Resedimentation of non-welded facies in the Miocene Muro Ignimbrite, Nara, southwestern Japan

Abstract

The Miocene Sekibutsu Tuff Member in Nara, southwestern Japan, is well preserved with resedimentation of volocaniclastic sediments of the Muro Ignimbrite. Reworked volocaniclastic deposits in the Sekibutsu Tuff Member is subdivided into three units, Unit A, B and C, in ascending order. Unit A is mainly comprised with debris-flow and hyperconcentrated-flow deposits, which buried eroding channel on the pyroclastic-flow deposits. Unit B consists of a massive to laminated tuff considered deposited from suspension in the standing water. Unit C is coarsening- and thickening-upward successions of interbedded debris-flow and streamflow deposits. These facies changes were represented in collapsing, erosion and resedimentation in the marginal distribution of the pyroclastic-flow deposits.