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The mid-Cretaceous coastal catastrophe along the eastern margin of Eurasia reconstructed by sedimentological analysis and chronostratigraphic correlation
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| Title: | The mid-Cretaceous coastal catastrophe along the eastern margin of Eurasia reconstructed by sedimentological analysis and chronostratigraphic correlation |
| Other Titles: | 堆積物の未固結時変形構造と複合年代層序対比を用いた白亜紀中期沿岸域大規模崩壊イベントの復元 |
| Authors: | 久保田, 彩 Browse this author |
| Issue Date: | 25-Mar-2019 |
| Publisher: | Hokkaido University |
| Abstract: | The first step for elucidation Earth’s surface events in a geological record starts with recognizing enigmatic deposits. And then the following researches try to reconstruct their detail process in high resolution and geographical scales by sedimentary, geologically, geochemical, and chronological analyses. Destructive events such as tsunamis, earthquakes, and landslides, have been, however, hardly recognized although they should have occurred repeatedly in the geological past. This is due to difficulty of enigmatic deposit identification and its poor preservation potential, and low-resolution of chronostratigraphy. Purpose of this study is to reveal large-scale destructive events on Earth’s surface in the geological record by novel approaches. In Chapter 1, the latest Aptian tsunamis archived in hemi-pelagic deposits are reconstructed by sedimentary structure of amber-concentrated turbidites at the boundary between the Sorachi and Yezo groups in northern Hokkaido, Japan. In Chapter 2 and 3, chaotic deposits at the lowest part of the Yezo Group, which have various litho-facies are recognized and these are correlated with tsunami deposits in a 20 km- (Chapter 2) and a 100 km-scale (Chapter 3, 4). At the boundary between the Sorachi and Yezo groups, drastic change of the litho-facies from volcanoclastic and siliceous sediments to terrigenous sediments are considered as a result of a remarkable shift of the tectonic setting of the hinterland from an oceanic island arc to the active continental margin along the Eurasia. In this study, it is cleared that the deposition of the Yezo Group in northern Hokkaido started with catastrophic deposition. The supply of the organic rich siliciclastic sediments had lasted continuously until the Maastrichtian. In Chapter 4, collapse event of the huge “living” carbonate platform is reconstructed in central Hokkaido by multiple chronostratigraphy and sedimentological analysis that focusing on soft-sediment deformation structures of sedimentary carbonate. In previous studies, drastic disappearance of typical Cretaceous Tethyan biota in Northwest Pacific in the latest Aptian has been proposed. The carbonate platform biota had not appeared in the Northwest Pacific during the Middle Albian to Paleocene interval. The wide destruction of their habitats can be a conceivable factor of those biotic events. In conclusion, these chaotic deposits, which distributed sporadically in a 200 km scale are correlated by integrated stratigraphy. A coastal catastrophe including large-scale tsunamis, submarine landslides and a collapse of carbonate platform occurred in the latest Aptian (about 114 Ma), Early Cretaceous are proposed. |
| Conffering University: | 北海道大学 |
| Degree Report Number: | 甲第13567号 |
| Degree Level: | 博士 |
| Degree Discipline: | 理学 |
| Examination Committee Members: | (主査) 准教授 伊庭 靖弘, 特任教授 鈴木 德行, 教授 竹下 徹, 准教授 小林 快次（総合博物館） |
| Degree Affiliation: | 理学院（自然史科学専攻） |
| Type: | theses (doctoral) |
| URI: | http://hdl.handle.net/2115/91628 |
| Appears in Collections: | 課程博士 (Doctorate by way of Advanced Course) > 理学院(Graduate School of Science)
学位論文 (Theses) > 博士 （理学）
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