坝上高原安固里淖粒度年纹层与环境变化

在安固里淖湖心区获取一未扰动沉积物样柱，分析发现了由冬季风搬运物与湖心沉积共同形成的粒度年纹层，建立了纹层年表，恢复了安固里淖湖区8507aB.P，以来的环境变化过程。8507-5429aB.P。冬季风活动较弱，后期的所波动；5429-3244aB.P.冬季风活动较强，3244-2494aB.P。冬季风活动减弱；2494-1165aB.P。冬季风活动略有增强；1165aB.P以来，冬季风活动减弱。安固里小淖粒度年纹层反映的冬季风变化情况与我国北方地区同期的环境变化和海平面变化有很好的对应关系。     

Luminescence chronology of incision and channel pattern changes in the River Ganga, India

The River Ganga in the central Gangetic plain shows the incision of 20 m of Late Quaternary sediments that form a vast upland terrace (T₂). The incised Ganga River Valley shows two terraces, namely the river valley (terrace-T₁) and the present-day flood plain (terrace-T₀). Terrace-T₁ shows the presence of meander scars, oxbow lakes, scroll plains, which suggests that a meandering river system prevailed in the past. The present-day river channel flows on terrace-T₀ and is braided, sensu stricto. It is thus inferred that the River Ganga experienced at least two phases of tectonic adjustments: (1) incision and (2) channel metamorphosis from meandering to braided.Optical dating of samples from three different terraces has bracketed the phase of incision to be <6 and 4 ka. Different ages of the top of terrace-T₂ show that this surface experienced differential erosion due to tectonic upwarping in the region, which also caused the river incision. River metamorphosis occurred some time during 4 and 0.5 ka.     

On the land use in Three Gorges Reservoir area

In this study the arable land changes in two counties (Zigui and Xingshan) in the Three Gorges Reservoir area in China are investigated. The statistical data from the officially published statistical books are used to study these changes in the two counties during the past 50 years since 1949. The changes of arable land, changes of arable land per capita, and changes of multiple crop index in Zigui and Xingshan counties are examined. Using an index method, we conclude that the two counties are critical in the sustainable utilization of arable land.     

北京地区3500a来的气候与环境变迁——兼论昆明湖的沧桑

通过对北京颐和园昆明湖中沉积物的沉积特征的研究,结合历史记载,对昆明湖水域的形成时间和发展过程有了深入的了解,据此对北京地区3500a以来的气候与环境变迁作出了科学的划分,为探讨北京地区未来的气候变化趋势将会有所启迪。     

中国东北样带NDVI的季节变化及其与气候因子的关系

NDVI是研究大尺度生态学问题一个非常有用的指数,它可以为估价全球植被动态模型提供足够的信息.中国东北样带是全球变化研究中首选样带之一,本文分析了分辨率为1km×1km的NDVI年内季节变化的两个特征值:年均NDVI(NDVI-I)和NDVI年内极差(NDVI-MM)在样带内5种不同植被类型间的变化及其与年平均气温和降水量之间的相关关系.结果表明,NDVI具有明显的季节变化格局,NDVI-I和NDVI-MM由东到西均呈下降趋势,NDVI-I与降水量具有显著的线性回归关系,降水量能够解释NDVI-I和NDVI-MM空间变异的绝大部分.这一结果说明NDVI反映了植被沿环境梯度的时空变化格局,可用于监测样带植被对气候变化的响应.     

Temporal variations of shear-wave splitting in field and laboratory studies in China

Observations of shear-wave splitting at seismic stations above a swarm of small earthquakes on Hainan Island, China, and other examples world-wide, suggest that the time-delays of split shear-waves monitor the build up of stress before earthquakes and the stress release as earthquakes occur. Rock physics experiments on marble specimens also show variations of shear-wave time-delays with uniaxial pressure analogous to the field observations. The rock experiments show an abrupt decrease in time-delays immediately before fracturing occurs. Similar precursory behaviour has been observed before earthquakes elsewhere, and is believed to be important for two reasons. Precursory changes in shear-wave splitting could be used for short-term forecasting, but of greater importance may be the information such behaviour provides about the source processes in earthquake preparation zones.     

福建龙永煤田二叠纪(竹蜓)生物带的面貌特征与对比

研究地层是有效寻找沉积矿产的重要基础,将龙永煤田内关于的层位及分带性与大区域上的相似层位作了对比,并论述了本煤田的特征与变迁的基本过程。最后,结合多年来的研究成果,就煤田内的产出情况,作了两点必要的说明。     

Paleoclimate Changes during the Early Oiigocene in the Hoh Xil Region, Northern Tibetan Plateau

Sedimentological, cyclic-stratigraphic, paleomagnetic, and clay-mineralogical studies on the early Oligocene Yaxicuo Group in the Hoh Xil Basin, the largest Cenozoic sedimentary basin in the hinterland of the Tibetan Plateau, provide abundant information of paleoclimate changes. A 350-m thick section in the middle-lower Yaxicuo Group was analyzed to reveal the climatic history that occurred in the Hoh Xil region during the early Oligocene interval 31.30-30.35 Ma, dated with the paleomagnetic chronostratigraphy. The results indicate that add and cold climate dominated the Hoh Xil region during the early Oligocene in general, being related to the global cooling and drying events that occurred in the earliest Oligocene. Within this period, relatively warm and wet climate accompanied by strong tectonic activity occurred in the 31.05-30.75 Ma interval; while add and cold climate and relatively inactive tectonics occurred in the 31.30-31.05 and 30.75-30.35 Ma intervals. Furthermore, spectral analyses of high-temporal resolution paleoclimatic records show orbital periods including eccentricity, obliquity, and precession. It is concluded that paleoclimate changes during the early Oligocene in the Hoh Xil region were forced by both tectonic activity and orbital periods.     

Global thermal and dynamical perturbations due to Cretaceous mantle avalanche

The numerical models of mantle convection agree to depict avalanches behaviour according to the level of endothermicity of the spinel → perovskite phase change. Their potential effects on the global thermal and dynamical states of the mantle have been computed thanks to a numerical code, which takes into account both the 400-km exothermic and the 660-km endothermic phase changes. The cycle followed by the avalanches is: local layering, destabilization of the 660-km thermal layer, travelling and spreading on the core, and reappearing of the local layering. Therefore, mantle convection is characterized by quiet periods of partial layering embedded in catastrophic events. During the avalanche, the amplitude of the surface velocity is multiplied by two, which would imply an enhanced plate tectonic and ridge activities. The global thermal effects of the avalanche are compatible with a high mantle temperature and an acceleration of Earth's rotation during the Cretaceous. They also offer a coherent explanation to locate the origin of mantle plumes both within the CMB and just below the transition zone.     

华北北部场源前兆观测资料分析(一)──场源前兆特征与机制

1976年唐山地震前，在距震源很远的地区内都观测到一些前兆趋势变化，如重力、重力位二次徽商W△、水氧、地电阻率、水位和油井出油量等变化。作者认为这些变化不是由震源体直接引起的，而是在区域应力场的作用下，在某些活动断层附近，浅层岩，尤其是含水砂岩层和含油层受挤压出现的一些与地震有关的异常现象。其特征是：（1）异常范围大，可能在距震源很远的地方发生，但就同一种方法的多个观测点来说却又是局部的，即只有其中部分测点才能观测到异常，不少测点观测不到异常。（2）异常发生的时间大致相同。有些异常有同步变化的特征，如同时上升或同时下降。（3）临震前多数异常有恢复的趋势。这些特征与引起异常的机理有关。作者还从理论上计算了这种趋势异常量级，重力变化100×10-6cm／s2左右，重力位二次微商变化（1～2）×10－9／s2，地电阻率变化2％～3％，Rn变化7．4～11．1Bq／L，这样的变化量在活动断层附近的一些台站可能观测到。作者还研究了干旱降雨对某些前兆的影响，其影响量级可以被一些方法观测到，因此在确定是否是地震异常时，必须注意利用综合分析的方法排除干旱降雨的影响，减少异常的多解性。