Late Paleozoic low-angle southward-dipping thrust in the Züünharaa area,Mongolia: tectonic implications for the geological structures in the Sayan-Baikal and Hangai-Daur belts

International Journal of Earth Sciences - The Central Asian Orogenic Belt (CAOB) is key to understanding the Paleozoic–Mesozoic geodynamics of Eurasian continent. The geological structure of...     

Provenance implications of Th–U–Pb electron microprobe ages from detrital monazite in the Carboniferous Upper Silesia Coal Basin, Poland

This paper reports the results of CHIME (chemical Th–U–Pb isochron method) dating of detrital monazites from Carboniferous sandstones in the Upper Silesia Coal Basin (USCB). A total of 4739 spots on 863 monazite grains were analyzed from samples of sandstone derived from six stratigraphic units in the sedimentary sequence. Age distributions were identified in detrital monazites from the USCB sequence and correlated with specific dated domains in potential source areas. Most monazites in all samples yielded ca. 300–320 Ma (Variscan) ages; however, eo-Variscan, Caledonian and Cadomian ages were also obtained. The predominant ages are comparable to reported ages of certain tectonostratigraphic domains in the polyorogenic Bohemian Massif (BM), which suggests that various crystalline lithologies in the BM were the dominant sources of USCB sediments.     

Discovery of a c.370 Ma granitic gneiss clast from the Hwanggangri pebble-bearing phyllite in the Okcheon metamorphic belt, Korea

The chemical Th–U total Pb isochron method (CHIME) of dating was carried out on accessory minerals in samples from the Okcheon metamorphic belt in Korea. Dated minerals include xenotime and monazite with overgrown mantles in a granitic gneiss clast from the Hwanggangri Formation, metamorphic allanite in garnet-bearing muscovite–chlorite schist of the Munjuri Formation, and polycrase and monazite in post-tectonic granite from the Hwanggangri area. Overgrowth of mantles took place at 369 ± 10 Ma on c. 1750 Ma cores of xenotime and monazite in the granitic gneiss. Allanite, occurring in textural equilibrium with peak metamorphic minerals, yields a CHIME age of 246 ± 15 Ma that is discriminably older than the polycrase (170 ± 6 Ma) and monazite (170 ± 3 Ma) ages of the post-tectonic granite. These chronological data suggest that some of the metasedimentary rocks in the belt formed through a single stage of metamorphism at c. 250 Ma from post-370 Ma sediments. Late Permian age signatures have also been reported from the Precambrian Gyeonggi and Yeongnam massifs that border the Okcheon metamorphic belt, and indicate that parts of the basement massifs and the metamorphic belt were affected by the same regional metamorphic event.     

Characteristics of alkenone distributions in suspended and sinking particles in the northwestern North Pacific

We investigated alkenones recorded in suspended particles and a settling particle time series collected at three stations, 40N (40°N, 165°E), KNOT (44°N, 155°E), and 50N (50°N, 165°E), in the northwestern North Pacific from December 1997 to May 1999. Emiliania huxleyi, the most abundant alkenone producer in this area, is present in surface to subsurface (to ∼50 m depth) waters. The alkenone concentrations recorded in the suspended particles indicated that the seasonal alkenone particle distribution differed significantly interannually. Alkenone export fluxes at the three sediment-trap stations ranged from 0.16 to 49.3 μg m⁻² day⁻¹, and the maximum export flux, which occurred in summer to fall (July-November), was associated with a high organic carbon export flux. The amount of alkenone produced during the maximum export season accounted for 60-80% of the total annual amount of alkenone, and the alkenones accumulated in the sediment below the traps had characteristics corresponding to subsurface waters during the summer-autumn season. Alkenone-derived temperatures recorded in suspended particles corresponded to the in situ temperature within ∼2 °C. Although alkenone-derived temperatures corresponded approximately to the temperatures observed in the stratified subsurface waters at the three trap stations during the high-export season, large differences were observed during the low-export (winter-spring) period. For example, the alkenone-derived temperatures observed at stations KNOT and 50N were much higher than the in situ subsurface temperatures reported in the World Ocean Atlas 2001. Relatively large differences between alkenone-derived temperatures and in situ temperatures in the subarctic might be due to (1) a low-light limitation or (2) contributions of allochthonous alkenones in particulate material transported from subtropical areas within a warm-core ring.     

Using VLBI fringe-phase information from geodetic experiments for short-period ionospheric studies

The usage of Very Long Baseline Interferometry (VLBI) fringe-phase information in geodetic VLBI is a new field of research, which can be used for the detection of short-period (i.e., several minutes) variations (scintillations) of the ionosphere. This paper presents a method for the extraction of such disturbances and discusses how dispersive influences can be separated from intra-scan delay variations. A proper functional and stochastic model for the separation of the different effects is presented and the algorithms are applied to real measurements. In an example, it is shown that a traveling ionospheric disturbance in Antarctica can be detected very precisely. A possible physical origin and the propagation properties of the disturbance are presented and the results are compared with GPS measurements. The benefit of this method for other applications is also discussed.     

Discrete‐like crack simulation by smeared crack‐based FEM for reinforced concrete

A numerical process that simulates crack propagation in reinforced concrete through post‐crack stress redistribution is presented. This process is developed within the context of the smeared crack approach. Continuity and orientation of the reinforcing bar components are automatically recognized in the pre‐processing stage. The process explicitly outputs crack widths by computing the bond slips along reinforcement, without imposing any additional nodes between the reinforcement and concrete. The process is incorporated with a finite element algorithm, and the validation is investigated through sample 3D static analyses of nine concrete specimens subjected to monotonic shear and flexure loads. These specimens contain relatively well‐distributed steel bars and fiber reinforced polymer (FRP) sheets of reinforcement ratio from 0.11 to 0.57%. The analyses predict the crack patterns and crack widths well, although some disagreements are found between the test and the analysis results. The proposed process outputs discrete, continuous in crack directions, and element boundary‐free crack patterns. Copyright © 2007 John Wiley & Sons, Ltd.     

Bacterial growth rate and the relative abundance of bacteria to heterotrophic nanoflagellates in the euphotic and disphotic layers in temperate coastal waters of Sagami Bay,Japan

This study aimed to clarify the vertical differences in bacterial growth and grazing pressure on bacteria by heterotrophic nanoflagellates (HNF) and to identify the controlling factors of bacterial growth in temperate coastal waters of Sagami Bay, Japan. In addition to environmental factors, the annual monthly variations in bacterial growth rate (BGR) and the relative abundance of bacteria to HNF (BA/HNFA) were investigated in the euphotic and disphotic layers between May 2012 and May 2013. Significant vertical differences in BGR and BA/HNFA were evident between the two layers during the thermal stratification times of May to October 2012 and April to May 2013. BGR indicated significantly stronger limitation of bacterial growth in the euphotic layer compared to the disphotic layer. In contrast, significantly lower BA/HNFA was observed in the euphotic layer, suggesting significantly higher grazing pressure on bacteria by HNF. However, significant differences in BGR and BA/HNFA were not observed between the two layers from November 2012 to Match 2013, when the water column was well-mixed vertically due to the cooling and wind-induced mixing of surface water. This study indicates that bacteria in the euphotic layer grow less actively and are more vulnerable to predatory grazing by HNF relative to the disphotic layer during the stratification period. Further, multiple regression analyses indicate that bacterial growth was most controlled by the concentrations of chlorophyll a and dissolved organic carbon in the euphotic and disphotic layers, respectively.     

Sedimentation properties and modeling of dredged soil

ABSTRACT

When dredged soil containing coarse soil is used for the construction of reclaimed ground that is in contact with the surface of seawater, there is a high possibility of the generation of nonuniformly reclaimed ground due to the segregation of fine-grained soil from coarse-grained soil. It is difficult to assume uniform properties of reclaimed ground because the properties are defined and formed by the spontaneously segregating sedimentation. Estimation of the soil’s volume change lacks accuracy if the properties of the reclaimed ground are assumed to be always uniform. Therefore, for pump-dredged reclamation, a predictive study and various experiments are required to estimate the physics and properties of the dredged soil sedimentation. Accordingly, this study demonstrates a modeling test to understand the characteristics of the sedimentary ground using the changing ratio of fraction of the sample passing through a 75-µm sieve. The effect of particle arrangement on hindered settling properties, sedimentation properties, the distribution of water content of sedimentary ground, and physical properties can be determined by the modeling test. The study also suggests the calculation method for the travel distance of the outlet and the volume of input soil based on the experimental results.     

Evaluation of Excess Pore Water Pressure Characteristics in Sand Mat Used for Recycling Dredged Soil

The design of sand mats should be reviewed on the basis of excess pore pressure behavior, which can be obtained by combining the characteristics of soft ground with the permeability of the mats. In this study, a banking model test was performed using dredged sand as the mat material to investigate the hydraulic gradient distribution of sand mats. The results were compared with numerical analysis results utilizing Terzaghi's one-dimensional consolidation equation. The results showed that the pore pressure was influenced by an increase in the amount of settlement at the central part of the sand mat as the height of the embankment increased. The measured decrease of the pressure head due to the residing water pressure in the sand mat was delayed compared to the numerical analysis results. Accordingly, sand mats should be laid to reduce the increased hydraulic gradient at the central part of the embankment.     

Experimental evidence on formation of imminent and short-term hydrochemical precursors for earthquakes

The formation of imminent hydrochemical precursors of earthquakes is investigated by the simulation for water–rock reaction in a brittle aquifer. Sixty-one soaking experiments were carried out with granodiorite and trachyandesite grains of different sizes and three chemically-distinct waters for 6 to 168 h. The experimental data demonstrate that water–rock reaction can result in both measurable increases and decreases of ion concentrations in short times and that the extents of hydrochemical variations are controlled by the grain size, dissolution and secondary mineral precipitation, as well as the chemistry of the rock and groundwater. The results indicate that water–rock reactions in brittle aquifers and aquitards may be an important genetic mechanism of hydrochemical seismic precursors when the aquifers and aquitards are fractured in response to tectonic stress.