Timing of Lateglacial vegetation dynamics and respective palaeoenvironmental conditions in southern Estonia: evidence from the sediment record of Lake Nakri     

Leeli Amon  Siim Veski  Atko Heinsalu  Leili Saarse 《第四纪科学杂志》2012,27(2):169-180

This paper investigates a detailed well‐dated Lateglacial floristic colonisation in the eastern Baltic area, ca. 14 000–9000 cal. a BP, using palynological, macrofossil, loss‐on‐ignition, and ¹⁴C data. During 14 000–13 400 cal. a BP, primarily treeless pioneer tundra vegetation existed. Tree birch (Betula sect. Albae) macro‐remains and a high tree pollen accumulation rate indicate the presence of forest‐tundra with birch and possibly pine (Pinus sylvestris L.) trees during 13 400–12 850 cal. a BP. Palaeobotanical data indicate that the colonisation and development of forested areas were very rapid, arising within a period of less than 50 years. Thus far, there are no indications of conifer macrofossils in Estonia to support the presence of coniferous forests in the Lateglacial period. Signs of Greenland Interstadial 1b cooling during 13 100 cal. a BP are distinguishable. Biostratigraphic evidence indicates that the vegetation was again mostly treeless tundra during the final colder episode of the Lateglacial period associated with Greenland Stadial 1, approximately 12 850–11 650 cal. a BP. This was followed by onset of the Holocene vegetation, with the expansion of boreal forests, in response to rapid climatic warming. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

The role of the chemical environment in frictional deformation: Stress corrosion cracking and comminution   总被引：23，自引：0，他引：23  

J. Dunning  B. Douglas  M. Miller  S. McDonald 《Pure and Applied Geophysics》1994,143(1-3):151-178

The roles of chemically assisted crack and fracture propagation and chemically assisted comminution in frictional deformation are evaluated in this study. Double cantilever beam (DCB) crack propagation data are presented which show that the role of pH in chemically assisted fracture, and to a lesser extent the role of ionic concentration are important in stress corrosion cracking. Data on very slow crack growth and the stress corrosion limit are also presented. These data suggest that stress corrosion cracking may play an important role in compound earthquakes and in asperity breakdown in faults. The comminution literature is also reviewed in order to assess the role of chemically assisted comminution in frictional deformation. It appears that chemically assisted comminution may be important at low and high ionic strength because it may reduce the effective viscosity and the shear strength of fault gouge. At intermediate ionic concentration the role of pH, as an agent which enhances crack and fracture propagation, appears to be more important in reducing the coefficient of sliding friction.  相似文献   

硝酸根对颗粒状铁降解三氯乙烯的影响(英文)     

Qiong LU　 Lai GUI　 Robert W.GILLHAM 《地学前缘》2005,12(Z1):176-183

为研究硝酸根对颗粒状铁降解三氯乙烯的影响,进行了柱实验和相应的反应铁腐蚀电位测定。在硝酸根离子存在条件下,铁的腐蚀电位相应升高,系统条件也因之发生变化,导致钝性的铁氧化物在铁表面生成。因而,三氯乙烯和硝酸根离子降解速率明显减小, 并且降解速率减小的程度与硝酸根离子的浓度成比例。当污染液流过反应柱时,硝酸根离子与铁反应, 被还原为氨根离子。该反应造成硝酸根离子的浓度梯度,使钝化区在柱中上移,从而影响了三氯乙烯的降解曲线。与三氯乙烯单独与铁反应相比,当含4 7 mg/L硝酸根的三氯乙烯溶液流经反应柱170 孔隙体积后,降解50% 三氯乙烯所需的时间(t50) 从小于4 h增加到大于10 h;而当三氯乙烯溶液中加入100 mg/L硝酸根离子,仅17 孔隙体积溶液流经反应柱后,三氯乙烯降解t50就已大于14 h。研究结果表明,由于硝酸根离子对铁的腐蚀电位和铁表面氧化膜的不利作用,在处理靶污染物为高浓度硝酸根离子和三氯乙烯共同污染的地下水时,铁渗透反应隔栅不是最佳选择。如果靶污染物中硝酸根离子浓度比较低,则在设计铁隔栅时应考虑到硝酸根离子造成的不利因素,相应增加铁墙的厚度,从而确保三氯乙烯的降解效果。  相似文献   

Study on rust layers on steel in different marine corrosion zone   总被引：1，自引：0，他引：1  

李言涛  侯保荣 《中国海洋湖沼学报》1998,16(3):231-236

IrmODUCnONTheMossbaureffect(ME)isalsoknOWnasrecoil-thenuclearresonaneabsorp-hon.MossbaursPeCboscoPy(MS)haspIDvedtobeaveryuSefultecheqUeforstudytngcormsionPimessesandcedon-cts.TheInainadvantagsofMSincormsionre-enhare:(l)thenon-deStrutivechateroftheteCboqUe;(2)possibilltyforquali-tativeandqUanitativephaanalsis;(3)uSehassinidenificationofPOOrlycrystal-lizedoramorphouscormsionpnhats.WththedeVfoPmntofInarineresomees,InansteelconstrUctionswerebulltatsea'MSwasusedforanalfongcormsion~t…  相似文献   

Slow crack growth in minerals and rocks: Theory and experiments     

M. Darot  Y. Gueguen 《Pure and Applied Geophysics》1986,124(4-5):677-692

Strength and mechanical behavior of rocks and minerals are modified by aqueous environments. This results in two effects: mechanical and chemical. The chemical effect is investigated from both a theoretical and an experimental point of view. It is shown that a thermodynamic approach leads to a satisfactory understanding of the chemical effect through an extended griffith concept. Predictions of the model have been tested using slow crack growth experiments. The experiments have been performed with a special Double Torsion apparatus which was built for this purpose. The good agreement observed between theory and experiments suggests that subcritical crack growth in rocks is controlled by adsorption onto the crack tip. This result was previously suggested by other authors (Dunning et al., 1984). However, the important consequences of the model are that (1) there should exist a threshold stress below which subcritical crack growth stops, and this threshold depends on the environment; (2) subcritical crack growth and time-dependent phenomena could take place in the crust in a stress interval which could be as high as 50% of the rupture stress.  相似文献   

A sequence of seismic activity in the Kanto area precursory to the 1923 Kanto earthquake     

Mitiyasu Ohnaka 《Pure and Applied Geophysics》1984,122(6):848-862

The Kanto earthquake (M=7.9) that occurred along the Sagami Trough in the Sagami Bay on 1 September 1923 was one of the most disastrous earthquakes in Japanese history. The Kanto area includes Metropolitan Tokyo and Yokohama which are densely populated, and hence it has been a matter of great concern, from the viewpoints of earthquake prediction and disaster prevention, whether or not the 1923 Kanto earthquake was preceded by precursory seismicity. A study using the most complete lists of earthquakes catalogued recently by Utsu and the Japan Meteorological Agency reveals that seismic activity in the Kanto area was appreciably higher before and after the Kanto earthquake, and that the Kanto earthquake was preceded by a sequence of anomalous seismic activity, quiescence, and foreshocks. Such higher activity before and after the Kanto earthquake is contrasted with low seismicity during the recent 30-year period. A model is proposed to explain the precursory seismic activity, subsequent quiescence, and foreshocks for the Kanto earthquake. In the model, the transition from precursory seismic activity to quiescence is ascribed to time-dependent fracture due to stress-aided corrosion. Foreshocks are related to an acceleration of premonitory slip shortly before the mainshock slip.  相似文献   

桂林城市地面岩溶热蚀沉降遥感预测   总被引：1，自引：0，他引：1  

吴虹  陈三明  阮贵华  李景文 《遥感学报》2002,6(2):150-154

通过对Landsat热红外波段TM6、近红外波段TM5和可见光波段TM1的综合信息图像处理，结合丫吉村岩溶水文地质试验场土层下石灰岩蚀随气温变化数据以有1987－1996年10年内桂林城市气温观测数据，发现城市热岛效应会对处于特殊岩溶地质环境中的桂林市造成一种特殊影响－－城市地面整体岩溶热蚀沉降。在此基础上，建立了桂林城市岩溶热蚀沉降动力学模型和发展演化模型，从而为开展基于t－GIS的桂林城市地面整体岩溶热蚀1沉降定量预测提供了理论与技术依据。  相似文献   

含铁地下水成因、危害及防治   总被引：3，自引：0，他引：3  

贾国东  钟佐燊 《水文地质工程地质》2000,27(1):7-10

含铁地下水形成于中偏酸性的还原性水文地球化学环境中,人为活动也可引发含铁水的出现。含铁水进入水井附近后,有沉淀析出铁矿物从而堵塞水井附近含水层和滤水管的危险,也因为其偏低的ＰＨ值和可能含有硫化物而对金属水井管材具有腐蚀作用。防治含铁水对水井破坏作用的根本方法是采取改善地下水水质的现场处理技术。  相似文献   

物探测井在地热开发中的应用   总被引：1，自引：0，他引：1  

冯来泉 《地球学报》2000,21(2):212-215

地热资源的开发利用愈来愈受到广泛的重视 ,本文阐述了物探测井在地热开发中的作用 ,并介绍了视电阻率、温度、套管磁测井等方法在地热开发中的应用。  相似文献   

泥浆对钻头WC基胎体材料冲蚀磨损的试验研究   总被引：2，自引：0，他引：2  

江新洪  段隆臣  刘志义 《煤田地质与勘探》2007,35(4):77-80

采用双喷嘴闭路循环试验装置,测试了钻头胎体材料在泥浆冲蚀作用下所产生的总质量损失TML和由纯机械冲刷作用所产生的质量损失E。通过计算得到了由腐蚀及机械冲刷与腐蚀相互作用所产生的质量损失C+S。结果表明,钻头胎体材料的冲蚀磨损不是纯由机械冲刷作用引起,而是由机械冲刷、腐蚀及他们的相互作用共同引起。因此,在有腐蚀性的泥浆中设计和选用PDC (金刚石复合片)钻头时,除了考虑胎体材料的抗冲刷磨损性能外,还应考虑钻头胎体材料的抗腐蚀性。   相似文献