Timing of remanent magnetization acquisition in red beds: A case study from a syn-folding sedimentary basin

We propose to explain the origin of the double trend in seismicity of the Macas swarm in the Subandean Cordillera of Cutucú (Ecuador) and characterize the corresponding active deformation of that region. For that purpose, seismological and geological data have been used, with the deployment of a temporary seismological array, with geological field observations and image processing. We found that some earthquakes are aligned on a well known NNE–SSW trend corresponding to the orientation of the nodal planes of the reverse focal mechanism of the M_w=7.0 1995 Macas earthquake as for its aftershocks. Nevertheless, many smaller events are aligned on an unexpected NNW–SSE trend inside the Cutucú Cordillera. We interpret these two orientations of the Macas swarm as linked to Subandean basement thrusts inherited from the inversion tectonics of a NNE–SSW trending Triassic–Jurassic rift, which has been uplifted and partly extruded in the Cutucú Cordillera. The present partitioning of this part of the Subandean deformation is controlled by pre-existing NNE–SSW to NNW–SSE Triassic–Jurassic normal faults that have been subsequently compressed–transpressed and reactivated into reverse faults. Major boundary faults of the rift were NNE–SSW oriented and correspond now to some main Subandean thrusts as confirms the focal mechanism of the 1995 main shock located on the eastern border (Morona frontal thrust) and the orientation of its aftershocks. In the Cutucú Cordillera, the double orientation of present swarm can be interpreted as the result of accommodation of deformation along NNW–SSE pre-existing faults inside the inverted rift system, linked to the motion of the Morona frontal NNE–SSW thrust.     

Isotopic Evaluation on the Genesis of the Kanamaru Pegmatite Deposit, Niigata Prefecture, Japan

Abstract: The Kanamaru pegmatite is one of the two largest pegmatite deposits in Japan and is rich in K–feldspar, which is maximum microcline. The mica minerals and microcline from this ore deposit were studied for K-Ar ages and δ¹⁸O ratios. Biotite gives K-Ar age of 78. 5 Ma, but microcline is much younger in age of 66. 0 and 58. 3 Ma. Oxygen isotopic equilibrium temperature of the biotite-quartz pair is 625°C. Using closure temperature of the K-Ar system for biotite and microcline, cooling rate of the pegmatite is calculated to be 88°C/m. y. at the beginning but 12°C/m. y. in the later period of the cooling history. The microcline is slightly depleted in ¹⁸O, yielding apparent equilibrium temperatures of 230°C and 155°C on quartz-microcline pairs. It is suggested that the fluid phase, magmatic and partly meteoric in origin, contained in the solidifying pegmatite, was interacted with the original orthoclase and converted it to microcline during the subsolidus stage.     

Wet deposition of sulfate in the Inland Sea region of Japan

Precipitation chemistry data derived from a sampling network operated in the Inland Sea model region (June 1984–May 1985) are used as a basis for discussing the wet deposition of sulfate on a regional scale in Japan. Horizontal distribution, seasonal variation, relationship between wet deposition and precipitation amount, sulfate/nitrate ratio, and transport of sulfate from the ocean are discussed. Temporal trends in concentrations of atmospheric sulfur compounds and sulfate wet deposition in the model region are also covered.     

Geochemical behaviour of iron and manganese ions in the Ningyo-Toge uranium deposit district, southwest Japan

The Ningyo-Toge uranium deposit is one of the typical sedimentary uranium deposits in Japan. In general, during weathering, U is removed from the basal granite through underground water. The underground water in this area is rich in U, and has a comparatively high concentration of Fe and Mn.

In this area, three types of Fe minerals can be recognized in different modes of occurrence: (1) in the oxide zone brownish Fe-hydroxide mineral with ferric ion, i.e. goethite (-FeOOH); (2) in the reduced zone of the mine gallery pale-blue Fe-hydroxide mineral with some ferrous ion, i.e. lepidocrocite (γ-FeOOH); and (3) Fe-sulphate minerals such as melanterite (FeSO₄·7H₂O), etc. Some uranyl sulphate minerals, uranopilite and zippeite, are closely associated with these Fe-sulphate minerals. Under weakly alkaline conditions of the oxidizing environment, Mn-hydroxide (MnOOH) coexists with goethite as alternative thin laminae with shale, or coprecipitates resembling a marine Mn nodule, in the size of 0.5 cm in diameter. Radioactive anomalies have been recognized frequently for these Mn sediments due to absorption of Ra by the sediments.     

Fast practical evaluation of soil–structure interaction of embedded structures

A simple and fast evaluation method of soil–structure interaction (SSI) effects of embedded structures is presented via a cone model. The impedances and the effective input motions at the bottom of an embedded foundation are evaluated by means of the cone model. Those quantities are transformed exactly to the corresponding values at the top of the foundation. The evaluated quantities are combined with the super-structure at the top of the foundation. The transfer function amplitude of the interstory drift of a single-degree-of-freedom super-structure is computed for various cases, i.e. no SSI, SSI without embedment, SSI with shallow embedment, SSI with deep embedment. Soil properties are also varied to investigate in more detail the SSI effects of embedded structures. It is found that, while the transfer function amplitude is reduced by the increase of embedment in general, the characteristics of the transfer function amplitude for a very small ground shear wave velocity and large embedment are irregular and complicated.     

Nonlinear surface ground analysis via statistical approach

A statistical approach is proposed for nonlinear surface ground analysis. In contrast to the conventional method which deals with only a single ground motion for equivalent linearization of soil properties, a design response spectrum defined at the upper level (bottom of the surface ground) of an engineering bedrock can be handled as the target design earthquake in the present paper. The effective shear strain in each soil layer is evaluated by means of a statistical procedure in which the mean peak shear strain is computed in terms of its standard deviation and the corresponding peak factor. The stiffness and damping ratio of each soil layer are obtained iteratively from the nonlinear relation of stiffness reduction factors and damping ratios with respect to the strain level. After the evaluation of the equivalent stiffness and damping ratio of every soil layer, the ground surface response spectrum is transformed from the design response spectrum defined at the upper level of the engineering bedrock via the one-dimensional wave propagation theory. The reliability and accuracy of the proposed analysis method is examined through the comparison with the results by the conventional method (represented by the program) for many simulated spectrum-compatible ground motions.     

Depositional environments of well‐sorted detrital limestone from the Minatogawa Formation in the southern part of Okinawa Island,the Ryukyu Archipelago,Japan

Well‐sorted detrital limestone is one of the typical lithofacies of the latest interval of the Pleistocene Ryukyu Group, which is exposed in the Ryukyu Archipelago in southwestern Japan. The depositional environments of the limestone are interpreted to be extremely shallow and to include back‐reef lagoons or moats and subaerial sand dunes. However, detailed micropaleontological analyses have not been performed on this limestone. In this study, the interpretation of the depositional environments and paleo‐water depths was improved by quantitative examination of foraminiferal assemblages for the well‐sorted detrital limestone of the Minatogawa Formation in the southern part of Okinawa Island. Thin sections of limestone collected from the Minatogawa (Horikawa) quarry were subjected to sedimentological and foraminiferal analyses. Comparison with modern foraminiferal distribution within the Ryukyu Archipelago indicates that back‐reef and fore‐reef dwelling foraminifers characterize the fossil assemblages from the well‐sorted detrital limestone (bioclastic grainstone). Three ratios of indicator foraminiferal taxa (ratios of back‐reef to fore‐reef taxa, planktonic foraminifers to Amphistegina lobifera and Amphistegina lessonii, and Calcarina gaudichaudii to other Calcarina species), as well as multivariate analyses suggest that the well‐sorted detrital limestone was deposited in fore‐reef setting shallower than 40 m in water depth. A comparable depth range was reconstructed from the coral assemblage in the associated coral limestone, suggesting that the Minatogawa Formation was deposited in a gently inclined ramp setting with patch reefs and/or fringing reefs. Stratigraphic changes in paleo‐water depth, together with evidence of several unconformities associated with paleosol layers suggest that there were repeated transgressions and regressions, with an amplitude up to several tens of meters, when the Minatogawa Formation was deposited.     

Transport measurement with a horizontal and a vertical pipe microphone in a mountain stream: taking account of particle saltation

The pipe microphone has been shown to be an effective means for monitoring bedload transport in mountain streams. It is commonly installed perpendicular to the flow direction on a stable river bed, such as that of a check dam. Acoustic pulses caused by bedload collisions with the pipe are detected by a microphone. However, bedload particles saltating over the pipe remain undetected. To overcome this disadvantage, we installed a horizontal as well as a vertical pipe microphone in the Ashi‐arai‐dani supercritical channel located in the Hodaka mountain range, Japan. The vertical pipe was installed on the wall of the channel and the horizontal pipe was installed on the channel bed. The acoustic response of the horizontal pipe is expected to be larger than that of the vertical pipe, because the bedload concentration decreases with increasing height above the bed. However, at high amplifications, the peak pulse value from the vertical pipe is higher than that from the horizontal pipe. We explain this observation as follows: under high bedload discharge conditions, the pulses of the horizontal pipe are saturated but those of the vertical pipe are not. We proposed a ratio (R_hv) between the pulses detected by these sensors, and applied this ratio for calibrating the contemporaneous pulses detected by a microphone located immediately upstream of a bedload slot sampler. Indeed the R_hv‐corrected pulses correlated well with the bedload discharge calculated from the sampler, supporting our explanation. We conclude that bedload monitoring using concomitant vertical and horizontal pipe microphones can be used to calibrate centrally located pipe microphones when the bedload concentration is approximately homogeneous laterally across the width of the channel cross‐section, and thereby represent bedload discharges more accurately than with only a single pipe microphone. Copyright © 2017 John Wiley & Sons, Ltd.     

Characteristic of the vertical seismic waves associated with the 1995 Hyogo‐ken Nanbu (Kobe), Japan earthquake estimated from the failure of the Daikai Underground Station

The dynamic behaviour of underground structures built by cut‐and‐cover methods is discussed. A simple model analysis shows that a column supporting the overburden at midspan (central column) can resonate upon incidence of an elastic wave of a specific frequency. The analytical results indicate that not only the size and material properties of the column, but also the static load acting on the column (overburden) is a decisive factor that influences the resonant frequency. Based on the results obtained by the analysis, the mechanism of the failure at the Daikai Underground Station in Kobe caused by the 1995 Hyogo‐ken Nanbu, Japan, earthquake is investigated. It is shown that the wave‐induced damage to underground structures can concentrate on the sections with specific overburden, and from the induced damage, it is possible to estimate the frequency characteristics of the associated seismic waves. Copyright © 2000 John Wiley & Sons, Ltd.     

Effects of alkali and alkaline-earth cations on the high-pressure sound velocities of aluminosilicate glasses

Physics and Chemistry of Minerals - A black tourmaline sample from Seagull batholith (Yukon Territory, Canada) was established to be a schorl with concentrations of Fe2+ among the highest currently...