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

Abstract

A mass‐transport deposit named MTD1 (up to 100 m in thickness) is intercalated in the upper Kiwada Formation, a Pleistocene forearc basin fill on the Boso Peninsula, east‐central Japan. The present study aims to examine the origin, age, and distribution of MTD1. MTD1 consists mainly of mudstone blocks containing thin very fine‐ to medium‐grained sandstones, and ranges from tens of centimeters to more than tens of meters in length and thickness. Correlation of marker tuff beds and application of the biostratigraphy of calcareous nannofossils suggest that the blocks in MTD1 were derived from the underlying strata. The total thickness of the stratified blocks from the different stratigraphic horizons exceeds 60 m, implying that MTD1 originated from deeply‐excavated slope failure. The slope failure occurred in a short time interval at ca 1.3 Ma. MTD1 provides an estimate of the height of the escarpment on the basis of the stratigraphic origin of the blocks.

Forearc tectonics and submarine landslides recorded in the lower part of the Kazusa Group, eastern Boso Peninsula

“…Ts: Slip tendency for the map-scale NNE-SSW-trending faults under stresses I and II and the present-day stress (Morris et al, 1996). (a) Stratigraphic columns for MTD-8 and the surrounding deposits, including calcareous nannofossil biostratigraphic data for the horizons between the Kd38 and Kd8 tephra beds (Utsunomiya, 2018;Utsunomiya and Yamamoto, 2019). In the strata underlying MTD-8, there is a gradual increase in the maximum length of genus Gephyrocapsa spp.…”

Downslope variation in hemipelagic sedimentation in an active margin basin: An example from the lower Pleistocene Kiwada and Takamizo formations on the Boso Peninsula, Japan

“…3A and B). Locally, debrites, slumped deposits and injectites are also found in the formation (Ogiwara & Ito, 2011; Fukuda et al ., 2015; Utsunomiya, 2018; Fig. 3A).…”