Epikarst hydrology and implications for stalagmite capture of climate changes at Grotta di Ernesto (NE Italy): results from long‐term monitoring     

Renza Miorandi  Andrea Borsato  Silvia Frisia  Ian J. Fairchild  Detlev K. Richter 《水文研究》2010,24(21):3101-3114

Grotta di Ernesto is a cave site well suited for palaeoclimate studies because it contains annually laminated stalagmites and was monitored from 1995 to the end of 2008 for microclimate, hydrology and hydrochemistry. Long‐term monitoring highlighted that cave drips show three different hydrological responses to rainfall and infiltration: (1) fast seasonal drips in the upper part of the cave, which are mostly fed by fractures, (2) slow seasonal drips, located at mid‐depth in the cave characterized by mixed feeding and (3) slow drips, mostly located in the deeper gallery, which are fed by seepage flow from bulk porosity with a minor fracture‐fed component. The slow drips display daily cycles during spring thaw. Monitoring also indicated that drip waters are only slightly modified by degassing within the soil zone and aquifer and by prior calcite precipitation. Hydrochemical studies show a clear seasonality in calcite saturation index, which results in most cave calcite precipitation occurring during late autumn and winter with similar amounts of precipitated calcite on most stalagmites, regardless of drip rate (discharge) differences. Drip rate, and drip rate variability, therefore, has a minor role in modulating the amount of annual calcite formation. In contrast, drip rate, when associated with moderate reduction in calcite saturation index, clearly influences stalagmite morphology. Increasing drip rate yields a passage from candle‐, to cone‐ to dome‐shaped stalagmites. Very high drip rates feed speleothems with flowstone morphology. In summary, monitoring provides information about the karst aquifer and how hydrology influences those physical and chemical characteristics of speleothems which are commonly used as climate proxies. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Short-term environmental variability in cold-water coral habitat at Viosca Knoll,Gulf of Mexico     

Andrew J. Davies  Gerard C.A. Duineveld  Tjeerd C.E. van Weering  Furu Mienis  Andrea M. Quattrini  Harvey E. Seim  John M. Bane  Steve W. Ross 《Deep Sea Research Part I: Oceanographic Research Papers》2010,57(2):199-212

The Lophelia pertusa community at Viosca Knoll (VK826) is the most extensive found to date in the Gulf of Mexico. As part of a multi-disciplinary study, the physical setting of this area was described using benthic landers, CTD transects and remotely operated vehicle observations. The site was broadly characterised into three main habitats: (1) dense coral cover that resembles biogenic reef complexes, (2) areas of sediment, and (3) authigenic carbonate blocks with sparse coral and chemosynthetic communities. The coral communities were dominated by L. pertusa but also contained numerous solitary coral species. Over areas that contained L. pertusa, the environmental conditions recorded were similar to those associated with communities in the north-eastern Atlantic, with temperature (8.5–10.6 °C) and salinity (～35) falling within the known species niche for L. pertusa. However, dissolved oxygen concentrations (2.7–2.8 ml l^?1) and density (σ_Θ, 27.1–27.2 kg m^?3) were lower and mass fluxes from sediment trap data appeared much higher (4002–4192 mg m^?2 d^?1). Yet, this species still appears to thrive in this region, suggesting that L. pertusa may not be as limited by lower dissolved oxygen concentrations as previously thought. The VK826 site experienced sustained eastward water flow of 10–30 cm s^?1 over the 5-day measurement period but was also subjected to significant short-term variability in current velocity and direction. In addition, two processes were observed that caused variability in salinity and temperature; the first was consistent with internal waves that caused temperature variations of 0.8 °C over 5–11 h periods. The second was high-frequency variability (20–30 min periods) in temperature recorded only at the ALBEX site. A further pattern observed over the coral habitat was the presence of a 24 h diel vertical migration of zooplankton that may form part of a food chain that eventually reaches the corals. The majority of detailed studies concerning local environmental conditions in L. pertusa habitats have been conducted within the north-eastern Atlantic, limiting most knowledge of the niche of this species to a single part of an ocean basin. Data presented here show that the corals at VK826 are subjected to similar conditions in temperature, salinity, and flow velocity as their counterparts in the north-east Atlantic, although values for dissolved oxygen and density (sigma-theta: σ_Θ) are different. Our data also highlight novel observations of short-term environmental variability in cold-water coral habitat.  相似文献   

Planning Ground Water Monitoring Field Projects     

Kenneth H. Lister 《Ground Water Monitoring & Remediation》1989,9(3):101-111

Project organization problems are not uncommon in ground water monitoring projects, particularly those which occur at sites remote from the office. Successful project management depends on coordination of the personnel, supplies, and equipment necessary to carry out each phase of the project. Procedures for planning and organizing field projects involving well installation, ground water sampling, and aquifer testing are outlined. Methods are suggested that will aid the Project Manager in planning and scheduling field work to make efficient use of personnel and material resources. Cautions are given regarding common pitfalls of projects involving operations at remote sites, and means of avoidance are enumerated. A checklist of commonly used field equipment and supplies is provided.  相似文献   

Grossular activity-composition relationships in ternary garnets determined by reversed displaced-equilibrium experiments   总被引：1，自引：1，他引：1  

Andrea M. Koziol  Robert C. Newton 《Contributions to Mineralogy and Petrology》1989,103(4):423-433

Activity-composition relationships of Ca₃Al₂Si₃O₁₂ (grs) in ternary Ca-Mg-Fe garnets of various compositions have been determined by reversed displaced equilibrium experiments at 1000° C and 900° C and pressures of 8 to 17 kbar. The mixing of grs in garnet is nearly ideal at 30 mol% grs, with positive deviations from ideality at lower grs contents. Models of garnet mixing currently in the literature do not predict this trend. Analysis of the present reversals, in conjunction with a garnet mixing model based solely on calorimetry measurements on the binary joins, indicates that a ternary interaction constant for a ternary asymmetric Margules model (Wohl 1953) cannot be constrained. Apparently, some aspects of the garnet binary joins are still not well-known. An alternative asymmetric empirical model, based on analysis of pseudobinary joins of constant Mg/Mg + Fe(Mg #), reproduces the data well and is able to predict grs activity coefficients for garnets with grs contents between 3 and 40 mol% and Mg numbers between 0 and 0.60. The grossular activity coefficient, _grs, is given by:

相似文献    65. Shape analysis and multispectral classification in geological remote sensing      Andrea G. Fabbri  Freek D. van der Meer  Carlos R. Valenzuela  Cornelius A. Kushigbor 《Mathematical Geology》1993,25(7):773-793 This paper discusses the usage of mathematical morphology in image processing of remotely-sensed data for geologic interpretation. Particular attention is given to noise-reducing transformations of spectral bands before and after different methods of classification, and to the usage of textural context. The development of a viable processing strategy requires a multidisciplinary approach and expert knowledge in different areas: (a) geology, geomorphology, and vegetation in a study area, (b) properties of the sensor for imagery photointerpretation, (c) spectral/spatial properties of the digital data within an integrated dataset (remote sensing and ancillary data), and (d) data-processing tools including mathematical morphology theory. Examples of geometric characterization of Canadian LANDSAT scenes are described in which shape measurements are obtained using a PC-based hybrid image-processing and geographic information system, termed ILWIS, which was developed at ITC, in the Netherlands. Classes from supervised and unsupervised classification are compared to guide in geological mapping. Classes over individual occurrences of broad vegetation-landform units are studied to aid in environmental mapping. Field knowledge is the context necessary to construct expert procedures to drive sequences of data-processing steps toward a target result such as optimal classification, enhancement, or feature extraction. The interaction between expert rules and the image-processing steps can be based on synthetic measurements of shape to quantize the information either spatially or spectrally. Many useful geometrical transformations of spatially-distributed data are extensions or generalizations of spatial analysis functions typical of geographic information systems.  相似文献    66. The effect of crystallization on the rheology and dynamics of lava flows      Michele Dragoni  Andrea Tallarico 《Journal of Volcanology and Geothermal Research》1994,59(3) The dynamics of a lava flow is studied by a two-dimensional model describing a viscous fluid with Bingham rheology, flowing down a slope. The temperature in the flow is calculated assuming that heat is transferred through the plug by conduction and is lost by radiation to the atmosphere at the top of the flow. Taken into account is that the increasing crystallization takes place in the flow as a consequence of cooling. The lava viscosity and yield stress are expressed as a function of crystallization degree as well as of temperature: in particular it is assumed that yield stress reaches a maximum value above the solidus temperature, according to experimental data. Dynamical variables, such as velocity and thickness of the flow, are calculated for different values of the maximum crystallization degree and the flow rate. The model shows how the lava flow dynamics is affected by cooling and crystallization. The cooling of the flow is controlled by the increase of yield stress, which produces a thicker plug and makes the heat loss slower. The increasing crystallization has two opposing effects on viscosity: it produces an increase of viscosity, but at the same time produces an increase of yield stress and hence reduces the heat loss and keeps the internal temperature high. As a consequence, lava flows are significantly affected by the dependence of yield stress on temperature and scarcely by the maximum crystallization degree.  相似文献    67. Book reviews      Kacper R. Rybicki  Brian J. Mitchell  Louise H. Kellogg  Andrea Borgia  Allan M. Rubin  Douglas R. Schmitt  Douglas R. Schmitt  Edo Nyland  Zbigniew Fajklewicz  David Stevenson  Janusz L. Borkowski 《Pure and Applied Geophysics》1990,133(1):179-180   相似文献    68. The Faunal Remains from Evron Quarry in Relation to Other Lower Paleolithic Hominid Sites in the Southern Levant      Eitan Tchernov  Liora Kolska Horwitz  Avraham Ronen  Adrian Lister 《Quaternary Research》1994,42(3) The mammalian assemblage and archaeological finds from the Lower Palaeolithic hominid site of Evron Quarry, situated on the northern coastal plain of Israel, are described and discussed. In their lithic and faunal composition, the sites of Latamne (QfIII) (Latamne Formation, Orontes, Syria) and Sitt Markho (Nahr elKebir, Syria) resemble Evron and are probably contemporaneous. It is suggested here, based on their lithic and faunal composition, that these sites may be chronologically closer to the site of Ubeidiya ('Ubeidiya Formation, Jordan Valley, Israel; 1.4 myr) than to the sites of Gesher Benot Ya'akov (dated as <800,000 yr B.P.), which differs in both aspects from Evron. The mammalian faunule from Evron comprises a biogeographical mixture, a result of biotic exchanges with Africa, the Oriental region, and the Palaearctic. This exchange may have been associated with a post-'Ubeidiya hominid dispersal, either from Africa or south Asia via the Levantine "corridor."  相似文献    69. The international karakoram project: K.J. Miller (Editor). Cambridge University Press,Cambridge, 1984, Vol. 1, 412 pp., Vol. 2, 635 pp., price £40.00, US$ 79.50, ISBN 0 521 26339 5      H. Lister 《Physics of the Earth and Planetary Interiors》1985,39(2):145-146   相似文献    70. S-C Mylonites   总被引：2，自引：0，他引：2   G.S. Lister  A.W. Snoke   《Journal of Structural Geology》1984,6(6):617-638 Two types of foliations are commonly developed in mylonites and mylonitic rocks: (a) S-surfaces related to the accumulation of finite strain and (b) C-surfaces related to displacement discontinuities or zones of relatively high shear strain. There are two types of S-C mylonites. Type I S-C mylonites, described by Berthé et al., typically occur in deformed granitoids. They involve narrow zones of intense shear strain which cut across (mylonitic) foliation.Type II S-C mylonites (described here) have widespread occurrence in quartz-mica rocks involved in zones of intense non-coaxial laminar flow. The C-surfaces are defined by trails of mica ‘fish’ formed as the result of microscopic displacement discontinuities or zones of very high shear strain. The S-surfaces are defined by oblique foliations in the adjacent quartz aggregates, formed as the result of dynamic recrystallization which periodically resets the ‘finite-strain clock’. These oblique foliations are characterized by grain elongations, alignments of segments of the grain boundary enveloping surfaces, and by trails of grains with similar c-axis orientations.Examples of this aspect of foliation development in mylonitic rocks are so widespread that we suggest the creation of a broad class of S-C tectonites, and a deviation from the general tradition of purely geometric analysis of foliation and time relationships. Kinematic indicators such as those discussed here allow the recognition of kilometre-scale zones of intense non-coaxial laminar flow in crustal rocks, and unambiguous determination of the sense of shear.  相似文献    [首页] « 上一页 [2] [3] [4] [5] [6] 7 [8] [9] [10] [11] [12] 下一页 » 末  页»