Reconsideration of the subdivision of "alluvium' in enclosed coastal seas - the example of Osaka Bay

Unconsolidated muddy sediment, which forms the upper and middle parts of "Alluvium' in Japanese enclosed coastal seas, cannot be stratigraphically subdivided. The sandy part near the channel area and the muddy parts in the central bay and the area far away from the channels (both on the bottom surface) are in the relation of a contemporaneous heterotopic facies. The most obvious reflector in the acoustic record is better understood as the boundary between the upper and middle muddy "Alluvium' and the underlying "lower Alluvium'. -from English summary