Clay Mineralogy and its Paleoclimatic Significance of the OligoceneMiocene Sediments in the Gerze Basin,Tibet     

SONG Eping  ZHANG Kexin  CHEN Jiangjun  WANG Chaowen  JIANG Gaolei  YIN Ke  HONG Hanlie  CHURCHMAN Jock Gordon 《《地质学报》英文版》2014,88(5):1579-1591

This study collected the early Oligocene to middle Miocene sediments from the Gerze Basin of Tibet, and used X-Ray diffraction （XRD） and Scanning Electron Microscope （SEM） to discuss their clay mineralolgy, clay indices, better understand the clay mineralogy and its paleoclimatic significance. The results show that clay minerals of the Gerze Basin sediments are mainly composed of iilite and chlorite, with minor amounts of smectite and kaolinite, and their relative content varies along the section. Variations of relative contents and clay indices suggest that the Gerze Basin has experienced three-stage evolution of paleoclimate： I ） high ilUte and chlorite contents, with fluctuant smectite and low （I＋Ch）/（K＋S） ratio, indicative of a dominant seasonal arid climate from the early Oligoeene to late Oligocene; Ⅱ） higher illite and chlorite contents and larger （I＋Ch）/（K＋S） ratio but absence of kaolinite, indicating a colder and drier climate from the late Oligocene to early Miocene; Ⅲ） high iilite and chlorite contents with fluctuant （I＋Ch）/（K＋S） ratios and occasional occurrence of kaolinite, suggesting that the climate became warmer and more humid compared with that of stage Ⅱ in the mid-Miocene. These conclusions were also reinforced by the clay morphology, which suggests that physical weathering dominated in stage Ⅱ, while relatively strong chemical weathering was dominant in stages Ⅰ and Ⅲ Clay minerals of the sediments mainly consist of illite and chlorite, indicating that the source rock played a significant role in clay origin. It is inferred that global cooling and the enhancement of denudation and obstruction of northward moisture due to the uplift of the Qinghai-Tibet Plateau were responsible for the provenance of iUite and chlorite under weak chemical weathering. Though the Qinghai-Tibet Plateau reached a certain elevation by the mid-Miocene, yet the mid-Miocene widespread warming might have largely impacted the Gerze climate.  相似文献   

Variation with Depth in Temperate Seagrass-Associated Fish Assemblages in Southern Victoria,Australia   总被引：1，自引：0，他引：1  

Neil Hutchinson  Gregory P Jenkins  Andrew Brown  Timothy M Smith 《Estuaries and Coasts》2014,37(4):801-814

Variability in the abundance and distribution of seagrass-associated fish assemblages was examined at different depths in a temperate bay in southern Australia. Depth differences in seagrass-associated fish assemblages are poorly known but this information is critical given that seagrass loss can occur at specific depths depending on the cause. Overall, 69 species of fish from 26 families were recorded, with higher species richness in shallow than deep beds, with 12 species found only in deep beds and 22 species found only in shallow beds. While the total fish abundance (i.e. abundance of all species recorded) varied between years and seasons, and to some extent between sites, it was significantly higher in shallow than deep seagrass beds in the majority of cases. Although there was some variation between sites, seagrass tended to be longer and have a higher biomass in shallow than deep beds during both spring and autumn throughout the study. A positive relationship between seagrass biomass/length and total fish abundance/species richness was apparent. Assemblage structure tended to be distinct at each depth, with the largest species recorded in shallow seagrass. Large numbers of small schooling fish, such as atherinids, dominated in shallow seagrass but were not found in deep seagrass. Loss of seagrass could therefore have varying implications for distinct assemblages found at different depths.  相似文献   

Anatomy of a low temperature zircon outgrowth     

Duncan C. Hay  Tim J. Dempster  Martin R. Lee  David J. Brown 《Contributions to Mineralogy and Petrology》2010,159(1):81-92

Outgrowths of zircon and xenotime are abundant on detrital zircon in a greenschist facies regional metamorphic slate from the Scottish Highlands. Back-scattered electron images reveal that ca. 3-μm wide zircon outgrowths are porous, inclusion-rich and contain fine-grained intergrowths with xenotime. Focused ion beam milling, transmission electron microscopy and low-voltage scanning transmission electron microscopy show that the outgrowth microstructure is complex, composed of mis-orientated nano-crystalline zircon and a poorly crystalline zircon–xenotime complex. Well-defined micron-sized xenotime is also present within the outgrowth. Micro-textures show that the outgrowth developed in a polyphase history during cooling and exhumation. Accommodation space for the outgrowth is probably generated by a combination of thermal decompaction and the migration of defects in adjacent quartz driven by the force of crystallisation. Zircon may be unique in its ability to record textural evidence of events during uplift and exhumation that are not recorded in major silicate phases.  相似文献   

Seasonal survey of copper-complexing ligands and thiol compounds in a heavily utilized, urban estuary: Elizabeth River, Virginia   总被引：1，自引：1，他引：0  

Christina L. Dryden  Andrew S. Gordon  John R. Donat   《Marine Chemistry》2007,103(3-4):276-288

Concentrations of thiol compounds, copper-complexing ligands, and total dissolved copper were followed over the course of 1 year (October 2002 until September 2003) in the Elizabeth River, Virginia to evaluate seasonality. Copper-complexing ligand concentrations were determined by competitive ligand equilibration-adsorptive cathodic stripping voltammetry (CLE/ACSV). Thiol detection was carried out by high performance liquid chromatography (HPLC) and calibration using a suite of nine thiol compounds (cysteine, glutathione, mercaptoacetic acid, 2-mercaptoethanesulfonic acid, 2-mercaptoethanol, 2-mercaptopropionic acid, 3-mercaptopropionic acid, mercaptosuccinic acid, and monothioglycerol). Total dissolved copper concentrations reached a January low of 13.1 nM to a June high of 24.7 nM and were found to vary seasonally with higher concentrations occurring from June to September. With a low of 26 nM during April to a high of 56 nM in October, copper-complexing ligand (average log K′_CuL of 12.0 ± 0.2) concentrations displayed a similar seasonal pattern to that of total dissolved copper. Free cupric ion concentrations remained below 1.5 pM for a majority of the year except during March, April, and December when values reached pM levels greater than 1.5. Six of the nine thiol compounds surveyed were detected in the Elizabeth River samples and ranged in concentration from below detectable concentrations (< 5 nM) to individual highs ranging from 25.3 to168.5 nM. The thiol compound concentrations displayed a clear seasonality fluctuating at below detection limits during November to February then increasing with increasing surface water temperatures from March to July. CLE/ACSV was used to assess whether or not the suite of thiol compounds detected by HPLC could contribute to the copper-complexing ligand pool. Conditional stability constants for each one of six thiol standards (average log K′_CuL  12.1 ± 0.5) were found to be statistically equivalent to the naturally occurring copper-complexing ligands (average log K′_CuL  12.0 ± 0.2). This suggests that these thiol compounds could act as copper-complexing ligands in natural samples and could contribute to the copper-complexing ligand pool detected by CLE/ACSV. This study involving seasonality of copper-complexing ligands and thiols in an industrialized, urban estuary underscored several points that have to be substantiated in future research efforts including copper-complexing ligands sources and the role that thiol compounds as well as other unidentified organic compounds play in the copper-complexing ligand pool.  相似文献   

Determination of the Photometric Calibration and Large-Scale Flatfield of the STEREO Heliospheric Imagers: I. HI-1     

D. Bewsher  D. S. Brown  C. J. Eyles  B. J. Kellett  G. J. White  B. Swinyard 《Solar physics》2010,264(2):433-460

The aim of this paper is to calculate an accurate large-scale flatfield for the STEREO HI-1 instruments. This is done by analysing the variation in intensity of stars in the background starfield as they pass across the CCD. In order to use the background starfield, a photometric calibration is performed which defines a HI magnitude scale and a conversion between this scale and measured intensity. The photometric calibration uses stellar spectra folded through the instrument response to make initial intensity predictions. However, a secondary prediction method based on the photometric calibration, which blends the R-, V- and B-magnitudes of a star, is derived for stars with no spectral information.  相似文献   

X-ray Spectromicroscopy of Mineral Intergrowths in the Santa Catharina Meteorite     

Paul F. Schofield  Andrew D. Smith  J. Frederick W. Mosselmans  Hendrik Ohldag  Andreas Scholl  Simone Raoux  Gordon Cressey  Barbara A. Cressey  Paul D. Quinn  Caroline A. Kirk  Simon C. Hogg 《Geostandards and Geoanalytical Research》2010,34(2):145-159

This work describes the application of microfocus X-ray absorption spectroscopy (XAS) and X-ray photo-emission electron microscopy (XPEEM) to the study of the complex mineralogical intergrowths within the Santa Catharina meteorite. The Santa Catharina meteorite of this study (BM52283 from the meteorite collection of the Natural History Museum, London, UK) primarily comprises a taenite bulk host phase (Fe:Ni ratio = 70.9 ± 0.8%:29.1 ± 0.8%) with a set of oxide-bearing cloudy zone textured regions (Fe:Ni:O ratio = 40.4 ± 0.3%:49.0 ± 0.7%:10.6 ± 0.8% at the core and Fe:Ni:O ratio = 34.4 ± 1.5%:42.7 ± 0.6%:22.9 ± 1.8% towards the rims) and numerous schreibersite (Fe:Ni:P ratio = 38.6 ± 1.6%:38.4 ± 0.9%:23.0 ± 0.5%) inclusions. Between the schreibersite and the taenite are rims up to 50 μm across of Ni-rich kamacite (Fe:Ni ratio = 93.4 ± 0.4%:6.6 ± 0.5%). No chemical zoning or spatial variations in the Fe and Ni speciation was observed within either the schreibersite or the kamacite phases. The oxide-bearing cloudy zone textured regions mostly comprise metallic Fe–Ni alloy, predominantly tetrataenite. Within the oxide phases, the Fe is predominantly, but not entirely, tetrahedrally co-ordinated Fe³⁺ and the Ni is octahedrally co-ordinated Ni²⁺. Structural analysis supports the suggestion that non-stoichiometric Fe₂NiO₄ trevorite is the oxide phase. The trevorite:tetrataenite ratio increases at the edges of the oxide-bearing cloudy zone textured regions indicating increased oxidation at the edges of these zones. The spatial resolution of the XPEEM achieved was between 110 and 150 nm, which precluded the study of either the previously reported ∼ 10 nm precipitates of tetrataenite within the bulk taenite or any antitaenite.  相似文献   

A framework for reading and unifying heliophysics time series data     

Jon Vandegriff  Lawrence Brown 《Earth Science Informatics》2010,3(1-2):75-86

We describe a framework designed to simplify the acquisition and integration of data from multiple, diversely formatted, geographically distributed science data sets. Our domain is Heliophysics where measurements of magnetic fields, plasmas, and charged particles are often made in-situ, with the data made available in relatively low volume data sets consisting of time series tables. Data format diversity has proven to be a significant barrier to the type of integrated, multi-mission analysis that is now very important in Heliophysics. Therefore we have developed a Java framework capable of reading, interpreting, and providing uniform access to the science content of any distributed time series data set. The framework exposes data only through fully abstract interfaces that represent data content while hiding all access details such as file format, data file granularity and access protocols. Furthermore, specialized interfaces for representing measurement-specific details are also employed, so that our framework enables data sets to be recast into scientifically interoperable representations. The context of our efforts is an increasingly distributed Heliophysics data environment that employs a collection of discipline-specific Virtual Observatories (VOs), each providing data search and retrieval services for one Heliophysics sub-discipline. Our framework is bundled in a library that ultimately will serve as a universal reader for Heliophysics data, solving the formats problem and serving as key infrastructure for advanced, science-sensitive data manipulation services.  相似文献   

Comparison study of methane emissions from landfills with different landfill covers   总被引：3，自引：0，他引：3  

Soyoung Park  K. W. Brown  J. C. Thomas  In-cheol Lee  Kijune Sung 《Environmental Earth Sciences》2010,60(5):933-941

Atmospheric methane, a more effective heat-trapping gas than CO₂ that may affect climate change, has its greatest man-made source in the US from municipal solid waste (MSW) landfills. Consequently, the wise management of landfills can reduce these greenhouse gas emissions to the atmosphere. Methane from modern MSW landfills built with composite covers is frequently vented directly to the atmosphere. Biofiltration of landfill gas could oxidize CH₄ to CO₂ and water. Methane oxidation in old landfills with conventional soil covers can be effective in reducing the amount of CH₄ emitted. In this study, comparison of methane emissions from three different landfill covers was conducted. Methane emissions from old landfills constructed with conventional soil covers, modern MSW landfills constructed with composite covers, and modern MSW landfills constructed with composite covers plus biofilters were calculated using the calculated CH₄ oxidation rates. The results showed that an average of only 14% of the generated CH₄ was emitted from landfills with modern composite covers plus biofilters, and an average of 85% of the generated CH₄ was emitted from landfills with conventional covers when 100% of the generated CH₄ emissions to the atmosphere from landfills with modern composite covers was assumed. By comparing the CH₄ emission rates from three different landfill types, the use of a properly sized biofilter should be an effective technique to reduce CH₄ emissions from landfills across the USA and potentially in many other areas of the world.  相似文献   

The linear stability of dilute particulate rings     

Henrik N. Latter  Gordon I. Ogilvie 《Icarus》2006,184(2):498-516

Irregular structure in planetary rings is often attributed to the intrinsic instabilities of a homogeneous state undergoing Keplerian shear. Previously these have been analysed with simple hydrodynamic models. We instead employ a kinetic theory, in which we solve the linearised moment equations derived in Shu and Stewart 1985 for a dilute ring. This facilitates an examination of velocity anisotropy and non-Newtonian stress, and their effects on the viscous and viscous/gravitational instabilities thought to occur in Saturn's rings. Because we adopt a dilute gas model, the applicability of our results to the actual dense rings of Saturn are significantly curtailled. Nevertheless this study is a necessary preliminary before an attack on the difficult problem of dense ring dynamics. We find the Shu and Stewart formalism admits analytic stability criteria for the viscous overstability, viscous instability, and thermal instability. These criteria are compared with those of a hydrodynamic model incorporating the effective viscosity and cooling function computed from the kinetic steady state. We find the two agree in the ‘hydrodynamic limit’ (i.e., many collisions per orbit) but disagree when collisions are less frequent, when we expect the viscous stress to be increasingly non-Newtonian and the velocity distribution increasingly anisotropic. In particular, hydrodynamics predicts viscous overstability for a larger portion of parameter space. We also numerically solve the linearised equations of the more accurate Goldreich and Tremaine 1978 kinetic model and discover its linear stability to be qualitatively the same as that of Shu and Stewart's. Thus the simple collision operator adopted in the latter would appear to be an adequate approximation for dilute rings, at least in the linear regime.  相似文献   

An examination of the spring 1997 mid‐latitude east pacific sea surface temperature anomaly     

Randy G. Brown  Lee‐Lueng Fu 《大气与海洋》2013,51(4):577-599

Abstract

We seek to document and explain the lifecycle of the warm Sea Surface Temperature (SST) anomaly that intensified and weakened off the west coast of the United States to peak anomalies of 4°C during April‐June 1997. We use remotely sensed observational data and model analyses to compute an energy budget for the warm anomaly. The bulk of the anomalous warming was confined to the top 50 m of ocean and occurred during May. The immediate cause for the warming was twofold: latent heat fluxes decreased in magnitude as a result of both lower wind speeds and positive moisture anomalies, while the net radiative flux into the ocean increased as a result of lower than normal fractional cloud coverage. During June, the wind speed strengthened and became northerly, resulting in larger than normal latent and sensible heat fluxes that weakened the SST anomaly. Examination of the National Centers for Environmental Prediction (NCEP) 1000‐mb geopotential height for May shows that the Aleutian low extended far south of its usual position and was responsible for the weaker southerly winds and suppressed latent heat fluxes in the warm anomaly area. Finally, we note that the near simultaneous appearance of this warm anomaly in conjunction with warm El Niño waters off Peru makes El Niño an unlikely trigger for the northeast Pacific warm anomaly. We suggest a possible alternative scenario in which both events are remotely triggered by the intraseasonal oscillation.  相似文献