Geochemical and geological studies were performed on the turbidite sequence of Anno Formation, Awa Group, Boso Peninsula, Chiba Prefecture. Based on the correlation of major, trace, and rare earth elements (REEs) contents with SiO2 content, elements are divided into positive correlation group (K, Rb, Zr, Nb, Ba, Hf, Ta, Pb, Th, U) and negative correlation group (Ti, total-Fe, Mn, Mg, Ca, P, Sc, V, Co, Cu, Zn, Sr, Y). This is considered to have been caused by an increase in the acidic component derived from the island-arc during the sea level declining period, and an increase in the basic component from fore-arc basalt during the sea level rising period. An increase in the organic carbon content and a decrease in organic carbon isotopic composition (δ13C) are recognized during the sea level declining period. This is thought to have been caused by the increase in the biogenic productivity related to the upwelling of deep seawater and the settling of organic matter-clay mineral compounds. 87Sr/86Sr ratio and other geochemical data (REE pattern, La/Yb ratio) indicate that the hemipelagite is mostly composed of fore-arc basalt with variable amounts of carbonate and acidic component probably derived from the island-arc. These geochemical variations with time are consistent with the variations of δ18O of foraminiferal shell carbonate, the amount of turbidite sedimentation, and the hemipelagite thickness. Therefore, the geochemical data obtained by this study support the conclusion of Ishihara et al. (1997) who indicated that the temporal variation of turbidite in the Anno Formation is caused by the variations of seawater level.
The Eastern margin of the Yokote Basin Fault Zone (EYBFZ) is one of the seismogenic reverse faults that developed in Northeast Japan, generating the 1896 Rikuu Earthquake (M7.2). The EYBFZ is divided into range boundary fault (Kawaguchi Fault) and frontal fault. The major segment of the frontal fault consists of three faults : the Shiraiwa Fault, the Ota Fault, and the Senya Fault, at which coseismic surface ruptures with irregular and highly sinuous traces, gaps and echelon steps occurred during the 1896 Earthquake. In the study area, the irregular coseismic surface ruptures probably originate from differences in fault geometries and sedimentary conditions, which are associated with thrust-front migration in the Quaternary. We discuss the relationships among fault traces, geomorphic displacements, and fault geometries on the Senya Fault and the Kawaguchi Fault, based on data from high-resolution seismic reflection profiling, investigations into tectonic geomorphology and structural geology with the help of the balanced cross-section method. The seismic image obtained shows changes of geomorphic and geologic features around the Senya Hills expressed as differences in faulting geometries along the Senya Fault and the Kawaguchi Fault. In fact, the Senya Hills are situated as an unsymmetrical ordering.The disparity in the timing of thrust-front migration affects the development of fluvial surfaces, which are related to the appearance of the fault scarp on the surface. That is why, in the central portion of the Senya Hills, the Senya Fault is a typical emergent thrust with flat-ramp structures associated with the uplifting and the back-tilting of late Quaternary fluvial terraces. On the other hand, in the northern portion, the Senya Fault is a concealed thrust with step-like geometry and prominent folding and small faults in the hanging wall. The small faults infer the structure of the tectonic scarp and short wavelength deformation on the surface. This means that the Senya Fault at the central portion preceded the northern portion as an emergent fault. Moreover, fault traces show different dips between central and northern portions. The dip of the central portion is lower than that of the northern portion. By restoring the balanced cross-sections and assuming the uniform net-slip rate, the initial thrusting along the boundary faults is retroactive to 2.02.6 Ma at the central portion and 1.8 2.3 Ma at the northern portion. The initiation of thrust front migration from the boundary faults to the frontal faults is ca.1.6 Ma at the central portion and 0.6Ma at the northern portion.
The Paleocene/Eocene thermal maximum (PETM) is an event characterized by abrupt warming, negative excursion of carbon isotopic composition, and extinction of benthic foraminifera, and is considered to have been caused by the release of a large amount of methane and/or carbon dioxide from methane hydrate. In this study, we try to reconstruct changes of the marine carbon cycle during that period using a one-dimensional marine carbon cycle model and the data set of marine carbon isotopic composition. We find that the bioproductivities of organic carbon and carbonate, and the global mean upwelling rate rapidly increased at the carbon isotope excursion event. The lower level of the carbon isotopic composition observed after the excursion event probably resulted from a large quantity of light carbon remaining in the ocean. These results can be interpreted as follows : the warming of climate intensifies vertical mixing of the ocean, so large quantities of nutrients are supplied to the surface water from the intermediate water, resulting in an increase in the bioproductivity at PETM.
The eastern margin of Echigo Plain, central Japan, is characterized by NNE-SSW trending active faults. The Anchi fault is made up of two segments : the Anchi-nishi fault and the Anchi-higashi fault. Each fault trace is approximately 2-km long. They may be short subsidiary faults on the hanging wall of the master fault in this region (the Tsukioka fault). Trench investigations across the Anchi fault reveal its rupture history as follows : 1) the Anchi-nishi fault and the Anchi-higashi fault are west-dipping reverse faults; 2) the Anchi-nishi fault shows a vertical offset of 1.3-1.9 m after ca. 30 ka; and, 3) the vertical displacement of 3.5 m is associated with two faulting events along the Anchi-higashi fault, one between ca. 30 and 60 ka and the other younger than ca. 30 ka. Geomorphic features indicate that a reverse fault branches into these two faults at a certain depth. Thus, the total vertical offset for the last ca. 30 ky is between 3.1 to 3.7 m. This value is one third of that along the master active fault. If the source fault consists of these active faults, we should evaluate the activity of the master fault taking account of the activity of the Anchi fault. It is very important to know the nature of subsidiary faults, even if they display very short traces.
Sclerotium grains, the resting structure of an ectomycorrhizal fungus, Cenococcum graniforme (currently, Cenococcum geophilum), are black and spherical, 1-2 mm in diameter have a characteristic hollow structure, and can be easily found in forest soils. The maximum content of sclerotium grains in surface soils of Japanese Andosols is 3.40 g kg-1, which suggests that the contribution of sclerotium grains to forest soils cannot be ignored as one of the soil organic components. This paper introduces the interests of the biological strategies of Cenococcum geophilum and sclerotium grains by reviewing the findings of advanced studies on micromorphological features, chemical composition, and microbial communities of sclerotium grains. Instruments such as scanning electron microscope (SEM) and energy dispersion X-ray fluorescence micro-analyzer (EDX), electron probe micro-analyzer of wave dispersion type (EPMA) and 27Al magic-angle spinning (MAS) nuclear magnetic resonance (NMR) were used to obtain the characteristics of sclerotium grains. A basic finding was that C is the major element in sclerotium grains associated with a relatively large concentration of octahedral Al, which suggests an Al-humus complex. The mean concentrations of major elements in sclerotium grains are quantitatively defined as C (47.6%), O (30.2%), H (3.32%), Al (1.4%), N (0.78%). Carbon in sclerotium grains took the form of large amounts of 0-alkyl C and was also associated with aromatic C and methyl C, which strongly showed a characteristic biological origin and completely different spectral feature to humic acids from an allophonic Andosol. AMS 14C age values obtained for sclerotium grains in surface soils of Japanese forest soils were from modern to 1800 yr BP, which proves its stability and long life as an Al-humus complex. Transmission Electron Microscope (TEM) and EDX techniques revealed the micromorphological features of the Al-oxyhydroxide polymorphs found in sclerotium grains. It is assumed that a biochemical process responsible for host fungi induced Al saturation and precipitation under acidic conditions to form Boemite inside the grain. Studies on microbial communities elucidated the predominance of specific species such as Sphingomonas sp. From a further investigation on the distributions of sclerotium grains in profiles of German Podsols, Braunfaherde and Brown Podsols, it is concluded that development of sclerotium grains was not always regulated by low pH but by the content of exchangeable Al and the status of Al in the soil, regardless of soil type. The sclerotium grain was likely to be formed in soils with high ratios (>0.6) of organic bonding Al (Alp) to amorphous Al (Alo), and with high contents of exchangeable Al (Al3+) (> 0.54 g kg-1). The Al accumulation in sclerotium grains and the close relationship between sclerotium grain density and the status of active Al in soils suggest the symbiotic function of Cenococcum geophilum with root by reducing the toxicity of Al under low pH in rhizosphere. Sclerotium grain may also serve as a shelter for microorganisms and preserve their diversity under severe environmental conditions. Although the findings we have are still very limited, the goal of the study is to understand further implications of sclerotium formation in a soil ecosystem, which may help us to learn what strategy is necessary for biota to survive a catastrophe.