福島県，会津盆地中西部地下における第四紀後期チフラの層序

摘要

東北日本弧南部，福島県会津坂下町で得た3本のボーリングコアからテフラを検出し，これらの認定を行い会津盆地中西部地下のテフラ層序を確立した.また放射性炭素年代測定も実施し，それらの結果と合わせて盆地堆積物の年代と堆積速度を求めた.地下約100m以浅の堆積物はシルト•泥炭•砂を主体とし，ところにより礫層やテフラを挟む.認定したテフラは上位からNm-NM(5.4ka),AT(30ka),DKP(55～66ka),Nm-KN,Ag-OK(＜85.1ka),TG(129ka),Sn-MT(180～260ka)である.最長コアから得た堆積速度は，地表/DKP間で0.46～0.55m/kyrs,DKP/TG間で0.19～0.23m/kyrsである.%Tephra layers were identified from three boring cores in Aizubange Town, middle west part of the Aizu Basin, one of the tectonic basins in the south part of Northeast Japan. Ages of seven horizons were determined by radiocarbon dating. These results clarified the tephrostratigraphy, chronology, and accumulation rates of subsurface sediments in the study area. Sediments with a depth less than ca.100 m are mainly composed of silt, peat, and sand with several intercalations of gravel beds and tephra layers. These tephra layers can be correlated with Nm-NM (5.4ka), AT (30ka), DKP (55-66ka), Nm-KN, Ag-OK (＜85.1ka)， TG (129ka), and Sn-MT (180-260 ka). Estimated accumulation rates determined for the longest core are 0.46-0.55 m/ kyrs after the deposition of DKP to present, whereas they are 0.19-0.23m/kyr at the depth between the horizons of DKP and TG.