Late Cretaceous uplift history of the Cretaceous volcanic arc in Southwest Japan: Provenance analysis of the Yuasa–Aridagawa basin based on U–Pb zircon ages

The Ryoke Metamorphic complex has undergone low‐P/T metamorphism and was intruded by granitic magmas around 100 Ma. Subsequently, the belt was uplifted and exposed by the time deposition of the Izumi Group began. The tectonic history of uplift, such as the timing and processes, are poorly known despite being important for understanding the spatiotemporal evolution of the Ryoke Metamorphic Belt. U–Pb zircon ages from sedimentary rocks in the forearc and backarc basins are useful for constraining uplift and magmatism in the provenance. U–Pb dating of detrital zircons from 12 samples (four sandstones and eight granitic clasts) in the Yuasa–Aridagawa basin, a Cretaceous forearc basin in the Chichibu Belt of Southwest Japan, gave mostly ages of 60–110 Ma. Granitic clasts contained in conglomerate suggest that granitic intrusions predate the formation of Coniacian and Maastrichtian conglomerate. Emplacement ages of granitic bodies originated from granitic clasts in Coniacian conglomerate are (110.2 ±1.3) Ma, (106.1 ±1.8) Ma, (101.8+5.8–3.8) Ma, and (95.3 ±1.4) Ma; for granitic clasts in Maastrichtian conglomerate, (89.6 ±1.8) Ma, (87.3+2.4–1.8) Ma, (85.7 ±1.2) Ma, and (82.7 ±1.2) Ma. The results suggest that detrital zircons in the sandstones were mainly derived from volcanic eruptions contemporaneous with depositional age, and plutonic rocks of the Ryoke Metamorphic Belt. Zircon ages of the granitic clast samples also indicate that uplift in the provenance began after Albian and occurred at least during the Coniacian to Maastrichtian. Our results, together with the difference of provenance between backarc and forearc basins suggest that the southern marginal zone of the Ryoke Metamorphic Belt was uplifted and supplied a large amount of clastic materials to the forearc basins during the Late Cretaceous.     

Nonlinear behaviour of scoria soil sediments evaluated from borehole records in eastern Shizuoka prefecture,Japan

We evaluate the non-linear behaviour of soil sediments, analysing five weak and four strong motions observed at depths of 1 m and 28 m, in eastern Shizuoka prefecture, Japan. We identify S-wave velocities and frequency-dependent damping factors by minimizing the residual between observed and theoretical spectral ratios, based on a linear one-dimensional model. We find that S-wave velocities identified from strong motions, whose peak ground acceleration are 440, 210, 176, and 140 cm/s², are significantly smaller than those identified from weak motions. The shear modulus reduction ratios estimated from identified S-wave velocities become clear above an effective shear strain of 10^-4 and agree with laboratory test results below an effective shear strain of 8×10^-4. The differences of damping factors between weak and strong motions are not clear below this effective shear strain, as the laboratory test suggested. The equivalent linear one-dimensional model, with frequency-dependent damping factors, is confirmed to be valid to simulate strong motions at least an effective shear strain of less than 4×10^-4. © 1997 John Wiley & Sons, Ltd.     

Effects of non‐uniform traction and specimen height in the direct shear test on stress and deformation in a rock fracture

In the direct shear test (DST), an internal moment is distributed within the rock specimen by non‐coaxial shear loads applied to the specimen, which cause non‐uniform distributions of both the traction on the loading planes and the stress and deformation in the specimen. To examine the validity of the DST for a rock fracture and to clarify the effect of specimen height, both the stress and deformation in a fracture in the DST were analyzed for specimens with three different heights using a three‐dimensional finite element method with quadratic joint elements for a fracture model. The constitutive law of the fracture considers the dependence of the non‐linear behavior of closure on shear displacement and that of shear stiffness on normal stress and was implemented in simulation code to give a conceptional fracture with uniform mechanical properties to extract only the effect of non‐uniform traction on the stress and deformation in the fracture. The results showed that both normal and shear stresses are concentrated near the end edges of the fracture, and these stress concentrations decrease with a decrease in the specimen height according to the magnitude of the moment produced by the non‐coaxial shear loads. Furthermore, although closure is greater near the end edges of the fracture, where normal stress is concentrated, this concentration of closure is not so significant within the range of this study because of the non‐linear behavior of closure, that is, closure does not significantly increase with an increase in normal stress at large normal stresses. Copyright © 2012 John Wiley & Sons, Ltd.     

Carbon-14 age and chemical evolution of Ca(HCO3)2-type groundwater of age less than 8,000 years in a confined sandy and muddy Pleistocene aquifer, Japan

The Pleistocene Kimitsu aquifer was selected for examination of the relationship between groundwater age and chemical evolution of Ca(HCO₃)₂-type groundwater. For the most part, the aquifer is confined and composed mainly of quartz and feldspar with a small amount of calcite. The groundwater ages calculated by ¹⁴C were adjusted by using a carbon mass-balance method and corrected for effects of ¹⁴C diffusion. Groundwater ages in the Kimitsu aquifer vary from modern (upgradient) to approximately 2,400 years at 4.4 km from the edge of the recharge area. The ¹⁴C age was verified by groundwater velocity calculated from the hydraulic gradient and hydraulic conductivity. The confined groundwater evolved to Ca(HCO₃)₂-type around 50 years after recharge and this has been maintained for more than 8,300 years due to low chemical reactivity, derived from equilibrium with calcite, kaolinite and Ca-montmorillonite. In addition, high pH prevents the dissolution of Fe and Mn. Consequently, the rate of increase in electrical conductivity ranges from 10 to 30 μS/cm per 1,000 years. On the other hand, leakage from the deep region, which is recognized from high Cl^– levels, causes remarkable increases in CH₄ and HCO₃ ^– concentrations, resulting in an apparent sulfidic zone at 500-m depth in most downgradient regions.     

Assessing the resilience of Delhi to climate-related disasters: a comprehensive approach

The study addresses disaster risks in Delhi through a resilience approach. It utilizes the Climate Disaster Resilience Index (CDRI) tool, which assesses disaster resilience from five dimensions: physical, social, economic, institutional, and natural. Each dimension comprises 5 parameters, and each parameter consists of 5 variables. The study is carried out in the nine revenue districts of Delhi and reveals that East Delhi is least resilient and New Delhi is most resilient. The CDRI analysis in East Delhi points out the urgent need to focus on key parameters such as housing and land use, population, intensity and frequency of natural hazards, ecosystem services, and land use in natural terms. On the other hand, New Delhi is the most resilient due to all five dimensions, where most significant parameters responsible for its high resilience are housing and land use, population, income, employment, intensity and frequency of natural hazards, ecosystem services, and land use in natural terms. In addition, the overall results of all nine districts show an inverse relationship between resilience score and population density. For example, districts with higher population density show low resilience and vice versa. Moreover, districts located on hazard-prone areas show low resilience. For example, East Delhi and North East Delhi scored low resilience because they both are situated on the Yamuna flood catchment areas. The study further develops key suggestions that are required to address disaster risk in all nine districts of Delhi and discusses future implications of CDRI to address city??s vulnerability. The approach??s distinctness is reflected through its consideration of micro-level diversities and presents some implications to resilience.     

Detrital anisotropic grandite garnet as an indicator of denudation level of Permian volcanic arc in the provenance of the South Kitakami Belt,Northeast Japan

In this study, the chemical and optical features of detrital garnets from the Middle Permian to Upper Triassic sandstones in the South Kitakami Belt, Northeast Japan, were examined to reveal the tectonic movement in the provenance. The sandstones contain a large amount of detrital grandite garnet grains with a wide range of andradite content. Among them, some grandite garnet grains show optically anisotropic features and rarely oscillatory zoning and sector twinning. The proportion of the detrital anisotropic grandite garnet increases from the Permian to the Middle Triassic and decreases in the Late Triassic. Such grandite garnets with various andradite contents occur in skarn deposits. Isotropic grandite garnets in the early stage of skarn evolution are distributed widely around a pluton, which affects the thermal metamorphism of the surrounding strata. However, anisotropic grandite garnets are formed along veinlets and fractures in the middle to late hydrothermal stage as the pluton cools, and their distribution is limited to a narrower area near the pluton compared to the metamorphic aureoles formed in the early stage. Changes in the chemical and optical features of the detrital garnets indicate a progressive denudation of the plutonic body accompanying skarn deposits in the provenance. The proportion of detrital anisotropic grandite garnet grains among all of the detrital grandite garnet is considered to be a sensitive indicator of the denudation level in a deeper part of the volcanic arc in association with skarn deposits, together with traditional sandstone composition datasets. This newly proposed method should be useful for clarifying the paleogeography during the Permian to Triassic in the East Asian continental margin, associated with uplift and denudation of the Permian volcanic arc, which seems to have been induced by the collision of the North China and South China Blocks.     

Potential of submarine-cave sediments and oxygen isotope composition of cavernicolous micro-bivalve as a late Holocene paleoenvironmental record

A sediment layer (43 cm thick) and surface sediments (5 cm thick) in a submarine limestone cave (31 m water depth) on the fore-reef slope of Ie Island, off Okinawa mainland, Japan, were examined by visual, mineralogical and geochemical means. Oxygen isotope analysis was performed on the cavernicolous micro-bivalve Carditella iejimensis from both cored sediments and surface sediments, and the water temperature within the cave was recorded for nearly one year. These data show that: (1) water temperature within the cave is equal to that at 30 m deep in the open sea; (2) the biotic and non-biotic environments within the cave have persisted for the past 2000 years; (3) mud-size carbonate detritus is a major constituent of the submarine-cave deposit, and may have come mainly from the suspended carbonate mud produced on the emergent Holocene reef flat over the past two millennia; (4) the δ¹⁸O-derived temperature (T_δ18_O) of C. iejimensis suggests that the species grows between April and July; (5) the T_δ18_O of C. iejimensis from cored sediments implies that there were two warmer intervals, at AD 340 ± 40 and AD 1000 ± 40, which correspond to the Roman Warm Period and Medieval Warm Period, respectively. These suggest that submarine-cave sediments provide unique information for Holocene reef development. In addition, oxygen isotope records of cavernicolous C. iejimensis are a useful tool to reconstruct century-scale climatic variability for the Okinawa Islands during the Holocene.