Sequence stratigraphic analysis was carried out for the Middle to Upper Miocene Ponsubetsu, Subetsu, Ichibangawa and Morai formations distributed in the southern part of the Kabato Mountains, forming a part of the Rebun-Kabato belt in the central Hokkaido, Japan. These formations are divided into four depositional sequences, Depositional sequence 1 to 4, which comprise various depositional systems such as fan delta, sandy shelf to shallow marine, slope to basin floor and submarine fan systems. Spatial distribution of these depositional systems changed temporally, responding to relative sea level changes. Result of basin subsidence analysis at several portions of the study area suggests that basin morphology and distribution of the depositional systems within the seqences were strongly affected by basin tectonics, represented by three tectonic events, which showed the beginning and ceasing of tectonic subsidence.

View full abstract

Late-Pliocene pyroclastic flow deposits are individually distributed in the Takayama Basin, Omine Belt and southern part of the Matsumoto Basin, central Japan. In the Takayama Basin, these are devided into the Nyukawa Pyroclastic Flow Deposit, the Chayano Tuff I/II and the Ebisutoge Pyroclastic Deposits in ascending order. Then, the Omine Belt resides in the western margin of the northern Fossa Magna, is composed mainly of gravel, sand and intercaleted with pyroclastic flow deposits. Long distance correlations of these pyroclastic flow deposits have been achieved by using field and petrographic criteria: 1) stratigraphic sequences 2) lithofacies 3) mineral assemblage 4) refractive index of the volcanic glass and orthopyroxene. Accordingly, the Nyukawa Pyroclastic Flow Deposit is correlated to the both of the Takagariyama Tuff I in the Omine Belt and the Seba Pyroclastic Flow Deposit in the southern part of the Matsumoto Basin. The Ebisutoge Pyroclastic Deposits can be correlated also to the Takagariyama Tuff II in the Omine Belt. Therefore, Pliocene formation distributed in the western and eastern sides of the Northern Alps was firstly correlated by the simultaneous pyroclastic flow deposits.

View full abstract

In the Shiretoko Peninsula, east Hokkaido, the active faults are known on the ridge of Mt. Iwozan to Mt. Tenchouzan through Mt. Rausudake. We have found another active faults on the ridges of Mt. Shiretokodake and Mt. Chinishibetsudake to Mt. Onnebetsudake by air-photograph interpretation and aerial survey of the Shiretoko Peninsula. The active faults are characterised by fault scarp, fault scarplet, reverse scarplet and graben displacing Quaternary lava flow and/or lava dome. They are divided into three types by the related characteristic geological phenomena, as follows: (1) the active faults associated with volcanism, which are featured by graben, eruption of lava flow and lava dome, and crater, (2) the active faults associated with earthquake, which are deficient in effect of volcanic activity, (3) the active faults associated with large landslides.

View full abstract

Fossil pollen assemblages from the Middle-Late Pleistocene transgressive sequence in the upper part of Negoya and the Kusanagi Formations in the Udo Hills facing the Suruga Bay, Central Japan can be divided into five pollen zones. Paleovegetation is reconstructed for each of the pollen zones. These pollen zones are correlated with pollen stratigraphy in Kinki, Kanto and Tokai districts. The upper part of the Middle Pleistocene, Negoya Formation, can be divided into three pollen assemblage zones: N-I, N-II and N-III in upward sequence. The Kusanagi Formation of the late Pleistocene can be divided into two pollen assemblage zones: K-I and K-II in upward sequence. The N-I zone is composed mainly of Fagus and Quercus (subgenus: Quercus) accompanied by Picea and Betula indicating cool temperate climate. N-I zone is subdivided into three subzones namely N-I a (Fagus), N-I b (Picea-Cryptomeria) and N-I c (Abies) subzones. N-II zone is characterized by temperate elements, namely Pinus, Fagus and Ulmus-Zelkova, accompanied by Lagerstroemia indicating warm temperate to tropical. N-II zone is subdivided into four subzones: N-II a (Lagerstroemia), N-II b (Pinus-Fagus), N-II c ( Tsuga-Fagus) and N-II d (Picea-Cryptomeria) subzones. Pollen assemblages of N-III zone is composed mainly of Picea. The paleoclimatic condition in N-I, N-II and N-III zones representing one cycle is changed from cool to warm in N-I and N-II zones, and became cool in N-III zone. K-I zone of Kusanagi Formation is characterized by Picea, Tsuga, Betula, Fagus and Alnus, is subdivided into four subzones, namely K-I a, K-I b, K-I c and K-II d subzones. K-II zone indicates warm temperate climate. It is characterized by Tsuga, Lagerstroemia, Sapium and cf. Ulmus-Zelkova, and is subdivided into K-II a and K-II b subzones based on the Pinus content. The pollen assemblages of N-II zone in the upper part of Negoya Formation is correlated with the pollen assemblages of the P9 zone in Osaka, Kinki (Furutani 1989) and Diploxylon-Fagus-Ulmaceae zone in Yokohama, Southern Kanto (Nishimura 1980). The pollen assemblages of K-II zone in the Kusanagi Formation is correlated with the pollen assemblages of the P3b subzone (Furutani 1989), Ka-II zone in Oiso Hills, Southern Kanto (Tsuji 1980) and conifer-Ulmus-Zelkova zone (Nishimura 1980).

View full abstract