Younger Dryas to mid-Holocene environmental history of the lowlands of NW Transylvania, Romania   总被引：2，自引：1，他引：2  

Angelica Feurdean  Volker Mosbrugger  Bogdan P. Onac  Victor Polyak  Daniel Veres   《Quaternary Research》2007,68(3):364-378

Pollen, micro-charcoal and total carbon analyses on sediments from the Turbuta palaeolake, in the Transylvanian Basin of NW Romania, reveal Younger Dryas to mid-Holocene environmental changes. The chronostratigraphy relies on AMS ¹⁴C measurements on organic matter and U/Th TIMS datings of snail shells. Results indicate the presence of Pinus and Betula open woodlands with small populations of Picea, Ulmus, Alnus and Salix before 12,000 cal yr BP. A fairly abrupt replacement of Pinus and Betula by Ulmus-dominated woodlands at ca. 11,900 cal. yr BP likely represents competition effects of vegetation driven by climate warming at the onset of the Holocene. By 11,000 cal yr BP, the woodlands were increasingly diverse and dense with the expansion of Quercus, Fraxinus and Tilia, the establishment of Corylus and the decline of upland herbaceous and shrubs taxa. The marked expansion of Quercus accompanied by Tilia between 10,500 and 8000 cal yr BP could be the result of low effective moisture associated with both low elevation of the site and with regional change towards a drier climate. At 10,000 cal yr BP, Corylus spread across the region, and by 8000 cal yr BP it replaced Quercus as a dominant forest constituent, with only little representation of Picea abies. Carpinus became established around 5500 cal yr BP, but it was only a minor constituent in local woodlands until ca. 5000 cal yr BP. Results from this study also indicate that the woodlands in the lowlands of Turbuta were never closed.  相似文献   

利用FY-2C静止卫星资料反演云粒子有效半径的试验研究   总被引：5，自引：0，他引：5  

陈英英  周毓荃  毛节泰  杨军 《气象》2007,33(4):29-34

为充分发挥FY-2C静止卫星在人工影响天气和气候领域的重要作用，基于SBDART辐射传输模式，利用该卫星通道4（3．5～4．0μm）的探测数据，反演了云粒子有效半径，并与TERRA上MODIS的相应产品做了比较。结果表明，FY-2C和MODIS资料能一致地反映云粒子有效半径分布的主要特征，但反演的粒子大小存在差异。反演算法、卫星分辨率及选取通道的不同可能是造成两种资料间差异的主要原因。  相似文献   

FY-2C积雪判识方法研究   总被引：1，自引：1，他引：1  

李三妹  闫华  刘诚 《遥感学报》2007,11(3):406-413

介绍了利用FY-2C资料进行积雪判识的原理,在阈值法基础上的辅助因子函数积雪判识方法以及相应的FY-2C积雪判识结果精度验证分析等。一般较为常用的卫星遥感积雪判识方法为简单阈值法,由于其带有一定的随机性,很难客观反映下垫面条件差异对阈值选取的影响。以阈值法为基础,将所使用的主要变量以函数形式表达,以海拔高度、地理位置、季节、土地覆盖类型等作为阈值函数的变量,通过大量采样建立起多种阈值函数,从而实现随时空特点变化的阈值实时计算。该方法用于FY-2C积雪判识,较好地解决了FY-2C全圆盘范围内广大区域不同下垫面类型下的实时积雪监测。通过与NOAA-17人机交互积雪判识结果对比分析,该方法的积雪判识精度可达85%左右。  相似文献   

Genesis of the Changba–Lijiagou Giant Pb-Zn Deposit, West Qinling, Central China: Constraints from S-Pb-C-O isotopes     

WEI Ran  WANG Yitian  MAO Jingwen  HU Qiaoqing  QIN Siting  LIU Shengyou  YE Dejin  YUAN Qunhu  DOU Ping 《《地质学报》英文版》2020,94(4):884-900

The extensive Changba-Lijiagou Pb-Zn deposit is located in the north of the Xihe–Chengxian ore cluster in West Qinling. The ore bodies are mainly hosted in the marble, dolomitic marble and biotite-calcite-quartz schist of the Middle Devonian Anjiacha Formation, and are structurally controlled by the fault and anticline. The ore-forming process can be divided into three main stages, based on field geological features and mineral assemblages. The mineral assemblages of hydrothermal stage I are pale-yellow coarse grain, low Fe sphalerite, pyrite with pits, barite and biotite. The mineral assemblages of hydrothermal stage II are black-brown cryptocrystalline, high Fe shalerite, pyrite without pits, marcasite or arsenopyrite replace the pyrite with pits, K-feldspar. The features of hydrothermal stage III are calcite-quartz-sulfide vein cutting the laminated, banded ore body. Forty-two sulfur isotope analyses, twenty-five lead isotope analyses and nineteen carbon and oxygen isotope analyses were determined on sphalerite, pyrite, galena and calcite. The δ34 S values of stage I(20.3 to 29.0‰) are consistent with the δ34 S of sulfate(barite) in the stratum. Combined with geological feature, inclusion characteristics and EPMA data, we propose that TSR has played a key role in the formation of the sulfides in stage I. The δ34 S values of stage II sphalerite and pyrite(15.1 to 23.0‰) are between sulfides in the host rock, magmatic sulfur and the sulfate(barite) in the stratum. This result suggests that multiple S reservoirs were the sources for S2-in stage II. The δ34 S values of stage III(13.1 to 22‰) combined with the structure of the geological and mineral features suggest a magmatic hydrothermal origin of the mineralization. The lead isotope compositions of the sulfides have 206 Pb/204 Pb ranging from 17.9480 to 17.9782, 207 Pb/204 Pb ranging from 15.611 to 15.622, and 208 Pb/204 Pb ranging from 38.1368 to 38.1691 in the three ore-forming stages. The narrow and symmetric distributions of the lead isotope values reflect homogenization of granite and mantle sources before the Pb-Zn mineralization. The δ13 CPDB and δ18 OSMOW values of stage I range from-0.1 to 2.4‰ and from 18.8 to 21.7‰. The values and inclusion data indicate that the source of fluids in stage I was the dissolution of marine carbonate. The δ13 CPDB and δ18 OSMOW values of stage II range from-4 to 1‰ and from 12.3 to 20.3‰, suggesting multiple C-O reservoirs in the Changba deposit and the addition of mantle-source fluid to the system. The values in stage III are-3.1‰ and 19.7‰, respectively. We infer that the process of mineralization involved evaporitic salt and sedimentary organic-bearing units interacting through thermochemical sulfate reduction through the isotopic, mineralogy and inclusion evidences. Subsequently, the geology feature, mineral assemblages, EPMA data and isotopic values support the conclusion that the ore-forming hydrothermal fluids were mixed with magmatic hydrothermal fluids and forming the massive dark sphalerite, then yielding the calcite-quartz-sulfide vein ore type at the last stage. The genesis of this ore deposit was epigenetic rather than the previously-proposed sedimentary-exhalative(SEDEX) type.  相似文献   

Quantitative Morphology Of C/1995 O1 (Hale–Bopp) In February – April 1997     

Vanscheidt  R.  Bleul  H.  Manthey  E.  Jütte  M.  Pohlen  M.  Schmidtobreick  L.  Altmann  M.  Dieball  A.  Geffert  M.  Sanner  J.  Notni  P.  Schmoll  J. 《Earth, Moon, and Planets》1998,81(3):223-231

Extensive widefield CCD direct imaging of C/1995 O1 (Hale-Bopp) at UBVRI was carried out at Hoher List Observatory with the 1.06 m telescope (field of view 20′ × 20′) and at Potsdam Observatory with the 0.70 m telescope (field of view 8′ × 8′). The corresponding spatial resolution is 850–1000 km pix^-1and 525–590 km pix^-1, respectively. The data covers 25 nights from February 20 to April 21, 1997. In order to quantify the various features in the apparent inner coma we introduce a new tomographic method that minimizes the morphological bias caused by image processing. The tomographic analysis leads to quantitative maps refering to the position and intensity of the dust ejections for each image frame. Variability and periodicity within the inner coma can be thoroughly deduced due to various sets of consecutive nights in the observation period mentioned above. The results are compared with applications of adaptive Laplace filtering. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

激光法气相合成纳米Si/C/N复相粉体     

赵东林  潘正伟  周万城 《地球科学与环境学报》1998,20(4):20

用大功率５ｋＷＣＯ２激光器为能源,以六甲基二硅胺烷［（ＣＨ３）３Ｓｉ］２ＮＨ（简称ＨＭＤＳ）和ＮＨ３为原料,合成纳米非晶Ｓｉ／Ｃ／Ｎ复相粉体。研究了ＨＭＤＳ流量和ＮＨ３对纳米复相粉体组成的影响。ＮＨ３的加入可以大幅度降低纳米复相粉体的碳含量,提高氮含量。Ｓｉ／Ｃ／Ｎ纳米复相粉体的粒径分布范围为１０～５０ｎｍ,为非晶态。  相似文献   

中国东部新生代碱性玄武岩中的流体组成及其碳,氧同位素地球化学特征   总被引：16，自引：2，他引：14  

张铭杰  王先彬 《地球化学》1998,27(5):452-457

利用热分解质谱法测定了中国东部新生代碱性玄武岩中流体挥发分的组成,并对不同温度段释放出的ＣＯ２气体测定了Ｃ,Ｏ同位素值,流体组成和ＣＯ２的Ｃ,Ｏ同位素值表明中国东部上地幔源区的不均一性,与其中所含幔源岩捕体相比,碱性玄武岩浆发育在相对氧化的环境中,并有外来流体组分的加入。  相似文献   

直流电法在水文地质勘查中的应用研究     

张玉池 《矿产与地质》1998,12(6):421-426

直流电法主要有电阻率法（联合剖面法和电测深法）和充电法,广泛应用于工程地质和水文地质勘察中,如地基勘察,水库涌水处理,矿山岩溶水测量等。直流电法能有效地圈定含水体的位置,确定其产状,特别是选择的方法组合应用效果更佳,为工程水文地质提供准确的资料。  相似文献   

C_(60)研究现状及前景   总被引：1，自引：0，他引：1  

杨翔  李嘉 《地学前缘》1998,5(1):163-170

碳除了具有传统观念上的石墨和金刚石两种同素异形体外,近年来人们又发现了第三种同素异形体———Ｃ６０。Ｃ６０以其独特的类似足球状的结构及性能,吸引了各国的科学家,对Ｃ６０的研究在全世界范围内如火如荼地开展起来。笔者在总结Ｃ６０的合成技术、分子结构与性能的基础上,探索了Ｃ６０作为一种新型材料所具有的应用潜力;回顾了从Ｃ６０发现至今十多年的研究历程,并首次将Ｃ６０的研究过程分成三个阶段,即起步阶段（１９８５年～１９９０年）、起飞阶段（１９９１年～１９９３年）和成熟阶段（１９９４年以后）;预测了Ｃ６０及其化合物的应用性研究将成为今后研究的重点和热点。最后,对当前Ｃ６０研究中存在的问题和难点进行了讨论。  相似文献   

Dating of post-glacial landforms in the central howgills     

A. M. Harvey  F. Oldfield  A. F. Baron  G. W. Pearson 《地球表面变化过程与地形》1981,6(5):401-412

Little is known of Holocene landform development in Upland Britain. This paper describes a site at Middle Langdale in the Howgill Fells of Cumbria where large, but now stabilized and inactive gullies cut through periglacial material. At the base of the gullies large debris cones have buried earlier alluvial sediments on the valley floor. On these sediments and buried by the debris cones is a well-developed organic soil from which two ¹⁴C dates have been obtained in an attempt to estimate the age range of the soil. These dates range from 2580±55 years BP for the fine particulate fraction from the base of the organic horizon to 940±95 years BP for fossil rootlets from the uppermost organic layer, immediately below the overlying debris cones. The pollen evidence suggests that the valley floor site was initially dominated by alder carr and later by a Juncus marsh with birch, alder and hazel nearby. The pollen, from the surrounding upland area suggests woodland on the valley sides, dominated by oak and elm that was later replaced by a more open environment rich in heath species and in which disturbed ground species were present. The magnetic evidence indicates a stable local environment during soil formation but shows a sudden inwash of unweathered debris at the top of the buried soil. The evidence suggests that the valley floor was geomorphologically stable throughout the period of soil formation, although there was a local change in valley floor vegetation and a reduction of woodland cover on the valley sides at sometime during the period. The evidence then points to major geomorphological changes; a wave of soil erosion, gully development and debris cone deposition, perhaps following the Scandinavian introduction of sheep farming in the tenth century A.D.  相似文献