『Abstract
　The problem of a geochemical baseline in areas differing in basic geology was studied by comparing the results of regional geochemical mapping programmes undertaken in Finland and Lithuania using different sample media and a variety of analytical methods. The authors discuss issues relevant to the definition of a geochemical baseline.
　Most of the differences in geochemical baselines between Lithuania and Finland are due to the dissimilarities in basic geology, which in Lithuania is controlled by Palaeozoic and Mesozoic sedimentary rocks, but in Finland by Archaean and Proterozoic metamorphic and intrusive rocks. Other important factors are the geological processes that after the last glaciation created the present surficial materials. In Finland, for instance, the abundances of potentially harmful elements derived from crystalline bedrock tend to be higher than in Lithuania. However, in both countries element concentrations are higher in finely-grained marine and lacustrine sediments than in glacial till, and they are also higher in the finer grain size fractions than in the coarser fractions of till samples. Only a small proportion of the total heavy metal concentrations is bioavailable. Thus the baseline concentrations depend not only on the basic geology, but also on sample material collected, its grain size and the extraction method.』

1. Introduction

『The term ‘geochemical baseline’ was introduced in the International Geological Correlation Programme (IGCP) projects 259 and 360 (Darnley et al., 1995) in order to create a global reference network for national regional geochemical data sets and as international background data for environmental legislation. The recommendations of IGCP 259 and 360 projects include the concept of multimedia multipurpose regional geochemical mapping. However, the term geochemical baseline was not well defined.
　Tidball and Ebens (1976) used the term regional geochemical baseline in order to describe the natural background in areas of a heavy anthropogenic impact from the coal based electric generating industry in the Powder River Basin in Montana-Wyoming. Their definition was that a baseline encompasses the central 95％ of the observed concentrations. The basis of this definition has been discussed earlier by Tidball et al. (1974) and it was applied in wide regional geochemical mapping programs in Wyoming and Montana during the 1970s (Severson, 1979; Severson and Tidball, 1979; Ebens and Connor, 1980).
　The term geochemical background, in contrast, has been defined in many different ways in textbooks of geochemistry (cf. e.g. Levinson, 1974; Beus and Grigorian, 1977; Rose et al., 1979). The most common definition is the natural abundance of an element in a particular material (e.g. soil, sediment, rock) with reference to a particular area or data set. It is usually expressed as a single value showing the limit (threshold) between anomalous and background concentrations. this definition is used mainly in exploration, and is not appropriate for environmental purposes. A new concept including an anthropogenic factor was therefore developed in Germany (LABO, 1995). According to this definition, the background content of a soil is composed of its geogenic basic content and ubiquitous substances distributed as a consequence of diffuse entry into the soil. Another definition is that of the International Standardisation Organisation (ISO 11074-1, 1996): “geogeneous or pedogeneous average concentration of a substance in an examined soil”. this definition, however, leaves many questions unanswered.
　Yet another way to determine the natural abundance of a particular element is to calculate its Clarke value, which is the average concentration of an element in the Earth's crust. The concentrations of elements differ so much, however, from one geologic unit to another that use of the Clarke value of an element in national or local contexts does not permit a sufficiently thorough study of variations in element distributions caused by mineralization or contamination in a particular sampling medium.
　Geochemical baseline refers to the prevailing variation in the concentration of an element in the surficial environment. Geochemical baselines are very important in environmental legislation, which prescribes limits for heavy metals in contaminated land and other surficial materials as defined by environmental authorities. In certain areas in Finland, for instance, natural concentrations of several heavy metals exceed the recommended or limit values designated for contaminated land. Thus baselines must always be verified in any assessment of sites for contamination (Gregorauskiene and Kadunas, 1997; Salminen and Tarvainen, 1997).
　The authors present some thoughts on how to establish geochemical baselines with the aid of regional geochemical mapping data from Finland and Lithuania and highlight the problems associated with differences in basic geology on both regional and local variation. In addition, attention is paid to sampling material, grain size fraction and choice of analytical methods.』

2. Main features of the basic geology in Lithuania and Finland
3. Influence of basic geology on the geochemical baselines of elements
4. Relevance of the sampling material and analysed grain size fraction
5. Discussion
References