Observations of nitric acid perturbations in the winter Arctic stratosphere: Evidence for PSC sedimentation     

Frank Arnold  Veit Bürger  Klaus Gollinger  Michael Roncossek  Johannes Schneider  Stefan Spreng 《Journal of Atmospheric Chemistry》1998,30(1):49-59

Gaseous nitric acid (HNO3) and hydrogene fluoride (HF) have been measured in the winter Arctic stratosphere using balloon- and aircraft-based Ion Molecule Reaction Mass Spectrometry (IMRMS) instruments. Strong HNO3 perturbations were found in 1993 and 1995 which may indicate nitrification around 11-13 km and denitrification around 20 km altitude. Most likely these perturbations were caused by sedimentation of HNO3 containing aerosols followed by aerosol evaporation at lower altitudes.  相似文献   

湖北省巴东栖霞组沉积成岩作用地球化学特征研究   总被引：8，自引：3，他引：5  

颜佳新  伍明  李方林  方念乔 《沉积学报》1998,16(4):78-83

在详细的沉积作用、成岩作用研究基础上,利用多元统计分析方法重点对湖北省巴东水布垭剖面栖霞组碳酸盐岩地球化学特征进行了分析。研究表明,该组碳酸盐岩中 CaO 、Al₂O₃ 、K₂O 、Fe₂O₃ 、P、Ba 和 Mn的含量主要与沉积环境或原岩岩性有关,地层中SiO₂、MgO 、Sr 和 Na 的含量主要与成岩作用有关。建立了栖霞组沉积成岩作用地球化学模式。该研究合理地解释了本组岩石特殊的地球化学特征,深化了对该组岩石形成环境,特别是成岩环境的认识,区分了沉积作用和成岩作用对该组岩石地球化学特征的影响,对合理地选取有关地球化学参数研究该组岩石及类似地层的沉积作用和成岩作用具参考价值。  相似文献   

辫状河现代沉积研究与相模式──中国永定河剖析   总被引：29，自引：5，他引：24  

廖保方  薛培华 《沉积学报》1998,16(1):34-39

永定河是一条多河型河流,自上而下,包括了辩状河→曲流河→分流网状河的河型空间转换。其间辫状河段可明显区分为两类亚型:即冲积扇区的高坡降辫状河和冲积平原区低坡降辫状河。二者在河流形态、沉积物特征等方面显示不同。而沉积作用机制和砂体沉积模式是近似的,二者均进行垂向加积作用,均发生五个级次的沉积再作用面,均发育三个级次类型的薄夹层:滞留层、落淤层、颗粒降纹层与颗粒流纹层。其中落淤层最具指相意义。在河道经常摆动迁移过程中,最终形成砂体广泛展布的“叠覆泛砂体”。这种辫状河沉积模式──“叠覆泛砂体”为油气储集提供了良好的储集空间和场所。  相似文献   

Hydrothermal sedimentation characteristics of the Dajiangping superlarge pyrite deposit, Yunfu, Guangdong   总被引：1，自引：1，他引：0  

陈多福  陈光谦等 《中国地球化学学报》1998,17(4):331-337

The Dajiangping pyrite deposit is hosted in a carbonate-clastic rock series which is characterized by a bioreef-chert suite in its middle part.Conformable lenses of various sizes constitute the orebodies which often branch transitionally into the surroundings.Syngenetic deformation fabrics can be observed in orebody NO.3.Orebody No.4 is composed almost entirely of massive pyrite,with conspicuous hydrothermal sedimentation and bacterium-alga features.The hydrothermal sedimentation origin is also reflected by simple chemistry of the ore (predominated by quartz and pyrite),the presence of U and Th,and the REE compositions of pyrite and ankerite.The ores are rich in organic matter and the difference in organic content between the banded ores and the massive ores is mainly owing to the difference in the clastic components they contain rather than to the subsequent processes of reworking .Co/Ni rations in the ore may reflect the temperature pattern during hydrothermal sedimentation.  相似文献   

中子活化技术在层序地层学中的应用   总被引：3，自引：0，他引：3  

周瑶琪  吴智平 《地学前缘》1998,5(1):143-149

中子活化分析是一种重要的核分析技术,具有灵敏度好、精密度和准确度高、多元素分析、免除试剂的空白、基体效应小、不损坏样品等优点,在地学研究领域具有广阔的应用前景。笔者将它应用于层序地层学的研究中。通过对地层中宇宙化学特征元素（如Ｃｏ,Ｉｒ等）及ＲＥＥ元素丰度值的测定,建立了一套计算海相地层的沉积速率、相对海平面变化、间断面的精细时间结构的定量计算方法,并成功地运用于贵州紫云海相地层的层序地层学研究,恢复了该地区晚二叠世具线性时标的相对海平面变化定量曲线。  相似文献   

秦岭旬阳盆地下古生界钠长石岩岩石学和地球化学特征   总被引：8，自引：1，他引：8       下载免费PDF全文

刘淑文  薛春纪李 强 朱经祥 王 涛 赵国斌 《中国地质》2005,32(3):424-433

热水沉积钠长石岩在南秦岭上古生界中颇具特点，与南秦岭众多的大型、超大型铅锌成矿关系密切。最近，在南秦岭旬阳盆地下古生界铅锌矿集区内的志留系梅子垭组地层中首次识别出一条近东西方向延伸长达10余千米的钠长石沉积岩带，与地层整合产出，渐变过渡，厚层块状、条带状、角砾状构造，均粒微-细晶结构、内碎屑结构；其化学成分以富含SiO2、Al2O3及Na2O为特征，富Fe、Mn，贫Co、Ni、Cu等微量元素；该钠长石岩的∑KEE、LKEE、HREE均较围岩偏低，具明显Eu亏损的特征。球粒陨石标准化配分曲线为右倾曲线。通过与秦岭泥盆纪热水沉积钠长石岩的岩相学及岩石化学对比，结合本区下古生界属于扬子北缘被动陆缘裂谷环境，初步认为这里下古生界钠长石岩可能属于热水沉积成因。  相似文献   

Mass movement-induced fold-and-thrust belt structures in unconsolidated sediments in Lake Lucerne (Switzerland)   总被引：2，自引：0，他引：2  

MICHAEL SCHNELLMANN  FLAVIO S. ANSELMETTI  DOMENICO GIARDINI†  JUDITH A. McKENZIE 《Sedimentology》2005,52(2):271-289

High-resolution seismic imaging and piston coring in Lake Lucerne, Switzerland, have revealed surprising deformation structures in flat-lying, unconsolidated sediment at the foot of subaqueous slopes. These deformation structures appear beneath wedges of massflow deposits and resemble fold-and-thrust belts with basal décollement surfaces. The deformation is interpreted as the result of gravity spreading induced by loading of the slope-adjacent lake floor during massflow deposition. This study investigated four earthquake-triggered lateral mass-movement deposits in Lake Lucerne affecting four sections of the lake floor with areas ranging from 0·25 to 6·5 km² in area. Up to 6 m thick sediment packages draping the subaqueous slopes slid along the acoustic basement. The resulting failure scars typically lie in water depths of >30 m on slopes characterized by downward steepening and inclinations of >10°. From the base-of-slope to several hundred metres out onto the flat plains, the wedges of massflow deposits overlie deeply (10–20 m) deformed basin-plain sediment characterized by soft sediment fold-and-thrust belts with arcuate strikes and pronounced frontal thrusts. The intensity of deformation decreases towards the more external parts of the massflow wedges. Beyond the frontal thrust, the overridden lake floor remains mostly undisturbed. Geometrical relationships between massflow deposits and the deformed basin-plain sediment indicate that deformation occurred mainly during massflow deposition. Gravity spreading induced by the successive collapse of the growing slope-adjacent massflow wedge is proposed as the driving mechanism for the deformation. The geometry of fjord-type lakes with sharp lower slope breaks favours the deposition of thick, basin-marginal massflow wedges, that effectively load and deform the underlying sediment. In the centre of the basins, the two largest massflow deposits described are directly overlain by thick contained (mega-)turbidites, interpreted as combined products of the suspension clouds set up by subaqueous mass movements and related tsunami and seiche waves.  相似文献   

Bar and dune development during a freshet: Fraser River Estuary, British Columbia, Canada     

P. V. VILLARD  M. CHURCH 《Sedimentology》2005,52(4):737-756

Bi-weekly multi-track sonar surveys collected along a 2-km reach of the estuarine South Arm of the Fraser River, British Columbia, Canada, during seasonal high flows document the initiation, development and interaction of dune and bar morphologies. Bedforms of several scales developed in well-delineated fields. Bedforms that appear to fit accepted equilibrium depth-scaling developed in the main channel during rising discharge when there was little local aggradation. During the rising stage, a bar also formed along the tidal shelf of the channel, migrated downstream and expanded into the main channel. Dunes that formed along the bar crest, a region of rapid deposition, lagged flow conditions and were larger than expected based on depth-scaling relations. The larger dunes developed simultaneously, although bar growth lagged dune development and was initially partially obscured by the more rapidly developing dune field. It appears that rapid deposition enhances dune development along the channel tidal shelf to dimensions larger than would be expected by simple depth-scaling rules. Smaller dunes that fit equilibrium depth-scaling relations re-established themselves throughout the study area during falling discharge when there was again little or no aggradation. Bed-material transport rates estimated from the migration rates of the large dunes suggest that, at high flows, the dunes transport the majority of the material found within the bar.  相似文献   

苏皖坡缕石粘土中蛋白石特征及其成因意义   总被引：1，自引：0，他引：1  

陈天虎  徐晓春  XU Hui-fang  岳书仓 《矿物学报》2005,25(1):81-88

TEM和XRD研究表明，在苏皖坡缕石粘土矿床的蛋白石坡缕石层中存在0pal-A和0pal-CT两种结构的蛋白石。蛋白石坡缕石层主要含坡缕石、opal-A、opal-CT，以及少量白云石和其它矿物，由富opal-A层和富opal-CT层互层组成，交互层的厚度在几个厘米左右。蛋白石坡缕石层中的矿物基本是自生矿物，从蒸发湖水中化学沉淀形成。矿物组成特征研究表明，蛋白石坡缕石层的矿物组分(Si、Mg、Al)来源于盆地周围玄武岩淋滤的浅层地下水。根据Opal-A和Opal-CT溶解度图解和城缕石、白云石形成物理化学条件图解，当湖水具有高浓度溶解SiO2和Mg^2 时，有利于opal-A和坡缕石形成，当湖水具有低浓度溶解SiO2时，有利于opal-CT结晶。因此，沉淀SiO2的结构状态取决于地下水补给的湖水溶解SiO2浓度。富opal-A和富opal-CT交互层的形成是古气候、古水文周期性变化的指示。富opal-CT层指示高地下水补给流入量，低蒸发量，湖水低盐度和溶解组分，代表湿润气候时期；而富opal-A层代表低地下水补给流入量，高蒸发量，高溶解组分浓度，代表干旱气候时期。  相似文献   

Blanket peat erosion and sediment yield in an upland reservoir catchment in the southern Pennines,UK     

D. E. Yeloff  J. C. Labadz  C. O. Hunt  D. L. Higgitt  I. D. L. Foster 《地球表面变化过程与地形》2005,30(6):717-733

This paper investigates temporal variations in fluxes of peat and other sediment in the catchment of March Haigh Reservoir, West Yorkshire. Long‐term estimates of sediment yield were derived from a study of reservoir sediments. Magnetic properties were used to correlate ten cores to a master profile dated using ²¹⁰Pb and ¹³⁷Cs. A ¹⁴C date suggests that most of the organic component of the sediment is allochthonous and derived from peat eroded from the catchment. Organic sediment yields suggest low catchment erosion rates between 1838 and 1963. Blanket peat erosion increased significantly after 1963, and peaked between 1976 and 1984. Estimates of total sediment yield range between 2 and 28 t km^?2 a^?1. These yields are significantly lower than those from some previous studies examining reservoir sedimentation in other blanket peat‐covered catchments. The low yield estimates may be due to relatively low rates of erosion in the basin, but may also be partly explained by maintenance of silt traps during the early life of the reservoir and removal of sediment by scouring. Sedimentation within the reservoir is spatially variable, and bathymetry and sediment source appear to be the dominant controls on sedimentation patterns within the reservoir. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献