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Journal Articles

Intense chemical weathering in southwest Japan during the Pliocene warm period

Hatano, Nozomi*; Yoshida, Koki*; Adachi, Yoshiko*; Sasao, Eiji

Journal of Asian Earth Sciences, 184, p.103971_1 - 103971_13, 2019/10

 Times Cited Count:0 Percentile:100(Geosciences, Multidisciplinary)

Whole rock major and REE geochemistry and mineral compositions of the Pliocene sediments in southwest Japan reveal the effects of source rock compositions and grain sizes, as well as the relationship between sedimentary environments and the degree of chemical weathering in the Pliocene warm period. A wide variation in the degree of chemical weathering, source rock compositions and grain sizes were observed with vertical and spatial changes in the sedimentary environment. Regardless of the wide variety of source rock compositions and grain sizes, REE and kaolinite-rich clay mineral concentrations in sediments, of which CIA values are generally above 90, are indicative of the intense weathering conditions that prevailed in the Pliocene period (3-4 Ma) in southwest Japan.

Journal Articles

Effects of grain size on the chemical weathering index; A Case study of Neogene fluvial sediments in southwest Japan

Hatano, Nozomi*; Yoshida, Koki*; Sasao, Eiji

Sedimentary Geology, 386, p.1 - 8, 2019/05

 Times Cited Count:1 Percentile:27.67(Geology)

Grain size variation of sediments generally complicates the assessment of the degree of chemical weathering. Mineralogical and geochemical research was carried out on Miocene and Pliocene fluvial sediments in southwest Japan to evaluate the effects of grain size on the degree of chemical weathering. We indicated that the Al$$_{2}$$O$$_{3}$$/SiO$$_{2}$$ ratio may be suitable as a grain size index. Most of the fine-grained sediments have higher CIA values. In contrast, coarse-grained sediments, display a wide range of CIA values. The CIA values for intermediate grain sized samples reflect distinctive differences in the degree of chemical weathering between Miocene and Pliocene sediments. In the intermediate grain sized samples, the Miocene sediments have higher CIA values than Pliocene sediments. To compare the degree of chemical weathering, it is desirable to evaluate with the Al$$_{2}$$O$$_{3}$$/SiO$$_{2}$$ ratios limited to the intermediate grain size range.

Oral presentation

Variations in source rock assemblage recorded in the Tokiguchi Porcelain Clay Formation, central Japan

Hatano, Nozomi*; Yoshida, Koki*; Sasao, Eiji; Yasue, Kenichi; Adachi, Yoshiko*; Iwano, Hideki*; Danhara, Toru*

no journal, , 

The Miocene Tokiguchi Porcelain Clay Formation consists mainly of muddy sediments, which were deposited in the tectonical-controlled small inland basin in the southern part of the Gifu Prefecture, central Japan. This research focuses the U-Pb radiometric ages of detrital zircon grains in the sandy sediments in this formation in order to clarify the provenance variations by radio metric ages. Additionally bulk rock assemblage of the hinterland was estimated by the REE chemical composition of the muddy sediments. The age of detrital zircon grains were concentrated at the 12-15 and 70-80Ma. Some grains showed 200, 1700, 1800, 1900 and 2900 Ma. REE composition of the muddy sediments indicates various source rocks in the hinterland including basic, intermediate and felsic rocks. The wide range of age assemblage of detrital zircons shows significant difference, implying provenance variation. Also REE geochemistry is indicative of various source rock assemblage in the hinterland.

Oral presentation

Areal comparison of the geochemistry of the Todo Porcelain Clay Formation; For reconstruction of paleo-weathering condition in the Neogene period

Hatano, Nozomi*; Yoshida, Koki*; Sasao, Eiji; Kubota, Mitsuru; Adachi, Yoshiko*

no journal, , 

Weathered zone is located between earth surface and geological environment. Understanding of weathered zone is important for safety assessment of HLW geological disposal. Porcelain clay formation, distributed in southeastern Gifu and eastern Aichi prefectures, consists of fine-grained sediment derived from strongly weathered granite. Discussion on relationship between topographic and weathering conditions of basement rock and porcelain clay is needed to understand paleo-environment when porcelain clay was formed. The authors investigate chemical and mineral composition of porcelain clay. Mineral composition varies considerably with location. Si content of porcelain clay is significantly higher than basement rock and PAAS which represents average chemical composition of crust. The result suggests that chemical composition of host rock was altered by strong weathering. Variation of Ti content with location is possibly caused by topographic and weathering condition of provenance.

Oral presentation

Paleoweathering condition in middle Miocene to early Pliocene period in Japanese Island; From paleopedology and chemistry of muddy sediments

Hatano, Nozomi*; Yoshida, Koki*; Sasao, Eiji; Kubota, Mitsuru; Adachi, Yoshiko*

no journal, , 

In Japanese Islands, the middle Miocene to Pliocene fluvial formations include aluminous clayey horizons. These formations can be a useful to reconstruct of weathering conditions. Description of paleosols and geochemical research were carried out in the middle Miocene (10-11 Ma) and the early Pliocene (3-4 Ma) sediments in central Japan in order to illuminate the weathering condition. The major elemental geochemistry shows that the Miocene sediments were supplied from severe weathered sources with CIA values of 80-94. The Pliocene sediments show the CIA values of 72-90 showing the relatively weak weathering condition. The weathering condition in the middle Miocene to Pliocene in Japanese Islands may be affected by the influence of warm water current and initiation of the Eastern Asian monsoon. The middle Miocene period is considered to have been under the intenser weathering condition than one in the early Pliocene period.

Oral presentation

Paleoweathering environments recorded in the Pliocene-Pleistocene Kobiwako Group, southwest Japan

Yoshida, Koki*; Hatano, Nozomi*; Sasao, Eiji

no journal, , 

Plio-Pleistocene sediment, distributed around southern part of Shiga prefecture and northern part of Mie prefecture, provides important paleoweathering records during Pliocene and Pleistocene periods. The authors estimated paleoweathering condition by means of geological and geochemical studies. The sediments derived from differentiated rock type display high weathering index showing the intense chemical weathering environments in hinterland. Meanwhile, the sediments supplied from not-differentiated rock type indicate the derivation under weak chemical weathering environments. The paleoweathering degree estimated with provenance analysis represents the reality of paleoweathering environments even in the sediments derived from mixed source rocks.

Oral presentation

History of paleoweathering intensity in the middle Miocene and the Pliocene period; From paleosol facies, chemical weathering degree and clay mineral assemblages

Hatano, Nozomi*; Yoshida, Koki*; Irie, Shiori*; Mori, Saori*; Natori, Wakako*; Adachi, Yoshiko*; Sasao, Eiji

no journal, , 

Understanding of climate change is one of important issue to consider future climate change. In this study paleoweathering condition of middle Miocene and Pliocene periods is examined based on paleosol facies, chemical weathering degree and clay mineral composition of Miocene to Pliocene sediments distributed in central to southwestern part of Japan.

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