Discovery of the large magnetocaloric effect in HoB$_2$ has highlighted the practical advantage of heavy rare-earth ions. Other holmium compounds are of interest, and we here report the synthesis and the magnetic properties of HoSi$_{1.67}$ and HoGe$_{1.67}$ which form the same AlB$_2$-type structure but with vacancies. They are found to show the antiferromagnetic order with the Neel temperature 17.6(2)K for HoSi$_{1.67}$ and 9.9(2)K for HoGe$_{1.67}$, and the magnetic entropy changes at the temperature are 0.05(1)J/cm$^3$K for HoSi$_{1.67}$ and 0.08(1)J/cm$^3$K for HoGe$_{1.67}$. Magnetic orders were suppressed by replacing vacancies with nickel, resulting in an increase of magnetic entropy changes. Distance between the in-plane Ho$^{3+}$ ions appears to be an important parameter leading to the transition between the antiferromagnetic (HoSi$_{1.67}$) and the ferromagnetic (HoB$_2$) order. The finding may aid the exploration of other heavy rare-earth compounds for similar applications.
In 2010 the MD179 project was undertaken aiming at recovery of deep seated gas hydrate, methane induced carbonate, and deep sediments older than 300 ka. Sediment samples were obtained in the Umitaka Spur, Joetsu Channel, Toyama Trough, Japan Basin, Nishi Tsugaru and Okushiri Ridge areas. Small amounts of sandy sediment have been retrieved as thin intercalations in Pleistocene and Holocene muddy layers, where trace fossils and strong bioturbations are commonly observed.Those sandy sediments consist of very fine- to fine-grained sand grains, and are sometimes tuffaceous. Pore-size distribution measurements and thin-section observations of these sands were undertaken, which indicated that porosities of muddy sediments are around 50 % but those of arenites range from 42 to 52%. Mean pore sizes and permeabilities of those arenites are larger than those of mudstones. While the presence of gas hydrate in intergranular pores of sands has not been confirmed, the soupy occurrence in recovered sediments may strongly indicate the presence of hydrate filling the intergranular pore system of sands. Such arenites have been recognized till now in the Mallik, NW Territory Canada, as well as in the Nankai Trough areas, which are expected common even in the subsurface sandy sediments at the eastern margin of Japan Sea. Concentration of gas hydrate may need primary intergranular pores large enough for gas hydrate to occur within host sediments likely deposited in the sedimentary environment such as deep sea channels. Small amounts of sandy sediment were retrieved as thin intercalations in Pleistocene silty layers, because supplying sediments may not be abundant due to sea level fluctuation during Pleistocene ice age. As time of deposition of coarse-grained sediments can be recognized by the thermoluminescence (TL) dating method, sandy sediments are usually tuffaceous and contain a small amount of quartz grains, and TL dating has been completed only for seven samples, which indicate 48 to 980 ka in age. This study was performed as a part of the MH21 Research Consortium.
In 1995, Japan launched a national project to assess methane hydrates as future gas resources, which successfully identified and recovered hydrate-cemented sandy sediments from Pleistocene turbidite units at the Nankai Trough. Extensive geological and geophysical exploration over 20 years reveals a wide distribution of hydrate-induced BSR at the eastern Nankai Trough. The amounts of hydrates in sandy sediments are estimated to be 17 to 39 vol.% based on low salinity anomalies of squeezed pore waters. Hydrate amounts equivalent to 6 to 7 vol.% of sediment volume extend from the seafloor to the base of gas hydrate stability (BGHS). A probabilistic approach to assess amounts of hydrates based on 2D/3D seismic profiles, LWD geophysical parameters, and geochemical analysis of cores provides an approximation of the amounts of resources in place at 40 tcf of methane gas in the entire BSR area (4,687 km2) and at 20 tcf in the hydrate concentrated zone (767 km2) of the eastern Nankai Trough. An integrated academic, industrial, and national program carried out since 2004 identifies another type of hydrate in the eastern margin of the Sea of Japan. Japan Sea hydrates occur as massive aggregates in a chimney-like acoustic blanking zone of a few 100 m across and 100-120 m thick (gas chimney) in Pleistocene hemipelagic sediments. MBES and SBP surveys confirm 1,742 gas chimneys along the eastern margin of the Sea of Japan and around Hokkaido Island. Amounts of hydrates estimated from combined elastic wave velocity Vp and low salinity anomalies are 35 to 74 vol.% of the volume of the gas chimney structure. BSRs in hydrate-bearing gas chimneys exhibit a sharp pull-up structure within the gas chimneys, reflecting high Vp. Assuming that the Vp of massive hydrate is 3.7 km/sec and Vp of the host sediments in gas chimneys is same as Vp of the sediments around gas chimneys, the amounts of hydrates in the gas chimneys are calculated to be 15 to 65 vol.% of chimney volume. High Vp anomalies of hydrate-bearing sediments is also applied to hydrates estimate at the Nankai trough.
Research Article| November 01, 2007 Age variation of pore water iodine in the eastern Nankai Trough, Japan: Evidence for different methane sources in a large gas hydrate field Hitoshi Tomaru; Hitoshi Tomaru 1Department of Earth and Environmental Sciences, University of Rochester, Rochester, New York 14627, USA Search for other works by this author on: GSW Google Scholar Zunli Lu; Zunli Lu 1Department of Earth and Environmental Sciences, University of Rochester, Rochester, New York 14627, USA Search for other works by this author on: GSW Google Scholar Udo Fehn; Udo Fehn 1Department of Earth and Environmental Sciences, University of Rochester, Rochester, New York 14627, USA Search for other works by this author on: GSW Google Scholar Yasuyuki Muramatsu; Yasuyuki Muramatsu 2Department of Chemistry, Gakushuin University, Tokyo 171-8588, Japan Search for other works by this author on: GSW Google Scholar Ryo Matsumoto Ryo Matsumoto 3Department of Earth and Planetary Science, University of Tokyo, Tokyo 113-0033, Japan Search for other works by this author on: GSW Google Scholar Geology (2007) 35 (11): 1015–1018. https://doi.org/10.1130/G24198A.1 Article history received: 29 Mar 2007 rev-recd: 08 Jul 2007 accepted: 10 Jul 2007 first online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Hitoshi Tomaru, Zunli Lu, Udo Fehn, Yasuyuki Muramatsu, Ryo Matsumoto; Age variation of pore water iodine in the eastern Nankai Trough, Japan: Evidence for different methane sources in a large gas hydrate field. Geology 2007;; 35 (11): 1015–1018. doi: https://doi.org/10.1130/G24198A.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract The 129I geochronology of marine pore water is useful for the understanding of the origin of methane in gas hydrates because of the close association between I and marine organic materials responsible for methane generation. We report 129I/I ratios in pore waters from three deep cores in the eastern Nankai Trough gas hydrate field, two located on the outer ridge and one in the forearc basin. As in previous studies of gas hydrate fields, I ages of pore water are consistently older than those of the host sediments. For the first time, however, the results demonstrate that the potential I source formations vary considerably across the forearc setting: While I at the basin site reaches ages close to 50 Ma, all I ages at the two ridge sites are <32 Ma. The latter two sites also demonstrate the influence of I from formations younger than 10 Ma. The results suggest that I and, by association, methane on the outer ridge are derived mainly from Miocene to Pliocene forearc sediments through the active faults, while the main source for the forearc basin is the old accretionary wedge related to an earlier subduction configuration of Eocene age, which acts as a backstop in the current subduction system. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
Logging data are measurements of physical properties of the formation surrounding a borehole, acquired in situ after completion of coring (wireline logging) or during drilling (Logging-While-Drilling, LWD). The range of data (resistivity, gamma radiation, velocity, density, borehole images,…) in any hole depends on the scientific objectives and operational constraints.
Logging data are measurements of physical properties of the formation surrounding a borehole, acquired in situ after completion of coring (wireline logging) or during drilling (Logging-While-Drilling, LWD). The range of data (resistivity, gamma radiation, velocity, density, borehole images,…) in any hole depends on the scientific objectives and operational constraints.
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