Nondestructive spectroscopic and petrochemical investigations of Paleoarchean spherule layers from the ICDP drill core BARB5, Barberton Mountain Land,South Africa

A Paleoarchean impact spherule‐bearing interval of the 763 m long International Continental Scientific Drilling Program (ICDP) drill core BARB5 from the lower Mapepe Formation of the Fig Tree Group, Barberton Mountain Land (South Africa) was investigated using nondestructive analytical techniques. The results of visual observation, infrared (IR) spectroscopic imaging, and micro‐X‐ray fluorescence (μXRF) of drill cores are presented. Petrographic and sedimentary features, as well as major and trace element compositions of lithologies from the micrometer to kilometer‐scale, assisted in the localization and characterization of eight spherule‐bearing intervals between 512.6 and 510.5 m depth. The spherule layers occur in a strongly deformed section between 517 and 503 m, and the rocks in the core above and below are clearly less disturbed. The μXRF element maps show that spherule layers have similar petrographic and geochemical characteristics but differences in (1) sorting of two types of spherules and (2) occurrence of primary minerals (Ni‐Cr spinel and zircon). We favor a single impact scenario followed by postimpact reworking, and subsequent alteration. The spherule layers are Al₂O₃‐rich and can be distinguished from the Al₂O₃‐poor marine sediments by distinct Al‐OH absorption features in the short wave infrared (SWIR) region of the electromagnetic spectrum. Infrared images can cover tens to hundreds of square meters of lithologies and, thus, may be used to search for Al‐OH‐rich spherule layers in Al₂O₃‐poor sediments, such as Eoarchean metasediments, where the textural characteristics of the spherule layers are obscured by metamorphism.     

Shuram-Wonoka carbon isotope excursion:Ediacaran revolution in the world ocean's meridional overturning circulation

The late Ediacaran Shuram-Wonoka excursion, with δ~(13)C_(carb) values as low as-12‰(PDB) in marineshelf deposits and spanning up to 10 Myr, is the deepest and most protracted δ~(13)C_(carb) negative anomaly recognised in Earth history. The excursion formed on at least four continents in low(≤32°) palaeolatitudes, and in China is associated with a major phosphogenic event. Global and intrabasinal correlation, magnetostratigraphy, isotope conglomerate tests and further geochemical data are consistent with a primary or syn-depositional origin for the excursion. Continental-margin phosphorites are generated by oceanic upwelling driven by surface winds, and δ~(13)C_(carb) negative anomalies are explicable by oceanic upwelling of 13 C-depleted deep oceanic waters, arguing that a feature common to these exceptional Ediacaran events was unprecedented perturbation of the world ocean. These events occurred during the transition from an alien Proterozoic world marked by low-palaeolatitude glaciation near sea level and strong seasonality to the familiar Phanerozoic Earth with circum-polar glaciation and temperate climate, suggesting that the Shuram-Wonoka excursion is related to this profound change in Earth's climate system. Of various hypotheses for Proterozoic low-palaeolatitude glaciation, only the high obliquity(54°) hypothesis, which posits secular decrease in obliquity to near the present-day value(23.5°) during the Ediacaran, predicts an unparalleled revolution in the Ediacaran world ocean. The obliquity controls the sense of the world ocean's meridional overturning circulation, which today is driven by the sinking of cold, dense water at the poles and upwelling driven by zonal surface winds.When the decreasing obliquity passed the critical value of 54° during the Ediacaran the meridional temperature gradient reversed, with the equator becoming warmer than the poles and Hadley lowlatitude(30°-35°) atmospheric zonal circulation reversing. This reversal of the temperature gradient is unique to the Ediacaran Period and caused reversal of the oceanic meridional overturning circulation,with upwelling of anoxic, 13 C-depleted deep oceanic waters producing a deeply negative and protractedδ~(13)C_(carb) signature on late Ediacaran marine-shelf deposits.     

Measurement and modeling of moisture content above an oscillating water table: implications for beach surface moisture dynamics

This study examined the influence of tidally‐induced oscillations of the beach water table in regulating beach surface moisture dynamics. A series of laboratory experiments were conducted to assess the influence of hysteresis and transient flow effects on surface moisture variability. The experimental apparatus utilized a column of well‐sorted fine sand partially immersed in a reservoir of water. The water level in the reservoir was raised and lowered via a diaphragm‐metering pump to simulate tidally induced fluctuations of the water table, and the moisture content profile within the column was monitored using an array of Delta‐T probes. Moisture contents at specific elevations within the column were utilized as proxies to represent various ‘surface’ elevations (relative to the high water table). Results indicate that surface moisture content behaves in a distinctly hysteretic manner. Examination of water flow scanning curves illustrated that for all surface elevations considered, higher moisture contents for a given pressure head occurred during the drying cycle than during the wetting cycle. This observation is particularly evident with shallow surface elevations (i.e. water table close to the surface) where the Haines Jump phenomenon was found to have a significant influence on moisture content dynamics. Additionally, an assessment of the accuracy of hysteretic and non‐hysteretic models to predict the measured moisture contents demonstrated that hysteretic simulations consistently provide a better representation of the observed moisture contents than non‐hysteretic simulations. A time lag was found between the respective maxima and minima in water table elevation surface moisture content. At the near surface water table positions the time lag ranged between 30 and 100 minutes, and it increased to 240 minutes (four hours) with the high water table at 60 cm below the surface. Copyright © 2013 John Wiley & Sons, Ltd.     

Estimating traveler populations at airport and cruise terminals for population distribution and dynamics

In recent years, uses of high-resolution population distribution databases are increasing steadily for environmental, socioeconomic, public health, and disaster-related research and operations. With the development of daytime population distribution, temporal resolution of such databases has been improved. However, the lack of incorporation of transitional population, namely business and leisure travelers, leaves a significant population unaccounted for within the critical infrastructure networks, such as at transportation hubs. This paper presents two general methodologies for estimating passenger populations in airport and cruise port terminals at a high temporal resolution which can be incorporated into existing population distribution models. The methodologies are geographically scalable and are based on, and demonstrate how, two different transportation hubs with disparate temporal population dynamics can be modeled utilizing publicly available databases including novel data sources of flight activity from the Internet which are updated in near-real time. The airport population estimation model shows great potential for rapid implementation for a large collection of airports on a national scale, and the results suggest reasonable accuracy in the estimated passenger traffic. By incorporating population dynamics at high temporal resolutions into population distribution models, we hope to improve the estimates of populations exposed to or at risk to disasters, thereby improving emergency planning and response, and leading to more informed policy decisions.     

塔里木河下游生态输水后植被景观格局动态变化研究

2000-2005年, 塔里木河流域管理局先后7次向塔里木河下游断流区进行了生态输水, 输水河道两岸的植被得到了一定的恢复. 以2000-2005的中巴资源卫星CCD影像为主要数据源, 获得了6 a的植被/非植被二值图, 并计算各年的景观格局指数, 分析了6 a植被景观格局的变化. 结果表明: 植被景观动态度在第四时段(2003-2004年)最大, 为47.83%; 在第三时段(2002-2003年)最小, 为-1.39%; 2000-2005年植被景观的动态变化呈正向趋势. 2000-2005年, 植被景观斑块个数与景观形状指数增加, 蔓延度指数下降了36.9, 斑块结合度指数均高于99, 表明研究区的植被景观破碎化程度、分离程度增加, 而景观类型联通性较高. 植被斑块面积均处于增加趋势且远离河道植被恢复率越小, 但植被景观的比重仍小于50%, 说明非植被类型是研究区的基质类型, 组成了景观的最大斑块. 针对缓冲区Zone 1, 植被景观的平均分维数处于减小趋势且2005年的斑块个数最小, 斑块结合度指数处于增加趋势, 表明近河道区域植被较为稳定, 受生态输水的干扰度较小, 植被景观斑块之间越来越聚集. 6 a间Zone 1的植被最大斑块指数均大于10%, 远高于其它5个缓冲带, 表明离河道越近植被景观的优势度最大.     

Influence of human pressure on forest resources and productivity at stand and tree scales: The case study of Yunnan pine in SW China

This paper examines human impact on stands and individual trees of Pinus yunnanensis growing near the small mountain villages of Pianshui and Yangjuan in southwestern Sichuan Province,China.In an effort to assess whether use of these forests was sustainable,we examined the effects of human use in two ways.First,we directly measured the effect of cutting branches,for fuel and fodder,on tree growth.We hypothesized that branch cutting would negatively impact tree growth.We established 12 plots on four hills and compared 14 pairs of trees,one tree in each pair with an apparently full crown and the other with a considerable portion of the crown removed.Second,we assessed stand and tree properties over a 500 m elevation gradient above the villages where we hypothesized that as elevation increases,stand and tree properties should show fewer human impacts.Although extensive branch cutting reduced the live crown,tree height and diameter,compensatory processes likely enabled trees to recover and to add basal area increments(BAIs) similar to those added by trees with full crowns.Trees and stands close to villages showed less growth and lower basal areas,respectively,than stands and trees at intermediate or distant elevations from villages.Areas relatively close to the villages showed considerable effects of human-related disturbances such as branch cutting,grazing,tree and shrub removal,losses of litter,and human and animal trails.Such areas had increased soil erosion and often loss of the ‘A’ horizon.Stands close to villages had younger trees,lower stand basal areas,smaller basal area increments,and more stumps.Our results suggest an increasingly vulnerable interface between occupants of these two villages and their surrounding forests.     

The reinforcement contribution to the cyclic behaviour of reinforced concrete beam hinges

The cyclic behaviour of plastic hinges is an essential component in tracking the behaviour of RC frames to failure, not only for monotonically increasing force/pressure loads such as under extreme wind loads but also for dynamic displacement-driven loads such as under earthquake ground motions. To describe member deformations at ultimate loading, traditional moment–curvature techniques have required the use of an empirical hinge length to predict rotations, and despite much research a definitive generic expression for this empirical hinge length is yet to be defined. To overcome this problem, a discrete rotation approach, which directly quantifies the rotation between crack faces using mechanics, has been developed for beams and been shown to be accurate under monotonic loading. In this paper, the discrete rotation approach for monotonic loads is extended to cope with cyclic loads for dynamic analyses, and this has led to the development of a new partial interaction numerical simulation capable of allowing for reversals of slip of the reinforcing bars. This numerical tool should be very useful for the nonlinear analysis of reinforced concrete beams and reinforced concrete columns with small axial loads under severe dynamic loads. Copyright © 2011 John Wiley & Sons, Ltd.     

Book Reviews

Wolfgang Torge. Gravimetry. New York: Walter de Gruyter, 1989. 465 pp. U.S. $94.95.

W. H. Berger, V. S. Smetacek, and G. Wefer (eds.). Productivity of the Ocean: Present and Past. Chichester: John Wiley and Sons, 1989. 471 pp. Hardcover. U.S. $146.00.     

Overcoming the problem of locking in linear elasticity and poroelasticity: an heuristic approach

In this paper, we examine heuristically the reasons for locking in poroelasticity. As a first step, we first reexamine the problem of locking in linear elasticity. From this, we discover how the problem arises in the poroelasticity setting and how the problem might be overcome.     

Rates of stream incision in the middle part of the Arkansas River basin based on late Tertiary to mid-Pleistocene volcanic ash

Ages and elevations of ash layers correlated with late Tertiary and Pleistocene eruptions in the western US and present stream elevations are used to calculate net rates of incision by streams in the middle reaches of the Arkansas River basin in the south central US. The mean of the 23 measurements of rate of stream incision in the study area is 4.2±2.7 cm/ky with a range of 0.6 to 9.7 cm/ky. Major influences on rate of stream incision in the study area include the arid to semi-arid climate of the region, the type of material being incised by streams, stream captures, and salt dissolution in the bedrock that underlies the region. Rates of incision exceeded rates of basin filling but significant deposits of unconsolidated late Cenozoic sediments occur in the study area. Basins of streams that have incised the slowest since the late Tertiary contain the thickest and most extensive amounts of unconsolidated Quaternary sediments. Rates of incision by streams in the study area are similar to or slower than rates reported for streams elsewhere in the US and the world. Streams in mountainous regions and areas affected by rapid uplift have incised at rates orders of magnitude faster than streams in the study area.