報告書番号

N08063

タイトル（和文）

段丘の対比・編年の信頼性向上のための風化指標の検討－新潟県中越地域等に分布する段丘の観察・分析結果に基づいて－

タイトル（英文）

Study on weathering index for improving the reliability of terrace correlation and chronology- Based on the observation and analysis of terrace deposit distributed in the Mid Niigata region and others

概要 （図表や脚注は「報告書全文」に掲載しております）

詳しい段丘対比・編年が確立された新潟県中越地方と他２地点の数10万年～１万年前程度に形成された段丘を対象として，風化指標の野外調査・室内分析を行った．段丘堆積物にみられるさまざまな風化指標を段丘ごとに整理した結果，風化皮膜の幅およびクサリ礫の段丘礫層中の含有率が，とくに段丘対比に有効であることが分った．風化皮膜の幅は，風化皮膜は，苦鉄質で細粒な岩種に現れることが多い．クサリ礫は，MIS6に対比される中位段丘の礫層中に僅かに含まれ，MIS8より古いと推定される高位段丘群の段丘礫層中で卓越する．さらに，高位段丘群は，構成礫のほとんどがクサリ礫からなる段丘と，構成礫の半数程度がクサリ礫からなる段丘とに区分できる．これらの指標とともに，風成ローム層，礫層基質のそれぞれについて風化程度を指標とし，これらを組合せた総合的な段丘対比を行うことにより，地形・地質・火山灰層序の調和のとれた，段丘対比の信頼性向上に寄与する．

概要 （英文）

We carried out field survey and laboratory analysis to investigate various weathering indexes in loam and terrace deposit at outcrops of the terraces distributed in Mid-Niigata area and other two areas, which were correlated and chronologized accurately,. We also collect and analyze the data of color and hardness of eolian loam, matrix of terrace deposit, thickness of decolorated and/or browning rim of terrace gravels, color and roughness of gravel surface and effective porosity on each terrace. According to result of the analysis, thickness of weathering rind can be an useful index for terrace correlation. Weathering rind is observed frequently in mafic and fine gravels, as a result of statistical survey of occurrence of the patterns of weathering type. According to the result of our field survey, Middle terrace contains few decayed gravels and Higher terrace group, which is older than MIS8 terrace, contains large amounts of decayed gravels. We can distinguish two different age terraces according to ratio of decayed gravel concentration in terrace deposit. Combination of data of thickness of weathering rind of gravel and concentration of decayed gravel in terrace deposit, adequate terrace correlation can be obtained with increased reliability. Difference of weathering degree can be detected by a combination of several indexes that can be observed in outcrops, it is possible to distinguish between different age terraces. Color and hardness of loam, thickness of weathering rind of terrace gravel can be indexes of weathering, these can explain the facts observed in outcrops.

報告者

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