Abstract
Visual observations were conducted at the mouth of the Tokyo Submarine Canyon (TSC), at the junction of the TSC and the Misaki Depression, in August 2010, from the ROV Hyper-Dolphin. Examination of the topography and geology of the TSC and Miura Basin revealed four lithostratigraphic units in area, Units I to IV (in stratigraphically descending order). Unit I consists of Recent unconsolidated mud that thinly covers the bottom of the TSC and two deep-sea terraces. Unit II is a middle Pleistocene conglomerate observed at water depths of 1148-1096 m; the lithology and areal distribution of Unit II suggest deposition from a debris flow that surged down the canyon. Unit III is a middle Pleistocene semi-consolidated muddy deposit consisting of alternating horizontal beds of sandstone and mudstone, observed at water depths of 1120-809 m; Unit III is present throughout the Misaki Depression. Unit IV is a consolidated muddy deposit consisting of N-dipping alternating beds of sandstone and mudstone, observed at water depths of 1174-1120 m; the unit is partly eroded and is overlain by Unit II. The stratigraphic relationships and distributions of lithofacies at the mouth of the TSC help clarify the nature of tectonism in the area of the TSC and Miura Basin.
