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Core A9-EB2 from the eastern Bransfield Basin, Antarctic Peninsula, consists of pelagic (diatom ooze-clay couplets and bioturbated diatom ooze) and hemipelagic (bioturbated mud) sediments interbedded with turbidites (homogeneous mud and silt–clay couplets). The cyclic and laminated nature of these pelagic sediments represents alternation between the deposition of diatom-rich biogenic sediments and of terrigenous sediments. Sediment properties and geochemical data explain the contrasting lamination, with light layers being finer-grained and relatively rich in total organic carbon and biogenic silica content. Also, the high-resolution magnetic susceptibility (MS) variations highlight distinct features: high MS values coincide with clastic-rich sections and low MS values correspond to biogenic sections. The chronology developed for core A9-EB2 accounts for anomalous ages associated with turbidites and shows a linear sedimentation rate of approximately 87 cm/103 yr, which is supported by an accumulation rate of 80 cm/103 yr calculated from 210Pb activity. The late Holocene records clearly identify Neoglacial events of the Little Ice Age (LIA) and Medieval Warm Period (MWP). Other unexplained climatic events comparable in duration and amplitude to the LIA and MWP events also appear in the MS record, suggesting intrinsically unstable climatic conditions during the late Holocene in the Bransfield Basin of Antarctic Peninsula. 相似文献
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Drilling at the site UBGH1-9, offshore Korea in 2007, revealed varied gas-hydrate saturation with depth and a wide variety of core litholgies, demonstrating how the variations in the lithology are linked with those in gas-hydrate saturation and morphology. Discrete excursions to low chlorinity values from in situ background chlorinity level occur between 63 and 151 mbsf. In this occurrence zone, gas-hydrate saturations estimated from the low chlorinity anomalies range up to 63.5% of pore volume with an average of 9.9% and do not show a clear depth-dependent trend. Sedimentary facies analysis based on grain-size distribution and sedimentary structures revealed nine sediment facies which mainly represent hemipelagic muds and fine- to medium-grained turbidites. According to the sedimentary facies distribution, the core sediments are divided into three facies associations (FA): FA I (0–98 mbsf) consisting mainly of alternating thin- to medium-bedded hemipelagic mud and turbidite sand or mud beds, FA II (98–126 mbsf) dominated by medium- to very thick-bedded turbidite sand or sandy debris flow beds, and FA III (126–178 mbsf) characterized by thick hemipelagic mud without intervening discrete turbidite sand layers. Thermal anomalies from IR scan, mousse-like and soupy structures on split-core surfaces, non-destructive measurements of pressure cores, and comparison of gas-hydrate saturations with sand contents of corresponding pore-water squeeze cakes, collectively suggest that the gas hydrate at the site UBGH1-9 generally occurs in two different types: “pore-filling” type preferentially associated with thin- to medium-turbidite sand beds in the FA I and “fracture-filling” type which occurs as hydrate veins or nodules in hemipelagic mud of the FA III. Gas-hydrate saturation in the FA II is generally anomalously low despite the dominance of turbidite sand or sandy debris flow beds, suggesting insufficient methane supply. 相似文献
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Hong Seok-Hwi Yoo Dong-Geun Lee Gwang-Soo Kim Jin Cheul Yi Sangheon Kim Gil-Young Bahk Jang-Jun Yu Shin 《Marine Geophysical Researches》2022,43(4):1-18
Marine Geophysical Research - This study entails the characterization of the depositional environment of the Hupo Basin shelf. By means of sedimentary structure analysis, grain size, textures,... 相似文献
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Jae Seong Lee Eun-Soo Kim Sung-Hyun Kahng Seok-Hyun Yoon Jin-Hyung Cho Kyung-Soo Bahk Dong-Jin Kang 《Ocean Science Journal》2012,47(4):489-495
We have developed a novel miniature in situ microprofiler (NAFRI BelpI) for coastal and deep-sea studies. The BelpI can carry up to three oxygen microsensors, and it allows for simultaneous replicate measurements in a relatively small area. All functions can be controlled and programmed via a small magnetic bar and three reed switches; this feature facilitates the initial setup both onboard and underwater. The large LCD window shows basic information such as the movement intervals of the linear stage, number of replicate measurements, waiting time between measurements, and the pA from the microsensors. From high-resolution vertical profiles of oxygen in coastal sediment measured using the microsensors, the diffusivity boundary layer thicknesses was determined to be in the range 0.30–0.35 mm. In addition, the time-series measurement of oxygen profiles in permeable sandy sediment showed advective transport of oxygen into pore water by tidal agitation. Two examples of in situ measurement using a BelpI suggest that it can be widely applied to the study of the sediment-water interface. 相似文献
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We investigated the biogenic components (biogenic opal, calcium carbonate, and organic carbon) of the marine sediments in core TY99PC18 recovered from the southeastern part of the Ulleung Basin, East Sea (Japan Sea). Our results indicate that primary productivity by diatoms increased after the last glaciation (15,000 14C years b.p.) probably because of the onset of vertical mixing of seawater and nutrient supply from the deep water. Between 5,000 and 10,000 14C years b.p. a shift in the dominant primary producer, i.e. from diatoms to coccolithophores, coincides with decreased productivity, which could be related to the influx of warm, low-nutrient waters at that time. During the late Holocene (after 5,000 14C years b.p.) the productivity of diatoms increased once more probably due to renewed ventilation and vertical mixing. 相似文献
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Sang Hoon Lee Jang J. Bahk Han J. Kim Kyung E. Lee Hyeong T. Jou Bong C. Suk 《Geo-Marine Letters》2010,30(2):133-142
The depositional characters of densely dated turbidite successions originating from the southwestern margin of the Ulleung
Basin reveal changes in high-resolution frequency, failing areas, and relative volumes of slope failures over the past 29.4
cal. ka. Between 29.4 and 19.1 cal. ka B.P., various thin- to very thick-bedded turbidites accumulated at an average recurrence
interval of ca. 605 years. After 19.1 cal. ka B.P., turbidites were deposited with an average recurrence interval of 3,183
years, and their thickness abruptly decreased upward. These features suggest that various-scale slope failures occurred frequently
during the eustatic lowering of sea level, and the frequency and relative volumes of slope failures suddenly decreased after
sea level began to rise. When sea level was lowest (20.0–19.1 cal. ka B.P.), successive stacks of very thick turbidites can
most likely be ascribed to larger-volume mass failures. An upward change from muddy to sandy turbidites around 21.4 cal. ka
B.P. suggests that the failing areas retrograded from the muddy upper-middle slope to the sandy uppermost slope when sea level
was nearly at its lowest. Based on these findings together with published evidence, frequent mass failures between 29.4 and
19.1 cal. ka B.P. were plausibly triggered by earthquakes, in combination with reduced hydrostatic pressure that promoted
gas-hydrate dissolution during the eustatic lowering of sea level. These data on the frequency, scale, failing areas, and
triggering causes of slope failures along the southwestern margin over the past 29.4 cal. ka, not documented in earlier studies,
provide invaluable information to better understand the basin-scale characters and occurrences of latest Quaternary slope
failures in the Ulleung Basin. 相似文献
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Changho Lee Tae Sup Yun Jong-Sub Lee Jang Jun Bahk J. Carlos Santamarina 《Engineering Geology》2011,117(1-2):151-158
The geotechnical characteristics of Ulleung Basin sediments are explored using depressurized samples obtained at 2100 m water depth and 110 m below the sea floor. Geotechnical index tests, X-ray diffraction, and SEM images were obtained to identify the governing sediment parameters, chemical composition and mineralogy. We use an instrumented multi-sensor oedometer cell to determine the small-strain stiffness, zero-lateral strain compressibility and electromagnetic properties, and a triaxial device to measure shear strength. SEM images show a sediment structure dominated by microfossils, with some clay minerals that include kaolinite, illite, and chlorite. The preponderant presence of microfossils determines the high porosity of these sediments, defines their microstructure, and governs all macroscale properties. The shear wave velocity increases as the vertical effective stress increases; on the other hand, porosity, permittivity, electrical conductivity, and hydraulic conductivity decrease with increasing confinement. All these parameters exhibit a bi-linear response with effective vertical stress due to the crushable nature of microfossils. Well-established empirical correlations used to evaluate engineering parameters do not apply for these diatomaceous sediments which exhibit higher compressibility than anticipated based on correlations with index properties. Settlements will be particularly important if gas production is attempted using depressurization because this approach will cause both hydrate dissociation and increase in effective stress. 相似文献
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Jong-Hwa Chun Byong-Jae Ryu Byeong-Kook Son Ji-Hoon Kim Joo Yong Lee Jang-Jun Bahk Hag-Ju Kim Kyung Sik Woo Odette Nehza 《Marine and Petroleum Geology》2011,28(10):1787-1800
A mound related to a cold vent in a columnar seismic blanking zone (CSBZ) was formed around site UBGH1-10 in the central Ulleung Basin (2077 m water depth), East Sea, Korea. The mound is 300–400 m wide and 2–3 m high according to multi-beam bathymetry, 2–7 kHz sub-bottom profiler data, and multi-channel reflection seismic data. Seafloor topography and characteristics were investigated using a remotely operated vehicle (ROV) around site UBGH1-10, which is located near the northern part of the mound. The origin of the mound was investigated through lithology, mineralogy, hydrate occurrence, and sedimentary features using dive cores, piston cores, and a deep-drilling core. The CSBZ extends to ∼265 ms two-way traveltime (TWT) below the seafloor within a mass-transport deposit (MTD) unit. Gas hydrate was entirely contained 6–141 m below the seafloor (mbsf) within hemipelagic deposits intercalated with a fine-grained turbidite (HTD) unit, characteristically associated with high resistivity values at site UBGH1-10. The hydrate is commonly characterized by veins, nodules, and massive types, and is found within muddy sediments as a fracture-filling type. Methane has been produced by microbial reduction of CO2, as indicated by C1/C2+, δ13CCH4, and δD4CH analyses. The bowl-shaped hydrate cap revealed at 20–45 ms TWT below the seafloor has very high resistivity and high salinity, suggesting rapid and recent gas hydrate formation. The origin of the sediment mound is interpreted as a topographic high formed by the expansion associated with the formation of the gas hydrate cap above the CSBZ. The lower sedimentation rate of the mound sediments may be due to local enhancement of bottom currents by topographic effects. In addition, no evidence of gas bubbles, chemosynthetic communities, or bacterial mats was observed in the mound, suggesting an inactive cold vent. 相似文献
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Parallel laminated, graded, and homogeneous muds of turbidity current origin are the predominant facies in the non-fan slope-centered Ulleung marginal basin during the last glacial period. Dilute turbidity currents were probably generated from slumps, slides, and debris flows on the slope. A mid-slope core contains poorly sorted mud-clast muds of debris flow origin. During the period of 75,000 and 10,000 years BP, turbidity currents occurred approximately every 125 years, each depositing about 0.5 km3 of mud with an accumulation rate of up to 40 cm/103 years. The basin was largely suboxic with a rare incursion of bottom currents. 相似文献
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