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広島県東広島市の七ツ池では，排水時の池底で赤色風化した堆積物を観察できる。この池底堆積物の柱状試料を4 本採取し，各柱状試料について層相，pH，酸化還元電位測定，色彩測定，及び赤色部の詳細観察を行った。その結果，（1）風化層の多くは，砂層の上位に位置し，地下水面の変動帯に位置していること，（2）赤色化メカニズムのモデルについては，砂層の間隙水中での拡散供給のプロセスが適用できたが，無機的な酸化還元反応だけではなく，硫酸還元菌や鉄酸化細菌などの微生物の関与を考慮する必要があること，（3）色彩データのうち，彩度が化学的風化（鉄酸化物生成）の進行状況の指標として有用性があることが明らかとなった。また，これらの結果に基づいて七ツ池の堆積物の地学の学習素材としての可能性を考察した。, During drainage, reddish weathered sediments can be observed at the bottom of Nanatsu-ike Pond in Higashihiroshima City, Hiroshima Prefecture. Four columnar samples of this reservoir-bottom sediment were collected. Each columnar sample was subjected to facies, pH, redox potential measurement, color measurement, and detailed observation of the red part. The results showed the following: (1) most weathered layers were located above the sand layer and in the zone of groundwater-surface fluctuation; (2) for the model of the reddening mechanism, the process of diffusion-supply in the pore water of the sand layer could be applied, but it was necessary to consider the involvement of microorganisms such as sulfate-reducing bacteria and iron-oxidizing bacteria in addition to the inorganic redox reaction; and (3) among the color data, chroma was found to be a useful indicator of the progress of chemical weathering (iron oxide formation). Based on these results, the potential of the Nanatsu-ike Pond sediments for geoscience educational materials is discussed.