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AbstractThis paper is a geological and topographical description of the sea bottom off northeastern Hokkaido district, stretching Soya Misaki to Shiretoko Misaki. The continental shelf off Soya Misaki to Notoro Misaki region shows broad width and its outer edge is fairly deep ranging 169 to 230 m. The sea area off the coast of Notaro Misaki to Shiretoko Misaki has narrow shelf and the depth of edge ranges 135 to 150 m. There is Kitami YamatoTai (bank) off Notoro Misaki, and continental slope is developed around this bank. From the results of continuous seismic profiling, subsurface strata are divided into several formations; A, B, C, D and E descending order. The E Formation which is the lowest acoustically opaque layer is named the basement in the investigated area. The authors concluded the process of geotectonic development in the investigated area as follows． The D Formation had deposited in the continental shelf off Soya Misaki to Notoro Misaki excluding northern part of outer front of continental shelf area. Then coastal area off Yamausu to Saroma Ko (lake) and Monbetsu Tai in adjacent to outer front zone had been upheaved. As a result of the movement, a part of this area became island which was eroded. During this tectonic movement，flat zone of the middle of shelf had been continuously subsided down so that CL Formation had deposited there. After deposition of the CL Formation the sedimentary basins reduced their areas. During the Cu Stage, the areas have subsided and the basins have gradually enlarged when the Cu Formation has overlapped the CL Formation, as well as the B Formation to Cu Formation. The A Formation has buried the depression where the B Formation has down warped. The central flat zone was filled with much sediments consisting of several formation, and outer margin of shelf and coastal zone were connected by sedimentation. The Kitami Yamato Tai was uplifted during deposition of the D Formation for’the tectonic movement. The CL, CM, Cu, and B Formations were overlapping each of their under posed layer and these formations became thinning out to the top of bank. After the B Formation deposited or during the AL Formation was depositing, tectonic movement with fault was occurred. The result of that continental shelf and the bank have separated each other. After all, present form of Kitami Yamato bank was shaped in this stage. When the lowering of sea level at the glacial age, the continental shelf margin was formed and the top of Kitami Yamato Tai was suffered from wave erosion and continuously tilting movement occurred which has resulted western incline on the northern part and east incline on the southern part of bank.
JournalReport of Hydrographic and Oceanographic Researches