Landslide occurrence and geology of the Triassic Nariwa Group, Southwest Japan

Geological and topographical study of landslides in the Triassic Nariwa Group has been carried out. Nariwa Group is mostly composed of non-marine deposites and is characterized by cycle of fining upward successions. Landslides abundantly occur in the non-marine successions. Slip surface occure in coaly mudstones that have conspicuously less strength than sandstones. Creeps immediately below slip surfaces contribute to the occurrence of landslides in the Nariwa Group

Distributions and ages of the Paleogene deposits in the Kibi Plateau Area, and Paleogene paleogeography

The "Kibi Plateau" forms a unique geomorphic province with the gently-sloping and stable continental feature. Gravel deposites called the "Mountain Gravels", are distributed sporadically in the Kibi Plateau, and have been considered Pliocene deposits. However, recent fission-track ages of the tuff beds intercalated in the deposits have indicated that the ago of deposits are Paleogen in the age. So far, fission-track ages (using zircon) of 61 to 65, 55, 37, 34 to 35 and 27 Ma are obtained. Remaining the belt-like distributions of the Paleogene gravelly valley-full deposits suggest that the Kibe Plateau has been keeping as a stable block, and repeated periods of incision followed by sedimentation of valley-fill deposits are occurred in the area during Paleogene period