Abstract
The author has traced the basal surface of the Recent Alluvium in the submarine area near Ube City, by analyzing over about two hundred boring data in the sea-bottom (Fig. 2). The followings are some of the cor_clusions; (1) The basal surface of the Recent Alluvium is found at the depth of 20 to 35.7 meters below the present sea-level in the area to the south of the mouth of the Koto, where it inclines south wardwith an uniform gradient (Fig, 5). The reconstructed surface is regarded as the floor of the entrenched Koto valley system, owing to the lowering of the sea-level in the last glacial stage. (2) The basal surface of the Recent Alluvium in the mouth of the Asa and the Ariho continues to that of the Koto, although it exists between 14 and 17 meters below the present sea-level. The threestreams (the Koto, the Asa and the Ariho) belong to the same river system on the land which has emerged by the eustatic regression in the last glacial stage. (3) A submarine terrace with gravels underlying the Recent Alluvium is found off Cape Ubemisaki. The depth of the surface ranges from 6 to 14 meters below the present sea-level (Fig. 7). By the fact that the surface is discontinuons to the ancient river floors, it is considered that the submarine terrace was formed before the eustatic regression in the last glacial stage. (4) The homogeneous muddy bed which has occasionally over a hundred meters thick is correlated to the strata containing Stegoclon orientalis OWEN (Fig. 9). This muddy bed is chronicled to the I2 period by the other fossils. The author concieves that the sedimentation of this mud coincides with the formation of Setouchi erosion surface.
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call