According to the hypothesis of ocean floor spreading, oceanic crust has no rocks older than 0.2Ga and of continental origin. The Atlantic oceanic crusts, however, include the rocks back to 1.85Ga and of continental constituents, such as granitoids, gneisses, schists, granulites, coarse-grained terrigenous clastics, continental peridotites. This paper describes these rocks from 42 localities and groups them into 4 types. The occurrence of these rocks has modified the hypothesis of sea floor spreading with ceased expansion, older sediment patches left behind, non-spreading segment, multiple ridge jumping, oscillatory spreading, small roll-like cells bilateral under a spreading axis, delamination, etc. The modifications are on little substantial data and on ad hoc mechanisms, so that the hypothesis is required to comprehend all of the exotic rocks. Instead, the ancient continental rocks are compatible with the hypotheses of oceanization and Earth's minute expansion differential between ocean and continent, as evidences for the continental outer-layer preexisted in the ocean. These hypotheses are required to propose their concrete mechanisms with relic rocks. Since marine geological surveys are still extremely sparse, so that further drilling and dredging will prove the presence of ancient continental rocks much more. All hypotheses on the origin of the Atlantic should be reexamined with substantial evidences from the ocean floor.

View full abstract

The capacity of waste disposal sites is absolutely inadequate for the discharge volume of waste in and around the Metropolitan area. Plans to construct waste and surplus soil disposal sites are likely to increase in future. Any disposal site has a risk to cause serious environmental pollution since even small quantity of leakage of waste water may cause pollution. It is important, therefore, to evaluate the permeability of a stratum under the construction area of a disposal site. However, scientific preliminary surveys of the hydrologic cycle have not been conducted except the cases of large-scale construction projects. Especially in the areas of Tertiary and Quaternary systems, it is difficult to accurately evaluate the permeability of a stratum from a technical point of view. This paper records the findings of a survey of the hydrologic cycle in the area where mainly a muddy layer is distributed. The area was in the upstream hilly area of a river at the southernmost tip of the Boso Peninsula, and the survey consisted of a hydrogeological survey, discharge measurement and water quality analysis. An occurrence of the interaction between groundwater and surface water was confirmed even in areas underlain by muddy layers which are generally considered suitable for the construction of a waste disposal site. Especially in a period of water shortage, geological condition is an important factor for the interaction between groundwater (which springs out) and surface water (which infiltrates underground). It is necessary, therefore, to produce a precise geological map with detailed geological description. It is risky to evaluate the suitability of a place for construction of disposal sites by just confirming geological outline with existing data. In summary, a field survey, river water discharge measurement and water quality analysis under different hydrogeological and seasonal conditions make it possible to study the permeability of a stratum and the characteristics of the hydrologic cycle in the mountain areas.

View full abstract

The Miocene strata are distributed in the Chichibu sedimentary Basin in the northwestern part of the Kanto Mountains. The north and northeastern margin of the Chichibu Basin where the lowermost part of the Miocene is distributed has been studied to elucidate the genetic process of the Chichibu sedimentary basin. As a result, the stratigraphy of the Miocene in Chichibu sedimentary basin north-northeastern margin part was divided into the Ushikubi, Tomita, Nenokami, and Miyato Formations in ascending order, mostly similar to the northwest-western margin region, and the relationship of the Nenokami and Tomita Formation is local unconformity. The forming age of this unconformity is about 16Ma. at the boundary between the early Miocene series and the middle Miocene series. Moreover, the observation and the isopac map etc. of the relation between the Miocene and the basement are made; as a result, it is thought that the origin of the sedimentary basin in north and northeastern margin was generated from collapse by the tectonic movement of the basement. In that case, a regional subsidence is caused after some small collapsing occurs and they unite, and this subsidence region seems for the subsidence center to have moved in the direction of the south or the southeast while reducing the difference of the amount of a regional subsidence and advancing of overall subsidence at the sedimentation from the Shirasu sandstone Member to the Tomita Formation. It is possible to think the movement style of such a subsidence region to be appearance in the basin northern edge of the so-called Shogidaoshi structure seen in the Chichibu sedimentary basin.

View full abstract

This paper presents the results of detailed studies of the Budokubo Collapse Basin, which was formed in the Latest Pleistocene. The basin is located in the northern part of Uonuma Hills, attacked by the 2004 Mid-Niigata Earthquake. The basin is surrounded by hills, and the topography of the basin is a polygon, 2km long and 1.5km wide. The Budokubo Formation within the basin is composed of irregularly alternating beds of gravels, sands and silts, intercalated with the Aira Tn tephra bed (AT; approx. 2.6〜2.9ka). The formation contains peat layers which characterized static slack - water environments. The marginal facies of the Budokubo Formation are poorly sorted, and the formation is in high-angle unconformable contact with Neogene basement. The investigation reveals that just before the Budokubo Collapse Basin was formed, the main stream of the Shinano River had run through the area studied. Four step fluvial terraced surfaces are recognizable in the basin. The forming process of the Budokubo Collapse Basin is considered as follows: At first, we estimate the land was uplifted more than 25m, in a larger area containing the studied area that included the Shinano River, so, the stream had its way blocked and took another course. Later, the land collapsed approximately 25m in this small area called Budokubo. The process and the scale of the Budokubo Collapse Basin are almost the same as those of the Tamugiyama Collapse Basin, about 5km south of the Budokubo Collapse Basin, an area reported on in 2006. Moreover, these basins were formed during the same period. These facts suggest that the upheaval movement preceding the collapse movement occurred in a wide range of the region including the two basins. The region is inferred to contain Yamamotoyama Block and the place where the Uono River joins the Shinano River, which are near the two basins. In the Yamamotoyama Block, the land has been vigorously uplifted since the Latest Pleistocene. Along the junctions of the smaller blocks within the uplifted region both rivers obviously wind their way. These phenomena apparently resulted from active movements like upheaval in this region. The geodetic survey data by the Geographical Survey Institute indicate that the area of the Budokubo Collapse Basin corresponds to the highest uplifted segment in the 2004 Mid-Niigata earthquake. The eleven step fluvial terraced surfaces show that active and intermittent upheaval movements repeatedly followed from the Late Pleistocene to Holocene in this area. Therefore, this sequence of active movements in this region appears to follow the 2004 Mid-Niigata earthquake.

View full abstract

The Sanukite lava is found in the Kasugayama andesite mass middle Miocene in the Nijyo Group, southeast of Osaka Prefecture. The Sanukite lava of irregular shaped block is included in aphyric andesite lava near the eruption vent. The aphyric andesite lava contains many light gray small spherical grains in 0.2-3mm diameter. Silica minerals and micas are found in the grains. The aphyric andesite magma may have reached second boiling point by increasing gaseous pressure during crystallization process. In contrast, the Sanukite lava blocks show homogeneous glassy texture free from the grains. It is supposed that the Sanukite was formed by magma with low volatile content, whereas the aphyric andesite magma hosted larger amount of volatiles. These two magmas were mingling while eruption of the host aphyric andesite magma.

View full abstract