Three pyroclastic flow deposits named Ftm-Bio, Ftm-A, and Ftm-B, in southwest Kyushu, are intercalated in the Futami gravel beds (FGB) distributed in the Futami Basin, at the western end of the Kyushu Mountains.

In this study, we described these pyroclastic flow deposits and correlated them to Middle Pleistocene widespread tephras based on detailed petrographic properties (glass chemistry, refractive indices of glass and hornblende and orthopyroxene). The results show that Ftm-Bio is correlated to Kb-Ks (530-520ka) from the Kobayashi caldera 55km ESE of the basin, Ftm-A to Kkt (340-330ka) from the Kakuto caldera 45km SE of the basin, and Ftm-B to Ata-Th (240ka) from the Ata caldera 140km SSE of the basin. In conclusion, the deposition of FGB probably began immediately before the eruption of Kb-Ks, and ended in a period between the eruption of Aso-4 (89ka) and the eruption of Ata-Th (240ka).

Measured values of twelve elements analyzed by scanning X-ray analytical microscope (SXAM) have been evaluated by comparing them with that of conventional X-ray fluorescence spec-trometry analysis (XRF). The samples used were powder-pressed pellets of the GSJ (Geological Survey of Japan) geochemical reference samples and Lake Inawashiro-ko lacustrine sediments. The chemical compositions obtained by the SXAM were quantified by fundamental parameter (FP) method with one standard spectrum. The measured values of titanium, aluminum, iron, manganese and potassium by the SXAM are consistent with a recommended value of the GSJ geochemical reference samples, and fulfill a level comparable to that of the XRF FP-method analysis. The quantifications of silicon, magnesium, calcium and sulfur have a systematic deviation from the recommended values of the GSJ geochemical reference samples, however each element indicates good linear regression relations based on the least squares method. Data of arsenic show relatively low regression relations, however, the values can be used semi-quantitatively only for samples which have low values of lead, such as sediments in Lake Inawashiro-ko. The quantifications of sodium and phosphorus could not be obtained using this method. As a worked example, the non-destructive and sequential SXAM analyses of lacustrine sediments in Lake Inawashiro-ko were performed. Eleven peaks of manganese, iron and sulfur from IN2.5-11 core sample and twelve peaks of iron from IN2.5-11 core sample were identified from the profiles of individual elements. Consequently, these peaks of iron and sulfur profiles can be correlated to the horizons of dark clay layers.

We analyzed the major element chemical composition of volcanic glass shards in Azuma tephra on Mount Aizu-komagatake and the Gassan volcano in northern Japan by means of electron probe X-ray microanalysis. This analysis confirmed that the two samples of Azuma tephra obtained from those mountains can be identified as the same tephra. We also examined three members of Towada Chuseri tephra (i.e., Chuseri pumice layer, Kanegasawa pumice layer, and Utarube volcanic ash layer) whose age is ca. 6.0 calkaBP in the proximal area of the Towada volcano in northern Japan for comparison with the Azuma tephra on Aizu-komagatake and Gassan. It was found that Azuma tephra originates primarily from Kanegasawa pumice. Azuma tephras found on Aizu-komagatake and Gassan were composed of widespread fine particles derived from the plinian eruption that produced the Kanegasawa pumice layer. Fallout Towada Chuseri tephra is expected to be discovered in the more southern area of Mount Aizu-komagatake, ca. 400km from the Towada volcano.