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971.
济阳孔店构造转型期沉积盆地的特征及勘探意义 总被引:1,自引:0,他引:1
济阳孔店组的归属问题一直是济阳盆地演化研究的焦点.通过大量的构造、沉积的基础性研究,提出孔店组是中生代向新生代转换的构造转型期,孔店期盆地叠置于中生代北西向半地堑之上,恰逢印度板块碰撞冈底斯及太平洋板块向欧亚板块俯冲,构造应力场具有双重性质,使得孔店组沉积盆地构造特征复杂,由于不同部位构造应力场强度的不同,虽为同期沉积盆地但是构造特征、盆地充填方式具有较大的差异,济阳盆地孔店组主要分布在惠民凹陷和东营凹陷,勘探重点应放在这两个凹陷. 相似文献
972.
973.
Throughout history, humans have transformed natural forests into agricultural land, settlement areas and managed forests. Studies on the dynamics of forest change are one of the mainstays in land change science. The forest transition theory offers a powerful tool to analyze changes in human interference with forests. At the national level, a range of factors have been found to influence a country's forest change. The role of international wood product trade has, however, rarely been studied based on empirical data. We offer a global assessment of how this trade helps shape observed forest change, by relating forest stock change to net trade of wood products for the period 1997-2007 and by localizing the origin of wood consumed in a given nation. For many nations, traded wood products have a relevant impact on the course of ongoing forest transitions. We develop a general typology of how wood product trade can influence forest change and place various nations within this framework. We find that many wealthy nations with returning forests seem to accelerate this return by importing wood products. These imports appear to be provided by two main types of wood exporters: (a) by wealthy countries with low population densities and stable forests and (b) by relatively poor countries with declining forests, employing increasing population and welfare levels. We discuss these findings in the light of general theories on land use transitions and forest change and conclude by highlighting implications for national forest policies and global environmental governance, aiming at reducing negative impacts of wood products and enhancing the positive role they can play in replacing more fossil fuel intensive products. 相似文献
974.
Clearly defined distal tephras are rare in rockshelter sediment records. Crvena Stijena, a Palaeolithic site in Montenegro, contains one of the longest (> 20 m) rockshelter sediment records in Europe with deposits ranging in age from Middle Pleistocene to mid-Holocene. A distinctive tephra is clearly exposed within the well stratified record approximately 6.5 m below the present land surface. We present geochemical data to confirm that this tephra is a distal equivalent of the Campanian Ignimbrite deposits and a product of the largest Late Pleistocene eruption in Europe. Originating in the Campanian volcanic province of southwest Italy, this tephra has been independently dated to 39.3 ka. It is a highly significant chronostratigraphic marker for southern Europe. Macrostratigraphic and microstratigraphic observations, allied with detailed particle size data, show that the tephra layer is in a primary depositional context and was transported into the rockshelter by aeolian processes. This site is unique because the tephra forms an abrupt boundary between the Middle and Upper Palaeolithic records. Before they can be used as chronostratigraphic markers in rockshelter and cave-mouth environments, it is essential to establish the stratigraphic integrity of distal tephras and the mechanisms and pathways involved in their transport and deposition. 相似文献
975.
The tightly coupled, strongly nonlinear nature of non-isothermal multi-phase flow in porous media poses a tough challenge for numerical simulation. This trait is even more pronounced, if miscibility is also considered. A primary reason why inclusion of miscibility tends to be problematic are the difficulties stemming from phase transitions: on the one hand, phase transitions need to be included since the presence or absence of fluid phases has a major impact on the flow behavior; on the other hand, convergence of the nonlinear solver may be severely affected if they are not handled robustly.In this work, we present a mathematically sound approach to include phase transitions in the nonlinear system of equations: first, the transition conditions are formulated as a set of local inequality constraints, which are then directly integrated into the nonlinear solver using a nonlinear complementarity function. Under this scheme, Newton-Raphson solvers exhibit considerably more robust convergence behaviour compared to some previous approaches, which is then illustrated by several numerical examples. 相似文献
976.
通过对陈耳金矿床两类不同构造-岩相带微量元素分布特征分析,发现元素特别是成矿元素Au的含量从片理化带→破碎蚀变带→石英脉逐渐增强。构造-岩相带内变形岩石的石英Rf/φ法有限应变测量表明,片理化带应变强度最大,破碎蚀变带应变强度小,应变集中在韧性剪切带边部的片理化带内。R型聚类分析表明Au与Ag、Cu、Pb及Zn的相关系数远大于Au与Ni、Co元素的相关系数,甚至接近于1。研究认为:破碎蚀变带内由于应变软化导致脆性裂隙大量发育,易于成矿流体的迁入与淀积而强富集;片理化带由于应变集中,造成成矿流体的迁出而弱富集。韧性剪切带脆-韧性变形转换不仅控制了矿体就位空间,同时也决定着元素迁移的方向。 相似文献
977.
978.
The structural stability of manganese titanate MnTiO3 at high pressure was investigated by X-ray diffraction and Raman spectroscopy with diamond anvil cells. Ilmenite-type MnTiO3 is stable at least to 26.6 GPa, and lithium niobate type MnTiO3 reversibly transforms at room temperature to perovskite at 2.0 GPa. Bulk moduli (K300) of ilmenite, lithium niobate and perovskite are 174(4) GPa, 179(8) GPa, and 208(5) GPa, respectively (at fixed first pressure derivative K′ = 4). The Grüneisen parameter γ has been estimated to be 1.28 for ilmenite and 1.75 for perovskite. In ilmenite phase, TiO6 octahedra become more regular with increasing pressure. In perovskite phase structural distortion increases with pressure increase. 相似文献
979.
980.
利用欧洲格点资料,应用天气学方法,从环流场演变、B效应、不对称结构等方面对1005号热带气旋“乌鲁伊”活动过程进行了分析,探讨了“乌鲁伊”不同阶段路径变化的原因.结果表明,澳大利亚大陆高压维持稳定以及热带气旋“托马斯”与“乌鲁伊”之间的相互作用是“乌鲁伊”西行北抬的根本原因.在“乌鲁伊”台风西行过程中,中高纬度环流场进行强烈调整是引起“乌鲁伊”移动路径南翘西折的关键,大陆高压在低纬向“乌鲁伊”北侧嵌入、以及地面气压场上从北指向南的气压梯度力突然增强,对热带气旋“乌鲁伊”移动路径南翘有直接影响.对西风指数的分析表明,“乌鲁伊”的南翘过程与西风指数从最低值484.4m。/s。向644.3m。/s。升高过程相对应,“乌鲁伊”移动路径西折与西风指数维持在644.3m。/s。以上有关.500hPa位势高度梯度场分析表明,热带气旋“乌鲁伊”从东向西、向南、向西南稳定移动过程中,东南侧和西北侧等梯度线中心数值的差值几乎为0,呈现出对称分布的特点;在热带气旋“乌鲁伊”南翘、西折时,东南侧与西北侧等梯度线数值发生显著变化,南翘时差值为一16.6m/s。,西折时差值则为12.0m/s。.500hPa位势高度梯度场的变化对“乌鲁伊”南翘西折路径具有很好的预示作用. 相似文献