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排序方式: 共有341条查询结果,搜索用时 15 毫秒
121.
HSU WeiBiao 《中国科学D辑(英文版)》2007,50(6):886-896
Numerous round to oblate opaque assemblages (OAs) are found in chondrules and matrix of the Ningqiang carbonaceous chondrite. They are mainly composed of Ni-rich metal,magnetite,Fe,Ni-sulfides,with minor amounts of phosphate,phosphoran-olivine,pyroxene and trace amounts of nano-sized platinum-group metal alloys. The mineralogy of Ningqiang OAs is very similar to that of OAs previously reported in Ca,Al-rich inclusions of CV chondrites. Being a rare mineral phase in nature,phosphoran-olivine is thought to form by nonequilibrium reactions between P-bearing molten metal and olivine crystals during rapid cooling. Its occurrence in Ningqiang OAs indicates that the precursor of OAs was locally produced during chondrule formation,rather than directly condensed from the solar nebula as previously thought. The petrographic and mineralogical characteristics of Ningqiang OAs reveal that OAs formed by low temperature alterations of pre-existing homogeneous alloys within chondrules on a planetary body. 相似文献
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花岗岩构造岩浆组合 总被引:5,自引:0,他引:5
花岗岩的构造岩浆组合主要反映花岗岩的岩浆类型与大地构造环境之间的成因联系。从全球范围来看,结合中国的地质实际,花岗岩的构造岩浆组合可以区分为5种主要类型:(1) 洋壳俯冲消减型,如太平洋两岸的大陆边缘;(2)陆—陆碰撞型,如喜马拉雅—冈底斯碰撞造山带;(3)陆缘伸展型,如中国东南部伸展型大陆边缘、北美西部盆岭省;(4)陆内断裂拗陷型,如长江中下游断裂拗陷、钱塘江—信江断裂拗陷;(5)裂谷型,如东非裂谷、攀西裂谷。通过钙碱指数(CA)和铝饱和指数(ASI)的计算,可以大体获知花岗岩的岩浆类型。造山带花岗岩的时空演变规律是:俯冲型→碰撞型→伸展型。亦可表述为:前碰撞花岗岩→同碰撞花岗岩→后碰撞花岗岩。但不能一概而论,只有在对不同造山带花岗岩的具体情况进行认真分析对比之后,才能对花岗岩的构造岩浆组合作出判断。 相似文献
125.
对南海北部大洋钻探184航次1146站晚上新世以来底栖有孔虫属种组合的Q型因子分析, 发现底栖有孔虫组合以2.1Ma, 1.5Ma和0.7Ma为界, 分为Stilostomella-Globocassidulina subglobosa-Nodogenerina, Bulimina alazanensis, Uvigerina perigrina和Melonis barleeanus-Globobulimina affinis-Bulimina aculeata4个组合.结合底层水溶解氧含量和浮游、底栖有孔虫碳同位素分析, 认为底栖有孔虫组合的变化是南海底层水影响所致, 以及南海北部表层和底层海水营养盐含量变化的共同结果. 相似文献
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D. Zúñiga F. Alonso-PérezC.G. Castro B. ArbonesF.G. Figueiras 《Continental Shelf Research》2011,31(5):414-424
The aim of this study is to explore the contribution of living phytoplankton carbon to vertical fluxes in a coastal upwelling system as a key piece to understand the coupling between primary production in the photic layer and the transfer mechanisms of the organic material from the photic zone. Between April 2004 and January 2005, five campaigns were carried out in the Ría de Vigo (NW Iberian Peninsula) covering the most representative oceanographic conditions for this region. Measurements of particulate organic carbon (POC), chlorophyll-a (chl a), phaeopigments (phaeo), and identification of phytoplankton species were performed on the water column samples and on the organic material collected in sediment traps.The POC fluxes measured by the sediment traps presented no seasonal variation along the studied period ranging around a mean annual value of 1085±365 mg m−2 d−1, in the upper range of the previously reported values for other coastal systems. The fact that higher POC fluxes were registered during autumn and winter, when primary production rates were at their minimum levels points to a dominant contribution of organic carbon from resuspended sediments on the trap collected material. On the contrary, fluxes of living phytoplankton carbon (Cphyto) and chl a clearly presented a seasonal trend with maximum values during summer upwelling (546 mg m−2 d−1 and 22 mg chl a m−2 d−1, respectively) and minimum values during winter (22 mg m−2 d−1 and 0.1 mg chl a m−2 d−1, respectively). The contribution of Cphyto to the vertical flux of POC ranged between 2% and 49% in response to the pelagic phytoplankton community structure. Higher values of Cphyto fluxes were registered under upwelling conditions which favour the dominance of large chain-forming diatoms (Asterionellopsis glacialis and Detonula pumila) that were rapidly transferred to the sediments. By contrast, Cphyto fluxes decreased during the summer stratification associated with a pelagic phytoplankton community dominated by single-cell diatoms and flagellates. Minimal Cphyto fluxes were observed during the winter mixing conditions, when the presence of the benthic specie Paralia sulcata in the water column also points toward strong sediment resuspension. 相似文献
128.
Daniel Peyrot Fernando Barroso-Barcenilla Eduardo BarrónMaría José Comas-Rengifo 《Cretaceous Research》2011,32(4):504-526
The palynological assemblages from three Cenomanian-Turonian sections from the Castilian Platform are described. The 49 levels analysed yielded a well-diversified palynological content including dinoflagellate cysts, acritarchs, prasinophytes and miospores. The comparison of the terrestrial and marine assemblages from these three sections reveals significant differences that are mainly related to their relative palaeogeographical locations. The quantitative study performed on dinocyst assemblages suggests an association interpreted as inner neritic including Xenascus ceratioides, Cribroperidinium exilicristatum, Canningia reticulata and Kallosphaeridium? ringnesiorum. On the contrary, the group inferred to show outer neritic preferences is integrated by Palaeohystrichophora infusorioides, Spiniferites spp., Odontochitina spp., Trichodinium castanea and Impletosphaeridium polytrichum. In the Castilian Platform, the Cenomanian-Turonian Boundary Event (CTBE) may be manifested by a higher proportion of Cyclonephelium spp. in the distal dinocyst assemblages. 相似文献
129.
江苏南通市四甲镇全新世以来有孔虫动物群的发现及其地质意义 总被引:1,自引:1,他引:0
对江苏省南通市四甲镇CSJA6钻孔上部近43m的沉积物岩心进行了沉积学、年代学研究和有孔虫鉴定及组合划分,发现41属77种(含8个未定种)有孔虫。根据有孔虫动物群的垂直分布特征与AMS14C年龄,初步建立了时间被部分标定的全新世有孔虫化石组合,自上而下为Ammonia beccarii vars.-Cribrononion subincertum Asano组合、Ammonia beccarii vars.-Globigerinira glutinata组合和Ammonia beccarii vars.-Elphidium magellanicum组合。组合2、3带的时间界线约为8.1ka cal BP,组合3带的下界至少是10ka cal BP。这3个组合带的特征与以珠海、上海地区为代表的中国东部沿海平原全新世有孔虫组合相似。若将前人全新世海侵的14C年龄做进一步的校正,并结合本文钻孔研究成果可初步推测,在8.5~8ka cal BP时长江三角洲地区达到最大海侵,形成以镇江、扬州为顶点的长江巨大河口湾。 相似文献
130.
湿地在全球环境变化中扮演着十分重要的角色,湿地表土中的植硅体分析是恢复第四纪古环境的重要途径。文中选取长白山区的桦南到哈尼一线的6处湿地表土,并采用PCA和CA分析植硅体组合的环境指示意义,结果显示:温度因子是造成长白山不同湿地表土植硅体组合差异的第1环境因子,且植硅体的种类和含量与采样点上覆植被、湿度与海拔等环境条件都存在相关性。结合方差分析和植硅体大小变化趋势分析曲线可以看出,不同表土中符合方差分析条件的植硅体类型的大小随着温度的升高而增大。总体来看,长白山区6处湿地中,植硅体类型基本相同,但温暖指数和植硅体的大小差异较显著,说明植硅体大小及其组合对温度都有较敏感的响应。 相似文献