Shoji Nishimoto

• Ph.D.
• Professor at Aichi University

Carbonate concretions occur in sedimentary rocks of widely varying geological ages throughout the world. Recently, more than 100 gigantic carbonate concretions with diameters ranging from 1 to 9 m have been identified along the Unosaki coast of Oga Peninsula, Akita Prefecture, Japan. The formation process of such gigantic concretions, some of which...

Understanding climate variability and stability under extremely warm ‘greenhouse’ conditions in the past is essential for future climate predictions. However, information on millennial-scale (and shorter) climate variability during such periods is scarce, owing to a lack of suitable high-resolution, deep-time archives. Here we present a continuous...

In sedimentary rocks rich in Fe-oxide, such as red beds, white bleached spots that are free of Fe-oxide minerals are often observed. The spot formation has been explained by localized reduction reactions in relation to organic substances, such as fluids including hydrocarbon and organic debris as a precursor, and the recent major prevalent approach...

A good durability of concrete under nuclear conditions is essential for the safe operating of nuclear powerplants. In this case, concrete is generally exposed to a relatively high range of temperature compared to ordinary situations, and the understanding of its thermomechanical behavior becomes required for a fair safety assessment. To achieve thi...

Zebra rock, found in the eastern Kimberley region of northern Western Australia, is a Late Proterozoic sedimentary rock with a rhythmic Liesegang-type Fe-oxide banding. The striped rhythmic pattern in sedimentary rocks is an important key to infer chemical conditions of water-rock reactions. Although past studies have discussed the zebra rock forma...

The determination of the mineral composition of aggregates which constitute an important component of concrete is essential to understand and estimate the durability of structures. The modal (quantitative mineralogical) analysis of rocks is generally determined by point-counting method on thin sections or slabs. However, there is a difficulty of mi...

Isolated silica concretions in calcareous sediments have unique shapes and distinct sharp boundaries and are considered to form by diagenesis of biogenic siliceous grains. However, the details and rates of syngenetic formation of these spherical concretions are still not fully clear. Here we present a model for concretion growth by diffusion, with...

This paper discusses the formation of veins less than 20 cm in width which are abundant in the Nakamura Formation of the Miocene Mizunami Group. These veins consist of a central clastic and adjacent dense portions. Field observations and chemical and X-ray diffraction analyses show that the clastic part was formed by hydraulic fracturing under hydr...

‘Liesegang patterns’, rinds and bands are commonly observed in nature and form by self-organised periodic precipitation of Fe-oxyhydroxide following a nonlinear reaction-diffusion process. Although strictly Liesegang patterns consist of bands that increase in width with increasing distance from the source of the Fe that precipitated as Fe-oxyhydrox...

Spherical Fe-oxide concretions on Earth, especially in Utah, USA, have been investigated as an analog of hematite spherules found in Meridiani Planum on Mars to support interpretations of water-rock interactions in early Mars. Although several formation mechanisms have been proposed for the Fe-oxide concretions on Earth, it is still unclear whether...

Carbonate concretions occur in sedimentary rocks of widely varying geological ages throughout the world. Many of these concretions are isolated spheres, centered on fossils. The formation of such concretions has been variously explained by diffusion of inorganic carbon and organic matter in buried marine sediments. However, details of the syn-depos...

Long-term history of water conducting fracture is key issue to evaluate deep geological environment for geological disposal of high-level radioactive waste. Thus, we carried out study on the geological features and the long-term behavior of water conducting fractures based on the data obtained at －300 m levels in the Mizunami Underground research l...

Episyenite is a quartz-depleted vuggy rock resulting from hydrothermal alteration of granitic rocks. This is the first report of its existence in an island arc, which is identified in a deep drill core of the Toki Cretaceous granite distributed in central Japan. In order to understand the petrographical features of the episyenite, neutron porosity...

Redox buffering is one important factor to be considered when assessing the barrier function of potential host rocks for a deep geological repository for long-lived radioactive waste. If such a repository is to be sited in fractured crystalline host rock it must be demonstrated that waste will be emplaced deeper than the maximum depth to which oxid...

Weathering rinds formed in Mesozoic sandstone and basalt cobbles buried in terrace deposits for up to 300ka have been investigated. The aim was to determine the formation process and elemental mass balances during rind development. The ages of terraces distributed in the western part of Fukui prefecture, central Japan have been determined as 50ka,...

This paper investigates the mineralogical effects of hydrothermal alteration at depth in fractures in granite. A fracture accompanied by an alteration halo and filled with clay was found at a depth of 200m in a drill core through Toki granite, Gifu, central Japan. Microscopic observation, XRD, XRF, EPMA and SXAM investigations revealed that the mic...

In the orogenic field Japanese islands, there are wide areas of crystalline rocks that inevitably contain groundwater conductive fractures associated with alteration zones. However, little attention has been given to the formation process and possible influence on the radionuclides migration from radioactive waste repository that might be sited wit...

地下における花崗岩の変質プロセスを解明することを目的に, 岡山市で掘削されたボーリングコアの深さ約100mまでについて, 割目帯近傍における花崗岩中の造岩鉱物の変質状態を調べた. この花崗岩は, 粗粒の石英, 正長石, 斜長石, 黒雲母などからなり, 割目帯に沿って水-岩石反応により形成されたと思われる変質帯が伴われる. 今回, 地下40～50m付近の変質帯を伴う割目帯を詳細に調べた結果, 斜長石の絹雲母化と黒雲母の緑泥石化は割目帯や深度と関係なくコア全体に確認することができた. また, 割目帯の近傍ほど斜長石のスメクタイト化と水酸化鉄の沈殿が明らかに進行しており, 割目帯内部では黒雲母の一部がバーミキュライト化していた. 一方で, カリ長石には変質はほとんど認められない. これら造岩鉱物の...

地下深部花崗岩の変質プロセスを解明することを目的に, 岐阜県土岐市で深度約500mまで掘削したボーリングコアについて花崗岩の変質状態と割目等との相関を調べた. 変質鉱物として, 絹雲母, 緑泥石, 方解石, 水酸化鉄が認められた. 黒雲母の緑泥石化や斜長石の絹雲母化は, 開口割目が発達する部分と勇断を伴うシーリングされた割目が多い部分で顕著であり, 深度との相関は認められない. 方解石は, 勇断を伴うシーリングされた割目近傍において充填鉱物として認められるが, 開口割目の多い部分では見られない. 開口割目と剪断を伴うシーリングされた割目が同時期に形成されたとは考えにくく, 異なる時期の熱水変質があったと考えられる. 水酸化鉄は, 一部の開口割目やその近傍の鉱物粒間において観察され, 黒雲母や...

Modal analysis of stained granite slabs is performed using image processing software “Adobe photoshop TM”with personal computer and scanner. The areas corresponding to the rock-forming minerals of [K-feldspar], [plagioclase], [quartz+mafic minerals] and [mafic minerals] are selected from a digital image of the slabs. The procedure was carried out o...

This paper examines textural relationships and compositional zoning patterns of some K-feldspar phenocrysts from the granitic rocks in the Tsukuba district, and discusses the growth process of the phenocryst and genetic conditions of the granites. -from Authors