2021 Volume 62 Issue 1 Pages 2-12
Provenance analysis is one of the methods used to clarify the formation process of mountains, which is important for safety assessments of geological disposal. In this study, provenance analysis, based on the simultaneous analysis of the chemical composition, mineral species, and abundance ratios of heavy minerals using an electron probe microanalyzer （EPMA）, was applied to samples from the Pleistocene Sarabetsu Formation in Horonobe region, Hokkaido. The concentrations of 16 elements were measured in individual grains to identify the mineral species based on their chemical compositions. This mineral species identification was consistent with thin section microscopic observations. In addition to the gravel composition analysis, the analyses of the heavy minerals suggest that the major provenance rocks of the Sarabetsu Formation were derived from Soya Hill and the Teshio Mountains. Furthermore, Soya Hill rose above sea level by at least 1.5 Ma or later. These results are consistent with the tectonic history of the Horonobe region, as shown by previous studies. In contrast, amphibole is abundant in parts of the Sarabetsu Formation, but is uncommon in both Soya Hill and the Teshio Mountains. This finding suggests that future studies should consider the possibility of a sediment supply from distant areas, such as those transported by the Teshio River.
