eine gute geophysikalische Übersichtskarte ergibt, von der ausgehend weitere — in der Hauptsache seismische — Forschungen zweckentsprechender geplant werden können, sondern sie leistet auch recht gute Dienste bei der Lösung von Detaiproblemen. Die Hypothese über die Anisotropie der Sedimente bzw. ihr Effekt wurde auch durch die Ergebnisse von Modellversuchen bestätigt.