Supercritical-flow sedimentary structures of fluvial deposits in the Plio-Pleistocene Katata Formation, Kobiwako Group, Japan

Abstract

増田富士雄 1＊ ・服部 昇 2 ・石田志朗 3 Supercritical-flow sedimentary structures of fluvial deposits in the Plio-Pleistocene Katata Formation, Kobiwako Group, Japan Fujio Masuda 1＊ , Noboru Hattori 2 and Shiro Ishida 3Sedimentary structures related to supercritical-flows, including antidunes, chutes-and-pools and cyclic steps, have been identified from fluvial flood deposits in the Plio-Pleistocene Katata Formation, Kobiwako Group, Shiga, Japan. The characteristics of sedimentary structures by high-energy flood flows are 1) backset laminae and backstepping lamina sets with up-stream migration, 2) sigmoidal, wavy and HCS-mimics laminae, 3) scour and fill gravel, sand and mud, 4) cyclically scoured erosional bases, and 5) mixed beds with heterolithic and well and poorly sorted deposits. The observed sedimentary structures considered as supercritical-flow deposits have high diversity. The deposits with much mud-content show fast sedimentation rate from the supercritical-flows contained large amount of suspended mud. We have to observe furthermore the sedimentary structures linked to supercritical-flow bedforms from deposits of various ages, areas and depositional environments.

Sedimentological and micropaleontological characteristics of tsunami deposits associated with the 2024 Noto Peninsula earthquake

“…Unit 1 (7-9.5 cm from the top of the deposit), the lowest unit, was characterized by the presence of faint parallel laminations. Unit 2 (6-7 cm from the surface) was very thin and de ned by a relatively high mud content and the presence of parallel laminations and hummocky cross-strati cation (HCS) mimics 32 . Unit 3 (2-6 cm from the surface) was the middle part of the tsunami deposit and contained prominent climbing ripples with their leesides to seaward.…”