The stratigraphy, geologic structure of the Tokai Group in the southern part of the Naruko, the Arimatsu, and the northern part of the Obu hills are briefly described. The Tokai Group in the study area is divided into the Higashiura, the Obu and the Narumi Formations, in ascending order. The Tokai Group of the area intercalates nine volcanic ash layers. These are the Ishihama, the Ogawa, the Aioi, the Morioka, the Itayama, the Yoshida, the Odaka I, the Odaka II, and the Hosoguchi Volcanic Ash Layers in ascending order. The Ishihama, the Ogawa, the Morioka, the Itayama, the Odaka I, and the Odaka II Volcanic Ash Layers can be correlated with the Marune, the Togo, the Nagakute I & II, the Kumanomae, the Takinomizu I, and the Takinomizu II Volcanic Ash Layers in the Seto Group, respectively. Also, the Ishihama, the Ogawa, the Aioi, the Morioka, the Itayama, the Yoshida, and the Odaka I Volcanic Ash Layers can be correlated with the Kosugaya, the Otani, the Higashidani, the Souri, the Okada, the Yokosuka, and the Tenjinike Volcanic Ash Layers in the Tokoname Group, respectively. The most remarkable findings of the geologic structure in the Tokai Group in our study area are the folds trending in the two directions of NE, and NNW to NW. The folds trending in the NE direction are cut by the folds trending in the NNW to NW directions. Based on the tephrochronology and biostratigraphy, it can be said that the Tokai Group in the study area deposited during the Early Pliocene and the Late Pliocene. The Sanage-Chita uplift zone, which is the remarkable tectonic zone in the Tokai sedimentary basin, is thought to be a single uplift zone turning the trend from NE to SW directions in the study area. Asa result of this study, it is proved that the uplift zone is divided into two uplift zones: i. e., the Sanage Uplift Zone trending in the NE direction, and the Chita Uplift Zone trending in the NNW to NW directions. The Chita Uplift Zone cut the Sanage Uplift Zone, Consequently, it is revealed that the former zone started uplifting later than the latter zone.

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Plio-Pleistocene pyroclastic flow deposits are widely distributed in the Takayama Basin, Gifu prefecture. They are divided into the Matsubara Gravel Bed, Matsumoto Gravel Bed, Ogaya Formation, Nyukawa Pyroclastic Flow Deposit, Miyamae Formation, Naberidani Ash Fall Deposit, Chayano Tuff I・II, Ebisutoge Pyroclastic Deposits, Kiriyama Gravel Bed, Uwano Mudflow Deposit, Enako Gravel Bed, Kamitakara Pyroclastic Flow Deposit, and Yamaguchi Gravel Bed in ascending order. The Kiriyama Gravel Bed unconformably overlies the Ebisutoge Pyroclastic Deposits. Plio-Pleistocene volcanic activity has been evaluated using geologic and petrographic evidence. The lithology and petrography are as follow: 1) The Ogaya formation is composed mainly of gravel, and contains one intercalated pyroclastic flow deposit, seven vitric ash layers, and one crystal rich ash layer. The Pyroclastic flow deposit and vitric ash layers consist of garnet-allanite-bearing rhyolitic pyroclastic material. 2) The Nyukawa Pyroclastic Flow Deposit ('boiling-over' type flow-forming eruption) consists of clinopyroxene-orthopyroxene-bearing dacitic welded tuff. 3) The Naberidani Ash Fall Deposit consists of orthopyroxene-hornblende-biotite-bearing dacitic plinian pumice fall material. 4) The Chayano Tuff I・II and Ebisutoge Pyroclastic Deposits (derived from phreatomagmatic and 'column collapse' type eruption) consist of hornblende-orthopyroxene-bearing dacitic pyroclastic material. The Chayano Tuff I・II is characterized by accretionary lapilli. 5) The Kamitakara Pyroclastic Flow Deposit is a biotite rhyolitic pumice flow deposit.

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Erosional and depositional processes on a rocky coast are controlled by many factors, e. g., relative sea-level changes, sediment supply, mechanical properties of the coastal rocks, marine conditions surrounding, and tectonic movement. The Miocene Namigata Formation is a sediment accumulated on a rocky coast, which bounding the northern margin of an intra-arc basin of the Southwest Japan arc. This paper reconstructs the sedimentary environment of the formation, and discusses the eustatic cycles affecting environmental changes and the kinematic process forming the rocky coast. The rocky coast has a staircase morphology consisting of wave cut terraces and sea cliffs, which morphology is a product of smaller-scale rises and stillstands of relative sea-level during a cumulative rise more than 120m. In the maximum flooding stage, sea level rose to the altitude of the elevated peneplain spreading on the north of the rocky coast, so that the shoreline retreated significantly. The retreat led to a marked reduction of terrigenous supply by trapping on the submerged elevated peneplain and to the consequent accumulation of a condensed section comprising non-tropical carbonate. During the subsequent highstand stage, terrigenous supply gradually recovered and gravely sediments formed a progradating fan delta at the succeeding fall. The Namigata Formation thus consists of a transgressive and a highstand systems tract, forming a depositional sequence as a whole. Since the depositional age of the formation is inferred to be ca. 16.5-15.5Ma, the depositional sequence and the maximum flooding surface are comparable respectively with the third-order eustacy cycle TB 2.3 and the downlap surface of 16Ma. The smaller-scale rises and stillstands producing the staircase morphology of the rocky coast are hence interpreted to be the manifestation of the forth-order eustacy cycle. In the maximum flooding to early highstand stage, the significant northward transgression beyond the rocky coast seems to have encountered with a southward transgression in the neighboring intra-arc basin to the north, through lowered portions of the elevated peneplain separating these parallel intra-arc basins. Consequently appeared is a trans-arc seaway connecting the Pacific and the Japan Sea. Paleoenvironmental studies indicate the northward gentle tilting of the block ranging from the northern intra-arc basin to the elevated peneplain. Hence the differential movement between the northern tilting block and the southern subsiding basin may have formed the rocky coast accumulating the Namigata Formation. Thus, the sedimentary history of the formation was controlled essentially by the eustacy cycle TB 2.3 and the differential movement between the neighboring intra-arc basins.

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The origin of red shales from the Mugi Formation, Tokushima Prefecture, Shikoku, is investigated in terms of the occurrence and geochemistry. The Campanian to early Maastrichtian Mugi Formation occurs as an east-west trending 4km wide belt tectonically sandwiched between the Campanian to early Maastrichtian Hiwasa Formation to the north and the Eocene formation to the south. The Mugi Formation is represented by shale and greenstone with sand-mud mixed rock, acidic tuff and red shale. Chemical features and occurrence of greenstones suggest that they were emplaced in connection with ridge-forearc collision during the Campanian-early Maastrichtian. Red shales in the Mugi Formation are found closely associated with greenstones. Red shales of various thicknesses ranging from several centimeters to several meters occur as interbedded layers in shale and in immediate contact with basaltic lava, and occasionally grade into the over-and underlying shales. The modes of occurrence and microscopic features of red shales indicate that they were deposited in proximity to a source of detrital sediment and in relation to submarine volcanism. The red shales are richer in Fe, Mn, P, Y, As, Ni, Zn and Ba, and poorer in Si than shales. Some geochemical signatures of red shales most closely resemble those of hydrothermally-derived metalliferous sediments found around the crests of active ridges. In this context, we conclude that the red shales were deposited in the trench area by a reaction between hydrothermal solution and sea water along with contamination by continent-derived detrital materials.

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Middle Miocene submarine felsic volcanic rocks predominate in the Tadami district, a southern part of the Inner Zone of Northeast Japan. The Oshio Formation is one of these successions. The Oshio Formation in main area is divided into the Shiozawagawa Mudstone Member, the Gamogawa Volcaniclastic Rock Member and the Oshirasawa Lava Member, the Managawa Lava Member, the Kogamosawa Volcaniclastic Rock Member, the Yagisawa Lava Member, the Namesawa Volcaniclastic Rock Member, the Omakidake Mudstone Member, and the Ishitakasawa Volcaniclastic Rock Member in ascending order. And in northeastern part of studied area it is divided into the Shiozawagawa Mudstone Member, the Gamogawa Volcaniclastic Rock Member, the Higashimatayama Volcaniclastic Rock Member, the Koganeiyama Lava Member, the Okuzozawa Mudstone Member, and the Koyuyama Basaltic Volcaniclastic Rock Member in ascending order. The Gamogawa Volcaniclastic Rock Member, the Kogamosawa Volcaniclastic Rock Member, the Ishitakasawa Volcaniclastic Rock Member, and the Higashimatayama Volcaniclastic Rock Member are composed mainly of pyroclastic or debris flow deposits. The Oshirasawa Lava Member, the Managawa Lava Member, the Yagisawa Lava Member, and the Koganeiyama Lava Member consist of rhyolite lavas and autoclastic rocks. The Namesawa Volcaniclastic Rock Member is made up of resedimented deposits. The Koyuyama Basaltic Volcaniclastic Rock Member comprises basaltic hyaloclastite. The volcanic activity during the Oshio Stage is divided into four stages. During Stage I, rhyolitic magma with 5.3% phenocrysts of plagioclase, is erupted to form the Gamogawa Volcaniclastic Rock Member and the Oshirasawa Lava Member. During Stage II, rhyolitic magma with 2.7% phenocrysts of plagioclase, is erupted to form the Managawa Lava Member, and is intruded as Type A dikes. During Stage III, rhyolitic magma, containing few percent plagioclase and quartz phenocrysts, is erupted to form the Kogamosawa Volcaniclastic Rock Member, the Yagisawa Lava Member, the Higashimatayama Volcaniclastic Rock Member, the Koganeiyama lava Member, and is intruded as Type B dikes. During Stage IV, rhyolitic magma containing few tens percent large plagioclase phenocrysts and few percent large quartz phenocrysts, is erupted to form the Ishitakasawa Volcaniclastic Rock Member, and is intruded as Type D dikes and sills. Basaltic activities during the Oshio Stage are initiate after Stage I at southern area, and after Stage III at northern area.

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