Abstract
This study investigated downslope variations in sedimentation rate, grain size, magnetic susceptibility, and clay mineral composition of hemiplelagic siltstones in the Kd8 (ca. 1.2 Ma) and O7 (ca. 0.9 Ma) volcanic ash key bed horizons in the Pleistocene Kazusa Group on the Boso Peninsula, Japan. In general, sedimentation rates decrease in the downslope directions in association with the decrease in grain size, except for local increases in sedimentation rates and grain size as a response to additional supply of fine-grained sediment particles from turbidity currents. In contrast, although the magnetic susceptibility shows a downslope variation in harmony with that in grain size in the O7 volcanic ash key bed horizon, it is also influenced by local development of authigeneic magnetic minerals in the Kd8 volcanic key ash bed horizon. Regardless of the spatial variations in sedimentation rates, grain size, and magnetic susceptibility, clay mineral composition does not show any distinct spatial variation and can be used as a proxy of temporal variation in hinterland geology and paleoclimates in a one-dimensional stratigraphic record.
