On the Natural Remanent Magnetization of the Tephra in Diluvial Deposits, Yamaguchi Prefecture, Southwest Japan.

In the Kichinan district of the coastal area of Suo Nada of the Seto Inland Sea, Yamaguchi Prefecture, Southwest Japan, the so-called ”Ube volcanic ash” bed is widely distributed. This bed is correlated to the Yame clay and the Aso pyroclastic flow in the Northern Kyushu and also to the Musashino loam in the Kwanto district. In general, the questioned ash bed has been deposited having the thickness of few centimeters to few meters and consists of two layers such as the upper layer deposited successively almost at the same time geologically, say 20-30 thousand years before present. Over two score samples were taken from the volcanic ash bed at several localities in the Kichinan district and were divided into two groups: brown and white in colour. The natural remanent magnetization (nrm) of those samples was determined by means of an astatic magnetometer and the obtained data were examined to draw the paleo-/or archeo-magnetic discussions in connection of the tephrochronology and geology.Those groups have slightly different nrm-directions each other and also both of them seem the depositions which might not be caused by any smooth sedimentation because of a fairly large scattering of the fasion of their nrm-directions. The magnetic study of the tephra bed which has been formed at the middle