Geological age of the Yokawa Formation of the Kobe Group (Japan) on the basis of terrestrial mammalian fossils

Abstract   The age of the Yokawa Formation of the Cenozoic Kobe Group distributed in Hyogo Prefecture of western Japan based on mammalian fossils is discussed. Two fossil dental specimens of terrestrial mammals discovered from the lowest part of the Yokawa Formation in the Sanda area are described. These two fossils described here are: (i) a right mandibular fragment with p2–m3 of Bothriodon sandaensis sp. nov. (selenodont anthracotheriid artiodactyl), which appears to be the most primitive among the species of the genus; and (ii) right m1–m3 of cf. Hyrachyus sp. (primitive rhinocerotoid perissodactyl). In the lower part of the Yokawa Formation, Zaisanamynodon (amynodontid perissodactyl) was previously reported. The morphology ('evolutionary stage') of B. sandaensis is indicative of the latest Middle to Late Eocene, that of cf. Hyrachyus sp. is indicative of the Early to Middle Eocene, and Zaisanamynodon is indicative of the Late Middle to Late Eocene. Therefore, the fossil mammals of the Yokawa Formation indicate an latest Middle Eocene ( ca . 38 Ma) correlation for the lower part of the formation, as a working hypothesis. Although the resolution of the geological age based on these mammalian fossils is relatively low compared to that based on marine index fossils, this result is concordant with the recent radiometric correlation of the lower part of the Yokawa Formation in the Sanda area.     

Strain and tilt changes measured during a water injection experiment at the Nojima Fault zone, Japan

Abstract In order to make geophysical and geological investigations of the Nojima Fault on Awaji Island, Japan, three boreholes measuring 1800 m, 800 m and 500 m deep were drilled into the fault zone. The fault is one of the seismic source faults of the 1995 Hyogo-ken Nanbu earthquake of M 7.2. A new multicomponent borehole instrument was installed at the bottom of the 800 m borehole and continuous observations of crustal strain and tilt have been made using this instrument since May 1996. A high-pressure water injection experiment within the 1800 m borehole was done in February and March 1997 to study the geophysical response, behavior, permeability, and other aspects of the fault zone. The injection site was located approximately 140 m horizontally and 800 m vertically from the instrument. Associated with the water injection, contraction of approximately 0.7 × 10⁻⁷ str (almost parallel to the fault) and tilt of approximately 1 × 10^-7 rad in the sense of upheaval toward the injection site were observed. In addition to these controlled experiments, the strainmeter and tiltmeter also recorded daily variations. We interpret strain and tilt changes to be related to groundwater discharge and increased ultra-micro seismicity induced by the injected water.     

Possible europium-normal rare-earth abundances estimated from the lunar samples,and the terrestrial analogue

From the mathematical analysis of the rare-earth data on some of the Apollo 12 samples studied by Hubbard et al. (1971), the possible europium-normal primitive rare-earth pattern, in which europium is normal with respect to the adjacent rare-earth elements, has been estimated. A fact that the igneous rocks (Japanese geosynclinal basalts) appearing to reflect the analogous effect occur locally on the earth enhances our interests in the pattern resulting from the above estimation.     

Rare earth elements in metagabbros from the Mid-Atlantic Ridge and their possible implications for the genesis of alkali olivine basalts as well as the lizard peridotite

Two foliated metagabbros from the Mid-Atlantic Ridge near 30° N were analyzed for rare earth elements. The chondrite-normalized rare earth pattern for one of them is quite similar to those for abyssal tholeiites. The pattern for another sample, however, is somewhat different from the above one. A new set of bulk partition coefficients for rare earth elements has been estimated correspondingly. This set throws a new light on the interpretation that many alkali olivine basalts were produced by a zone melting or partial melting of primary-liquid-type material. Also the same partition coefficients lead us to an inference that the high-temperature peridotite intrusion in the Lizard area, Cornwall, England, is a secondary-solid-type material which was once in equilibrium with a primary-solid-type material, whereas the pyroxenite, Canyon Mountain, Oregon, is a primary-solid-type material.Both of the metagabbros studied show positive europium anomaly.     

Structure and time variations of the Jovian ionosphere

The problem of the ionospheric formation in the Jovian upper atmosphere is examined. By adopting two plausible atmospheric models, we solve coupled time-dependent continuity equations for ions H₂⁺, H₅⁺, H⁺, H₃⁺ and H_eH⁺ simultaneously. It is shown that both radiative and three body association of H⁺ to H₂ are important for the determination of the structure of the Jovian ionosphere. The maximum electron density in the daytime is found to be about 10⁵ cm^?3. It is also shown that diurnal variation with large-amplitude can exist in the Jovian ionosphere.     

利用场地观测计算地表通量

高原地表的感热和潜热通量在亚洲季风系统中有很重要的作用。由于高原地域辽阔，且自然环境较严酷，不利于建立完善的地面观测系统。因此，卫星遥感观测就成为测算高原整体感热和潜热通量的有效工具。地面场地的观测结果作为地表通量的真实值，对于卫星遥感测算是非常重要的。它也为构建陆面—大气模型提供了科学依据，是卫星资料的资料同化系统中的重要组成部分。 计算场地热量通量有几种不同的处理方法。最简单的方法利用有效的观测和试验的参数，可以给出稳定连续的估计。愈精确的Bowen比或者廓线的观测能给出愈精确的信息。综合了湍流测量及辐射测量、土壤热通量的观测结果的估计对陆面—大气相互作用进行了详细的描述，以适应模式的发展。从1998年开始，这些方法联合应用到青藏高原；场地通量观测方面的成果以及目前对其理解将在本文中做一概述。     

Climate Warming and Water Management Adaptation for California

The ability of California's water supply system to adapt to long-term climatic and demographic changes is examined. Two climate warming and a historical climate scenario are examined with population and land use estimates for the year 2100 using a statewide economic-engineering optimization model of water supply management. Methodologically, the results of this analysis indicate that for long-term climate change studies of complex systems, there is considerable value in including other major changes expected during a long-term time-frame (such as population changes), allowing the system to adapt to changes in conditions (a common feature of human societies), and representing the system in sufficient hydrologic and operational detail and breadth to allow significant adaptation. While the policy results of this study are preliminary, they point to a considerable engineering and economic ability of complex, diverse, and inter-tied systems to adapt to significant changes in climate and population. More specifically, California's water supply system appears physically capable of adapting to significant changes in climate and population, albeit at a significant cost. Such adaptation would entail large changes in the operation of California's large groundwater storage capacity, significant transfers of water among water users, and some adoption of new technologies.     

Characteristics and implication of clay minerals in the northern and southern parts of the Chelung-pu fault, Taiwan

In this study, we report the characteristics of clay minerals present in the Chelung-pu fault in Taiwan. In the 1999 Chi-Chi earthquake, different slip motions were recorded along the Chelung-pu fault in the northern and southern parts of the fault. The characteristics of clay minerals present in the fault zones can be attributed to the differences in motion. We analyzed the shallow drill core samples obtained from the northern and southern sites penetrating the fault. The clay minerals identified in most of the samples from both the sites are smectite, illite, and chlorite. There are illite–smectite mixed layers with a high illite content and no chlorite–smectite mixed layer. In some samples, no smectite is detected. We also examined the iron content and symmetry of iron and magnesium in the silicate and hydroxide layers in chlorite. At the northern site, the total iron content in chlorite of gouge is larger than that of the host rocks. On the other hand, at the southern site, the total iron content varies widely. It is hypothesized that the smectite consumption and differences in the characteristics of chlorite may be controlled by the differences in the lithology, fluid chemistry, fluid temperature, or fault activities (heating or breakage) between the northern and southern sites.     

Relationship between chemical composition of Japanese Island-Arc volcanic rocks and gravimetric data

1670 published chemical analyses from 137 Quaternary eruption centers of Kurile, Japan and Izu—Mariana arcs are collected and K₅₅ and K₆₀ values of individual centers are calculated. Along with the well-established trend of increase of K₅₅ and K₆₀ values across the arc towards the continent, longitudinal change is also recognizable. Interrelation between K₅₅ or K₆₀ value pattern and a map of Bouguer anomaly distribution along the volcanic front is characteristic.To develop one possible simplified model to explain the facts, we assume first that the asthenosphere has a homogeneous thermal state beneath the volcanic zone, second that the thickness of the crust is quite variable areally, and third that the mean density of the crust is constant throughout the area. Thus, the composition of the magma generated along a zone corresponding to equal depths along the Benioff zone should be identical throughout the volcanic arc, and lower values of the Bouguer anomaly should be observed where the crust is thicker. We then assume that magma generated in the asthenosphere ascends into the crust, then cools as fractional crystallization proceeds. Depths of fractional crystallization would be deeper where the crust is thicker. The ratio of the clinopyroxene phase separated from the magma to the plagioclase phase should be larger where the level of fractionation is deeper. Thus, magmatic liquid should be enriched in K where K-poor crystal fractions are subtracted at the deeper level.