Numerical analysis of the interaction of soil-structure under earthquake loading   总被引：1，自引：0，他引：1  

章根德  宁书成 《地震学报(英文版)》1997,10(4):489-495

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Diagenesis of a mixed siliciclastic/evaporitic sequence of the Middle Muschelkalk (Middle Triassic), the Catalan Coastal Range, NE Spain   总被引：1，自引：0，他引：1  

S. MORAD  I. S. AL-AASM†  F. J. LONGSTAFFE‡  R. MARFIL§  L. F. DE ROS  H. JOHANSEN¶  M. MARZO 《Sedimentology》1995,42(5):749-768

The Middle Muschelkalk (Middle Triassic) of the Catalan Coastal Range (north-east Spain) comprises sandstone, mudstone, anhydrite and minor carbonate layers. Interbedded sandstones and mudstones which are dominant in the north-eastern parts of the basin are terminal alluvial fan deposits. South-westward in the basin, the rocks become dominated by interbedded evaporites and mudstones deposited in sabkha/mudflat environments. The diagenetic and pore water evolution patterns of the Middle Muschelkalk suggest a strong facies control. During eodiagenesis, formation of microdolomite, anhydrite, baryte, magnesite, K-feldspar and mixed-layer chlorite/smectite was favoured within and adjacent to the sabkha/mudflat facies, whereas calcite, haematite, mixed-layer illite/smectite and quartz formed mainly in the alluvial facies. Low δ¹⁸O_SMOW values for microdolomite (+23.7 to +28.4%) and K-feldspar overgrowths (+17.3 to +17.7%) suggest either low-temperature, isotopic disequilibrium or precipitation from low-¹⁸O porewaters. Low-¹⁸O waters might have developed, at least in part, during low-temperature alteration of volcanic rock fragments. During mesodiagenesis, precipitation of quartz overgrowths and coarse dolomite occurred in the alluvial sandstones, whereas recrystallization of microdolomite was dominant in the sabkha/mudflat facies. The isotopic compositions of these mesogenetic phases reflect increasing temperature during burial. Upon uplift and erosion, telogenetic calcite and trace haematite precipitated in fractures and replaced dolomite. The isotopic composition of the calcite (δ¹⁸O_SMOW=+21.5 to +25.6%o; δ¹³C= 7.7 to - 5.6%o) and presence of haematite indicate infiltration of meteoric waters.  相似文献   

Profiling of aerosol concentrations, particle size distributions and relative humidity in the atmospheric surface layer over the North Sea   总被引：1，自引：0，他引：1  

GERRIT DE LEEUW 《Tellus. Series B, Chemical and physical meteorology》1990,42(4):342-354

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Diagenesis and formation water chemistry of Triassic reservoir sandstones from southern Tunisia   总被引：5，自引：0，他引：5  

S. MORAD  H. N. BEN ISMAIL†  L. F. DE  ROS  I. S. AL-AASM‡  N-E. SERRHINI† 《Sedimentology》1994,41(6):1253-1272

The fluvial Triassic reservoir subarkoses and arkoses (2409·5–2519·45 m) of the El Borma oilfield, southern Tunisia, were subjected to cementation by haematite, anatase, infiltrated clays, kaolinite and K-feldspar at shallow burial depths from meteoric waters. Subsequently, basinal brines controlled the diagenetic evolution of the sandstones and resulted initially in the precipitation of quartz overgrowths, magnesian siderite, minor ferroan magnesite and anhydrite. The enrichment of siderite in ¹²C isotope (δ¹³C_PDB= - 14·5 to - 9‰) results from derivation of carbon from the thermal decarboxylation of organic matter. During further burial, the precipitation of dickite and pervasive transformation of kaolinite into dickite occurred, followed by the formation of microcrystalline K-feldspar and quartz, chlorite and illite, prior to the emplacement of oil. Present day formation waters are Na-Ca-Cl brines evolved by the evaporation of seawater and water/mineral interaction and are in equilibrium with the deep burial (≤ 3·1 km) minerals. These waters are suggested to be derived from the underlying Silurian and Devonian dolomitic mudstones.  相似文献   

A long Upper Pleistocene pollen record from Les Echets, near Lyon, France   总被引：11，自引：0，他引：11  

JACQUES-LOUIS DE BEAULIEU  MAURICE REILLE 《Boreas: An International Journal of Quaternary Research》1984,13(2):111-132

Analysis of 732 samples through 39 m of sediments from the ancient lake of Les Echets, 15 km northeast of Lyon, France, resulted in a long, continuous pollen diagram covering the interval from the Late Rissian to the Holocene. Above a complete Ecmian sequence, there are two Early Wiirmian temperate cycles (the older one including two climatic optima separated by a brief deterioration) with forest successions characterized by the spread of Carpinus at the end of the early temperate phase. These episodes, whose exact equivalents are found at Grande Pile in the Vosges area, are correlated with the Early Wiirmian trilogy Amersfoort-Brorup-Odderade of northern Europe. The absolute dates proposed for the Grande Pile sequence arc accepted, whereas those for the three northern European stratotypes are rejected. The Early Wiirmian is thus placed between 115,000 and 70,000 years B.P. In the Middle Wiirm, three undated intcrstadials arc characterized by a sparse forest cover. The long Late Wiirmian section is a characteristic feature of the sediment history at Les Echets. Very cold and arid conditions prevailed during this interval, without any unequivocal indications of intcrstadial episodes. A rise in Artemisia around 15,000 B.P. marks the transition from the Pleniglacial to the Oldest Dryas.  相似文献   

Quantification of electron microprobe compositional maps of rock thin sections: an optimized method and examples   总被引：1，自引：0，他引：1  

V. DE ANDRADE  O. VIDAL  E. LEWIN  P. O'BRIEN  P. AGARD 《Journal of Metamorphic Geology》2006,24(7):655-668

Quantification of discrete pressure–temperature domains in deformed chlorite + white mica‐bearing metapelites was undertaken on mineral compositions derived by two‐dimensional microprobe compositional mapping of selected areas of rock thin sections. In order to achieve compositional information at sufficient analytical precision, spatial resolution and sample coverage within a typical analysis time of 1 day, an optimization of measurement methods was necessary. The method presented here allows collection of raw counts for eight different element concentrations at an analytical precision of ～1–2 wt%. X‐ray intensity multiplane maps (one map per measured chemical element) are translated into concentration multiplane maps, utilizing selected conventionally measured spot analyses combined with the Castaing approximation for each mineral. As this step requires identification of the different minerals present in the mapped area, a statistical clustering technique to identify different groups of composition was developed, guided by simple petrographic inspection of the thin section, to delineate the important minerals in the mapped area. Finally, the compositions of each pixel are translated into a mineral structural formula thus yielding a new kind of image with a high content of petrological information. The reliability of the mineral composition images was emphasized by carrying out precision tests on the analytical data. The possible use of chemical maps to infer the P–T–deformation history of metamorphic rocks is illustrated with two samples from the Spitzbergen and the Sambagawa blueschist facies belts. In both samples, a strong correlation between structures and chemistry is observed. Qualitative estimates of P–T conditions from the Si‐content of mica and chlorite are in good agreement with their location in microstructures that formed at different times. Therefore, the combination of chemical maps with microstructural observations is a very powerful approach to understand both the evolution of complex metamorphic rocks and the control by deformation of mineral reactivity.  相似文献   

Stomatal and non-stomatal fluxes of ozone to a northern mixed hardwood forest   总被引：2，自引：0，他引：2  

ALAN HOGG  JOHAN UDDLING  DAVID ELLSWORTH  MARY ANNE CARROLL  SHELLEY PRESSLEY  BRIAN LAMB  CHRISTOPH VOGEL 《Tellus. Series B, Chemical and physical meteorology》2007,59(3):514-525

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Sedimentology and stratigraphy in the cave Hamnsundhelleren,western Norway     

VIDAR VALEN  JAN MANGERUD  EILIV LARSEN  ANNE KARIN HUFTHAMMER 《第四纪科学杂志》1996,11(3):185-201

The stratigraphy in Hamnsundhelleren is as follows. A basal weathered rock bed of unknown age is followed by laminated clay deposited under stadial conditions and correlated with palaeomagnetism to the Laschamp excursion (43–47 000 yr BP). Angular blocks, bones and clay above this are ¹⁴C dated to the Ålesund Interstadial (28–38 000 yr BP). Another stadial laminated clay following the Ålesund Interstadial includes a palaeomagnetic excursion correlated with Lake Mungo (28 000 yr BP). The newly discovered Hamnsund Interstadial above this consists of frost-weathered clay and scattered angular blocks. It is ¹⁴C dated to 24 500 yr BP on bones mixed into the Ålesund Interstadial. The Hamnsund Interstadial is succeeded by another stadial laminated clay and then a Late-glacial–Holocene mixture of bones and blocks. In Hamnsundhelleren and other similar caves four successive phases of sedimentary environments for each ice-free–ice-covered cycle have been identified: (i) ice-free phase (deposition of bones and frost-weathered blocks); (ii) subaerial ice-dammed lake phase (sand or silt deposited in a lateral glacial lake); (iii) subglacial ice-dammed lake phase (cave closed by ice, deposition of till, debris flows and laminated clay); (d) ice-plugged phase (cave is plugged by frozen lake water and/or glacial ice, no deposition).  相似文献   

INVESTIGATION OF INFILTRATION CHARACTERISTICS AND DEBRIS FLOW INITIATION CONDITIONS IN DEBRIS FLOW SOURCE AREAS USING A RAINFALL SIMULATOR     

H. M. BLIJENBERG  P. J. DE GRAAF  M. R. HENDRIKS  J. F. DE RUITER  A. A. A. VAN TETERING 《水文研究》1996,10(11):1527-1543

Rainfall was simulated on unconfined plots on regolith in debris flow source areas using a portable simulator. In total, 351 simulations were carried out on steep slopes (27–54°) with rainfall intensities of 28–291 mm/h. From these rainfall simulations the infiltration parameters sorptivity (S) and steady-state infiltration capacity (K) of the regolith, and a threshold for the occurrence of micro-scale mass movements, were obtained. Two evaluation methods were used to obtain the infiltration parameters K and S. The ‘infiltration envelope’ method uses rainfall intensity and time to ponding from multiple tests and fits an infiltration envelope through the data from which K and S can be obtained. The ‘constant runoff’ method uses rainfall intensity and overland flow intensity to calculate K, after which S can be calculated in several ways by using time to ponding. The constant runoff method produced K values of 16.6–128 mm/h, which usually show a log-normal distribution. K values depend on the regolith parent material and rainfall intensity. Using this method, S values are 0.088–0.381 cm/min^1/2. The infiltration envelope method produced K values of 9.8–131 mm/h and S values of 0.14–0.32 cm/min^1/2. It can be argued that both methods overestimate K as well as S, but quantitative relations between measured/calculated and actual values of K and S have not yet been obtained. At high rainfall intensities, typically 100 mm/h or more, micro-scale mass movements sometimes occur. A lower threshold curve for the occurrence of these micro-scale mass movements has been constructed. It is a function of both slope angle and rainfall intensity. The micro-scale mass movements could play an important part in the initiation of debris flows in the study area, possibly by delivering sediment to overland flow. On the very steep slopes, the sediment-rich overland flow can easily mobilize coarse material.  相似文献   

Geomorphology of the Sub-Antarctic Australian Territory of Heard Island-McDonald Island     

KEVIN KIERNAN  ANNE McCONNELL 《The Australian geographer》1999,30(2):159-195

The geomorphology of Heard Island-McDonald Island is primarily the product of close interplay between volcanism, glaciation, and vigorous marine processes in a stormy sub-Antarctic environment. The dominant landform is the strato-volcano Big Ben (2745m), which is the highest mountain on Australian territory outside Antarctica. Other volcanic landforms include scoria cones, domes, open vertical volcanic conduits, lava flows and lava tubes. Volcanic activity is ongoing from the summit of Big Ben, and from Samarang Hill on McDonald Island. Early, but unproven, glacial sediments may exist within the Late Miocene - Early Pliocene Drygalski Formation, which forms a 300m high plateau along the northern coast of Heard Island. Growth of the present glaciers, some of which reach sea level, has been a response to progressive growth of the volcanoes. A variety of erosional and depositional glacial landforms is present, including major lateral moraines and extensive hummocky moraines. Vigorous longshore drift and an abundant sediment supply have produced a large spit at the downdrift end of the island, and formed bars from reworked glacigenic sediment that now impound proglacial estuarine lagoons, some of which have grown rapidly over recent decades as tidewater glaciers have retreated. Integrated study of the volcanic, glacial and coastal sequences offers the possibility of constructing a well-dated record of climate change. Research into the geomorphology, surficial sediments, and contemporary geomorphological processes, including glaciofluvial sediment flux, is also important as an aid to environmental management on land, and to management of the adjacent marine environment.  相似文献