Portal de Periódicos da CAPES

Tsunozu Group

1970; Volume: 9; Issue: 3-4 Linguagem: Inglês

10.4116/jaqua.9.149

1881-8129

Ikuo Onishi, Katsuyuki CHOSHI,

Ecology and Conservation Studies

The Tsunozu Group is developed in the western part of San-in district facing the Japan Sea. In the hilly-land neighbouring Gotsu and Tsunozu (the stratotype), it is composed of loose sediments of gravels, sands and muds which belong to five sedimentary cycles. Each cycle, with the exception of uppermost one, has a marine clay bed that is called M1, M2, M3 and M4, respectively, in ascending order. As the uppermost cycle consists of wethered gravels, it is named the Upper Gravel Bed.In the hills around Mt. Ôe-takayama, the pyroclastic flow and fall deposits are embedded in the clastic sediments in which M4 and aeolian sand beds (ancient dune deposits) are included.As Stegodon elephantoides(?) and plant remains, such as Pseudolarix, Glyptostrobus, Sequoia, Liquidambar, Nyssa, and Paleodavidia, are found in M1 cycle, the lower part of the Tsunozu Group is correlated to the Pliocene age. Some elements of the Mesasequoia flora, such as Picea koribai, Metasequoia, Cunninghamia, and Juglans megacinerea, are found in M4 cycle, so the upper part belongs in the Pleistocene.Though much parts of depositional surface of the Tsunozu Group suffer the erosion and the lowering of hight, some parts are well presarved. The Tsunozu Surface (the summit level of the hills consisted of the Tsunozu Group) is the depositional surface of the early Pleistocene in age.Relict red soils are formed at least two periods, that is, pre-Tsunozu or Tsunozu (late Pliocene) and post-Tsunozu stage (early Pleistocene).