上海地区全新世海平面的变化

本文通过对位于上海冈身西侧的赵巷孔进行孢粉和微古分析，论述上海地区全新世海平面变化，上海地区在全新世时期海平面经历6次波动，3次海平面上升，3次海平面下降，在7000-6000a,B.P气候最佳时期上海地区海平面表现出升中有降的现象，本文对这一短暂的海退现象作了简要的分析。     

末次间冰期以来陆地生态系统的碳储量与气候变化

陆地生态系统的碳收支是全球气候变化和碳循环研究的核心内容之一.准确估算陆地生态系统的碳储量及其收支状况,对正确评价陆地生态系统在全球碳循环中的作用有重要意义.本文总结了近10年来各国研究者利用不同方法对陆地碳储量变化的研究进展,并对估算陆地碳储量的不确定性进行评价.同时,对陆地生态系统碳储量变化研究结果的分析表明,末次间冰期以来,全球陆地生态系统碳储量存在较大幅度的变化.在末次间冰期5e阶段、末次盛冰期和全新世中期,陆地生态系统碳储量分别为现在的l30～150%、50～85%和105～130%.并且,陆地生态系统碳储量与气候变化有显著的正相关性,但不同区域的生态系统碳储量随气候变化并非具有相同的变化规律.     

鄂尔多斯东部4000余年来的环境与人地关系的初步探讨

本文依据地处39°28′08″N,110°09′92″E,海拔1219m的伊金霍洛旗杨家湾古土壤剖面取得的高时间分辨率孢粉分析和炭屑含量统计资料揭示:4500aB.P.之前,鄂尔多斯东部的毛乌素沙地地区曾出现明显的流沙扩展,此后,气候变得比较湿润,流动沙丘逐渐被固定下来;4200～3500aB.P.是本区的气候适宜期,这里曾有针阔叶混交林生长;3500aB.P.以后,气候变得干燥起来,森林从本区消失;2700～2400aB.P.,草原植被中藜科植物增加,气候进一步向干的方面发展,但降水量仍比现在高;2400aB.P.以后,在全新世晚期气候变干和人类活动的共同作用下,全新世中期本区发育的黑垆土遭到严重破坏,流动沙丘再次活跃起来。鄂尔多斯杨家湾古土壤剖面的炭屑浓度变化、考古遗址的发现较好地反映了人类活动强度的变化。     

层序地层分析与海平面变化研究—进展与争论

当代地质学之热点层序地层分析提出于70年代,至今正在成为被广泛注意和应用的学科。在石油勘探领域应用这一新的概念体系和方法已经为储集砂体的预测带来了战略性的变化,并取得了重要成就,特别是低位体系域底界面上的深切谷充填砂体的预测和发现。但是目前也存在着理论上的尖锐争论,其中主要针对全球海平面变化问题,许多学者根据新的资料和模拟结果论证了层序地层样式受控于构造、海平面变化、沉积物补给等多种因素;在许多地区证实的相对海平面变化事件不能轻易地当作全球性事件去进行对比。本文选择了一些重要的代表性著作以及1992年AAPG年会和在北美考察所获信息针对主要的进展和争论进行了综述。     

探索气圈与水圈变化过程的地质科学

地质科学的任务正从资源勘探扩展到环境预测,从面向过去变为也要面向未来。与此相应,除地球的固态圈层外,气圈和水圈的历史演变也成为其直接的研究对象。古海洋学、古湖泊学、古水文学、古大气化学和古气象学等新学科应运而生。新的研究领域要求改革研究方法,应用严格的数据采集和处理技术、经过模式的建立和检验过程的定量研究,其结果必将推动整个地质科学的现代化。最后对我国开展相应研究提出了若干建议。     

Sequential velocity imaging and microseismic monitoring of mining-induced stress change

Sequential imaging of the temporal changes inP-wave velocity offers a practical tool to monitor a rock mass. Using established correlations between the location of seismic events and velocity structure, the temporal seismic potential characteristics of the rock may be monitored. Furthermore, the temporal velocity differences isolate the time dependent factors effecting velocity such as stress, while cancelling static factors such as lithology. Various sequential imaging techniques were compared with respect to accuracy. Differences between successive velocity images were found to have relatively high associated error estimates. However, images of velocity differences calculated from measured travel time delays between successive velocity surveys were found to have lower error estimates. In particular, travel time delays measured using cross-correlation techniques resulted in the most accurate sequential image. Two 3D sequential imaging studies were carried out at Strathcona Mine in Sudbury, Ontario, Canada. Results of the average static images indicated an association between the location of induced microseismicity and a zone of both high velocity and high gradient. Additional examples are described from the global seismology literature which also show a similar correlation between seismicity and velocity structure. We attribute this association to an interrelated stress and strength effect. The Strathcona Mine sequential images show zones of significantly decreased velocity in regions of concentrated microseismic activity, which are postulated to be indications of localized destressing and relaxation of the clamping forces resulting in the microseismicity. The zones of decreased velocity corresponded to an increase in the velocity gradient. One of the case studies also shows an increase in velocity in a zone of high static velocity, which is later the site of am _N 2.5 mining-induced seismic tremor. The increase in velocity is believed to correspond to a region of stress concentration, resulting in the subsequent seismic tremor.     

Seismic velocity changes during fracture and frictional sliding

Fracture and frictional sliding are considered as phenomena involving brittle failure. Brittle failure is preceded by the formation of small (subcritical) cracks. In non-water-saturated rock, the distribution, shape and size of these suberitical cracks determine the change in the physical properties prior to failure. A model is proposed which suggests that the spatial and temporal distribution, shape and size of subcritical cracks within a stressed rock depend upon the rate of deformation and the volatile content.As a rock is stressed beyond about 50 percent of its ultimate failure stress, dilatancy is initiated. With increasing stress a broad zone of cracks develops within the dilatant region. The seismic velocities through this zone decrease markedly and the cracks grow more numerous., changing in size and shape. Before brittle failure of the rock occurs, the subcritical cracks interact, leading to a concentration of the zone. During the stage when the zone narrows, the seismic velocities in crease in the surrounding volume due to local rotation of stresses and consequent closure of some cracks. In most laboratory experiments the stage during which the velocity increases and the now intense deformation zone becomes narrow is very short and difficult to observe experimentally. At very low strain rates and with volatiles present, the crack growth and subsequent interaction lead to the narrowing of the intense deformation zone and therefore to an observable increase in velocity.The above is based upon an interpretation of a number of experiments. Using optical holography we have observed the development and subsequent intensification of a deformation zone. Ultrasonic velocity measurements showed a distinct anomaly (decrease followed by an increase) before failure. The anomaly was only detectable at our lowest experimental strain rates (3×10^–8/sec).     

The geomorphological effectiveness of floods—a contribution stimulated by two recent events in mid-wales

The occurrence of two ‘rare’ floods (August 1973, August 1977) in the Plynlimon experimental catchments has confirmed the susceptibility of small upland catchments to summer flooding and provided clues to complications in the geomorphological interpretation of floods in terms of their magnitude and frequency. Magnitude may be treated both in terms of work and effectiveness; the emphasis here is on effectiveness, as revealed by simple surveys. The first Plynlimon flood was more effective on slopes and the second in channels, despite peak discharges of similar return periods and almost identical rates of work revealed by bedload trapping. Effectiveness/frequency studies are likely to require a much more detailed approach, subdividing both the characteristics of the flood and the spatial elements of the affected catchments; a simple slope/channel subdivision is found to be suitable for accounts of effectiveness found in the literature on British floods this century. Effectiveness studies also require regular surveys throughout the recovery period following major flooding; in upland catchments these surveys should concentrate on identifying threshold phenomena and illustrating the relationship between effectiveness and work assessments of magnitude.     

流体溃变与天气系统的转折性变化

简单介绍了溃变图方法,并运用溃变观点研究了天气系统的转折性变化问题。研究表明,溃变图比通常的天气图具有更为丰富的信息,尤其是非均匀和不连续信息,它对天气系统转折性变化的预测是一种更为有效的方法     

全球变化研究的新思维

地球系统及其各圈层都是个复杂系统。全球变化研究需要针对此种特点 ,运用中国传统文化的精髓———整体观方法论 ,开展整体地球以及更大整体系统的整体研究 ,从中找出关键因子和关键性物理过程 ,力戒“瞎子摸象”。文中探讨了多种时间尺度的全球变化与相应的天文参数变化的密切联系 ,认为天地耦合有可能是引起全球变化的重要途径。同时 ,讨论了有关全球变化的若干新观点和新的物理机理。