No. 35 (2000) pp.115-124 The Late Quaternary stratigraphy in the western margin of Yodobashi- dai, northern part of Setagaya-ku, Tokyo Jiro KOMORI, Kunihiko ENDO, Fumihiko HASEGAWA, and Sei TAMURA (Received November 1, 1999) Late Quaternary deposits were exposed at outcrops in the construction site of College of Humanities and Sciences, Nihon University, northern part of Setagaya-ku, Tokyo, central Japan. The studied area is situated in the shallow dissected valley along the western margin of Yodobashi-dai (S surface: isotope stage 5), where is close to the border between Yodobashi-dai (S) and Musashino (M) terraces. These deposits in the shallow valley are classified into seven layers of A to G from the top to bottom. According to the comparison with the results of the preceded studies (Inako et al., 1977 and 1978) older construction sites of the same college, gravel (Layer G) and hard silt (Layer F) which exist on Edogawa formation of hard sand layer, correspond to both Tokyo Gravel and Tokyo formation. Moreover, lower volcanic ash (tuffaceous loam : Layer E) similar to the Musashino Loam, and upper volcanic ash (tuffaceous loam : Layer C) and peat (Layer D) are supposed to be correlated to the deposits of the Tachikawa Loam stage, because AT tephra from Aira Caldera, is found from the bottom of Layer C. Consequently, the unconformity dividing Tokyo formation and the deposit of Musashino Loam stage, may be between Layers E and F. Based on these deta, the Tama and Shimosueyoshi were eroded in the Musashino stage. This erosion surface may correspond to Musashino 2 terrace. Keywords : AT tephra, Late Quaternary, peat, soil color, Tachikawa Loam, Yodobashi-dai 1 1960 8m 1 4 1) 156-8550 3-25- 40 2 Department of Geosystem Sciences, College of Humanities and Sciences, Nihon University : 3-25- 40 Sakurajousui, Setagayaku, Tokyo 156-8550, Japan 115 33
1a, b 2 1978 1 2 km 1b 2 1978 1979 300m 2 2 39m 2 3m 1978 34 116
3 N 35 39 9 E 139 38 12 T.P. 32.0 39.5m 1999 1 3 4.3 m 3 3.6 m 4 20cm 20 cm 5cm 1cm X X 2cm 1 2 MINOLTA SPAD 503 5cm Lab L 0 100 a b 3 117 35
L 2 3 4 CHBr 2 CHBr 2. 2.97g/cm 3 RIMS 86 JSM5200 AT AT EDS JEOL 5400 S / Link QX2000 4 A B C D E F1 F2 G 3b ab B D F1 L 20 40 b 0 5 C E G L 40 55 b 5 10 3 L C E G a 2 10 1 1 3c a b c 4 36 118
1 0m 1m 2m 3m 4m 4m 5m 6m 7m 7.5m 4.5m 1m 2m 3m 4m 5m 6m 7m 2 X 119 37
0.0 4.5m X 3m 4.0 7.6 m 3m 6.0 7.0m) 1m 38 120 5.4 6.3m 2
5 8 121 39
C 3.35m 1.498 range = 1.495 1.501 4a.b 3.35m 3.35m 1976 AT AT AT 3.35m EDS WDS EPMA 1983 Furuta et al. 1986 AT SiO 2 FeO 3.35m 4c 5 5 1 6 G 2cm 32m 3 4m 6 40 122
20cm 4m 31 32m 1979 1984 1979 F 1989 N 50 E F 5.7m Hk TP E C D AT 20cm AT 1982 10cm AT 50cm AT 5 2 E F E F 32m Pm 1 3m 2.5 m M2 6 8m 1) A G 7 A B C D E F G 2) 1978 1979 123 41
M2 3) 3.35m AT 5.7m Hk TP EDS IUK 1982 1 fall unit 89 115 115 1983 35 38 Furuta, T., Fujioka, K. and Arai, F. (1986) : Widespread submarine tephras around Japan-petrographic and chemical properties. Marine Geology, 72, 125 142. 1978 13 31 42. 1979 14 31 38 1984 5 1 148p 1991 42 11 553 653 1976 Tn 46 339 347 1992 276p 1998 2 21 53 1979 248p 1996 5c 192 192 1994 292p 1972 11 29 39 42 124