Sand–mud couplets deposited by spontaneous remobilization of subaqueous transitional flows     

Woong Mo Koo  David Mohrig  James Buttles  Daniel Sturmer  Anna Pontén  Thomas Hess 《Sedimentology》2020,67(1):78-95

Clean basal and capping argillaceous sandstone couplets in deep water settings have been previously interpreted as the result of spatially segregated turbidity currents and debris flows or spatio-temporal transitioning of a turbulent flow to a transitional/laminar state. However, this paper presents three-dimensional laboratory experiments demonstrating that a single sediment-gravity flow can develop sand–mud couplets by autogenic remobilization of sediments that are still in the process of being deposited. This remobilization appears common to flows composed of mixtures of sand and mud with viscosities and strengths measurably greater than water, but not so high as to fully suppress the settling of sand through the depositional current. Dewatering in the early sand deposit acts to lubricate the basal portion of the increasingly muddy upper division of the flow, causing it to accelerate downslope, triggering a secondary flow with a sediment composition distinct from the original mixture. Sediment deposition and remobilization processes in a single sediment-gravity flow and their resultant deposit were imaged acoustically and cored at representative locations within the deposit. The acoustic data and cores show sand–mud couplets that are qualitatively similar to interpreted turbidite–debrite-like couplets in natural systems.  相似文献   

Galactic HCO<Superscript>+</Superscript> absorption toward compact extragalactic radio sources     

Geumsook Park  Bon-Chul Koo  Kee-Tae Kim  Do-Young Byun  Carl E. Heiles 《Astrophysics and Space Science》2018,363(7):150

As part of the search for the “dark molecular gas (DMG),” we report on the results of HCO⁺\(J=1\mbox{--}0\) absorption observations toward nine bright extragalactic millimeter wave continuum sources. The extragalactic sources are at high Galactic latitudes (\(|b| > 10^{\circ} \)) and seen at small extinction (\(E(B - V)\lesssim 0.1\) mag). We have detected the HCO⁺ absorption lines toward two sources, B0838+133 and B2251+158. The absorption toward B2251+158 was previously reported, while the absorption toward B0838+133 is a new detection. We derive hydrogen column densities or their upper limits toward the nine sources from our observations and compare them to those expected from CO line emission and far-infrared dust continuum emission. Toward the seven sources with no HCO⁺ detection, CO emission has not been detected, either. Thus the sight lines are likely to be filled with almost pure atomic gas. Toward the two sources with HCO⁺ detection, CO emission has been also detected. Comparison of the H₂ column densities from HCO⁺ absorption and CO emission suggests a non-negligible amount of DMG toward B0838+133.  相似文献   

Modeling Stream-Aquifer Interactions Under Seasonal Groundwater Pumping and Managed Aquifer Recharge     

Hyeonju Lee  Min-Ho Koo  Sebong Oh 《Ground water》2019,57(2):216-225

In South Korea, a significant amount of groundwater is used for the heating of water-curtain insulated greenhouses during the winter dry season, which had led to problems of groundwater depletion. A managed aquifer recharge (MAR) project is currently underway with the goal of preventing such groundwater depletion in a typical cultivation area, located on an alluvial aquifer near the Nam River. In the present study, FEFLOW, a three-dimensional finite element model, was used to evaluate different strategies for MAR of the cultivation areas. A conceptual model was developed to simulate the stream-aquifer dynamics under the influence of seasonal groundwater pumping and MAR. The optimal rates and duration of MAR were assessed by analyzing the recovery of the groundwater levels and the change in the groundwater temperature. The simulation results indicate that a MAR rate of 8000 m³/d effectively restores the groundwater level when the injection wells are located inside the groundwater depletion area. It is also demonstrated that starting the MAR before the beginning of the seasonal pumping is more effective. Riverbank filtration is preferable for securing the injection water owing to plentiful source of induced recharge from the river. Locating the pumping wells adjacent to the river where there are thick permeable layers could be a good strategy for minimizing decreases in the groundwater level and temperature.  相似文献   

Mercury in Human Hair and Fish: is there a Hong Kong Male Subfertility Connection?   总被引：1，自引：0，他引：1  

M. D. Dickman  K. M. C. Leung  L. C. L. Koo 《Marine pollution bulletin》1999,39(1-12):352-356

Hair is a useful indicator of a person’s exposure to mercury. For this reason, hair samples from 94 fertile and 117 subfertile Hong Kong residents were compared over four separate age groups. A typical 30 year old Hong Kong male had a hair mercury concentration of approximately 3.3 mg/kg mercury while a 60 year old Hong Kong subfertile male had a hair mercury concentration of about 7.5 mg/kg. Most of this mercury comes from seafood consumption. Individuals consuming four or more meals of fish per week had a hair mercury of 4.07 mg/kg dry weight of hair while those consuming fish less frequently had significantly lower levels (2.56 mg/kg). Hong Kong residents that consumed no fish had only 1.21 mg/kg hair mercury. The relative risks of males with moderate and high levels of mercury in their hair were significant (p=0.062). Age corrected estimates of risk indicated that compared with men with low levels of mercury in their hair, men with higher levels were twice as likely to be subfertile (relative risk, 1.95) and there was a dose–response trend that was highly significant (p < 0.0005). In light of these risks we concluded that the maximum permitted mercury level in food sold in Hong Kong should be lowered from 0.5 mg/kg wet weight to a level to be determined by risk analysis. In Japan, where fish mercury levels and fish consumption rates are lower than those in Hong Kong, the maximum amount of mercury permitted in food for human consumption is 0.3 mg/kg wet weight.  相似文献   

A study of igneous rocks related to Zn–Pb mineralization in the Shinyemi and Gagok deposits of the Taebaeksan Basin,South Korea     

Jieun Seo  Seon‐Gyu Choi  Minho Koo  Chang Whan Oh  In&#x;Chang Ryu  Gilljae Lee 《Resource Geology》2020,70(3):215-232

The Shinyemi and Gagok deposits, located in the Taebaeksan Basin, South Korea, display Zn–Pb mineralization along a contact between Cretaceous granitoids and Cambrian–Ordovician carbonates of the Joseon Supergroup. The Shinyemi mine is one of the largest polymetallic skarn‐type magnetite deposits in South Korea and comprises Fe and Fe–Mo–Zn skarns, and Zn–Cu–Pb replacement deposits. Both deposits yield similar Cretaceous mineralization ages, and granitoids associated with the two deposits displaying similar mineral textures and compositions, are highly evolved, and were emplaced at a shallow depth. They are classified as calc‐alkaline, I‐type granites (magnetite series) and were formed in a volcanic arc. Compositional variation is less in the Shinyemi granites and aplites (e.g., SiO₂ = 74.4–76.6 wt% and 74.4–75.1 wt%, respectively) than in the Gagok granites and aplites (e.g., SiO₂ = 65.6–68.0 wt% and 74.9–76.5 wt%, respectively). Furthermore, SiO₂ vs K/Rb and SiO₂ vs Rb/Sr diagrams indicate that the Shinyemi granitoids are more evolved than the Gagok granitoids. Shinyemi granitoids had been already differentiated highly in deep depth and then intruded into shallow depth, so both granite and aplite show the highly evolved similar chemical compositions. Whereas, less differentiated Gagok granitoids were separated into two phases in the last stage at shallow depth, so granite and aplite show different compositions. The amounts of granites and aplite are similar in the Shinyemi deposit, whereas the aplite appears in an amount less than the granite in the Gagok deposit. For this reason, the Shinyemi granitoids caused not only Fe enrichment during formation of the dolomite‐hosted magnesian skarn but also was associated with Mo mineralization in the Shinyemi deposit. Zn mineralization of the Gagok deposit was mainly caused by granite rather than aplite. Our data suggest that the variation in mineralization displayed by the two deposits resulted from differences in the compositions of their associated igneous intrusions.  相似文献   

Erratum to: Physical modeling of baffles influence on landslide debris mobility     

C. W. W. Ng  C. E. Choi  D. Song  J. S. H. Kwan  R. C. H. Koo  H. Y. K. Shiu  K. K. S. Ho 《Landslides》2015,12(3):627-627

  相似文献   

Yumokjeong Landslide: an investigation of progressive failure of a hillslope using the finite element method   总被引：1，自引：0，他引：1  

Ben Leshchinsky  Farshid Vahedifard  Ho-Bon Koo  Seung-Hyun Kim 《Landslides》2015,12(5):997-1005

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Experimental restoration of a salt marsh with some comments on ecological restoration of coastal vegetated ecosystems in Korea     

Bon Joo Koo  Jong Geel Je  Han Jun Woo 《Ocean Science Journal》2011,46(1):47-53

Since the 1980s, the coastal wetlands in Korea have been rapidly degraded and destroyed mainly due to reclamation and landfills for coastal development. In order to recover damaged coastal environments and to develop wetland restoration technologies, a 4-year study on ecological the restoration of coastal vegetated ecosystems was started in 1998. As one of a series of studies, a small-scale experiment on salt marsh restoration was carried out from April 2000 to August 2001. The experiment was designed to find effective means of ecological restoration through a comparison of the changes in environmental components and species structure between two different experimental plots created using sediment fences, one with and one without small canals. Temporal variation in surface elevation, sedimentary facies, and benthic species were measured seasonally in each plot and in the adjacent natural reference sites. Monthly exposure occurred from 330 cm to mean sea level, which represents the critical tidal level (CTL) at which salt marsh plants colonize. Vegetation, especially Suaeda japonica, colonized the site the following spring and recovered to a similar extent in the natural marshes 16 months later. The sedimentary results indicated that the sediment fences had effects on particle size and sediment accumulation, especially in the plot with small canals. This experiment also showed that tidal height, especially that exceeding the CTL, is an important factor in the recovery of the benthic fauna of salt marshes. From these results, we suggested that designs for the restoration of salt marsh ecosystems must consider the inclusion of a tidal height exceeding CTL, as this may allow reconstruction of the previous natural ecosystem without artificial transplanting.  相似文献   

Spatial polychaeta habitat potential mapping using probabilistic models     

Jong-Kuk Choi  Hyun-Joo Oh  Bon Joo Koo  Joo-Hyung Ryu  Saro Lee 《Estuarine, Coastal and Shelf Science》2011

The purpose of this study was to apply probabilistic models to the mapping of the potential polychaeta habitat area in the Hwangdo tidal flat, Korea. Remote sensing techniques were used to construct spatial datasets of ecological environments and field observations were carried out to determine the distribution of macrobenthos. Habitat potential mapping was achieved for two polychaeta species, Prionospio japonica and Prionospio pulchra, and eight control factors relating to the tidal macrobenthos distribution were selected. These included the intertidal digital elevation model (DEM), slope, aspect, tidal exposure duration, distance from tidal channels, tidal channel density, spectral reflectance of the near infrared (NIR) bands and surface sedimentary facies from satellite imagery. The spatial relationships between the polychaeta species and each control factor were calculated using a frequency ratio and weights-of-evidence combined with geographic information system (GIS) data. The species were randomly divided into a training set (70%) to analyze habitat potential using frequency ratio and weights-of-evidence, and a test set (30%) to verify the predicted habitat potential map. The relationships were overlaid to produce a habitat potential map with a polychaeta habitat potential (PHP) index value. These maps were verified by comparing them to surveyed habitat locations such as the verification data set. For the verification results, the frequency ratio model showed prediction accuracies of 77.71% and 74.87% for P. japonica and P. pulchra, respectively, while those for the weights-of-evidence model were 64.05% and 62.95%. Thus, the frequency ratio model provided a more accurate prediction than the weights-of-evidence model. Our data demonstrate that the frequency ratio and weights-of-evidence models based upon GIS analysis are effective for generating habitat potential maps of polychaeta species in a tidal flat. The results of this study can be applied towards conservation and management initiatives for the macrofauna of tidal flats.  相似文献   

Pattern and origin of spherulites in a rhyolite dike swarm,northeastern Cheongsong, Korea     

Sang Koo Hwang Chang Oh Choo 《东北亚地学研究》2006,9(1):60-79

IntroductionThe northeastern Cheongsong area is underlainby a sequence of sedi mentary rocks together within-trusive and extrusive volcanic rocks all of late Creta-ceous age(Lee&Hong,1973;Ki m&Park,1970;Hwang,1998).Theintrusions,comprising astock,a plug and numerous dikes,are well exposedat the current surface due tothe enormous erosion ofany sedi mentary or volcanic covered rocks.Thedikes forma dike swarmand some are intruded intothe plug.The dikes swarm may represent the subsurfaceexpress…  相似文献