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1.
Petrographic observations of two Vindhyan black shales (Rampur Shale of the Semri Group and Bijaigarh Shale of the Kaimur
Group) revealed the following features:
These features are indirect evidence of microbial mat colonization during the Proterozoic. The microbial mats probably fixed
carbon at the sediment surface, stabilized sediment and recycled organic matter and were the primary producers, unlike during
the Phanerozoic time. 相似文献
– | •general wavy lamination, |
– | •contorted and folded thin shreds of organic matter, |
– | •wavy pyritic laminae, |
– | •‘teeth and socket’ structure. |
2.
The paper presents an efficient finite difference based 2D-inversion algorithm, EM2INV, for geoelectromagnetic data. The special
features of the algorithm are
The algorithm is tested rigorously by setting up exercises of diverse nature and of practical significance. The stability
of the algorithm is established by inverting the synthetic response corrupted with Gaussian noise. The inversion experiments
are aimed at studying
It has been observed that the Magneto-telluric data deciphers better the vertical position of the target and Geomagnetic Depth
Sounding data deciphers the horizontal variations in a better way. The conductive and resistive bodies are better resolved
by inversion of E- and B-polarization data respectively. The results of multi-frequency inversion imply that the increase
in the number of frequencies does not necessarily enhance the inversion quality especially when the spread of observation
points is sufficiently large to sense the target. The study of a minimum number of observation points highlights the importance
of single point inversion that furnishes useful information about the inhomogeneity. 相似文献
– | • optimal grid generation based on grid design thumb rules, |
– | • finite domain boundary conditions, |
– | • interpolation matrix that permits generation of response at observation points different from grid points, |
– | • Gaussian elimination forward matrix solver, that enables reuse of already decomposed coefficient matrix, |
– | • super-block notion that reduces the number of blocks with unknown resistivities and, in turn, the size of Jacobian matrix and |
– | • bi-conjugate gradient matrix solver for inverse problem which circumvents the need of explicit Jacobian matrix computation. |
– | • relative performance of response functions, |
– | • inversion quality of E- and B-polarization data, |
– | • efficacy of single and multi-frequency data inversion, |
– | • minimum number of frequencies and observation points needed for successful data inversion. |
3.
Scientific objectives and payloads of Chang’E-1 lunar satellite 总被引:1,自引:0,他引:1
Sun Huixian Dai Shuwu Yang Jianfeng Wu Ji Jiang Jingshan 《Journal of Earth System Science》2005,114(6):789-794
China plans to implement its first lunar exploration mission Chang’E-1 by 2007. The mission objectives are
To achieve the above mission goals, five types of scientific instruments are selected as payloads of the lunar craft. These
include stereo camera and spectrometer imager, laser altimeter, microwave radiometer, gamma and X-ray spectrometers and space
environment monitor system. In order to collect, process, store and transmit the scientific data of various payloads a special
payload data management system is also included. In this paper the goals of Chang’E-1 and its payloads are described 相似文献
– | • to obtain a three-dimensional stereo image of the lunar surface, |
– | • to determine distribution of some useful elements and to estimate their abundance |
– | • to survey the thickness of lunar soil and to evaluate resource of3He and |
– | • to explore the environment between the Moon and Earth. |
4.
The aeolian sedimentation record of the Thar desert 总被引:1,自引:0,他引:1
A review of the aeolian sedimentary record of the Thar desert is presented. This includes a regional survey of the major dune
forms, their genesis and their relationship to climate and other regional landforms. A key aspect of this work is the chronometry
of the dunes using luminescence methods. Luminescence dating of sand has enabled quantification of the duration of the phases
of sand aggradation and quiescence, time scales of dune migration and the dating of pedogenic carbonates. We demonstrate that
the conventional wisdom of synchronicity of dune aggradation with glacial epoch is not true in the context of Thar sands and
here only a short durationwindow of opportunity existed for dune aggradation. Luminescence ages further suggest that this window occurred during a transitional climatic
regime from glacial to interglacial about 4–10 ka after the glacial epoch. Other inferences included are that:
相似文献
– | • the aeolian activity in the Thar began over > 150 ka, resolving that Thar is not of anthropogenic origin as suggested previously; |
– | • the present spatial extent of the aeolian activity in the Thar is in a contracted stage compared to that in the geological past, which refutes the arguments on its rapid north-eastward expansion; |
– | • the current dune migration rates in areas of significant human-induced disturbances are much higher than during the geological past; |
– | • the monsoon activity in the Thar varied significantly, from being minimal during the isotopic marine stages 4 and 2 to being close to the present during stage 3; |
– | • on shorter time scales the dune activities correlated with the lacustrine records of the region with a phase difference of a few centuries and a periodicity of ∼ 1500 years; |
– | • the sand aggradation climate in the southern margin in Gujarat gradually shrank northwards such that in general dunes older than 10 ka are seen in the extreme southern margin and dunes younger than 2ka ages occur mostly in the western part of Rajasthan. |
5.
Susanta Kumar Samanta 《Journal of Earth System Science》2001,110(3):191-203
Petrographic studies of samples of the Rajmahal basalt reveal a variety of microscopic joints within phenocrysts, which seem
to have developed under the influence of thermal stresses during cooling. The theoretical analysis shows that:
In order to understand the effects of cooling rate on the mode of jointing, analogue model experiments were performed by quenching
melt films of organic, crystalline materials under varying cooling conditions. In experiments, non-branching linear joints
developed at relatively lower rates of cooling by a process of sub-critical crack propagation. On the other hand, at higher
rates of cooling the mechanism of crack propagation was essentially supercritical leading to the development of branching
joints. 相似文献
– | •thermal stresses develop in a system only under unsteady state of cooling, |
– | •the stresses responsible for the development of joints are tensile in nature, and |
– | •the magnitude of stresses increases with increasing rates of cooling. |
6.
The eastern Dharwar Craton of southern India includes at least three ∼ 2700Ma supracrustal belts (schist belts) which have
mesothermal, quartz-carbonate vein gold mineralization emplaced within the sheared metabasalts. In the Hutti and the Kolar
schist belts, the host rocks are amphibolites and the ore veins have been flanked by only a thin zone of biotitic alteration;
in the Ramagiri belt, however, the host rocks to the veins have been affected by more extensive but lower temperature alteration
by fluids. The rare earth element (REE) geochemistry of the host metabasalts, alteration zones, ore veins and the bulk sulfides
separated from the ore veins and the alteration zones suggest that
Because alteration and mineralization involved addition of REE, more LREE compared to HREE, the fluids could be of higher
temperature origin. The initial Nd isotope ratios in the host rocks (εNd calculated at 2700 Ma) showed a large variation (+8 to -4) and a deep crustal source for the fluid REE seems likely. A crustal
source for Pb and Os in the ore samples of Kolar belt has previously been suggested (Krogstadet al 1995; Walkeret al 1989). Such a source for ore fluids is consistent with a late Archean (2500Ma) accretionary origin for the terrains of the
eastern Dharwar Craton. 相似文献
– | •the REE chemistry of the immediate host rocks has been modified by fluids which added LREE, |
– | •the REE abundance of the ore veins vary with the amount of host rock fragments included in the veins, |
– | •the sulfides formed during mineralization have significant REE concentration with patterns nearly identical to the ore veins and alteration zones and |
– | •therefore the ore fluids involved in gold mineralization here could be LREE enriched. |
7.
Analysis of optimal strategies for soft landing on the Moon from lunar parking orbits 总被引:1,自引:0,他引:1
Optimal trajectory design of a probe for soft landing on the Moon from a lunar parking orbit by minimizing the fuel required
is obtained. The problem is formulated as an optimal control problem with the thrust direction being the control variable.
Using the maximum principle of Pontryagin, the control variable is expressed as a function of co-state variables and the problem
is converted into a two-point boundary value problem. The two-point boundary value problem is solved using an optimization
technique, i.e., controlled random search. The strategies such as
are analyzed and an optimal strategy that achieves the goals is suggested. Also, appropriate design parameters are selected
using this analysis 相似文献
– | • direct landing from a lunar parking orbit using powered braking |
– | • direct landing from an intermediate orbit using powered braking |
– | • by executing powered braking in two phases: through horizontal braking and vertical landing |
8.
A. Sarkar R. Ramesh S. K. Bhattacharya N. B. Price 《Journal of Earth System Science》2000,109(1):157-169
δ18 O and δ13C of G.sacculifer have been measured in five cores from the northern Indian Ocean. In addition, high resolution analysis (1 to 2 cm) was performed
on one core (SK-20-185) for both δ18O and gd13C in five species of planktonic foraminifera. CaCO3 variation was measured in two cores. The results, presented here, show that
相似文献
– | • the summer monsoon was weaker during 18 ka and was stronger during 9 ka, relative to modern conditions; |
– | • δ13C variations are consistent with independent evidence that shows that during the last glacial maximum (LGM; 18 ka) the upwelling was reduced while during 9 ka it was vigorous; |
– | • calculation of CaCO3 flux shows that the LGM was characterized by low biogenic productivity in the Arabian Sea while during the Holocene productivity increased by ∼65%, as a direct consequence of the changes in upwelling. Similar changes (of lesser magnitude) are also seen in the equatorial Indian Ocean. The amount of terrigenous input into the Arabian Sea doubled during LGM possibly due to the higher erosion rate along the west coast. |
– | • δ18O values indicate that the Arabian Sea was saltier by 1 to 2%o during LGM. The northern part was dominated by evaporation while in the equatorial part there was an increased precipitation. |
9.
O. K. Manuel 《Journal of Earth System Science》2000,109(1):195-203
The notion of remote element synthesis has recently been modified to explain the presence of nucleogenetic isotopic anomalies
and decay products of short-lived nuclides by injection of a small amount ofexotic nucleogenetic material. Even with this modification, remote element synthesis seems inconsistent with the following observations:
相似文献
– | Evidence of coupled variations in the chemical and isotopic compositions of the source material for meteorites. |
– | Residual coupling of chemical and isotopic heterogeneities across planetary distances in the solar system today. |
– | The mass-fractionation relationship seen across isotopes of elements in the planetary system, in the solar wind, and in solar flares. |
– | Linkage of short-lived radioactivities with isotopic anomalies and with physical properties of their host grains, as expected for early condensate of fresh stellar debris. |
– | Temporal and spatial distributions of short-live nuclides and their decay products. |
– | Mirror-image (+ and −) isotopic anomalies in meteorite grains that sum to “normal” isotopic ratios, as expected of unmixed products of the same nuclear reactions that produced our bulk elements. |
– | The lac supporting evidence for “presolar” grains or nearby stars that injectedexotic material into the early solar nebula. |
10.
Partha Pratim Chakraborty 《Journal of Earth System Science》2006,115(1):23-36
The Rewa Group of the Vindhyan Supergroup in the Son valley begins with a thick (∼200m) dominantly shaly, shelfal succession,
occurring between the Dhandraul Formation of the Kaimur Group (fluvial sandstone) below and Drammondganj Formation of the
Rewa Group (marginal marine sandstone) above. Such a stratigraphic disposition indicates a sharp rise in relative sea level
at the onset of Rewa sedimentation, inducing a shelfal depth to the Vindhyan basin. However, a number of wedge-shaped, sandstone/conglomerate
bodies (maximum thickness 23.5 m) occur at multiple stratigraphic levels within the aforesaid deeper water shale succession,
which appear to be of much shallow water origin representing regressive deposits. Though these bodies do not define a single
physically continuous unit, either vertically or laterally, they are still designated by a single term ‘Asan Sandstone’ in
the literature. On the other hand, the encasing shelfal shales are termed as Panna and Jhiri Shales, in accordance with their
occurrence below or above the so-called ‘Asan Sandstone’. The present study reveals that in different sections spread over
the Son valley, there are several discrete regressive wedges occurring vertically, and their depositional environment is also
variable, ranging between braided fluvial, shoreface fan and braid delta. The features common to most of the regressive coarser
clastic bodies are:
相似文献
– | •invariable presence of deeper water, shelfal shale below (Panna or Jhiri); |
– | •the underlying shale at places shows signatures of emergence at the top; |
– | •laterally impersistent, wedge-like geometry; and |
– | •presence of granular transgressive lags at the top. These coarser clastic wedges record several episodes of regressive deposition during short-term falling stage or lowstand of relative sea level at the early phase of Rewa sedimentation. Each individual phase of regressive deposition was, however, followed by flooding and resumption of shelf mud deposition. |
11.
12.
Assessment of different topographic corrections in AWiFS satellite imagery of Himalaya terrain 总被引:2,自引:0,他引:2
V. D. Mishra J. K. Sharma K. K. Singh N. K. Thakur M. Kumar 《Journal of Earth System Science》2009,118(1):11-26
The influence of topographic effects in optical satellite imagery is not investigated very extensively in the Himalayan terrain.
The topographic variability causes a problem of differential illumination due to steep and varying slopes in rugged Himalayan
terrain. Therefore, topographic corrections are essential for qualitative and quantitative analysis of snow cover applications.
The present paper discusses the implementation of different topographic correction models on AWiFS sensor onboard IRS P6 satellite
images and the qualitative and quantitative comparative analysis in detail. Both the Lambertian and non-Lambertian assumptions
have been considered in the present analysis with the aim to explore best suitable empirical model for rugged terrain. The
main topographic methods implemented are:
Lambertian assumptions are found to be very unrealistic over Himalayan terrain as these lead to either underestimation or
overestimation of physical parameters significantly both on sunlit slopes as well as the slopes away from the Sun. This problem
is overcome by considering non-Lambertian assumption. Minneart constant and C-correction coefficients for all AWiFS satellite
bands are estimated using regression analysis. All the results due to topographic effects are investigated qualitatively and
quantitatively using four criteria namely visual analysis, validation with field measurements (in-situ observations), spectral reflectance of training samples of snow on the south and north aspects and graphically. The visual
analysis confirms the minimization of three dimensional relief effects in two-stage normalization and slope matching methods
and retrieves some of the information under mountain shadow. Due to the very bright surface of snow fields there is likely
to be more diffuse reflected light in these areas than over darker vegetated surfaces. The qualitative analysis in other methods
does not extract any information on shady slopes. The quantitative validation of topographic results in satellite imagery
with in-situ observations shows underestimation of spectral reflectance of snow significantly except for slope matching technique. It
is also apparent that although all the topographic methods correct the reflectance of training snow samples on the south and
north aspects but most acceptable values are achieved using slope matching. The results obtained from graphical analysis reveal
that mean reflectance after all topographic corrections are independent of illumination. This study also suggests that the
suitability of topographic models can not be concluded as successful based on single criterion. Slope matching technique is
the only technique which satisfies all the four criteria successfully and produces the best result for Himalayan terrain. 相似文献
• | C-correction |
• | Minneart corrections |
• | Civco’s modified version of cosine correction |
• | two-stage normalization and |
• | slope matching technique. |
13.
Systematic and random error and their growth rate and different components of growth rate budget in energy/variance form are
investigated at wavenumber domain for medium range tropical (30‡S-30‡N) weather forecast using daily horizontal wind field
of 850 hPa up to 5-day forecast for the month of June, 2000 of NCEP (MRF) model. Part I of this paper deals with the study
at physical domain. The following are the major findings in this paper:
相似文献
– | •Tropical systematic error is associated with large scale wave of wavenumber 2, unlike the tropical random error, in which case dominant spectra of random error are observed at higher spectral band of wavenumbers 4–7 in comparison to that of systematic error. |
– | •Systematic error growth rate peak is observed at wavenumber 2 up to 4-day forecast then the peak is shifted to wavenumber 1 at 5-day forecast. Random error energy shows maximum growth at wavenumber 4 for 2-day forecast, wavenumber 6 for 3–4 day forecasts and at wavenumber 7 for 1-day and 5-day forecasts. |
– | •In the error growth rate budget, flux of systematic error shows the net increase of error energy at wavenumber 1 through the triad interactions with the pairs of waves of other wavenumbers. Flux and pure generation of random error energy are found to be accumulated at wavenumber 4. Resolving the possible triads in wavenumber 4 associated with these terms, it is shown that the wave receives more energy from the pairs of waves of different wavenumbers than it loses, leading to the error energy peak at wavenumber 4. However, the significant triad interaction occurs among the wavenumber 2 and higher wavenumbers in systematic error energy flux. |
14.
Weakening of lower tropospheric temperature gradient between Indian landmass and neighbouring oceans and its impact on Indian monsoon 总被引:2,自引:0,他引:2
S. M. Bawiskar 《Journal of Earth System Science》2009,118(4):273-280
The study shows that in the scenario of global warming temperature gradient (TG) between Indian landmass and Arabian Sea/Bay
of Bengal is significantly decreasing in the lower troposphere with maxima around 850 hPa. TG during pre-monsoon (March to
May) is reducing at a significant rate of 0.036°/year (Arabian Sea) and 0.030°/year (Bay of Bengal). The above alarming results
are based on sixty years (1948–2007) of daily temperature and wind data extracted from CDAS-NCEP/NCAR reanalysis datasets.
TG based on ERA-40 data also indicates a decreasing trend of 0.0229°/year and 0.0397°/year for Arabian Sea and Bay of Bengal
respectively. As TG is not governed by any type of significant oscillation, there is a possibility of TG tending to zero.
It is further observed that the rate of warming over the oceans is more than that over the land which has resulted into the
weakening of TG. Pre-monsoon TG has significant correlations with
Except AISMR, the decreasing trends observed in all the above parameters are significant. All India rainfall for July and
August together shows a significant decreasing trend of 0.995mm/year. Reducing number of depressions and cyclonic storms and
increasing number of break days during monsoon over India are the reflections of the weakening of TG. 相似文献
• | All India Seasonal Monsoon Rainfall (AISMR) |
• | kinetic energy of waves 1 and 2 at 850 hPa |
• | kinetic energy, and |
• | stream function at 850 hPa over Indian landmass during monsoon season. |
15.
Albrecht Steck 《Swiss Journal of Geoscience》2008,101(2):515-546
This study presents a review of published geological data, combined with original observations on the tectonics of the Simplon
massif and the Lepontine gneiss dome in the Western Alps. New observations concern the geometry of the Oligocene Vanzone back
fold, formed under amphibolite facies conditions, and of its root between Domodossola and Locarno, which is cut at an acute
angle by the Miocene, epi- to anchizonal, dextral Centovalli strike-slip fault. The structures of the Simplon massif result
from collision over 50 Ma between two plate boundaries with a different geometry: the underthrusted European plate and the
Adriatic indenter. Detailed mapping and analysis of a complex structural interference pattern, combined with observations
on the metamorphic grade of the superimposed structures and radiometric data, allow a kinematic model to be developed for
this zone of oblique continental collision. The following main Alpine tectonic phases and structures may be distinguished:
It is suggested that movements of shortening in fan shaped NW, W and SW directions accompanied the more regular NW- to WNW-directed
displacement of the Adriatic indenter during continental collision.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. Editorial Handling: Stefan Bucher 相似文献
1. | NW-directed nappe emplacement, starting in the Early Eocene (~50 Ma); |
2. | W, SW and S-verging transverse folds; |
3. | transpressional movements on the dextral Simplon ductile shear zone since ~32 Ma; |
4. | formation of the Bergell – Vanzone backfolds and of the southern steep belt during the Oligocene, emplacement of the mantle derived 31–29 Ma Bergell and Biella granodiorites and porphyritic andesites as well as intrusions of 29–25 Ma crustal aplites and pegmatites; |
5. | formation of the dextral discrete Rhone-Simplon line and the Centovalli line during the Miocene, accompanied by the pull-apart development of the Lepontine gneiss dome – Dent Blanche (Valpelline) depression. |
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. Editorial Handling: Stefan Bucher 相似文献
16.
M. B. Potdar S. A. Sharma V. Y. Parikh P. C. S. Devara P. E. Raj Y. K. Tiwari R. S. Maheskumar K. K. Dani S. K. Saha S. M. Sonbawne Y. Jaya Rao G. Pandithurai 《Journal of Earth System Science》2004,113(1):103-116
With the launch of the German Aerospace Agency's (DLR) Modular Opto-electronic Scanner (MOS) sensor on board the Indian Remote
Sensing satellite (IRS-P3) launched by the Indian Space Research Organization (ISRO) in March 1996, 13 channel multi-spectral
data in the range of 408 to 1010 nm at high radiometric resolution, precision, and with narrow spectral bands have been available
for a variety of land, atmospheric and oceanic studies. We found that these data are best for validation of radiative transfer
model and the corresponding code developed by one of the authors at Space Applications Centre, and called ATMRAD (abbreviated
for ATMospheric RADiation). Once this model/code is validated, it can be used for retrieving information on tropospheric aerosols
over ocean or land. This paper deals with two clear objectives, viz.,
The data validation procedure essentially involves
The results show that the model performance is satisfactory and a relationship between the spectral parameters of MOS radiances
and aerosol optical thickness can be established. In this communication, we present the details of the experiments conducted,
database, validation of the ATMRAD model and development of the relationship between AOT and MOS radiance. 相似文献
1 | Validation of ATMRAD model/code using MOS data and synchronously measured atmospheric data, and if found performing well, then to |
2 | derive relationship between MOS radiances and Aerosol Optical Thickness (AOT). |
– | •near-synchronous measurements of columnar aerosol optical thickness and altitude profiles of aerosol concentration using ground-based multi-filter solar radiometers and Argon-ion Lidar, respectively and |
– | •computation of the top-of-the-atmosphere (TOA) radiances from a low reflecting target (near clear water reservoir in the present study) using the ATMRAD model. |
17.
Jon E. Bouch Jonathan Naden Thomas J. Shepherd John A. McKervey Brian Young Antony J. Benham Hilary J. Sloane 《Mineralium Deposita》2006,41(8):821-835
The North Pennine Orefield Alston Block has produced approximately 4 Mt Pb, 0.3 Mt Zn, 2.1 Mt fluorite, 1.5 Mt barite, 1 Mt witherite, plus a substantial amount of iron ore and copper ore from predominantly vein-hosted mineralisation in Carboniferous limestones. However, a significant proportion of this production (ca. 20%) came from stratabound deposits. Though much is known about the vein mineralisation, the relationship between the veins and the stratabound mineralisation is not well-understood. New petrographic, isotopic and fluid inclusion data derived from samples of stratabound mineralisation allow us to present a unified model that addresses the genesis of both the vein and stratabound styles of mineralisation. The mineralisation can be considered in terms of three episodes:
相似文献
1. | Dolomitisation and ankeritisation Limestones in the vicinity of the stratabound mineralisation were pervasively dolomitised/ankeritised, and developed vuggy porosity in the presence of a high-salinity brine consistent with fluids derived from adjacent mud and shale-filled basins. |
2. | Main stage fluorite–quartz–sulphide mineralisation Metasomatism of limestone was accompanied by brecciation, dissolution and hydrothermal karstification with modification of the existing pore system. The open space was filled with fluorite, galena, sphalerite, quartz and barite, formed in response to mixing of low-salinity sodic groundwater with high-salinity calcic brine with elevated metal contents (particularly Fe up to 7,000 ppm) relative to “normal” high total dissolved solids sedimentary brines. |
3. | Late-stage barite mineralisation paragenetically appears to represent either the waning stages or the distal portions of the main hydrothermal circulation system under cooler conditions. |
18.
Ligang Zhang 《中国地球化学学报》1988,7(2):109-119
Based on the oxygen isotopic compositions of 133 wolframite samples and 110 quartz samples collected from 30 tungsten ore
deposits in south China, in conjunction withδD values and other data, these deposits can be divided into four types.
Based on theδ
18O values of the coexisting quartz and wolframite and temperature data, two calibration equilibrium curves have been constructed,
and the corresponding equations have been obtained:
(1) | Reequilibrated magmatic water-hydrothermal tungsten ore deposits. Theδ 18O values of wolframite and quartz samples from this type of tungsten ore deposits are about +5–+12‰, respectively. The calculatedδ 18O values of ore fluids in equilibrium with quartz are about +6.5‰, and theδ values of fluid inclusions in quartz range from −40 to −70‰ |
(2) | Meteoric water-hydrothermal tungsten ore deposits. Theδ 18O values of wolframite in this type of tungsten deposits are around −1‰ |
(3) | Stratiform tungsten ore deposits. In these deposits, theδ 18O values of quartz and wolframite are about +17 and +3‰, respectively. It is considered that these stratiform tungsten ore deposits are genetically related to submarine hot-spring activities. |
(4) | Complex mixed-hydrothermal tungsten ore deposits. These tungsten ore deposits are characterized by multi-staged mineralization. Theδ 18O values of early wolframite are around +5‰, but of later wolframite are lower than +4‰, indicating that the early wolframite was precipitated from reequilibrated magmatic water-hydrothermal solutions and the late one from the mixture of hydrothermal solutions with meteoric waters or mainly from meteoric waters. |
相似文献
19.
Peter Blümling 《Geotechnical and Geological Engineering》2005,23(6):843-858
Within the context of the phase IV (1994–1996) research and development activities at the Grimsel Test Site (GTS), Nagra developed, in collaboration with the Agence Nationale pour la Gestion des Déchets Radioactifs (Andra), an investigation project for the sealing of boreholes drilled from underground. The project had the following goals:
20.
TL ages of 56 loess samples collected from Xinjiang and the middle reaches of the Yellow River were determined by using fine-grained quartz and man-made light source bleaching techniques.The results indicate that :1.The well-preserved loess sections in Xinjiang began depositing 400000 a ago.The loess/paleosol series may be comparable with that observed in the middle reaches of the Yellow River but the depositing time was probably delayed by 30000-50000a.2.The bottom boundary age of the Malan loess varies from one place to another.The TL dates can be divided into two group:70000-130000 a and 30000-50000 a.The TL data are con-sistent with the appearance of two warmer climate periods since the Pleistocene,indicating obvious regional differences in stratigraphic development of loess,i.e.,paleosol occurred in the warm climate period in the same location,but loess was deposited in other locations.The initial age of loess deposition tends to become older from west to east and from south to north .In contrast ,the cold cli-matic belt showed an opposite trend.The TL ages of loess provide strong evidence for the Quaternary stratigraphy throughout geological times and the shift tendency of climatic belt.3.The depositing rate of the Malan loess along the middle reaches of the Yellow River varies from place to place but the TL age shows a linear relationship with the depositing thickness.The de-positing rate of loess in the north is higher than that in the south,suggesting that loess materials are derived from desert areas of northern China. 相似文献
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