5:15 PM - 6:30 PM
[HQR04-P04] Landform evolution and estimation of crustal movement since MIS 12 in the central-northern part of the Kanto Plain
Keywords:Middle Pleistocene, crustal movement, Kanto plain
Kanto plain is one of the most studied tectonic basins in terms of landform evolution and crustal movement during the Late Quaternary in Japan, but the tectonic trends in the northern part of the plain, from Sashima to Takaragi terrace, have been little clarified. Miyamoto et al. (2020) and Nakanishi et al. (2020), based on the analysis of three all cores (GC-OY-1, OY-2 and NG-1), divided the cores into 19 sedimentary units, and compared Units 15-17 of GC-OY-2 and OY-1 to the Jizodo Formation, and Units 12-14 of GC-OY-2 and OY-1 are compared to the Yabu Formation. This presentation reports the outlines of landform evolution in this area since MIS 12 and the average crustal deformation rate during this period.
The upper surface elevation of the marine stratum in MIS 11 is -20.17 m above sea level for GC-OY-2 (foreshore) and -41.15 m above sea level for GC-OY-1 (delta front). Since the eustatic sea level in MIS 11 was about 6 m to 13 m higher than the present (Raymo and Mitrovica, 2012), the fluctuation amount since MIS 11 is estimated to be about -26 m to -33 m for GC-OY-2 (foreshore) and about -47 m to -54 m for GC-OY-1 (upper shoreface to foreshore). The water content ratio of the core does not decrease vertically downward, so the effect of consolidation is ignored. In addition, since the study area is located at the northern limit of the Paleo-Tokyo Bay expansion area and is heavily supplied by river sediments, it is assumed that the sea level at the time of the formation of the detached surface of the marine stratum approximates the highest sea level of the relevant evolution. From these results, the average rate of vertical change from MIS 11 to the present is estimated to be -0.08 mm/yr for GC-OY-2 and -0.13 mm/yr for GC-OY-1, indicating that the sediments have been settling at an average rate of about 0.1 mm/yr during this period.
The upper surface elevation of the marine stratum in MIS 9 is -9.74 m above sea level for GC-OY-2 and -24.13 m above sea level for GC-OY-1. Since the eustatic sea level in MIS 9 was about 9 m higher than the present (Spratt and Lisiecki, 2016), the fluctuation amount since MIS 9 is estimated to be about -19 m for GC-OY-2 and about -33 m for GC-OY-1. From these results, the average rate of vertical fluctuation during the period from MIS 9 to the present is calculated to be -0.06 mm/yr for GC-OY-2 and -0.11 mm/yr for GC-OY-1, indicating that the average rate of sedimentation during this period has been around 0.08 mm/yr.
The settling rate and the amount of settling are larger in the southern part of the region. This trend is in harmony with the fact that the center of settling is located around Kuki City, Saitama Prefecture in the southern part of the Sashima terrace (Kaizuka, 1987). The amount and rate of settling decrease with increasing age (MIS 11 and 9). This may reflect the shallowing and uplifting of the forearc basin throughout the Quaternary (Sugai et al., 2013).
Acknowledgements: This study used a part of the results of the research and developments funded by the Ministry of Economy, Trade and Industry (METI), Japan as part of its R&D supporting program titled “Establishment of Advanced Technology for Evaluating the Long-term Geosphere Stability on Geological Disposal Project of Radioactive Waste (Fiscal Years 2018 and 2019)
References: Miyamoto et al. 2020 AJG spring. Nakanishi et al. 2020 JpGU. Kaizuka 1987 Jour. of Geography. 96, 51-68. Sugai et al 2013 Jour. of Geography. 122(6), 921-948. Raymo and Mitrovica 2012 Nature 483, 453-456. Spratt and Lisiecki 2016 Climate of the Past 12, 1079-1092.
The upper surface elevation of the marine stratum in MIS 11 is -20.17 m above sea level for GC-OY-2 (foreshore) and -41.15 m above sea level for GC-OY-1 (delta front). Since the eustatic sea level in MIS 11 was about 6 m to 13 m higher than the present (Raymo and Mitrovica, 2012), the fluctuation amount since MIS 11 is estimated to be about -26 m to -33 m for GC-OY-2 (foreshore) and about -47 m to -54 m for GC-OY-1 (upper shoreface to foreshore). The water content ratio of the core does not decrease vertically downward, so the effect of consolidation is ignored. In addition, since the study area is located at the northern limit of the Paleo-Tokyo Bay expansion area and is heavily supplied by river sediments, it is assumed that the sea level at the time of the formation of the detached surface of the marine stratum approximates the highest sea level of the relevant evolution. From these results, the average rate of vertical change from MIS 11 to the present is estimated to be -0.08 mm/yr for GC-OY-2 and -0.13 mm/yr for GC-OY-1, indicating that the sediments have been settling at an average rate of about 0.1 mm/yr during this period.
The upper surface elevation of the marine stratum in MIS 9 is -9.74 m above sea level for GC-OY-2 and -24.13 m above sea level for GC-OY-1. Since the eustatic sea level in MIS 9 was about 9 m higher than the present (Spratt and Lisiecki, 2016), the fluctuation amount since MIS 9 is estimated to be about -19 m for GC-OY-2 and about -33 m for GC-OY-1. From these results, the average rate of vertical fluctuation during the period from MIS 9 to the present is calculated to be -0.06 mm/yr for GC-OY-2 and -0.11 mm/yr for GC-OY-1, indicating that the average rate of sedimentation during this period has been around 0.08 mm/yr.
The settling rate and the amount of settling are larger in the southern part of the region. This trend is in harmony with the fact that the center of settling is located around Kuki City, Saitama Prefecture in the southern part of the Sashima terrace (Kaizuka, 1987). The amount and rate of settling decrease with increasing age (MIS 11 and 9). This may reflect the shallowing and uplifting of the forearc basin throughout the Quaternary (Sugai et al., 2013).
Acknowledgements: This study used a part of the results of the research and developments funded by the Ministry of Economy, Trade and Industry (METI), Japan as part of its R&D supporting program titled “Establishment of Advanced Technology for Evaluating the Long-term Geosphere Stability on Geological Disposal Project of Radioactive Waste (Fiscal Years 2018 and 2019)
References: Miyamoto et al. 2020 AJG spring. Nakanishi et al. 2020 JpGU. Kaizuka 1987 Jour. of Geography. 96, 51-68. Sugai et al 2013 Jour. of Geography. 122(6), 921-948. Raymo and Mitrovica 2012 Nature 483, 453-456. Spratt and Lisiecki 2016 Climate of the Past 12, 1079-1092.