Natural and experimental structural evolution of dispersed organic matter in mudstones: The Shimanto accretionary complex,southwest Japan

Structural changes induced by thermal maturation of dispersed organic matter (OM) in the Shimanto accretionary complex, southwest Japan, were investigated using micro‐Fourier‐transform infrared spectroscopy and micro‐Raman spectroscopy. Natural dispersed OM exhibits systematic structural changes inferred from D1‐ and G‐band FWHM values, Raman band separation (RBS), and intensity ratios of the D1‐ and G‐bands (I_D1/I_G ratio) from diagenetic zone to anchizone (IC values: 0.75–0.30). Infrared spectra indicate a loss of aliphatic CH _x, aromatic CH _x, and oxygen‐containing structures as temperature increases. These changes are consistent with discontinuities in thermal structures bounded by out‐of‐sequence thrusts. Kinetic pyrolysis experiments indicate that the I_D1/I_G ratio of synthesized OM has a power law relationship with heat treatment time. Kinetic models of temperature dependence were fitted using the I_D1/I_G ratio, and an effective activation energy of 106 ±17 kJ/mol was estimated using an Arrhenius equation. The activation energies estimated by power law rate and Avrami models have a least‐square correlation coefficient of 0.93, indicating the temperature dependence of carbonization. The estimated effective activation energy is consistent with that of coal, lignin, cellulose, and hemicellulose during thermal degradation. On the other hand, RBS, and D1‐ and G‐band FWHM values of OM display more complex changes with increasing heating temperature and time, and it is difficult to constrain rate parameters during pyrolysis experiments. Our data indicate that the I_D1/I_G ratio is controlled by a simple thermally activated process, whereas RBS and D1‐ and G‐band FWHM values can be affected by lithostatic pressure, fluid activity, hydrogen index, and host lithology, as well as temperature. Structural evolution of dispersed OM in mudstones differs between natural and anhydrous closed experimental systems. Natural carbonization based on micro‐Raman spectroscopy should be applied for a limited indicator of thermal maturation, especially for dispersed OM in diagenetic zone.     

Naturally occurring radionuclides and rare earth elements in weathered Japanese soil samples

The activity concentrations of ²²⁶Ra and ²²⁸Ac in weathered Japanese soils from two selected prefectures have been measured using a γ-ray spectroscopy system with high purity germanium detector. The uranium, thorium, and rare earth elements (REEs) concentrations were determined from the same soil samples using inductively coupled plasma mass spectrometry (ICP-MS). For example, granitic rocks contain higher amounts of U, Th, and light REEs compared to other igneous rocks such as basalt and andesites. Therefore, it is necessary to understand the interaction between REEs and nature of soils since soils are complex heterogeneous mixture of organic and inorganic solids, water, and gases. In this paper, we will discuss about distribution pattern of ²³⁸U and ²³²Th along with REEs in soil samples of weathered acid rock (granite) collected from two prefectures of Japan: Hiroshima and Miyagi.     

A method for extending a general constitutive model to consider the electro-chemo-mechanical phenomena of mineral crystals in expansive soils

The mechanical behavior of expansive soils varies according to the chemical composition of the pore fluid. It is well known that electrochemical phenomena on the surface of clay mineral crystals considerably affect their macrostructural behavior. In particular, a change in the pore fluid composition causes osmotic consolidation or swelling. In this study, a model is constructed to describe the characteristic behavior of expansive soils by coupling the interlaminar behavior of clay mineral crystals and the soil skeleton behavior. The interlaminar behavior is derived from the electro-chemo-mechanical coupling equilibrium of mineral crystals, and the soil skeleton behavior is given by a general elastoplastic constitutive model for soils. This modeling approach extends a general model to consider the electro-chemo-mechanical phenomena of mineral crystals. Oedometer tests with the replacement of the cell fluid and the swelling pressure and deformation tests on expansive clays are simulated with the proposed model. The simulation results indicate that the proposed method can reasonably represent the typical behavior of expansive soils.     

Geometry of stress function surfaces for an asymmetric continuum

A two-dimensional stress field of dislocation or fault is geometrically studied for an asymmetric continuum. For geometric surfaces of the stress and couple-stress functions, the mean and Gaussian curvatures are derived. The mean curvature of couple-stress function surface is connected with the asymmetric of stress tensor. Moreover, the Gaussian curvature of stress function surface is characterized by both the stress and couple-stress. On the other hand, the mean curvature of stress function surface is not affected by the asymmetry of stress. Based on these geometric expressions, the Coulomb’s failure criterion and the friction coefficient are expressed by the curvatures of couple-stress function surface. Moreover, geometric structures of stress and couple stress function surfaces are shown for edge and wedge dislocations as faults. The curvatures of these surfaces show that the effect of couple-stress is constrained around the dislocations only.     

Late Holocene Asian monsoon variations recorded in Lake Rara sediment,western Nepal

The Himalayas are a key location for understanding centennial‐ to millennial‐scale variations in the Asian monsoon, yet few studies of the late Holocene have been conducted in this sensitive area. Direct evidence for shifts in monsoonal wind strength is often limited to marine proxy records, while terrestrial reconstructions (e.g. lake levels and spleothems) focus on precipitation. Here, we present the first evidence of terrestrial summer monsoon wind strength changes from Lake Rara, western Nepal, based on Mn/Ti ratios, a proxy for lake stratification. These data indicate a link between the Arabian Sea and the Himalayas, suggesting that centennial‐ to millennial‐scale changes in wind strength occurred synchronously. Distinct similarity is also observed between Lake Rara and the southern part of China, which may support previous suggestions that the southern part of China is influenced by Indian summer monsoon. Copyright © 2012 John Wiley & Sons, Ltd.     

Alkalinization and acidification of stream water with changes in atmospheric deposition in a tropical dry evergreen forest of northeastern Thailand

Field surveys on atmospheric deposition and stream water chemistry were conducted in an evergreen forest in northeastern Thailand characterized by a tropical savanna climate with distinct dry and wet seasons. Atmospheric deposition of ion constituents by throughfall and stemflow was shown to increase in the beginning and end of the wet season, reflecting the precipitation pattern. The pH and electrical conductivity of stream water increased with alkalinity and base cation concentrations due to mineralization of organic matter by the first rain and retention of anions in soil during the start of the wet season. After initial alkalinization, the pH and alkalinity declined rapidly with the highest SO₄^2? concentration displayed in the middle towards the end of the wet season. The magnitude of peaks in SO₄^2? concentration (13.5–60.6 μmol_c/L) reflects deposition during the first 2 months of the wet season (March and April) in respective years (60.8–170 mol_c/ha). Release of SO₄^2? with H⁺, which is retained in soil during the early wet season, may cause acidification later in the season. The deposition and concentration of SO₄^2? declined over 6 years. However, the pH of stream water declined with increasing concentrations of SO₄^2? and other major ions. The release of materials accumulated in the ecosystem was facilitated by the decrease in SO₄^2? concentration/deposition and increased precipitation in the middle–late wet season. The retention‐release cycle of SO₄^2? largely contributed to both seasonal and interannual variations in stream water chemistry in the tropical savanna climate studied.     

Effects of large-scale wind on the Kuroshio path south of Japan in a 60-year historical OGCM simulation

The effects of large-scale wind forcing on the bimodality of the Kuroshio path south of Japan, the large meander (LM) and non-large meander (NLM), were studied by using a historical simulation (1948–2007) with a high-resolution Ocean general circulation models (OGCM). The Kuroshio in this simulation spent much time in the NLM state, and reproduced several aspects of its long-term path variability for the first time in historical OGCM simulation, presumably because the eddy kinetic energy was kept at a moderate level. By using the simulated fields, the relationships between wind forcing (or Kuroshio transport) and path variation proposed by past studies were tested, and specific roles of eddies in those variations were investigated. The long-term variation of the simulated net Kuroshio transport south of Japan was largely explained by the linear baroclinic Rossby wave adjustment to wind forcing. In the simulated LM events, a triggering meander originated from the interaction of a wind-induced positive sea surface height (SSH) anomaly with the upstream Kuroshio and was enlarged by cyclonic eddies from the recirculation gyre. The cyclonic eddy of the trigger meander was followed by a sizable anticyclonic eddy on the upstream side. Subsequently, a weak (strong) Kuroshio favored the LM (NLM). The LM tended to be maintained when the Kuroshio transport off southern Japan was small, and increasing Kuroshio transport promoted decay of an existing LM. The supply of disturbances from upstream, which is related to the wind-induced SSH variability at low latitudes, contributed to the maintenance of an existing LM.     

Simulating present climate of the global ocean–ice system using the Meteorological Research Institute Community Ocean Model (MRI.COM): simulation characteristics and variability in the Pacific sector

A long-term spin-up and a subsequent interannual simulation are conducted for the ocean–ice component of the climate model intercomparison project (CMIP)-class earth system model of the Japan Meteorological Agency/Meteorological Research Institute. This experiment has three purposes: first is to assess the ability of our model with the Coordinated Ocean–ice Reference Experiments (COREs) forcing in reproducing the present ocean-climate; second is to understand the ocean-climate variability for the past 60 years; third is to present an example of evaluating an ocean–ice interannual variability simulation. The Pacific Ocean is focused on for the last two purposes. After integrating for about 1500 years with repeated use of a detrended CORE interannual forcing, the model reaches a quasi-steady state where the present climate is reproduced satisfactorily. Then, the interannual variability simulation is conducted with the retrieved forcing trend and the result is analyzed. The simulation is successful at reproducing the long-term variability in the Pacific and surrounding oceans. Brief analyses of the tropical and mid-latitude upper layer, deep circulation, and the Arctic sea ice are presented. A caveat in treating other parts of the globe is due to the recent intense convection in the Southern Ocean caused by a remarkably increasing trend of the Southern Hemisphere westerly. Overall, the current simulation with our CMIP-class ocean–ice model is shown to be useful for studying the present ocean-climate variability, specifically in the Pacific sector. It could also be used as a benchmark control experiment that facilitates further research, model development, and intercomparison.     

Sedimentary humic acid and fulvic acid as fluorescent organic materials

Fluorescence and absorption spectra of sedimentary humic acid (HA) and fulvic acid (FA), with molecular weights ranging from < 10,000 to >300,000, were measured at 20°C and pH 8. The maximum excitation and emission wavelengths of HA were longer than those of FA, being independent of molecular weight. The excitation and emission maxima can be utilized to differentiate between sedimentary HA and FA. It is suggested that the fluorophors in HA are of a higher molecular weight aromatic groups than those in FA.Smaller molecules were found to have a greater fluorescence than larger ones for sedimentary humic substances and this phenomenon is similar to those obtained for humic substances of terrestrial origin. The absorption coefficient (1/g/cm) of HA decreased, while that of FA increased with the increase in molecular weight. It was shown that fluorescence intensity per weight concentration unit of HA increases and that of FA decreases with increasing absorption coefficient.     

岩石碎裂作用的分形尺度(英文)

各种各样的统计幂定律关系经常成功地被用来描述碎屑大小分布和断口形状 (不平整度 )的分级规律 ,表明碎裂作用是一种尺度不变的作用过程。一条新的有关岩石碎裂作用破裂能量的尺度律 ,可以由分形几何以及Griffith能量平衡的概念推导出来 ,而且它与先前三条关于大小缩减或Hall Petch关系的理论是相一致的。从材料强度的观点来看 ,断口形状的分形维数是形状因子和岩石Weibull均质系数的函数。在任何一次采集中 ,如果碎屑都是致密压实的 ,那么大小分布和碎屑不平整度的分形维数是相同的。然而有些地壳碎屑在三维体积上已不再是致密压实的 ,破裂的地壳可被当作分形的多孔物质来处理。在此情况下 ,地壳碎屑形状的分形容量与地壳断口大小分布的分形维数相关 ,可以预期 ,在大地构造及地震强度的分形分析中 ,地壳断口大小分布的分形维数可作为断裂制约条件之一。