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991.
992.
Preface: Proceedings of the 5th International Symposium on Lithographic Limestone and Plattenkalk 总被引:1,自引:0,他引:1
Daniel Marty Jean-Paul Billon-Bruyat Christian A. Meyer Loïc Costeur Basil Thüring 《Swiss Journal of Geoscience》2011,104(1):1-29
Magmatic rocks from the pre-Mesozoic basements of the Sambuco and Maggia nappes have been dated by U–Pb zircon ages with the LA-ICPMS technique. Several magmatic events have been identified in the Sambuco nappe. The mafic banded calc-alkaline suite of Scheggia is dated at 540 Ma, an age comparable to that of mafic rocks in the Austroalpine Silvretta nappe. The Sasso Nero peraluminous augengneiss has an age of 480–470 Ma, like many other “older orthogneisses” in Alpine basement units. It hosts a large proportion of inherited zircons, which were dated around 630 Ma, a Panafrican age indicating the Gondwanan affiliation of the Sambuco basement. The calc-alkaline Matorello pluton yielded ages around 300 Ma, similar to numerous Late Carboniferous intrusions in other basement units of the Lower Penninic (Monte Leone, Antigorio, Verampio) and Helvetic domains (Gotthard and other External Crystalline Massifs). Associated lamprophyric dykes are slightly younger (300–290 Ma), like similar dykes sampled in gneiss blocks included in the sedimentary cover of the underlying Antigorio nappe (290–285 Ma). The Cocco granodiorite and Rüscada leucogranite, both intruding the basement of the neighbouring Maggia nappe, yielded ages of ca. 300–310 Ma, identical within errors to the age of the Matorello pluton. They are significantly older than former age determinations. This age coincidence, coupled with remarkable petrologic similarities between the Cocco and Matorello granodiorites, strongly suggests paleogeographic proximity of the Sambuco and Maggia nappes in Late Carboniferous times. In recent publications these two nappes have been interpreted as belonging to distinct Mesozoic paleogeographic domains: “European” for Sambuco and “Briançonnais” for Maggia, separated by the “Valais” oceanic basin. In this case, the similarity of the Matorello and Cocco intrusions would demonstrate the absence of any significant transcurrent movement between these two continental domains. Alternatively, according to a more traditional view, Sambuco and Maggia might belong to a single large Alpine tectonic unit. 相似文献
993.
V CHOWKSEY D M MAURYA PARUL JOSHI N KHONDE ARCHANA DAS L S CHAMYAL 《Journal of Earth System Science》2011,120(6):979-999
The Kachchh Mainland Fault (KMF) is a major E–W trending seismically active fault of the Kachchh palaeorift basin whose neotectonic
evolution is not known. The present study deals with the eastern part of the KMF zone where the fault is morphologically expressed
as steep north facing scarps and is divisible into five morphotectonic segments. The Quaternary sediments occurring in a narrow
zone between the E–W trending KMF scarps and the flat Banni plain to the north are documented. The sediments show considerable
heterogeneity vertically as well as laterally along the KMF zone. (The Quaternary sediments for a northward sloping and are
exposed along the north flowing streams which also show rapid decrease in the depth of incision in the same direction.) The
deposits, in general, comprise coarse as well as finer gravelly deposits, sands and aeolian and fluvial miliolites. The Quaternary
sediments of the KMF zone show three major aggradation phases. The oldest phase includes the colluvio-fluvial sediments occurring
below the miliolites. These deposits are strikingly coarse grained and show poor sorting and large angular clasts of Mesozoic
rocks. The sedimentary characteristics indicate deposition, dominantly by debris flows and sediment gravity flows, as small
coalescing alluvial fans in front of the scarps. These deposits suggest pre-miliolite neotectonic activity along the KMF.
The second aggradation phase comprises aeolian miliolites and fluvially reworked miliolites that have been previously dated
from middle to late Pleistocene. The youngest phase is the post-miliolite phase that includes all deposits younger than miliolite.
These are represented by comparatively finer sandy gravels, gravelly sands and sand. The sediment characteristics suggest
deposition in shallow braided stream channels under reduced level of neotectonic activity along the KMF during post-miliolite
time evidenced by vertical dips of miliolites and tilting of gravels near the scarps. The tectonically controlled incision
and dissection of the Quaternary deposits is the result of neotectonic activity that continues at present day. The overall
nature, sedimentary characteristics and geomorphic setting of the sediments suggest that the KMF remained neotectonically
active throughout the Quaternary period. 相似文献
994.
Hussein Mustapha 《Computational Geosciences》2011,15(3):385-397
We present G23FM, a mesh generation tool for discretizing two- and three-dimensional complex fractured geological media. G23FM
includes different techniques to generate finite element grids that maintain the geometric integrity of input surfaces, and
geologic data and produce optimal triangular/tetrahedral grids for flow and transport simulations. G23FM generates grid for
two-dimensional cross-sections, represents faults and fractures, for three-dimensional fractured media, and has the capability
of including finer grids. Different examples are presented to illustrate some of the main features of G23FM. 相似文献
995.
Chemical and Strontium Isotopic Compositions of the Hanjiang Basin Rivers in China: Anthropogenic Impacts and Chemical Weathering 总被引:1,自引:0,他引:1
The Hanjiang River, the largest tributaries of the Changjiang (Yangtze) River, is the water source area of the Middle Route
of China’s South-to-North Water Transfer Project. The chemical and strontium isotopic compositions of the river waters are
determined with the main purpose of understanding the contribution of chemical weathering processes and anthropogenic inputs
on river solutes, as well as the associated CO2 consumption in the carbonate-dominated basin. The major ion compositions of the Hanjiang River waters are characterized by
the dominance of Ca2+ and HCO3
−, followed by Mg2+ and SO4
2−. The increase in TDS and major anions (Cl−, NO3
−, and SO4
2−) concentrations from upstream to downstream is ascribed to both extensive influences from agriculture and domestic activities
over the Hanjiang basin. The chemical and Sr isotopic analyses indicate that three major weathering sources (dolomite, limestone,
and silicates) contribute to the total dissolved loads. The contributions of the different end-members to the dissolved load
are calculated with the mass balance approach. The calculated results show that the dissolved load is dominated by carbonates
weathering, the contribution of which accounts for about 79.4% for the Hanjiang River. The silicate weathering and anthropogenic
contributions are approximately 12.3 and 6.87%, respectively. The total TDS fluxes from chemical weathering calculated for
the water source area (the upper Hanjiang basin) and the whole Hanjiang basin are approximately 3.8 × 106 and 6.1 × 106 ton/year, respectively. The total chemical weathering (carbonate and silicate) rate for the Hanjiang basin is approximately
38.5 ton/km2/year or 18.6 mm/k year, which is higher than global mean values. The fluxes of CO2 consumption by carbonate and silicate weathering are estimated to be 56.4 × 109 and 12.9 × 109 mol/year, respectively. 相似文献
996.
Since the early 1980s, the Dead Sea coast has undergone a near catastrophic land deterioration as a result of a rapid lake-level
drop. One conspicuous expression of this deterioration is the formation of sinkholes fields that puncture the coastal plains.
The evolution of sinkholes along nearly 70-km strip has brought to a halt the regional development in this well-known and
toured area and destroyed existing infrastructures. Great efforts are being invested in understanding the phenomena and in
development of monitoring techniques. We report in this paper the application of airborne laser scanning for characterization
of sinkholes. We demonstrate first the appropriateness of laser scanning for this task and its ability to provide detailed
3D information on this phenomenon. We describe then an autonomous means for their extraction over large regions and with high
level of accuracy. Extraction is followed by their detailed geometric characterization. Using this high-resolution data, we
show how sinkholes of 0.5 m radius and 25 cm depth can be detected from airborne platforms as well as the geomorphic features
surrounding them. These sinkhole measures account for their embryonic stage, allowing tracking them at an early phase of their
creation. 相似文献
997.
This paper presents one of the richest and most complete vertebrate faunas of the late Middle Miocene (~12 Ma) of Central Europe. Up to now, sixty-two vertebrate taxa, comprising all major groups (fishes, amphibians, reptiles, birds, mammals), have been recorded. Based on sedimentological and palaeobiological evidences, this Fossillagerstätte is assumed to originate from a floodplain paleosol formed on top of a braided river sequence. The fauna points to a highly structured, somewhat vegetated landscape with a wide array of habitats (e.g., fluvial channels, sporadically moist floodplains, short-lived ponds, savannah-like open areas and screes). It was preserved due to a rapid drowning and the switch to a freshwater lake environment. Palaeoclimatological data, derived from pedogenic features as well as from biota, indicate an overall semi-arid, subtropical climate with distinct seasonality (mean annual precipitation 486 ± 252 mm, mean annual temperature ~15°C). This underlines the late Middle/early Late Miocene dry-spell in Central Europe. From taphonomical point of view, the irregularly distributed but roughly associated larger vertebrate remains refer to an in situ accumulation of the bone bed. Splintered bones, gnawing marks as well as rhizoconcretions and root corrosion structures record some pre- and post-burial modification of the taphocoenose. However, the findings of pellet remains argue for a very fast burial and thus to a low degree of time-averaging. For this reason, the fossil fauna reflects the original vertebrate community rather well and is a cornerstone for the understanding of late Middle Miocene terrestrial ecosystems in this region. Certainly, Gratkorn will be one of the key faunas for a high-resolution continental biostratigraphy and the comprehension of Europe’s faunal interchanges near the Middle/Late Miocene transition. 相似文献
998.
Prediction of Floor Water Inrush: The Application of GIS-Based AHP Vulnerable Index Method to Donghuantuo Coal Mine,China 总被引:6,自引:0,他引:6
Qiang Wu Yuanzhang Liu Donghai Liu Wanfang Zhou 《Rock Mechanics and Rock Engineering》2011,44(5):591-600
Floor water inrush represents a geohazard that can pose significant threat to safe operations for instance in coal mines in
China and elsewhere. Its occurrence is controlled by many factors, and the processes are often not amenable to mathematical
expressions. To evaluate the water inrush risk, the paper proposes the vulnerability index approach by coupling the analytic
hierarchy process (AHP) and geographic information system (GIS). The detailed procedures of using this innovative approach
are shown in a case study in China (Donghuantuo Coal Mine). The powerful spatial data analysis functions of GIS was used to
establish the thematic layer of each of the six factors that control the water inrush, and the contribution weights of each
factor was determined with the AHP method. The established AHP evaluation model was used to determine the threshold value
for each risk level with a histogram of the water inrush vulnerability index. As a result, the mine area was divided into
five regions with different vulnerability levels which served as general guidelines for the mine operations. The prediction
results were further corroborated with the actual mining data, and the evaluation result is satisfactory. 相似文献
999.
This study analyzes the response of glacier to climate change during the past 49 years in Urumqi River source region, the
Tianshan Mountains of China. The temporal and spatial variations of winter mass balance (bn-w) at different time scales were
analyzed to identify their response to climate change during 1988–2006 (The observation of winter mass balance observation
began in 1988) on the Glacier No.1 at the headwaters of the Urumqi River, Tianshan Mountains, China. The winter accumulation
shows a significantly decreasing trend. The results show that the cumulative values on Glacier No.1 is 2,202 mm water equivalent
during 1988–2006 and the mean values is 116 mm a−1. Furthermore, the trend analysis of the winter mass balance indicates a rapid decrease since 1990, and the mean mass balance
is only 79 mm a−1 during 1997–2006. Winter mass balance correlates well negatively with the total evaporation from September to April (r = −0.68, α = 0.01), and positively with the total precipitation from September to April (r = 0.74, α = 0.01). However, winter mass balance shows a weak correlation with mean minimum air temperature during September
to April (r = −0.35), and runoff on September (r = −0.13). 相似文献
1000.
Experimental investigations on the influence of cyclical freezing and thawing on physical and mechanical properties of saline soil 总被引:4,自引:1,他引:4
Uniaxial compressive strength experiments were performed on saline loess different water and salt contents, and multiple freeze/thaw
cycles at room temperature. The experiments revealed changes to the stress–strain curve and the failure mode of the saline
loess. The results indicated that soil strength is intensified or weakened during freezing and thawing due to the injection
of sodium sulfate solute. Cyclical freezing and thawing is a process to get a new dynamic equilibrium, and under these experimental
conditions, six freeze–thaw cycles are need for loess with sodium sulfate to reach a new dynamic equilibrium. 相似文献