大青山河谷地貌特征及新构造意义

论述了大青山河谷地貌的基本特征,河谷地貌的形成和演化明显地受大青山山前断裂带的控制。在山前断裂强烈活动的地段,河流深发呈峡谷,发育多级河流阶地,河谷纵剖面为上凸形,谷底宽度与谷肩山高度之比Ｖｆ值较小;在山前断裂活动较弱的地段,河流侧蚀呈宽谷,河流阶地级数较少,河谷纵剖面为下凹形,Ｖｆ值较大。河谷纵剖面凹度与大青山抬升幅度线性负相关。     

Point defects and non-stoichiometry in forsterite

Existing experimental evidence suggests that in pure Mg-forsterite with a fixed Mg/Si ratio, vacancies and interstitials on the Mg sublattice are the dominant intrinsic point defects, while O vacancies and conduction-band electrons are the primary oxygen-deficient defects. Orthopyroxene appears to dissolve readily in pure Mg-forsterite at high temperatures, the change in Mg/Si ratio being accommodated by Mg vacancies and Si interstitials; as a consequence, upper-mantle forsterite may be substantially non-stoichiometric. It is postulated that the amount of Fe that can be oxidized in the forsterite phase is directly related to the excess Si present, either incorporated in the structure, or available from another phase richer in SiO₂ such as pyroxene.     

太行山山前平原降水量特征及其分布的小波分析——以栾城为例

运用墨西哥帽函数(Mexican Hat Function)小波分析方法对太行山山前平原典型地区的栾城站40年来的降水量以及当地典型作物冬小麦不同生育期阶段的降水量进行了小波分析。结果表明，分时段的降水量并无一个稳定的周期，而是变周期。该区全年降水量变化在40年尺度上可分为1980年前的偏多期和其后的偏少期；10～30年尺度上可分为60年代末以前的偏多、1997年以后的偏少和这期间的动荡期；在较小时间尺度上存在5～7年的周期变化，今后10年内年降水量的总体趋势依旧偏少，5年内为少中有稍偏高于平均降水量的趋势。冬小麦全生育期均存在较明显的4个阶段的交替变化，1967年以前的偏多期、1967～1983年左右的偏少期、1984～1994年左右的偏多期、1995年以后的偏少期。     

L'érosion des chaînes de montagnes : influence de la sédimentation de piedmont

The applanation of mountain belts that results in peneplain is generally considered to be caused by the long-term activity of erosion. Peneplanation has been previously defined as the lowering of an elevated topography and the concomitant subduing of its relief. We propose a model following which piedmont sedimentation induces the base level rise, allowing applanation to develop at high elevation and resulting in an elevated ‘peneplain’. This model is illustrated by the morphological evolution of the southern flank of the Pyrenees during the Cainozoic. To cite this article: J. Babault, J. Van Den Driessche, C. R. Geoscience 337 (2005).     

A warning system for rainfall-induced shallow failures

It is widely recognised that soil slips and debris flows are triggered by short intense storms. Owing its geologic, geomorphologic and climatic settings, the Piedmont Region (NW Italy) is highly prone to the occurrence of this kind of landslides. In the last two centuries, in fact, a total of 105 severe meteoric events which triggered shallow failures occurred and, of these, 18 events took place from 1990 to 2002. A fair number of rainfall thresholds have been proposed in the literature, defined both on empirical or on physical bases. Empirical thresholds are defined collecting rainfall data for landslide meteoric events and for events without landslides, while physical thresholds are based on numerical models that consider the relation between rainfall, pore pressure and slope stability. The main objective of this paper is the identification of the empirical triggering thresholds for the Piedmont Region. Four meteoric events were selected and analysed (November 4–5, 1994; July 7–8, 1996; April 27–30, 2000; October 13–16, 2000) because they supply a wide range of variation for both rainfall parameters (duration, intensity, cumulative rainfalls) and the number of induced landslides. In the intensity–duration plot, the critical limit is described by the equation: I=19D^−0.50 (where I=rainfall intensity expressed in mm/h and D=rainfall duration expressed in hours). Such a limit is traced to envelop 90% of the points on the graph. In the NI–D diagram the triggering thresholds are given by the equations NI=0.76D^−0.33 and NI=4.62D^−0.79 (where NI=normalised intensity with respect to the annual precipitation, MAP, expressed in %, [(mm/h)/PMA]×100). In the article the different meaning of these thresholds is discussed. Finally, the diagram NI–NCR is proposed; the triggering threshold is given by the expression: NI=−0.09ln[NCR]+0.54 (where NCR is the normalised cumulative critical rainfall, [mm/PMA]×100). The application of the triggering thresholds as a fundamental element in a warning system dedicated to the safeguarding of population in landslide-prone areas is discussed. In detail an operating procedure which is presently being verified and tested in the studied area is described.     

Coupling of tectonic factors and precipitation variability as a driver of Late Quaternary aggradation in Northeast Brazil

The coupling between tectonic factors and climate processes is a key element in understanding landscape evolution. However, few studies address this issue in the context of unglaciated tropical areas in passive continental margins. Thus, this research aimed to understand the origins and evolution of the geomorphological landscape in the eastern sector of Northeast Brazil along the Late Quaternary, between the Last Interstadial (Marine Isotopic State 3) and the Upper Holocene. The morphostratigraphic approach, coupled with sedimentological analyses and optically stimulated luminescence dating of sediments, showed that the depositional record stored in the landscape ranges from at least 60 000 years BP until the Upper Holocene. Depositional intervals suggest that there were moments of climatic instability followed by moments of relative geomorphological quiescence. Such active moments coincide chronologically with Heinrich and Dansgaard-Oeschger events, which are likely linked to changes in paleo-pluviosity that might respond to the dismantling of elluvial covers and colluvial deposition in the area. Likewise, reworking of hillslope materials led to increased deposition in the fluvial realm. In addition, such deposits might have been affected by the neotectonic complexity of the area, responsible for the creation of non-concatenated accommodation spaces, indicating a dynamics of uplifting and subsidence of blocks typical of passive margin taphrogenic environments. Therefore, the formative processes that led to the Late Quaternary deposition of sediments in a platform margin context reflect a coupling between tectonic and climatic factors. The former, driven by precipitation variability on a regional scale, triggered fluvial and high-energy hillslope processes that resulted in ubiquitous valley floor and piedmont aggradation, whereas the latter led to the dismantling of local base levels, transforming depositional units into new denudational landforms subject to the current climate dynamics. © 2020 John Wiley & Sons, Ltd.     

Quantification of the degree of confinement of a turbidite-filled basin: A statistical approach based on bed thickness distribution

Bed thickness distribution within turbidite systems is related to basin geometry and to magnitude and duration of depositional events. Cumulative distribution of turbidite bed thicknesses is often interpreted in terms of a power law. Alternatively, these distributions have been described by a lognormal mixture model. Changes in the power-law exponent can be related to the rheological properties of the gravity-driven flows and to the geometry of the basin.     

A statistical methodology for assessing the long‐term effects of antecedent drought conditions on stream runoff: applications to the Piedmont Province,southeastern United States

A method was developed to investigate the long‐term (months‐to‐years) effects (both magnitude and duration) of antecedent rainfall upon subsequent runoff coefficients (RCs) or runoff/rainfall ratios. The method was applied to a four‐state region (Georgia, South Carolina, North Carolina, and Virginia) within the southeastern Piedmont Province of the United States and incorporated a 59‐year data set of 19 United States Geological Survey stream gages and 57 National Climatic Data Center rain gages. The method was designed to facilitate statistical comparisons [Mann–Whitney rank sum tests] between various groups of normalized runoff coefficients (NRCs) representing 6–36 month periods which differed in terms of antecedent rainfall conditions. The results of this study show that under all subsequent rainfall conditions, with the exception of excess rainfall, a 1‐year period of antecedent drought lowered NRCs for at least 1 year following the drought. The principal finding of this study is that a year‐long drought period within the southeastern Piedmont Province lowers NRCs by ～25% during the following year when rainfall returns to normal. In most cases, RCs are significantly lower during the second year following a drought than they would be when anteceded by normal rainfall; however, the effects of drought wane during this period. This is a statistical and regional method that can be modified to other study areas; however, it cannot be used to predict storm‐event rainfall–runoff relationships for any specific basin. Copyright © 2010 John Wiley & Sons, Ltd.     

Economic Efficiency of Residential Water Conservation Programs in a Pennsylvania Public Water Utility

This study examines the economic efficiency of implementing a residential water conservation program in a small Pennsylvania public water utility. Local demographic data and results from similar programs elsewhere were used to estimate potential water conservation for three programs: rebates for low-flow toilets, rebates for high-efficiency washing machines, and in-home water audits. Future water supply and wastewater treatment demand were estimated. The net present value of constructing, operating, and maintaining new capacity infrastructure (water supply, water storage tanks, and wastewater treatment plant capacity), as well as the costs of the conservation programs, was calculated for a range of scenarios that included future demand growth, construction costs, interest rates, and levels of participation in the conservation programs. Results indicate that investing in residential water conservation would be cost-effective for a small number of scenarios that generally combine higher growth rates, higher interest rates, higher construction costs, and relatively modest public participation in conservation. The results are affected by the timing of necessary supply-side investments relative to the most significant water conservation gains, the relatively inexpensive local water supply costs, and the relatively high local wastewater treatment costs. Water conservation might be cost-effective for a wider range of conditions in communities facing scarce and expensive water supply options.     

Lacustrine carbonate deposition in Middle Pennsylvanian cyclothems — the Upper Freeport Formation,Appalachian Basin,USA

The Upper Freeport Formation (Upper Allegheny Group, Middle Pennsylvanian) is one of the earliest non-marine cyclothems in the Appalachian Basin and contains carbonates, siliciclastics, and coal. A detailed facies analyses of 25 cores from the Upper Freeport Limestone in western Pennsylvania (Armstrong and Indiana Counties) identified four facies associations containing thirteen separate facies: rudstone-limestone (Association A), rudstone-laminated limestone (Association B), laminated limestone (Association C), and coal — siliciclastics (Association D). We interpreted them, respectively, as shallow, high energy lacustrine margin (A); littoral to sublittoral lacustrine (B); offshore lake (C); and vegetated swamp and marsh (D). The depositional environment is envisaged as an anastomosed channel system surrounded by extensive wetlands containing adjacent densely vegetated swamp and marsh areas and freshwater, carbonate-producing lakes.Lakes developed in the topographic lows of the alluvial plain, protected and filtered from siliciclastic deposition by vegetated swamps. These lakes were small in size (several square km), shallow, and stratified, as indicated by the abundance of laminated facies. They were hydrologically open, and interconnected by surface and ground waters. Carbonate production in this lacustrine system was not triggered by evaporative concentration but by biogenic algal production. Carbonates were continually being recycled, both physicochemically and biologically, within the depositional system. Various early diagenetic processes, including brecciation, pedogenesis and recrystallization, masked original evidence for transport mode. The Upper Freeport Limestone contains numerous features of palustrine carbonates, and provides a case study for one end-member of freshwater carbonate models, characterized by a very short period of subaerial exposure. Small-scale climatic changes or autocyclic processes such as small topographic differences, changes in local drainage patterns, and fluvial dynamics may have controlled Upper Freeport lake level changes.Facies analysis does not support a climate forcing as a control for cyclothem development of non-marine sequences during the Pennsylvanian. Tectonic and autocyclic processes better explain the evolution of these wetland (lacustrine/alluvial) systems with its associated coal formation.This is the seventh paper in a series of papers published in this issue on Climatic and Tectonic Rhythms in Lake Deposits.