Showing papers by "Ken Ikehara published in 2016"

The use of microstructures for discriminating turbiditic and hemipelagic muds and mudstones

Abstract: The microstructures of turbiditic and hemipelagic muds and mudstones were investigated using a scanning electron microscope to determine whether there are microstructural features that can differentiate turbiditic from hemipelagic sedimentary processes. Both types of muddy deposits are, in general, characterized by randomly-oriented clay particles. However, turbiditic muds and mudstones also characteristically contain aggregates of ‘edge-to-face’ contacts between clay particles with long-axis lengths of up to 30 μm. Based on observations of the clay fabric of the experimentally-formed muds settled from previously agitated muddy fluids, these types of aggregates, hereafter referred to as ‘aggregates of clay particles’, are interpreted as having been formed by the collision of component flocs in turbulent fluids. Furthermore, some aggregates of clay particles have ‘face-to-face’ contacts between clay particles; this is similar to face-to-face aggregates characteristically developed in fluid-mud deposits that are commonly recognized only in turbiditic mudstones, indicating the possibility of a final stage of deposition under highly-dense conditions, such as temporary fluid muds. In conjunction with earlier proposed lithofacies-based and ichnofacies-based criteria, aggregates of clay particles should be useful for the differentiation of turbiditic and hemipelagic muddy deposits, particularly with limited volumes of non-oriented samples from deep-water successions.

Deep-sea meiofauna off the Pacific coast of Tohoku and other trench slopes around Japan: a comparative study before and after the 2011 off the Pacific coast of Tohoku Earthquake

Abstract: We compared meiofaunal assemblages obtained from the landward slope of the Japan Trench off the Sanriku region of Honshu Island before the 2011 off the Pacific coast of Tohoku Earthquake, 4.5 months and 1.5 years after the earthquake. Sediment samples were collected after the earthquake along two transects. Meiofaunal density after the earthquake did not differ from that before the earthquake. However, meiofaunal composition after the earthquake was different from that before the earthquake, and the composition dispersion after the earthquake was lower than that before the earthquake. These results suggested that the turbidity current may have affected meiofaunal composition and reduced its variability. These changes were probably caused by the seismic motion and displacement of the substratum after the earthquake, rather than sediment redeposition induced by the earthquake. To assess the effect of the earthquake more thoroughly, we compared meiofaunal assemblage in the Sanriku region before and after the earthquake with that in the Kuril Trench (comparable productivity to the Sanriku region) and Ryukyu Trench (lower productivity). Differences in meiofaunal composition before and after the earthquake within the Sanriku region were lower than those between the Sanriku and Ryukyu regions. These results suggested that deep-sea meiofaunal assemblages are influenced by large-scale disturbances, but changes are within the range of variation generated by surface productivity levels.

The potential for a high-resolution, Quaternary paleo-observatory network in the Japan, Yamato, and Ulleung Basins

Abstract: 1.東京大学大学院理学系研究科地球惑星科学専攻、2.北海道大学大学院地球環境科学研究院地球圏科学専 攻、3.産業技術総合研究所地質情報研究部門 、4.サザンプトン大学海洋地球研究科、5.金沢大学大学院自然科 学研究科自然システム学専攻、6.国立科学博物館地学研究部、7.ボストン大学地球環境学部、8.テキサスA&M大 学国際深海科学掘削計画 1.Department of Earth and Planetary Science, Graduate School of Science, The Univeristy of Tokyo, 2.Graduate School of Environmental Science, Division of Earth System Science, Hokkaido University, 3.Reserch Institute of Geology and Geoinformation, Geological Survey of Japan, 4.School of Ocean and Earth Science, University of Southampton, 5.School of Natural System, Graduate School of Natural Science and Technology, Kanazawa University, 6.Department of Geology and Paleontology, National Museum of Nature and Science, 7.Earth and Environment, Boston University, 8.International Ocean Discovery Program, Texas A & M University