11:00 AM - 1:00 PM
[HQR04-P01] Sedimentary Facies and Stratigraphy of Pleistocene in the Southeastern Part of Musashino Terrace: Surface Peel Specimens and 100 m Non-core Boring Samples
Keywords:Musashino uplands, Musashino terrace, Musashino alluvial fan, Pleistocene, Kanto loam, Surface peel specimens
Surface peel and 100 m non-core boring samples were collected and examined for the investigation of the sedimentary facies and stratigraphy of Pleistocene in the southeastern part of Musashino M1 terrace.
We collected the samples at Okubo, Shinjuku-ku, Tokyo, where is located on the Musashino M1 terrace surface [1]. Non-core boring was carried out to a depth of 105 m under the ground. At the same site, four surface peel specimens were also collected from outcrops 2–10 m below the surface. At this site, the sediments show horizontal layers and the elevation of the ground surface is 31 m T.P.
The sedimentary facies and grain-size distributions were characterized as follows.
105–100 m below the surface: gravel layer coarsening upward and the uppermost sample contains shell fossils. This section is correlated to Johoku gravel member, base of Toneri Formation [2].
100–20 m: three or more depositional cycles consisting of sand and mud layers, implying transgressive-regressive cycles. This section is correlated to Toneri formation in Kazusa group [1, 2].
20–12 m: sand layers with a cycle of coarsening and fining. This section would be correlated to Kamiizumi formation [1] or the upper part of Tokyo formation in Shimousa group.
12–9.5 m: gravel layer with a grain size mainly of 30–50 mm and the largest of more than 100 mm. This section is correlated to Musashino gravel layer, consisting of Musashino alluvial fan formed by paleo-Tama river.
9.5–6.5 m: tuffaceous clay layer with a blackish-brown layer immediately below 7.4 m showing intra-layer disturbance. This section is correlated to Shimosueyoshi loam deposition affected by underwater argillation.
6.5–2 m: brown loam with a pumice layer at 6.1 m. This section is correlated to Tachikawa-Musasino loam and the key bed is correlated to Hk-TP (66.0±5.5 ka [3]).
[1] Naya et al. (2021), [2] Endo et al. (1978), [3] Aoki et al. (2008)
We collected the samples at Okubo, Shinjuku-ku, Tokyo, where is located on the Musashino M1 terrace surface [1]. Non-core boring was carried out to a depth of 105 m under the ground. At the same site, four surface peel specimens were also collected from outcrops 2–10 m below the surface. At this site, the sediments show horizontal layers and the elevation of the ground surface is 31 m T.P.
The sedimentary facies and grain-size distributions were characterized as follows.
105–100 m below the surface: gravel layer coarsening upward and the uppermost sample contains shell fossils. This section is correlated to Johoku gravel member, base of Toneri Formation [2].
100–20 m: three or more depositional cycles consisting of sand and mud layers, implying transgressive-regressive cycles. This section is correlated to Toneri formation in Kazusa group [1, 2].
20–12 m: sand layers with a cycle of coarsening and fining. This section would be correlated to Kamiizumi formation [1] or the upper part of Tokyo formation in Shimousa group.
12–9.5 m: gravel layer with a grain size mainly of 30–50 mm and the largest of more than 100 mm. This section is correlated to Musashino gravel layer, consisting of Musashino alluvial fan formed by paleo-Tama river.
9.5–6.5 m: tuffaceous clay layer with a blackish-brown layer immediately below 7.4 m showing intra-layer disturbance. This section is correlated to Shimosueyoshi loam deposition affected by underwater argillation.
6.5–2 m: brown loam with a pumice layer at 6.1 m. This section is correlated to Tachikawa-Musasino loam and the key bed is correlated to Hk-TP (66.0±5.5 ka [3]).
[1] Naya et al. (2021), [2] Endo et al. (1978), [3] Aoki et al. (2008)