生物硅的生成与溶解速率的研究——以胶州湾为例   总被引：1，自引：0，他引：1  

刘素美  Pall Tréguer  张经 《中国海洋大学学报(自然科学版)》2008,38(5)

营养盐的含量与元素间的比值直接控制着生态系统的生产力和浮游植物的种类组成.近岸海区硅藻可占初级生产的75%,但其生长速率受Si(OH)4含量的限制.胶州湾浮游植物的物种组成以硅藻为主.用29Si同位素示踪培养方法,采用四极杆质谱同位素稀释技术同时测定了胶州湾硅的生成速率与溶解速率.胶州湾生物硅(BSi)的含量为0.90～1.14 μmol/L,岩成硅(LSi)的含量为46.3～52.3 μmol/L.岩成硅是生物硅的约50倍.胶州湾BSi的含量处于世界近岸海区的低值范围,LSi的含量与LSi/BSi的比值均处于高值区.BSi的绝对生成速率为4～6 nmol/L*d,比生成速率为6～17/d.BSi的绝对溶解速率为<9 nmol/d,比溶解速率为<23/d.进一步开展胶州湾不同季节水体中BSi的生成速率与溶解速率的研究,是深入认识海湾浮游植物生长限制及其资源可持续利用的基础.  相似文献   

The Mesoproterozoic in the Nordic countries     

Bernard Bingen Jenny Andersson Ulf Soederlund Charlotte Moeller 《《幕》》2008,31(1):29-34

During the Mesoproterozoic, central Fennoscandia and Laurentia （Greenland） were characterized by a weakly extensional stress regime, as evident from episodic rapakivi granites, dolerite dykes, continental rift intrusives, sandstone basins and continental flood basalts. Along the southwestern active margin of Fennoscandia, the 1.64-1.52 Ga Gothian and 1.52-1.48 Ga Telemarkian accretionary events resulted in oceanwards continental growth. The 1.47-1.42 Ga Hallandian- Danopolonian event included high-grade metamorphism and granite magmatism in southern Fennoscandia. The pre-Sveconorwegian 1.34-1.14 Ga period is characterized by bimodal magmatism associated with sedimentation, possibly reflecting transcurrent tectonics. The Sveconorwegian orogeny involved polyphase imbrication of terranes between 1.14 and 0.97 Ga, as a result of a collision between Baltica and another major plate, followed by relaxation and post-collisional magmatism between 0. 96 and 0. 90 Ga. Recent geologic data support classical models restoring the Sveconorwegian belt directly to the east of the Grenville belt of Laurentia at 1.0 Ga. Fragments of Paleo-to Mesoproterozoic crust showing late Grenvillian-Sveconorwegian （1.00-0.92 Ga） magmatism and/or metamorphism are exposed in several tectonic levels in the Caledonides of Scandinavia, Svalbard and East Greenland, on both sides of the inferred Iapetus suture. Linking these fragments into a coherent late-Grenvillian tectonic model, however, require additional study.  相似文献   

Reversing buoyancy in turbidity currents: developing a hypothesis for flow transformation and for deposit facies and architecture     

David Pritchard  Charlotte Gladstone   《Marine and Petroleum Geology》2009,26(10):1997

A turbidity current that contains fresher or otherwise less dense water than its surroundings may initially be denser than the ambient and propagate as a bottom-hugging flow, but later reverse in buoyancy as its bulk density decreases through sedimentation to become lower than that of the ambient seawater. It is proposed that this reversal in buoyancy may be a significant mechanism controlling the structure and facies of turbiditic deposits. Buoyancy reversal followed by lofting may directly affect the relative distribution of fine and coarse material in the deposit, while buoyancy reversal itself may mediate the transformation between dilute and highly-concentrated suspension flows, particularly in distal regions, and thus lead to the formation of complex turbiditic beds: in particular, the generation of distal co-genetic debrites may be expected. Similar transformations occur within dilute pyroclastic density currents, where a mobile, basal concentrated flow, termed a surge-derived pyroclastic flow, develops through rapid sedimentation from the suspended load of the overlying surge. The physical mechanisms involved in these processes are discussed, leading to the proposal of some associated facies models; these are compared with field data from the Northern Apennines, with some striking similarities being noted as well as some differences. On the basis of this discussion, some directions are suggested for future experimental and modelling work on the topic.  相似文献   

The origin of shoshonites: new insights from the Tertiary high-potassium intrusions of eastern Tibet   总被引：1，自引：0，他引：1  

Ian?H.?CampbellEmail author  Aleksandr?S.?Stepanov  Hua-Ying?Liang  Charlotte?M.?Allen  Marc?D.?Norman  Yu-Qiang?Zhang  Ying-Wen?Xie 《Contributions to Mineralogy and Petrology》2014,167(3):983

The shoshonitic intrusions of eastern Tibet, which range in age from 33 to 41 Ma and in composition from ultramafic (SiO₂ = 42 %) to felsic (SiO₂ = 74 %), were produced during the collision of India with Eurasia. The mafic and ultramafic members of the suite are characterized by phenocrysts of phlogopite, olivine and clinopyroxene, low SiO₂, high MgO and Mg/Fe ratios, and olivine forsterite contents of Fo₈₇ to Fo₉₃, indicative of equilibrium with mantle olivine and orthopyroxene. Direct melting of the mantle, on the other hand, could not have produced the felsic members. They have a phenocryst assemblage of plagioclase, amphibole and quartz, high SiO₂ and low MgO, with Mg/Fe ratios well below the values expected for a melt in equilibrium with the mantle. Furthermore, the lack of decrease in Cr with increasing SiO₂ and decreasing MgO from ultramafic to felsic rocks precludes the possibility that the felsic members were derived by fractional crystallization from the mafic members. Similarly, magma mixing, crustal contamination and crystal accumulation can be excluded as important processes. Yet all members of the suite share similar incompatible element and radiogenic isotope ratios, which suggests a common origin and source. We propose that melting for all members of the shoshonite suite was initiated in continental crust that was thrust into the upper mantle at various points along the transpressional Red River-Ailao Shan-Batang-Lijiang fault system. The melt formed by high-degree, fluid-absent melting reactions at high-T and high-P and at the expense of biotite and phengite. The melts acquired their high concentrations of incompatible elements as a consequence of the complete dissolution of pre-existing accessory minerals. The melts produced were quartz-saturated and reacted with the overlying mantle to produce garnet and pyroxene during their ascent. The felsic magmas reacted little with the adjacent mantle and preserved the essential features of their original chemistry, including their high SiO₂, low Ni, Cr and MgO contents, and low Mg/Fe ratio, whereas the mafic and ultramafic magmas are the result of extensive reaction with the mantle. Although the mafic magmas preserved the incompatible element and radiogenic isotope ratios of their crustal source, buffering by olivine and orthopyroxene extensively modified their MgO, Ni, Cr, SiO₂ contents and Mg/Fe ratio to values dictated by equilibrium with the mantle.  相似文献   

The Tarim picrite–basalt–rhyolite suite, a Permian flood basalt from northwest China with contrasting rhyolites produced by fractional crystallization and anatexis     

Wei Tian  Ian H. Campbell  Charlotte M. Allen  Ping Guan  Wenqing Pan  Mimi Chen  Hongjiao Yu  Wenping Zhu 《Contributions to Mineralogy and Petrology》2010,160(3):407-425

We report major and trace element composition, Sr–Nd isotopic and seismological data for a picrite–basalt–rhyolite suite from the northern Tarim uplift (NTU), northwest China. The samples were recovered from 13 boreholes at depths between 5,166 and 6,333 m. The picritic samples have high MgO (14.5–16.8 wt%, volatiles included) enriched in incompatible element and have high ⁸⁷Sr/⁸⁶Sr and low ¹⁴³Nd/¹⁴⁴Nd isotopic ratios (εNd (t) = −5.3; Sr_i = 0.707), resembling the Karoo high-Ti picrites. All the basaltic samples are enriched in TiO₂ (2.1–3.2 wt%, volatiles free), have high FeOt abundances (11.27–15.75 wt%, volatiles free), are enriched in incompatible elements and have high Sr and low Nd isotopic ratios (Sr_i = 0.7049–0.7065; εNd (t) = −4.1 to −0.4). High Nb/La ratios (0.91–1.34) of basalts attest that they are mantle-derived magma with negligible crustal contamination. The rhyolite samples can be subdivided into two coeval groups with overlapping U–Pb zircon ages between 291 ± 4 and 272 ± 2 Ma. Group 1 rhyolites are enriched in Nb and Ta, have similar Nb/La, Nb/U, and Sr–Nd isotopic compositions to the associated basalts, implying that they are formed by fractional crystallization of the basalts. Group 2 rhyolites are depleted in Nb and Ta, have low Nb/La ratios, and have very high Sr and low Nd isotopic ratios, implying that crustal materials have been extensively, if not exclusively, involved in their source. The picrite–basalt–rhyolite suite from the NTU, together with Permian volcanic rocks from elsewhere Tarim basin, constitute a Large Igneous Province (LIP) that is characterized by large areal extent, rapid eruption, OIB-type chemical composition, and eruption of high temperature picritic magma. The Early Permian magmatism, which covered an area >300,000 km², is therefore named the Tarim Flood Basalt.  相似文献   

Two cycles of voluminous pyroclastic volcanism and sedimentation related to episodic granite emplacement during the late Archean: Eastern Yilgarn Craton,Western Australia     

Richard J. Squire  Charlotte M. Allen  Ray A.F. Cas  Ian H. Campbell  Richard S. Blewett  Alexander A. Nemchin 《Precambrian Research》2010

The thick piles of late-Archean volcaniclastic sedimentary successions that overlie the voluminous greenstone units of the eastern Yilgarn Craton, Western Australia, record the important transition from the cessation in mafic-ultramafic volcanism to cratonisation between about 2690 and 2655 Ma. Unfortunately, an inability to clearly subdivide the superficially similar sedimentary successions and correlate them between the various geological terranes and domains of the eastern Yilgarn Craton has led to uncertainty about the timing and nature of the region's palaeogeographic and palaeotectonic evolution. Here, we present the results of some 2025 U–Pb laser-ablation-ICP-MS analyses and 323 Sensitive High-Resolution Ion Microprobe (SHRIMP) analyses of detrital zircons from 14 late-Archean felsic clastic successions of the eastern Yilgarn Craton, which have enabled correlation of clastic successions. The results of our data, together with those compiled from previous studies, show that the post-greenstone sedimentary successions include two major cycles that both commenced with voluminous pyroclastic volcanism and ended with widespread exhumation and erosion associated with granite emplacement. Cycle One commences with an influx of rapidly reworked feldspar-rich pyroclastic debris. These units, here-named the Early Black Flag Group, are dominated by a single population of detrital zircons with an average age of 2690–2680 Ma. Thick (up to 2 km) dolerite bodies, such as the Golden Mile Dolerite, intrude the upper parts of the Early Black Flag Group at about 2680 Ma. Incipient development of large granite domes during Cycle One created extensional basins predominantly near their southeastern and northwestern margins (e.g., St Ives, Wallaby, Kanowna Belle and Agnew), into which the Early Black Flag Group and overlying coarse mafic conglomerate facies of the Late Black Flag Group were deposited. The clast compositions and detrital-zircon ages of the late Black Flag Group detritus match closely the nearby and/or stratigraphically underlying successions, thus suggesting relatively local provenance. Cycle Two involved a similar progression to that observed in Cycle One, but the age and composition of the detritus were notably different. Deposition of rapidly reworked quartz-rich pyroclastic deposits dominated by a single detrital-zircon age population of 2670–2660 Ma heralded the beginning of Cycle Two. These coarse-grained quartz-rich units, are name here the Early Merougil Group. The mean ages of the detrital zircons from the Early Merougil Group match closely the age of the peak in high-Ca (quartz-rich) granite magmatism in the Yilgarn Craton and thus probably represent the surface expression of the same event. Successions of the Late Merougil Group are dominated by coarse felsic conglomerate with abundant volcanic quartz. Although the detrital zircons in these successions have a broad spread of age, the principal sub-populations have ages of about 2665 Ma and thus match closely those of the Early Merougil Group. These successions occur most commonly at the northwestern and southeastern margins of the granite batholiths and thus are interpreted to represent resedimented units dominted by the stratigraphically underlying packages of the Early Merougil Group. The Kurrawang Group is the youngest sedimentary units identified in this study and is dominated by polymictic conglomerate with clasts of banded iron formation (BIF), granite and quartzite near the base and quartz-rich sandstone units containing detrital zircons aged up to 3500 Ma near the top. These units record provenance from deeper and/or more-distal sources. We suggest here that the principal driver for the major episodes of volcanism, sedimentation and deformation associated with basin development was the progressive emplacement of large granite batholiths. This interpretation has important implication for palaeogeographic and palaeotectonic evolution of all late-Archean terranes around the world.  相似文献   

Scale-dependent physical and geoacoustic property variability of shallow-water carbonate sediments from the Dry Tortugas, Florida     

Kevin P. Stephens  Peter Fleischer  Dawn Lavoie  Charlotte Brunner 《Geo-Marine Letters》1997,17(4):299-305

 Spatial variability of shallow-water carbonate sediments near Dry Tortugas, Florida, is scale-dependent. Wet bulk density, grain density, porosity, compressional wave velocity, and grain size variability generally increase down to 2.4 m vertically and 850 m laterally. Grain size is most variable, followed by porosity, wet bulk density, compressional wave velocity, and grain density bothvertically and laterally, consistent with Walther’s Law. Variability was empirically modeled by linear regression analysis to predict variability based on scale, characterize sediment property variability, and quantify sedimentisotropy.  相似文献   

Unraveling the health-related challenges of women in the informal economy: accounts of women in cross-border trading in Accra, Ghana     

Charlotte Wrigley-Asante 《GeoJournal》2013,78(3):525-537

The majority of urban informal sector workers lack basic health and social protection services and work in an unhealthy and unsafe environment. Women in cross-border trading are one such group. Even though they contribute significantly to and are an important component of many economies, they do so at their personal and economic risks. As these women travel, they experience health hazards which add to their existing occupational exposure. Using in-depth interviews and observation, this paper unravels the health-related risks that women in cross-border trading face. The most common physical health complaints were musculoskeletal problems such as body aches, back pains, waist pains and swollen feet as a result of long hours of travelling and poor road networks. In addition to the limited access to information on sexually transmitted diseases, women also go through psychosocial problems arising out of constant thinking and ‘worrying too much’ about their safety in the vehicles, the cash they carry along, the activities of gendarmes and armed robbers, untrustworthy clients as well as the safety of the children they leave behind. It is recommended that more attention should be paid to women’s work in the informal economy and cross-border trade in particular, so as to unravel the ways in which women’s work affects their physical and mental health. It is only through this that policies could be put in place to address the health-related challenges of women in the informal economy.  相似文献   

http://www.sciencedirect.com/science/article/pii/S1674987113000327   总被引：1，自引：0，他引：1  

Arnaud Pecher  Nicholas Arndt  Alexander Jean  Arthur Bauville  Clement Ganino  Charlotte Athurion 《地学前缘(英文版)》2013,4(5):571-581

The Panzhihua intrusion in southwest China is part of the Emeishan large igneous province and host of a large Fe-Ti-V ore deposit.In previous interpretations it was considered to be a layered,differentiated sill with the ore deposits at its base.New structural and petrological data suggest instead that the intrusion has an open S-shape,with two near-concordant segments joined by a discordant dyke-like segment. During emplacement of the main intrusion,multiple generations of mafic dykes invaded carbonate wall rocks,producing a large contact aureole.In the central segment,magmatic layering is oriented oblique to the walls of the intrusion.This layering cannot have formed by crystal settling or in-situ growth on the floor of the intrusion;instead we propose that it resulted from inward solidification of multiple,individually operating,convection cells.Ore formation was triggered by interaction of magma with carbonate wall rocks.  相似文献   

高分辨率合成孔径雷达卫星反演风场资料在中国近海风能资源评估中的应用研究   总被引：2，自引：0，他引：2  

常蕊  朱蓉  周荣卫  叶冬  张晓伟  Merete Badger  Charlotte Bay Hasager 《气象学报》2014,72(3):606-613

由于海上测风非常昂贵,实地测风资料严重不足,而卫星反演海面风场资料可以有效地弥补这一缺陷,对近海风能资源评估具有至关重要的意义。近年来,欧洲太空局2002年3月发射的Envisat卫星搭载合成孔径雷达（SAR）图像产品在欧洲近海风能资源评估中得到了广泛应用。文中探讨了空间分辨率约1 km×1 km的SAR卫星反演海面风场资料应用于杭州湾近海风能资源评估的技术方法,通过杭州湾海域的实测风速与SAR卫星反演海面风速数据的对比分析发现：（1）14个实测站点中13个站的相对误差小于20%,其中7个站的相对误差小于10%,平均标准差为2.29 m/s;（2）以SAR卫星反演风速数据为基础计算的风能参数（形状参数和尺度参数）与实测数据计算结果的一致性较高;（3）将该数据同化进入WRF数值模式中,与控制试验相比,大部分检验站点的风速相关系数明显提高,标准差和相对误差也得到改善。SAR卫星反演风场资料可用于中国的近海风能资源评估。  相似文献