Distribution, age, and origin of a submarine landslide deposit in the Pleistocene Kiwada Formation, forearc basin fill on the Boso Peninsula, east-central Japan: Constraints from tephro- and biostratigraphy

Island Arc ◽  
2018 ◽  
Vol 27 (4) ◽  
pp. e12254 ◽  
Author(s):  
Masayuki Utsunomiya
Keyword(s):  
Submarine Landslide ◽  
Forearc Basin ◽  
Central Japan ◽  
East Central ◽  
Boso Peninsula ◽  
Landslide Deposit ◽  
Basin Fill

Preferential formation of a slide plane in translational submarine landslide deposits in a Pleistocene forearc basin fill exposed in east-central Japan

2018 ◽  
Vol 477 (1) ◽  
pp. 241-253 ◽  
Author(s):  
Masayuki Utsunomiya ◽  
Atsushi Noda ◽  
Makoto Otsubo
Keyword(s):  
Pore Pressure ◽  
Slip Zone ◽  
Submarine Landslides ◽  
Forearc Basin ◽  
Central Japan ◽  
East Central ◽  
Preferential Formation ◽  
Lapilli Tuff ◽  
Tephra Beds ◽  
Basin Fill

AbstractTephra beds are considered to be potential failure planes for submarine landslides. Here, we report on an example of a coarse-ash/lapilli-tuff bed influencing translational slides. The studied mass-transport deposit (MTD) is intercalated in the Pleistocene forearc basin fill exposed in east-central Japan. This MTD consists of stacked siltstone blocks resulting from repeated imbricate thrusts branching from the décollement. The basal slide plane is located immediately below a pumice-rich coarse ash/lapilli-tuff bed. The material comprising the slip zone is injected into the overlying coarse-ash/lapilli-tuff bed, suggesting an upwards escape of excess porewater that resulted from elevated pore pressure. To explain this mode of occurrence, we propose that the detachment preferentially occurred at the top and base of the coarse-ash-tuff-rich interval which appears to have been stronger relative to the adjacent silt-dominated interval. The pumiceous coarse-ash and lapilli-tuff bed behaved as a rigid plate on top of the high-pore-pressure slip zone, which sustained the translational slide on the gentle continental slope. Therefore, in translational submarine landslides, the preferential formation of a slide plane is caused by differing frictional resistances in the layered sediments.

Bent incised valley formed in uplifting shelf facing subduction margin: case study off the eastern coast of the Boso Peninsula, central Japan

2020 ◽  
pp. SP505-2019-117
Author(s):  
Tomoyuki Sato ◽  
Seishiro Furuyama ◽  
Junko Komatsubara ◽  
Masanori Ozaki ◽  
Kazuo Yamaguchi
Keyword(s):  
Seismic Survey ◽  
Eastern Coast ◽  
Forearc Basin ◽  
Basal Surface ◽  
Central Japan ◽  
Offshore Area ◽  
Tectonic Plates ◽  
Incised Valley ◽  
Boso Peninsula ◽  
Forearc Basins

AbstractThe Boso Peninsula is located in central Japan near the junction of the subduction boundary of three tectonic plates. A forearc basin has been developing there since 3 Ma and has been uplifting since 1 Ma. The basal surface of the Holocene deposits in the offshore area was investigated based on a seismic survey and is very similar to the adjacent land areas (the Iioka Plateau, the Kujukuri Plain and the Kazusa Hills). The basal surface in the Kujukuri Plain and its corresponding offshore area contains many incised valleys. Most of them extend southeastward, parallel to the direction from the hinterland to the ocean, but one incised valley (Kujukuri-oki Buried Valley) lies perpendicular to the others. A buried terrace is located SE of the valley and along the area where mudstone (of the Kiwada Formation) is distributed. The present observations indicate that differential erosion formed the terrace, after which the valley bent to follow the terrace. The rivers tend to be perpendicular to the strike of the sediment in the forearc basin owing to tectonic movement. Thus, the valley must have been incised into the underlying strata with a perpendicular strike and may have become bent in uplifting forearc basins.

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