報告書番号

U01016

タイトル（和文）

浅海成堆積サイクルの詳細な解析による地殻変動復元手法の検討

タイトル（英文）

A reconstructing method of crustal movement analyzing shallow marine sedimentary cycles

概要 （図表や脚注は「報告書全文」に掲載しております）

沈降域における地殻変動を，段丘解析に匹敵する精度で復元する事は，日本列島における第四紀後半の地殻変動を総合的に理解し，地殻の長期安定性を評価する上で重要である． 本報告においては，堆積環境変化の記録である堆積サイクルの形成時期と汎世界的海水準の対応関係を，堆積物の形成水深および層厚の変化の追跡に基づき，従来より詳しく検討した．それにより，浅海成堆積サイクルを利用した沈降域にも適用可能な地殻の垂直変動復元手法を，日本各地に分布する中－上部第四系堆積サイクルに広く適用可能にした． 堆積サイクルを利用する方法と，従来の段丘の旧汀線高度を利用する方法を併用し，渥美半島太平洋岸の３地点において過去約40万年間の地殻の垂直変動史を復元した．更に各地点における地殻の垂直変動史を比較した結果，地殻変動様式が傾動から一様な隆起へと転じた地域，地殻変動様式が一様な沈降から一様な隆起へと転じた地域を抽出した．

概要 （英文）

It is necessary to evaluate not only uplift but also subsidence in order to understand crustal movements around the Japanese Islands. However, traditional method using altitudinal distribution of marine terraces is not suited for quantitative reconstruction of subsidence because of its property of restricted application to the uplift phenomena. Shallow marine sedimentary cycles are formed mainly by influence of eustatic sea level changes. We estimated depositional age of sedimentary cycles minutely using sedimentological method, for general application of reconstruction method of vertical crustal movement analyzing shallow marine sedimentary cycles, which is suited for reconstruction of subsidence, to the Quaternary shallow marine sedimentary cycles around Japan. Then, we reconstructed a crustal movement during the last 400 kys at the Atsumi Peninsula using both the new method analyzing sedimentary cycles and the traditional method analyzing marine terraces. Results of reconstruction made it possible to distinguish vertical crustal movement between a case continuing uplift during the last ca. 400 kys and the other case inverting from subsidence to uplift at ca. 300 ka. Combining the results of reconstructed vertical crustal movement at three sites, we can find out an area where crustal movement style changes from tilting to uniform uplift and the other area where crustal movement style changes from uniform subsidence to uniform uplift. It is important to accurately estimate depositional depth of sediments for the future improvement of this method, because depositional depth is essential for the correlation between estimation of depositional age and eustatic sea level curve.

報告者

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