The characteristics of chemical distribution patterns in and around Yamagata city –Geochemical map in the southern area of Yamagata Basin–

Abstract

We have made environmental assessment of the southern area of Yamagata Basin using geochemical map. Fifty-seven stream sediments and 15 rock samples were collected, and 51 elements were analyzed. The study area is roughly divided into four areas by the characteristics of geochemical maps and REE patterns. Statistical analysis of chemical composition in each area reveals that their distribution patterns are strongly affected by geological setting. However, we found the distribution patterns of some elements (As, Mo, Sn, Sb, Hg and Pb) independent on geological setting. In Yamagata City, highly enrichment of Cr, Ni, Cu, Zn, Sn, Sb and Pb is found. The geochemical maps show that the chemical compositions of stream sediments represent those of small river basins (1-50 km²). We have examined how large the catchment area the stream sediment will represent. It is proved that the stream sediment satisfactorily represents the watershed on a wide scale of 1-400 km².