近200年来黑河下游天鹅湖湖泊沉积记录的环境变迁   总被引：14，自引：2，他引：12  

马燕  郑祥民  曹希强  远藤邦彦 《湖泊科学》2006,18(3):261-266

根据2002-2004年洞庭湖水质监测数据,参照GB3838-2002中Ⅲ类水质标准,选用内梅罗水污染指数法和黄浦江污染指数对洞庭湖水质现状进行评价,结果表明:(1)洞庭湖水体的主要污染指标是总磷,总氮和粪大肠菌群;(2)黄浦江污染指数平均值为0．27,所以洞庭湖12个断面水质无黑臭现象发生;(3)枯水期西洞庭湖和南洞庭湖水质污染最严重,平水期西洞庭湖水质污染最严重,洞庭湖丰水期的污染程度小于平水期;(4)洞庭湖的大部分水体的水质主要处于轻度污染的状态,局部水体的水质在枯水期达到重污染的状态．  相似文献   

Cosmic‐ray exposure ages of six chondritic Almahata Sitta fragments          下载免费PDF全文

M. E. I. Riebe  K. C. Welten  M. M. M. Meier  R. Wieler  M. I. F. Barth  D. Ward  M. Laubenstein  A. Bischoff  M. W. Caffee  K. Nishiizumi  H. Busemann 《Meteoritics & planetary science》2017,52(11):2353-2374

The Almahata Sitta strewn field is dominated by ureilites, but contains a large fraction of chondritic fragments of various types. We analyzed stable isotopes of He, Ne, Ar, Kr, and Xe, and the cosmogenic radionuclides ¹⁰Be, ²⁶Al, and ³⁶Cl in six chondritic Almahata Sitta fragments (EL6 breccia, EL6, EL3‐5, CB, LL4/5, R‐like). The cosmic‐ray exposure (CRE) ages of five of the six samples have an average of 19.2 ± 3.3 Ma, close to the average of 19.5 ± 2.5 Ma for four ureilites. The cosmogenic radionuclide concentrations in the chondrites indicate a preatmospheric size consistent with Almahata Sitta. This corroborates that Almahata Sitta chondrite samples were part of the same asteroid as the ureilites. However, MS‐179 has a lower CRE age of 11.0 ± 1.4 Ma. Further analysis of short‐lived radionuclides in fragment MS‐179 showed that it fell around the same time, and from an object of similar size as Almahata Sitta, making it almost certain that MS‐179 is an Almahata Sitta fragment. Instead, its low CRE age could be due to gas loss, chemical heterogeneity that may have led to an erroneous ²¹Ne production‐rate, or, perhaps most likely, MS‐179 could represent the true 4π exposure age of Almahata Sitta (or an upper limit thereof), while all other samples analyzed so far experienced exposure on the parent body of similar lengths. Finally, MS‐179 had an extraordinarily high activity of neutron‐capture ³⁶Cl, ~600 dpm kg^?1, the highest activity observed in any meteorite to date, related to a high abundance of the Cl‐bearing mineral lawrencite.  相似文献   

Petrogenesis of lunar impact melt rock meteorite Oued Awlitis 001     

Axel Wittmann  Randy L. Korotev  Bradley L. Jolliff  Kunihiko Nishiizumi  A. J. Timothy Jull  Marc W. Caffee  Michael Zanetti  Anthony J. Irving 《Meteoritics & planetary science》2019,54(10):2167-2188

Oued Awlitis 001 is a highly feldspathic, moderately equilibrated, clast‐rich, poikilitic impact melt rock lunar meteorite that was recovered in 2014. Its poikilitic texture formed due to moderately slow cooling, which judging from textures of rocks in melt sheets of terrestrial impact structures, is observed in impact melt volumes at least 100 m thick. Such coherent impact melt volumes occur in lunar craters larger than ~50 km in diameter. The composition of Oued Awlitis 001 points toward a crustal origin distant from incompatible‐element‐rich regions. Comparison of the bulk composition of Oued Awlitis 001 with Lunar Prospector 5° γ‐ray spectrometer data indicates a limited region of matches on the lunar farside. After its initial formation in an impact crater larger than ~50 km in diameter, Oued Awlitis 001 was excavated from a depth greater than ~50 m. The cosmogenic nuclide inventory of Oued Awlitis 001 records ejection from the Moon 0.3 Ma ago from a depth of at least 4 m and little mass loss due to ablation during its passage through Earth's atmosphere. The terrestrial residence time must have been very short, probably less than a few hundred years; its exact determination was precluded by a high concentration of solar cosmic ray‐produced ¹⁴C. If the impact that excavated Oued Awlitis 001 also launched it, this event likely produced an impact crater >10 km in diameter. Using petrologic constraints and Lunar Reconnaissance Orbiter Camera and Diviner data, we test Giordano Bruno and Pierazzo as possible launch craters for Oued Awlitis 001.  相似文献   

东海岛屿风尘地层中火山玻璃的发现及环境意义   总被引：3，自引：0，他引：3  

郑祥民  Kunihiko ENDO  周立旻  赵健 《海洋地质与第四纪地质》2003,23(3):82-82,90

近年来通过对东海诸岛屿第四纪风尘沉积的研究表明 ,东海嵊泗列岛上广泛接受晚更新世以来的风尘堆积[1] 。嵊山岛是浙江沿海舟山群岛最外缘的岛屿之一 ,位于 30°4 5′N、12 2°5 0′E的东海海域 ;岛屿面积约 4 2 5km2 ,该岛屿主要由花岗岩基岩组成 ,岛屿最高点海拔达 10 0多米。岛屿大部分地区基岩直接出露地表 ,厚达数米的风尘黄土直接覆盖在基岩之上。该岛风尘堆积地层较为典型 ,保存较为完好 ,风尘地层记录诸多古气候、古环境变化的信息 ,是研究中国东部第四纪风尘沉积、第四纪环境演变和全球变化区域响应的良好载体。通过对岛屿风尘…  相似文献   

II-1 On the cross flow turbine for wave power plant (1st report, the characteristics of the turbine in steady air flow)     

Masahiko Akabane  Haruyuki Suzuki  Kunihiko Yamauchi 《Ocean Engineering》1985,12(6):562

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Stochastic processes of soil production and transport: erosion rates,topographic variation and cosmogenic nuclides in the Oregon Coast Range     

Arjun M. Heimsath  William E. Dietrich  Kunihiko Nishiizumi  Robert C. Finkel 《地球表面变化过程与地形》2001,26(5):531-552

Landscapes in areas of active uplift and erosion can only remain soil‐mantled if the local production of soil equals or exceeds the local erosion rate. The soil production rate varies with soil depth, hence local variation in soil depth may provide clues about spatial variation in erosion rates. If uplift and the consequent erosion rates are sufficiently uniform in space and time, then there will be tendency toward equilibrium landforms shaped by the erosional processes. Soil mantle thickness would adjust such that soil production matched the erosion. Previous work in the Oregon Coast Range suggested that there may be a tendency locally toward equilibrium between hillslope erosion and sediment yield. Here results from a new methodology based on cosmogenic radionuclide accumulation in bedrock minerals at the base of the soil column are reported. We quantify how soil production varies with soil thickness in the southern Oregon Coast Range and explore further the issue of landscape equilibrium. Apparent soil production is determined to be an inverse exponential function of soil depth, with a maximum inferred production rate of 268 m Ma^?1 occurring under zero soil depth. This rate depends, however, on the degree of weathering of the underlying bedrock. The stochastic and large‐scale nature of soil production by biogenic processes leads to large temporal and spatial variations in soil depth; the spatial variation of soil depth neither supports nor rejects equilibrium morphology. Our observed catchment‐averaged erosion rate of 117 m Ma^?1 is, however, similar to that estimated for the region by others, and to soil production rates under thin and intermediate soils typical for the steep ridges. We suggest that portions of the Oregon Coast Range may be eroding at roughly the same rate, but that local competition between drainage networks and episodic erosional events leads to landforms that are out of equilibrium locally and have a spatially varying soil mantle. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

Unusually low seismic activity in the focal region of the great Kanto earthquake of 1923     

Kunihiko Shimazaki 《Tectonophysics》1971

The epicenters of earthquakes which occurred in the vicinity of Tokyo during the period 1926–1967 have been plotted by an IBM 360/40 computer at the Earthquake Prediction Observation Center. As a result, a seismically quiescent area is found to the south of Tokyo. The area coincides with the shallower part of the focal plane of the great Kanto earthquake of 1923 as obtained from the analyses of seismological and geodetic data. In historical times, many large earthquakes having a magnitude of 7.0 or greater took place in this area. If it is assumed that the strain energy has been constantly accumulated in this area, an energy potentially equivalent to that of a large earthquake of which the magnitude exceeds 7.7 seems to be stored in the crust there.  相似文献   

Deep-sea spherules from Pacific clay: mass distribution and influx rate     

M.T. Murrell  P.A. Davis  K. Nishiizumi  H.T. Millard 《Geochimica et cosmochimica acta》1980,44(12):2067-2074

From 411 kg of Pacific clay, 22 mg of stony spherules and 50 mg of iron spherules larger than 150 μm were concentrated. The extraterrestrial origin of these particles was evaluated with the aid of both optical and electron microscopy as well as atomic absorption elemental analysis. The integral number (N) of stony particles from this sediment in the mass (M) range 20–300 μg is given by N( >M(g)) = 5.13 × 10^?6 × M^?1.65. The world-wide influx rate of stony particles in the mass range which survive atmospheric heating and ocean sediment storage is calculated to be 90 tons/yr. The relative contributions of ablation debris vs fused interplanetary dust to the influx of stony spherules is discussed, but as yet the question remains unanswered.  相似文献   

Characterization of sulfate ion in travertine     

Bokuichiro Takano  Yasuhiro Asano  Kunihiko Watanuki 《Contributions to Mineralogy and Petrology》1980,72(2):197-203

The mode of incorporation of sulfate ion in travertine was discussed on the basis of chemical compositions, i.r. and laser Raman spectra. These data strongly suggest that most of the sulfate ions in the calcitic travertine replace carbonate ions. This conclusion is in good harmony with the facts that calcite incorporates more sulfate ions than aragonite does and that the sulfate content of manganoan calcite decreases with increasing manganese content (Takano et al. 1977). Based on this conclusion, retarding effect of sulfate ion on the precipitation of calcite from solution was discussed.  相似文献   

Lead isotopes and age of Hawaiian lherzolite nodules     

Masana Morioka  Kunihiko Kigoshi 《Earth and Planetary Science Letters》1975,25(2):116-120

The reaction between enstatite (En_95.3Fs_4.7) and CaCO₃ has been studied at pressures between 23 and 77 kbars and at temperatures between 800° and 1400°C. At 1000°C enstatite and CaCO₃ react to form dolomite and diopside solid solutions at pressures below approximately 45 kbars and magnesite and diopside solid solutions at higher pressures. The curve for the reaction dolomite_ss + enstatite_ss ? magnesite_ss + diopside_ss lies between 40 to 45 kbars at 1000°C and between 45 and 50 kbars at 1200°C. It is very close to the graphite-diamond transition curve. These experimental results indicate that calcite (or aragonite) is unstable in the presence of enstatite, and that dolomite and magnesite are the stable carbonates at high pressures. The forsterite + aragonite assemblage is, however, stable to at least 80 kbars at 800°C. It is suggested that in the upper mantle where enstatite is present, dolomite is stable to depths of about 150 km and magnesite is stable at greater depths in the continental regions, assuming that the partial pressure of CO₂ is equal or close to the total pressure. It is also suggested that carbonate inclusions in pyroxene can be used as an indicator of the depth of their equilibration; dolomite inclusions in enstatite would be formed at depths shallower than 150 km and magnesite inclusions in diopside at greater depths. Eclogite and peridotite inclusions in kimberlite may be classified on this basis.  相似文献