Sequence-stratigraphic frameworks and their palaeogeographic patterns for the Permian Lopingian of the Dianqiangui Basin and its adjacent areas of Southwestern China

The Permian Lopingian in the Dianqiangui Basin and its adjacent areas is marked by the coal measures of the Wuchiapingian and the carbonate strata of the Changhsingian stages. For the Lopingian of the Dianqiangui Basin and its adjacent areas,the diversity of sedimentary facies and the obviousness of facies change provide an advantaged condition on a study of sequence stratigraphy. Approximately,the Wuchiapingian stage constitutes a third-order sequence and the Changhsingian stage forms an-other. For the Wuchiapingian stage in the study area,coal-measures were developed on the attached platform and,in addition,a special coal-measure that is composed of both limestone beds and coal beds was also developed in the central part of some isolated platforms. Grain-bank grainstones and packstones were formed on the margin of the attached platform as well as in the windward part of iso-lated platforms. For the Changhsingian stage in the study area,open-platform limestones were formed on the attached platform,while sponge-reef limestones were developed both on the margin of the at-tached platform and on the isolated platforms. The Lopingian Series is a set of basin-facies muddy shales with interbeds of silicalites in the inter-platform basin,which appears a set of the large-thick coarse clastic strata of molasses covering direct the deep-water strata from the Devonian to the Per-mian Yangsingian in the Qinzhou-Fangcheng region in the southern part of the study area. All of these features indicate the complexity of temporal-spatial facies-changes. Sequence-stratigraphic frame-works could be established,which would illustrate two types of facies-changing surfaces and dia-chronisms in the stratigraphic records,based on the combination of both biostratigraphic and chronostratigraphic materials and the regularity reflected by temporal evolutionary succession of sediments as well as spatial distributional patterns of sedimentary facies. Ultimately,features of sedi-mentary succession and palaeogeographical evolution of the Permian Lopingian in the study area are revealed clearly in a series of the panel diagrams of sequence-stratigraphic frameworks and the outline maps showing the sedimentary-facies and palaeogeography. The Permian Lopingian formed by two third-order sequences differs from the stratigraphy of the same era characterized by the constant re-gression along Euramerica. Most specially,if the end-Guadalupian mass-extinction event is genetically related to a regressive event represented by the unconformity of the first episode of the Dongwumovement in the study area,the mass-extinction event at the turn from the Permian to the Triassic is genetically related to a rapid transgressive event re-flected by the drowning unconformity in the study area. These phenomena might reveal a complex rela-tionship between mass-extinction events and trans-gressive-regressive events.     

Do hydraulic units define macroinvertebrate assemblages in mountain streams of central Argentina?

Methods to assess the physical habitat provide important tools for many aspects of river management. Hydraulic units (defined as a homogeneous patch of flow type and substrate) were described in mountain streams of Central Argentina and the distribution of macrozoobenthos in these habitat units was analyzed. Four streams from the upper Carcarañá River Basin (Córdoba, Argentina) were sampled in two hydrological periods. Hydraulic units (as substrate and flow type), current velocity, depth, macrophytes and macroalgae were assessed. Three benthic samples were taken in each hydraulic unit. A total of 12 hydraulic units were registered, which varied seasonally in their proportional abundance. The highest values of taxonomic richness, total abundance, diversity and evenness were found in the low-water period. The most heterogeneous hydraulic units (characterized by substrate of diverse grain size) presented the highest richness, diversity and evenness, whereas the highest total abundance was observed in hydraulic units with homogeneous substrate, such as bedrock or gravel sand. Canonical correspondence analysis grouped samples and taxa mainly in relation to the hydraulic units, and temporal variation in macroinvertebrate assemblages was observed. We found that the interaction between hydrological and geomorphological conditions affected benthic assemblages and that their organization is important at a mesoscale. Therefore, hydraulic units may be considered important tools in assessing stream integrity in lotic systems of central Argentina.     

型钢高强混凝土柱抗震性能的试验研究

通过14根型钢高强混凝土柱的低周反复加载试验，得到了型钢高强混凝土柱在压、弯、剪共同作用下的主要破坏形态，并探讨了剪跨比、配箍率、混凝土强度对型钢高强混凝土柱滞回曲线、耗能能力以及延性的影响。试验结果表明，型钢高强混凝土柱具有抵御二次地震作用的能力，其抗震性能优于钢筋混凝土柱。     

Use of a three‐dimensional laser scanner to digitally capture the topography of sand dunes in high spatial resolution

We herein report the results of a ?eld study that was designed to test the feasibility of using ground‐based LIDAR to map the topography of a sand dune in high spatial resolution. A portable Cyrax 2500 three‐dimensional (3D) laser scanner was used to digitally capture the topography of a barchan, roughly 4 m tall and 50 m long, located in the White Sands National Monument, New Mexico. We performed eleven scans around the barchan and obtained the elevation relative to the inter‐dune ?at at roughly ¹/₄ million points on the dune surface. The elevation point data were then interpolated to yield a continuous surface model of the dune topography with c. 10 cm spatial resolution and c. 6 mm position accuracy. The results from this ?eld study clearly demonstrate the potential of ground‐based LIDAR as a mapping tool for use in aeolian research and other earth science applications. The 3D surface model of the dune can describe the morphology with hitherto unprecedented detail. Moreover, the surface of the dune is mapped with a minimum of foot traf?c on the dune itself. Copyright © 2004 John Wiley & Sons, Ltd.     

Origin of honeycombs and related weathering forms in Oligocene Macigno Sandstone,Tuscan coast near Livorno,Italy

Two types of cavernous‐weathering features are exposed in the Oligocene Macigno Sandstone along 5 km of the Tuscan coast south of Livorno, Italy. Honeycomb cells (type 1 features) are typical closely spaced, more or less circular pits of centimetre scale that have been eroded 2 to 6 cm below the general surface of bedding planes or joints. ‘Aberrant honeycomb’ cells (type 2 features) are highly elongate, polygonal, or irregular ?at depressions of decimetre scale surrounded by walls rarely higher than 2 cm, some of which pass into long, free‐standing walls or tendrils. Thus, not all type 2 ‘honeycomb’ cells are fully enclosed. We measured the geometry of 551 honeycomb cells and examined various rock properties (microscopic texture and fabric, mineralogy, porosity, permeability, and chemical composition) to isolate factors that control the size, shape, distribution, and pattern of the honeycombs. Our goal was to narrow potential origins of the features and to understand their formation. The ubiquitous occurrence of sea salt in the honeycombs and scanning electron microscope evidence of physical weathering of silicates, especially micas, favours an origin for the honeycombs chie?y by salt weathering. Honeycombs do not form in siltstone, iron‐oxide‐impregnated sandstone, calcite‐cemented concretions, or in case‐hardened joints. Thus, salt weathering of type 1 and 2 honeycombs is not effective in very low permeability rocks. We propose for type 1 honeycombs that seawater is drawn into micropores of the sandstone and evolves into self‐organized diffusion cells (Turing patterns). Selective evaporation at the stationary nodes of diffusion cells, which form at the same site over time, leads to the precipitation of salt, then grains spall off, and pits are formed. The deepest pits (>40 mm) formed where Turing patterns consistently formed at the same sites. Although the walls are more porous and weathered than the host sandstone, they become selectively case hardened by an unidenti?ed component of low abundance. Initial honeycomb cell shape and gravity locally in?uenced type 1 honeycomb shapes. We suggest that type 2 honeycombs develop where diffusion‐controlled Turing patterns lead to case‐hardening along linear trends; gravity and rock fabric are important locally in in?uencing the orientation of the walls. Only type 2 cells are forming today, suggesting recent environmental changes. Gravity is not a fundamental control on honeycomb shape; in places it is a contributing factor. Pre‐existing depressions (quarry tool marks) have strongly in?uenced honeycomb shape locally. Copyright © 2004 John Wiley & Sons, Ltd.     

呼伦贝尔沙地沙丘砂来源的定量分析— 逐步判别分析(SDA)在粒度分析方面的应用

以呼伦贝尔沙地砂物质的粒度分析资料为基础,利用两组间的逐步判别分析(SDA) 来筛选决定不同沉积物间差异的主导因子,根据主导因子的个数、Mahalanobis距离D2、通过统计学检验的信度琢等3个因素,来定量地确定两个总体间的相似性大小。分析结果表明:呼伦贝尔沙地的风成沙丘砂主要来源于海拉尔组砂(Q3),但河流冲积砂和古土壤也有不可忽视的作用;在嵯岗镇附近及其以西的海拉尔河下游宽阔河谷中,自然条件下河流冲积砂也可以成为风成沙丘砂的主要沙源。     

中国种子植物特有科属的分布型

中国种子植物特有属有２６８属，归７８科，其中有８个单种属中国特有科。本文根据特有属的地理分布及与环境的关系，区分为９个分布型和２３个亚型（包括本分布型），对各分布型和亚型进行了统计分析和详细阐述，讨论了分布区的间断和替代现象。提出特有科属分布型的主要特点。     

Implications of Habitat Fragmentation on Climate Change-Induced Forest Migration

A rapid warming caused by the release of greenhouse gases could result in the displacement of climatic controls that limit the current ranges of many species. Projected northward displacement for loblolly pine is over 400 km, with only a narrow region of overlap between the current and projected future range limits. A model of dispersal developed for loblolly pine is presented. The model utilizes a GIS to assess the critical influence of land use patterns on climate change-induced migration through modern landscapes. Results from two relatively large (150 × 150 km) study areas in the eastern United States suggest that potential migration rates may fall short by at least an order of magnitude of that necessary to track projected range shifts. Management options of species transplanting and the establishment of greenways are explored with the model. Species that are unable to keep pace with changing range limits may experience a reduction in population size and exist in climatic disequilibrium.     

线形沙丘研究进展综述

本文回顾和总结了国外内关于线形沙丘研究的最新进展。阐明了线性沙丘的分布规律、发育模式和内部构造等方面的研究结果。