The Upper Devonian Kellwasser event recorded in a regressive sequence from inner shelf to lagoonal pond,Catalan Coastal Ranges,Spain     

《Sedimentology》2018,65(6):2055-2087

This study, conducted in the Catalan Coastal Ranges, north‐east Spain, describes the Upper Devonian Kellwasser event in a shallowing‐upward sequence of black shales, siltstones and quartz arenites. This sequence was deposited in a progradational and regressive coastal system where the sedimentary environment evolved from the inner shelf to a lagoonal pond located landward of the shoreline. Three anomalous succeeding steps have been identified by geochemical analysis. The first one, detected on the inner shelf, was characterized by oxygen depletion and high organic productivity. The second, detected in the nearshore, was caused by hydrothermal activity occurring under normal oxic conditions. The third and most intense step was identified in the muds of the lagoonal pond and has been linked to strong anoxic conditions, elevated clastic input derived from changes in the weathering regime at the source area and moderate hydrothermal activity. The Kellwasser event is thus defined in the study area as stepwise and multi‐causal. This is the first time that the Kellwasser event has been identified in a sedimentary environment behind the shoreline. It is also the first time that it has been reported in the Catalan Coastal Ranges.  相似文献   

环塔里木盆地绿洲城市发展与水环境质量协调度     

孜比布拉·司马义  杨胜天  杨晓东  王蕾  肖合来提·巴义 《中国沙漠》2020,40(1):88-96

解决好新疆环塔里木盆地绿洲城市发展与水环境质量之间的关系，对"一带一路"倡议顺利实施及新疆社会稳定具有十分重要的作用。基于2004-2017年环塔里木盆地绿洲城市发展与水环境变化状况，构建城市发展与水环境质量的综合评价模型及二者的协调度模型，以探讨环塔里木盆地绿洲城市发展、水环境质量变化及二者的协调关系。结果表明：2004-2017年，（1）环塔里木盆地绿洲城市发展综合指数呈现出逐年稳定上升的趋势，经济发展和城镇空间规模扩大是环塔里木盆地绿洲城市发展的主要形式；（2）环塔里木盆地绿洲城市的水环境质量综合指数呈现出逐年降低的趋势，水环境质量形势严峻；（3）环塔里木盆地绿洲城市发展-水环境质量系统的协调度呈现倒U型的稳定发展趋势，但总体上两者的协调度较低，城市发展和水环境质量之间的矛盾日益突出。  相似文献   

莱州湾南岸潍河下游地区咸水入侵灾害成因及特征   总被引：8，自引：1，他引：7  

刘恩峰  张祖陆  沈吉  宋俊峰 《地球科学与环境学报》2004,26(3):78-82,87

通过对莱州湾南岸咸水入侵较严重地潍河下游地区晚更新世以来沉积特征及现代自然环境条件变化的分析，探讨了沉积相对咸水入侵产生及空间范围特征的环境机理。晚更新世以来的三次海平面升降变化造成了潍河下游地区海陆沉积环境交替，形成了巨厚的海陆交互相沉积层。海进时期，大面积的滨海平原被淹没，在近海平原洼地滞留的海水经过蒸发、浓缩变为卤水，成为咸水入侵的物源；海退后陆源碎屑在滨海地区沉积形成了巨厚的古河道砂层。20世纪70年代末期以来，随着对地下淡水的过度开采，淡咸水水头压力差减小．卤水通过古河道砂层快速南侵。通过对潍河下游地区100余个地质钻孔水化学连续监测资料分析，阐明了咸水入侵的特征，有针对性地提出了咸水入侵的防治措施。  相似文献   

平凉隐伏岩溶水环境同位素研究     

马致远  马蒂尔·亨德尔 《地球科学与环境学报》2003,25(4):60-66

地下水资源可持续利用的一个急待解决的重要问题,是对地下水补给和更新能力的评价.利用环境同位素技术研究地下水的补给和可更新性是当前较为新颖的方法之一.在西北干旱、半干旱的隐伏岩溶地区,地下水埋藏条件复杂,常规的地质勘探方法所能提供的水文地质信息有限,环境同位素方法在研究地下水的补给及可更新能力方面发挥了优势,可对传统方法进行补充和验证.其结果表明,研究区隐伏岩溶水形成较早,且有大量现代水的混入,平均混入量为54%.说明区内隐伏岩溶水的补给和更新能力较好.环境同位素分析结果还显示,大岔河隐伏岩溶水为一相对独立、半开放的水文地质单元,其补给来源部分为流域内大气降水、地表水的补给,部分为东南部三道沟岩溶地下水的补给;根据环境同位素EPM模型计算,地下水的滞留时间为36 a.地下水储存量为1.314×108 m3; 储水系数为7.29×10-3.这一结果与传统勘探方法的计算结果基本吻合,说明环境同位素方法的实用性.  相似文献   

Size-Flux Relation in Solar Active Regions     

O.V.Chumak 《中国天文和天体物理学报》2003,3(2):175-182

We present a study of the relationship between integral area and corresponding total magnetic flux for solar active regions. It is shown that some of these relationships are satisfied to simple power laws. Fractal examination showed that some of these power laws can not be justified inside the simple models of stationary magnetic flux tube aggregation. All magnetic fluxes and corresponding areas were calculated using the data measured with the Solar Magnetic Field Telescope of the Huairou Solar Observing Station in Beijing.  相似文献   

The depolarization properties of powerful extragalactic radio sources as a function of cosmic epoch     

J. A. Goodlet  C. R. Kaiser 《Monthly notices of the Royal Astronomical Society》2005,359(4):1456-1468

We use the observed polarization properties of a sample of 26 powerful radio galaxies and radio-loud quasars to constrain the conditions in the Faraday screens local to the sources. We adopt the cosmological redshift, low-frequency radio luminosity and physical size of the large-scale radio structures as our 'fundamental' parameters. We find no correlation of the radio spectral index with any of the fundamental parameters. The observed rotation measure is also independent of these parameters, suggesting that most of the Faraday rotation occurs in the Galactic foreground. The difference between the rotation measures of the two lobes of an individual source, as well as the dispersion of the rotation measure, shows significant correlations with the source redshift, but not with the radio luminosity or source size. This is evidence that the small-scale structure observed in the rotation measure is caused by a Faraday screen local to the sources. The observed asymmetries between the lobes of our sources show no significant trends with each other or other source properties. Finally, we show that the commonly used model for the depolarization of synchrotron radio emission by foreground Faraday screens is inconsistent with our observations. We apply alternative models to our data and show that they require a strong increase of the dispersion of the rotation measure inside the Faraday screens with cosmological redshift. Correcting our observations with these models for redshift effects, we find a strong correlation of the depolarization measure with redshift and a significantly weaker correlation with radio luminosity. We do not find any (anti-)correlation of depolarization measure with source size. All our results are consistent with a decrease in the order of the magnetic field structure of the Faraday screen local to the sources for increasing cosmological redshift.  相似文献   

Can the inner gap sparking take place in millisecond pulsars？     

Hong-Guang Wang  Guo-Jun Qiao  Ren-Xin XuDepartment of Astronomy  Peking University  Beijing   《中国天文和天体物理学报》2003,3(5):443-452

The inner vacuum gap model has become the foundation stone of most theories on pulsar radio emission. The fundamental picture of this model is the sparking, which was conjectured to be induced by magnetic absorption of background gamma photons. However, a question is, can the sparking be triggered in the millisecond pulsars (MSPs) with magnetic fields (B) only about 108 G? We investigate this problem by including the pair production above the inner gap. Under the assumption that the magnetic field is dipolar, our results show the background gamma-ray emission can not be the key factor that triggers the sparking, at least not in MSPs with B - 108 G, if the temperature in the polar cap region is only so high as is observed (< 4 × 106 K). Some other mechanisms are required.  相似文献   

Minimal Energy and Gravitation     

Corrado Massa 《Astrophysics and Space Science》2006,305(4):377-384

Quantum theory in Robertson – Walker spacetime suggests the existence of a minimal energy ε of the order of 10⁻⁴⁵ erg. Reasonable forms for ε give the expansion factor R=R(t)(t= the cosmic time) with no need of gravitational field equations.Einstein's theory should be modified in gravitational fields of strength less than ε c/ħ ∼ 10⁻⁸ cm/s² where c is the speed of light and ħ is the reduced Planck constant. The cosmological term λ is expected to decrease as the universe expands.In the Appendix, ε is derived from a big bang – big crunch Newtonian cosmology.  相似文献   

Chromospheric activity and unique solution of SZ Psc     

Young Woon Kang  Woo-Baik Lee  Ho-il Kim  Kyu-Dong Oh 《Monthly notices of the Royal Astronomical Society》2003,344(4):1227-1232

  相似文献   

Three Super Active Regions in the Descending Phase of Solar Cycle 23   总被引：2，自引：0，他引：2  

Hong-Qi Zhang  Xing-Ming Bao  Yin Zhang  Ji-Hong Liu  Shu-Dong Bao  Yuan-Yong Deng  Wei Li  Jie Chen  Jin-Ping Dun  Jiang-Tao Su  Juan Guo  Xiao-Fan Wang  Ke-Liang Hu  Gang-Hua Lin  Dong-Guang WangNational Astronomical Observatories  Chinese Academy of Sciences  Beijing   《中国天文和天体物理学报》2003,3(6):491-494

We analyze the magnetic configurations of three super active regions, NOAA 10484, 10486 and 10488, observed by the Huairou Multi-Channel Solar Telescope (MCST) from 2003 October 18 to November 4. Many energetic phenomena, such as flares (including a X-28 flare) and coronal mass ejections (CMEs), occurred during this period. We think that strong shear and fast emergence of magnetic flux are the main causes of these events. The question is also of great interest why these dramatic eruptions occurred so close together in the descending phase of the solar cycle.  相似文献