1991/01/01 by Yoshinori Otsuki, Yoshinori OTSUKI
Earth and Planetary Sciences · #Geological and Geochemical Analysis #Geology and Paleoclimatology Research #earthquake and tectonic studies
paper · pdf · doi:10.5026/jgeography.100.7_1077
crossref issued 1991/01/01 · crossref published 1991/01/01 · crossref published-print 1991/01/01 · openalex publication_date 1991/01/01 · crossref created 2011/07/13 · crossref deposited 2021/05/19 · openalex created_date 2025/10/10 · crossref indexed 2026/07/30 · openalex updated_date 2026/07/30
The Takanosu Basin is located in the northern part of the Dewa Hills, the inner zone of the Northeastern Japan Arc, and filled with a series of deposits in which the Yuguruma Formation takes the uppermost part.The Yuguruma Formation is composed mainly of lacustrine blueish gray tuffaceous silt and contains intercalated gravel, sand, acid tuff, and lignite layers. Its total thickness is estimated to beabout 200 meters or more. Significant tectonic deformation of the formation is not recognizable. Paleomagnetic measurements indicate that the Yuguruma Formation is Middle Pleistocene in age, and its deposition finished a little later than 0.35 Ma.There are three higher terrace surfaces in the Takanosu Basin, i.e., the T-H1, T-H2, and T-H3 surfaces. The T-H1 surface provides the depositional surface of the Yuguruma Formation. The T-H1, T-H2, and T-H3 are indirectly dated as ca. 0.35-0.44 Ma, ca. 0.20 Ma, and ca. 0.16-0.19 Ma respectively, on the basis of accumulation rate of weathered tephra which covers the surfaces and intercalates dated Late Pleistocene marker-tephra layers.The presence of the higher terraces underlain by the thick sediments indicates a change in tectonism from subsidence since early Pliocene time (the end of Funakawa age) to uplift all over the basin in Middle Pleistocene time, because the Yuguruma Formation emerged and the T-Hl surface was formed around 0.35 Ma. The tectonic development of the besin has still continued to deformed the T-H3 surface and Late Pleistocene T-Lla surface.