Abstract
Some turbidite beds of the Middle Pleistocene Kokumoto Formation on the Boso Peninsula of Japan exhibit different types of vertical and lateral changes in grain size and sedimentary structures compared with the Bouma model, which is generally interpreted to represent turbidites deposited from surge-type, ephemeral turbidity currents. Some turbidite beds examined by this study are characterized by several repetitions of coarsening-to-fining upward patterns in association with climbing ripple lamination and parallel lamination. Furthermore, these turbidites are not necessarily laterally continuous in the two-dimensional cross section. Two thickest parts are separately observed within the same stratigraphic level. The geometry and internal organization of these turbidites are interpreted to be a product of hyperpycnal flows generated from a multi-source system associated with a shelf-margin delta in an upslope area during falling- and lowstand stages.
