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281.
Pascale Huyghe Romain Guilbaud Matthias Bernet Albert Galy Ananta Prasad Gajurel 《Basin Research》2011,23(3):332-345
Clay mineral assemblages of the Neogene Himalayan foreland basin are studied to decipher their significance with respect to tectonic and climate processes. Fluvial deposits of the Siwalik Group (west‐central Nepal), and sediment of the Ganga River drainage system were analysed for clay mineralogy. The observed clay mineral assemblages are mainly composed of illite (dominant), chlorite, smectite and kaolinite. Illite and chlorite are chiefly of detrital origin, derived from Himalayan sources. Kaolinite and smectite are authigenic, and mainly developed within pore space and as coating of detrital particles. With increasing burial, diagenetic processes affected the original clay mineral signature. Illitisation of smectite and kaolinite occurred below 2500 and 3500 m depth, respectively. Therefore, illite in the lower parts of the Siwalik Group consists of a mixture of inherited illite and illitised smectite and kaolinite, as suggested by illite crystallinity. Detrital grains that make up the framework of the Siwalik Group sandstones mainly consist of quartz, feldspar and lithic fragments, which are principally of sedimentary and metamorphic origin. Lithoclast content increases over time at the expense of quartz and K‐feldspar in response to uplift and erosion of the Lesser Himalaya Series since about 11–10 Ma. Despite mainly felsic source rocks, dominantly physical erosion processes in the Himalayan belt, and high‐energy fluvial depositional systems, smectite is abundant in the <7 Ma Siwalik Group deposits. Analyses of the Siwalik deposits and comparison with the clay mineralogy of the modern drainage system suggest that smectite preferentially formed in floodplains and intermontane valleys during early diagenesis because of downward percolating fluids rich in cations from weathering and soil development. In general, increasing seasonality and aridity linked to variability of the Asian monsoon from about 8 Ma enhanced clay mineral formation and development of authigenic smectite in paleo‐plains on the southern side of the Himalaya. 相似文献
282.
283.
Jordi LLORCA Josep M. TRIGO‐RODRÍGUEZ Jos L. ORTIZ Jos A. DOCOBO Javier GARCÍA‐GUINEA Alberto J. CASTRO‐TIRADO Alan E. RUBIN Otto EUGSTER Wayne EDWARDS Matthias LAUBENSTEIN Ignasi CASANOVA 《Meteoritics & planetary science》2005,40(6):795-804
Abstract— An impressive daylight fireball was observed from Spain, Portugal, and the south of France at 16h46m45s UTC on January 4, 2004. The meteoroid penetrated into the atmosphere, generating shock waves that reached the ground and produced audible booms. The associated airwave was recorded at a seismic station located 90 km north of the fireball trajectory in Spain, and at an infrasound station in France located 750 km north‐east of the fireball. The absolute magnitude of the bolide has been determined to be ?18 ± 1 from a casual video record. The energy released in the atmosphere determined from photometric, seismic, and infrasound data was about 0.02 kilotons (kt). A massive fragmentation occurred at a height of 28 ± 0.2 km, resulting in a meteorite strewn field of 20 × 6 km. The first meteorite specimen was found on January 11, 2004, near the village of Villalbeto de la Peña, in northern Palencia (Spain). To date, about 4.6 kg of meteorite mass have been recovered during several recovery campaigns. The meteorite is a moderately shocked (S4) L6 ordinary chondrite with a cosmic‐ray‐exposure age of 48 ± 5 Ma. Radioisotope analysis shows that the original body had a mass of 760 ± 150 kg, which is in agreement with the estimated mass obtained from photometric and seismic measurements. 相似文献
284.
Matthias Schmidt 《山地科学学报》2005,2(2)
IntroductionThe mountain forests of South Kyrgyzstan have a long history of human influence. The political and socio-economic conditions prevailing in the region have changed dramatically several times over the last century and have played animportant role in forest policy, management and use. To highlight the human-environment relationship, I have chosen here to use a political ecology approach as conceptual framework (cf. Bryant & Bailey 1997, Bryant 1998, Blaikie 1999). In this approach,… 相似文献
285.
Alastair S. Moore James Lazarus Matthias Hohenberger Joseph S. Robinson Edward T. Gumbrell Mike Dunne Roland A. Smith 《Astrophysics and Space Science》2007,307(1-3):139-145
We describe experiments that investigate the capability of an experimental platform, based on laser-driven blast waves created
in a medium of atomic clusters, to produce results that can be scaled to astrophysical situations. Quantitative electron density
profiles were obtained for blast waves produced in hydrogen, argon, krypton and xenon through the interaction of a high intensity
(I ≈ 1017 Wcm−2), sub-ps laser pulse. From this we estimate the local post-shock temperature, compressibility, shock strength and adiabatic
index for each gas. Direct comparisons between blast wave structures for consistent relative gas densities were achieved through
careful gas jet parameter control. From these we investigate the applicability of different radiative and Sedov-Taylor self-similar
solutions, and therefore the (ρ,T) phase space that we can currently access. 相似文献
286.
S. Laine † J.H. Knapen D. Pérez-Ramírez ‡ P. Englmaier M. Matthias 《Monthly notices of the Royal Astronomical Society》2001,324(4):891-898
We present for the first time a two-dimensional velocity field of the central region of the grand-design spiral galaxy NGC 5248, at 0.9-arcsec spatial resolution. The H α velocity field is dominated by circular rotation. While no systematic streaming motions are seen in the area of the nuclear grand-design spiral or the circumnuclear ring, the amplitude of residual velocities, after subtracting a model circular velocity field, reaches 20 km s−1 in projection. The rotation curve levels out at around 140 km s−1 , after a well-resolved and rather shallow rise. We have generated an analytical model for the nuclear spiral and fitted it to our observations to obtain estimates of the pattern speed of the spiral and the speed of sound in the central region of NGC 5248. Our results are consistent with a low pattern speed, suggesting that the nuclear spiral rotates with the same rate as the main spiral structure in NGC 5248, and thus that the spiral structure is coupled from scales of a few hundred parsecs to several kiloparsecs. We have also compared the observed structure and kinematics between the nuclear regions of NGC 5248 and M100. Several similarities and differences are discussed, including the location of the peak emission regions on major and minor axes, and the spiral arm streaming motions. We find no kinematic evidence for the presence of a nuclear bar in NGC 5248. 相似文献
287.
Mary J. Harner Nora Opitz Keith Geluso Klement Tockner Matthias C. Rillig 《Aquatic Sciences - Research Across Boundaries》2011,73(1):35-42
Most vascular plants form symbioses with mycorrhizal fungi that associate with roots and provide nutrients to hosts in exchange
for carbohydrates, as well as serve a range of other functions. Mycorrhizal fungi have been studied extensively in upland
ecosystems, but we know less about their ecology at aquatic-terrestrial interfaces, especially their distributions at depth.
Our objectives were to determine whether abundances of arbuscular mycorrhizal fungi (AMF) change as floodplain islands develop
and to describe vertical distributions of AMF from the forest floor to the water table along the freely flowing Tagliamento
River in northeastern Italy. We sampled surface sediments (0–10 cm) from three stages of island development on the floodplain—fresh
deposits, pioneer islands, and established islands. We also sampled sediments vertically (0–150 cm) from the ground surface
to the water table on an established island. We characterized abundance of AMF propagules (colonized roots, spores, and hyphae)
within sediments. Roots available to host fungi were absent on fresh deposits; however, some viable spores and hyphae were
available at these sites. Pioneer and established islands each had similar hyphal lengths (~860 cm cm−3) and colonized root lengths (~3 cm cm−3). Abundance of spores increased from depositional (3.5 ± 0.9 (±SE) cm−3) to pioneer (17 ± 6.1 cm−3) to established (32 ± 6.3 cm−3) islands. On an established island, AMF propagules were present at all depths sampled, including at the water table, providing
first documentation of these symbionts to such depths in a riparian setting. Mycorrhizal fungi likely link aquatic and terrestrial
habitats by connecting plants, soil, and ground water and may influence nutrient transfers among these subsystems. 相似文献
288.
Matthias G. W. Schmidt Alexander Lorenz Hermann Held Elmar Kriegler 《Climatic change》2011,104(3-4):783-791
We start from the observation that climate targets under uncertainty should be interpreted as safety constraints on the probability of crossing a certain threshold, such as 2??C global warming. We then highlight, by ways of a simple example, that cost-effectiveness analysis for such probabilistic targets leads to major conceptual problems if learning about uncertainty is taken into account and the target is fixed. Current target proposals presumably imply that targets should be revised in the light of new information. Taking this into account amounts to formalizing how targets should be chosen, a question that was avoided by cost-effectiveness analysis. One way is to perform a full-fledged cost-benefit analysis including some kind of monetary damage function. We propose multi-criteria decision analysis including a target-based risk metric as an alternative that is more explicite in its assumptions and more closely based on given targets. 相似文献
289.
Gerdhard L. JessenSilvio Pantoja Marcelo A. GutiérrezRenato A. Quiñones Rodrigo R. GonzálezJavier Sellanes Matthias Y. KellermannKai-Uwe Hinrichs 《Continental Shelf Research》2011,31(6):574-581
We studied for the first time the intertidal and subtidal gas seepage system in Mocha Island off Central Chile. Four main seepage sites were investigated (of which one site included about 150 bubbling points) that release from 150 to 240 tonnes CH4 into the atmosphere per year. The total amount of methane emitted into the atmosphere is estimated in the order of 800 tonnes per year. The gases emanated from the seeps contain 70% methane, and the stable carbon isotopic composition of methane, δ13C-CH4 averaged −44.4±1.4‰ which indicates a major contribution of thermogenic gas. Adjacent to one of the subtidal seeps, rocky substrates support a diverse community of microbial filaments, macroalgae, and benthic organisms. While stable carbon isotopic compositions of marine benthic organisms indicate a dominant photosynthesis-based food web, those of some hard-substrate invertebrates were in the range −48.8‰ to −36.8‰, suggesting assimilation of methane-derived carbon by some selected taxa. This work highlights the potential subsidy of the trophic web by CH4-C, and that its emission to the atmosphere justifies the need of evaluating the use of methane to support the energy requirements of the local community. 相似文献
290.
In this study, the largest ever carried out to measure noble gases in the pore water of unconsolidated sediments in lakes, the emission of terrigenic He through the sediment column of Lake Van was successfully mapped on the local scale. The main input of He to the water body occurs at the borders of a deep basin within the lake, which is probably the remains of a collapsed caldera. The 3He/4He ratio identifies the He injected into the sedimentary column of Lake Van as a mixture of He released from a mantle source and radiogenic He of crustal origin (3He/4He∼2.6-4.1×10-6). During passage through the pore space, terrigenic He seems to be further enriched in radiogenic He that is most likely produced in the sediment column. In fact, two distinct trends in isotopic composition can be distinguished in the He injected from the lake basement into the sediments. One of these characterizes samples from the shallow water, the other characterizes samples from the deep basin. However, both of these trends are related to the same source of terrigenic He. The He fluxes determined seem to be characteristic of each sampling location and might be considered as a proxy for the fluid permeability of the deep sediment column. These new findings provide insight into the process of fluid transport within the sediments and into the process of formation of the lake basin. Moreover, the isotopic signature of the He that emanates into the water column of Lake Van is strongly affected by the mixing conditions prevailing in the overlying water body. This fact misled previous studies to interpret the terrigenic He in Lake Van as being solely of mantle origin (3He/4He∼10-5). 相似文献