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[SGC36-P05] Temporal changes of chemical compositions in stream sediments around the Komorigawa River, western part of the Saitama Prefecture, central Japan
Keywords:Geochemical-map, Stream sediment, Alkali elements, Temporal change
Geochemical maps can be used as basic data for the chemical composition of surface rocks. In order to utilize the map, it is necessary to investigate the temporal changes of chemical composition in streams sediments.
In this study, we compared chemical composition in 48 stream sediments collected in 2008 and 2019 around the Komorigawa River in western part of Saitama Prefecture, central Japan. The geology of the Komorigawa River is roughly divided into sandstone and mudstone areas and chert areas, and limestone areas. The quantification of 41 elements in the sediments using the glass bead method with XRF and LA-ICP-MS showed that the contents of most elements were unchanged. However, in the limestone area, the contents of Na2O, K2O, Rb, and Sr in the sediments increased or decreased over time. The variation in these elemental contents is attributed to the chemical heterogeneous of the limestone that are the source of the stream sediments. Alternatively, the decrease in alkali content in the sediment may be due to the leaching of alkali from the limestone by rainwater. Therefore, geochemical mapping of these alkali elements in limestone areas requires updating the chemical composition by re-collecting stream sediments about every 10 years.
In this study, we compared chemical composition in 48 stream sediments collected in 2008 and 2019 around the Komorigawa River in western part of Saitama Prefecture, central Japan. The geology of the Komorigawa River is roughly divided into sandstone and mudstone areas and chert areas, and limestone areas. The quantification of 41 elements in the sediments using the glass bead method with XRF and LA-ICP-MS showed that the contents of most elements were unchanged. However, in the limestone area, the contents of Na2O, K2O, Rb, and Sr in the sediments increased or decreased over time. The variation in these elemental contents is attributed to the chemical heterogeneous of the limestone that are the source of the stream sediments. Alternatively, the decrease in alkali content in the sediment may be due to the leaching of alkali from the limestone by rainwater. Therefore, geochemical mapping of these alkali elements in limestone areas requires updating the chemical composition by re-collecting stream sediments about every 10 years.