加拿大LITHOPROBE地震反射资料显示的大陆地壳结构变化性     

Clow.  RM 金东淳 《世界地质》1994,13(1):136-147

岩石圈断面计划（ＬＩＴＨＯＰＲＯＢＥ）是加拿大全国性的多学科合作的地球物理项目，它的目的旨在提高对于北美板块演化的认识，研究范围内的横跨全国和不同地质年代的８个断面均是以地震反射波研究作为前提。这些研究成果与相关其它学科的研究相结合，给我们研究板块形成过程中不同地质构造是如何演化的提供了证据和思路。研究区的太古代Ｋａｐｕｓｋａｓｉｎｇ构造带，主要特征是斜切东西向的苏必利尔省构造带，被认为是位于一个重要的滑脱构造上的低角度推覆构造，沿着该构造带的５０～７０ｍ处发生了地壳缩短（挤压）作用，并且引起了一些地壳中部的岩石上升到地表，挤压作用以脆性断裂和在２０ｋｍ处的岩浆侵入作用及其下部地壳的韧性和流变构造作用而完成。位于Ｈｕｒｏｎ湖的ＧＬＩＭＰＣＥ断面的地震波特征是范围宽、向东倾斜、具地壳规模，该断面与Ｇｒｅｎｖｉｌｌｅ前构造单元的地震波相一致。两阶段模型包括地体在早元古代与克拉通地体边缘的碰撞，随后在中元古Ｇｒｅｎｖｉｌｌｉａｎ造山作用中发生了整个地壳的堆积和倾斜作用。在苏必利尔湖，ＧＩＬＩＭＰＣＥ数据表明，中元古代构造作用造成北美板块的分裂。岩石圈计划的东部断面横跨古生代新大陆阿巴拉契亚山脉，揭示了基于地震反射  相似文献   

预测油田混相水气交替驱动动态的新方法     

Gior.  RM 胥东梅 《国外石油地质》1999,21(2):37-43

油田提高原油采收率法（ＥＯＲ）的动态预测一般采用粗化法,因为三维有限差分模拟花费的ＣＰＵ时间过长。现有的粗化技术要求用户规定井网单元后,绘制出用于单元中每组注入井－生产井的动态曲线。精确分配这些单元的确很困难,因为波及体积的实际形态和大小对油藏断层、油井产量变化和区域性水侵都很敏感。事实上,虽然实际波及区域不是输入参数,但可根据井产量变化和钻新井而改变的区域压力场确定。因此,使用现有的粗化方法主要  相似文献   

Episodic ocean-induced CO2 greenhouse on Mars: implications for fluvial valley formation     

Gulick VC  Tyler D  McKay CP  Haberle RM 《Icarus》1997,130(1):68-86

Pulses of CO2 injected into the martian atmosphere more recently than 4 Ga can place the atmosphere into a stable, higher pressure, warmer greenhouse state. One to two bar pulses of CO2 added to the atmosphere during the past several billion years are sufficient to raise global mean temperatures above 240 or 250 K for tens to hundreds of millions of years, even when accounting for CO2 condensation. Over time, the added CO2 is lost to carbonates, the atmosphere collapses and returns to its buffered state. A substantial amount of water could be transported during the greenhouse periods from the surface of a frozen body of water created by outflow channel discharges to higher elevations, despite global temperatures well below freezing. This water, precipitated as snow, could ultimately form fluvial valleys if deposition sites are associated with localized heat sources, such as magmatic intrusions or volcanoes. Thus, if outflow channel discharges were accompanied by the release of sufficient quantities of CO2, a limited hydrological cycle could have resulted that would have been capable of producing geomorphic change sufficient for fluvial erosion and valley formation. Glacial or periglacial landforms would also be a consequence of such a mechanism.  相似文献   

Migration and the life course: is there a retirement transition?     

Bures RM 《International journal of population geography : IJPG》1997,3(2):109-119

"This paper focuses on pre-elderly (ages 55-64) net migration in the United States for the period 1980-90, to explore the hypothesis that there exists a ?retirement transition' that characterizes pre-elderly migration.... This research uses ordinary least squares regression to compare the effects of demographic, economic, and amenity factors on county-level net migration rates for five age groups: the young (25-44), the middle-aged (45-54), the pre-elderly (55-64), the young-old (65-74), and the old-old (75+). Pre-elderly migration patterns emerge as distinct from those of both younger and older age groups. Their net migration patterns are not fully shaped by labour force considerations. At the same time, pre-elderly migration appears to be driven by factors beyond retirement. These findings are discussed in the context of life-course change and their implications for the ageing baby-boom cohorts [considered]."  相似文献   

The effects of power station entrainment passage on three species of marine planktonic crustacean, Acartia tonsa (Copepoda), Crangon crangon (Decapoda) and Homarus gammarus (Decapoda)   总被引：6，自引：0，他引：6  

Bamber RN  Seaby RM 《Marine environmental research》2004,57(4):281-294

Experiments have been undertaken exposing larval common shrimp (Crangon crangon) and lobster (Homarus gammarus) and adult copepods (Acartia tonsa) to the key stresses of entrainment within power-station cooling-water systems. The apparatus has enabled the testing of mechanical, thermal, chlorine and realistic pressure effects both alone and in combination, the range of stressors spanning the standard conditions found within a temperate coastal direct-cooled power station. Mechanical stresses affected only lobster larvae, pressure changes affected only the Acartia adults. Residual chlorine caused significant mortality of Acartia and shrimp larvae, but had no effect on lobster larvae even at 1 ppm. The temperature increment significantly affected all three species, with a synergistic effect on chlorine sensitivity in the shrimp larvae, but only temperatures higher than would be experienced in a normally-operating power station affected the copepods. The majority of individuals of each species would survive passage through a power-station system under normal conditions. It is notable that, within the species tested, generalizations from the responses of one species to those of another are not valid.  相似文献   

东海晚更新世以来的氧同位素古气候与全新世底界划分   总被引：3，自引：0，他引：3  

钱建兴  施光春 《海洋学报》1986,8(1):66-71

本文应用东海南部7055站岩芯的氧同位素组成,绘制了东海26600年以来的古气候变化曲线,对东海玉木冰期以来的古气候变迁情况进行了探讨。将岩芯划分为九个氧同位素气候期,上述九个氧同位素气候期均可与欧洲的气候期相吻合,反映了较好的对应关系。并结合岩性、有孔虫组合标志,按气候地层学的原则,对比V28-238标准氧同位素曲线,把该区全新世底界定为13000年。  相似文献   

Adjoint simulation of stream depletion due to aquifer pumping     

Neupauer RM  Griebling SA 《Ground water》2012,50(5):746-753

If an aquifer is hydraulically connected to an adjacent stream, a pumping well operating in the aquifer will draw some water from aquifer storage and some water from the stream, causing stream depletion. Several analytical, semi-analytical, and numerical approaches have been developed to estimate stream depletion due to pumping. These approaches are effective if the well location is known. If a new well is to be installed, it may be desirable to install the well at a location where stream depletion is minimal. If several possible locations are considered for the location of a new well, stream depletion would have to be estimated for all possible well locations, which can be computationally inefficient. The adjoint approach for estimating stream depletion is a more efficient alternative because with one simulation of the adjoint model, stream depletion can be estimated for pumping at a well at any location. We derive the adjoint equations for a coupled system with a confined aquifer, an overlying unconfined aquifer, and a river that is hydraulically connected to the unconfined aquifer. We assume that the stage in the river is known, and is independent of the stream depletion, consistent with the assumptions of the MODFLOW river package. We describe how the adjoint equations can be solved using MODFLOW. In an illustrative example, we show that for this scenario, the adjoint approach is as accurate as standard forward numerical simulation methods, and requires substantially less computational effort.  相似文献   

Patterns of water, heat, and solute flux through streambeds around small dams   总被引：1，自引：0，他引：1  

Fanelli RM  Lautz LK 《Ground water》2008,46(5):671-687

Hyporheic exchange, enhanced by complex stream channel morphology, can influence biogeochemical processing in the streambed. These processes chemically alter water passing temporarily through the streambed, which eventually returns to the stream channel and can potentially affect surface water quality. To assess the degree of biogeochemical cycling induced by complex streambed morphology, we instrumented two 20-m reaches of Red Canyon Creek, Wyoming, each containing a small log dam, with in-stream minipiezometers and temperature data loggers. We simultaneously observed pore water geochemistry and streambed temperature dynamics in several bedforms located upstream or downstream of the dams. We modeled seepage flux into the streambed using heat transport modeling.
Upstream of the dams, low-permeability sediments have settled out in low-velocity pools, and enhanced anaerobic biogeochemical cycling occurred in the streambed. Rapid flux into the streambed occurred in glides immediately above the dams, where streambed temperature dynamics and geochemistry were nearly identical to the stream. In riffle sequences downstream of the dams, the streambed was oxygen rich, showed evidence of nitrification, and temperature dynamics indicated high connectivity between the streambed and the stream. Further downstream, streambed pore water geochemistry indicated ground water discharge occurring at the pool-riffle transition. Assessing streambed biogeochemical cycling may be facilitated by coupling streambed temperature measurements with pore water geochemistry and can aid in understanding how hyporheic exchange contributes to overall stream biogeochemistry.  相似文献   

Polycyclic aromatic hydrocarbons in surficial coastal sediments of the Ligurian Sea   总被引：1，自引：0，他引：1  

Bertolotto RM  Ghioni F  Frignani M  Alvarado-Aguilar D  Bellucci LG  Cuneo C  Picca MR  Gollo E 《Marine pollution bulletin》2003,46(7):907-913

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Spatial and temporal variation in hexachlorocyclohexane isomers in a temperate estuary     

Padma TV  Dickhut RM 《Marine pollution bulletin》2002,44(12):1345-1353

Hexachlorocylcohexanes (HCHs) are pesticides that persist in air and water of the Northern hemisphere. To understand the spatial and temporal variability in HCH levels in estuarine surface waters we measured concentrations of two HCH isomers (-HCH and γ-HCH) at six sites in the York River estuary at bimonthly intervals for a year. Bacterial abundance and activity were also monitored using acridine orange direct counts and uptake of tritiated substrates, respectively. -HCH was consistently observed to be significantly higher in marine water compared to river water entering the estuary, suggesting that the Chesapeake Bay or Atlantic Ocean is a larger source of this compound to the York River estuary compared to riverine input. Moreover, following periods of high freshwater flow into the estuary during spring and early summer, both - and γ-HCH mixing curves indicated an additional source of these pollutants to the estuary such as land-derived runoff or groundwater discharge. In contrast, during low freshwater flow (late summer and fall) the estuary was a sink for HCHs, with γ-HCH more rapidly removed from the estuary than -HCH. During the period of low freshwater flow, concentrations of both - and γ-HCH were negatively correlated with bacterial activity. Bacterial activity as opposed to abundance appears to control HCH degradation in estuarine surface waters.  相似文献