法国、中国断陷盆地厚煤层堆积机制分析   总被引：3，自引：0，他引：3  

王华  吴冲龙  Louis Courel  Michel Guiraud 《地学前缘》1999,6(Z1):157-166

从法国中央地块晚石炭世的3个内陆山间小型断陷聚煤盆地厚煤层的成因标志和沉积特征出发,讨论了这些煤层独特的堆积机制及其沉积-构造条件,并与中国东北早第三纪抚顺盆地超厚煤层的沉积条件做了比较分析,指出了2个大陆间在厚煤层的堆积背景与条件方面的差异性和共同点。尤其是这些盆地均发育于活动的构造背景之下,盆缘、盆内断层活动强烈,且控制着沉积相带的展布及富煤单元的时空分布;煤层内均发育有大量的重力流沉积物——碎屑流。稀性泥石流或浊流沉积物;煤层自身存在同沉积期的重力滑塌。变形构造和大量的再搬运-再堆积的记录,表明厚（巨厚、超厚）煤层在堆积时的湖泊环境为覆水较深、不稳定的沉积环境,并且煤（泥炭）在初次堆积后经过了再次搬运而成为异地堆积的产物。这为提出厚煤层新的堆积机制,即异地堆积提供了重要而可靠的证据和实例。  相似文献   

On the depth of oceanic earthquakes: Brief comments on “The thermal structure of oceanic and continental lithosphere”, by McKenzie,D., Jackson,J. and Priestley,K., Earth Plan. Sci. Let., 233, [2005], 337–349     

Louis Géli  John Sclater 《Earth and Planetary Science Letters》2008,265(3-4):766-772

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Phosphorus Sorption and Availability from Biochars and Soil/Biochar Mixtures   总被引：2，自引：0，他引：2       下载免费PDF全文

Rajesh Chintala  Thomas E. Schumacher  Louis M. McDonald  David E. Clay  Douglas D. Malo  Sharon K. Papiernik  Sharon A. Clay  James L. Julson 《洁净——土壤、空气、水》2014,42(5):626-634

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An Approximate Model for Well Productivity in Heterogeneous Porous Media   总被引：2，自引：0，他引：2  

Louis J. Durlofsky 《Mathematical Geology》2000,32(4):421-438

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Impact of terrestrial runoff on organic matter,trophic state,and phytoplankton in a tropical,upland reservoir     

Duc Anh Trinh  Thi Nguyet Minh Luu  Quan Hong Trinh  Hai Sy Tran  Tien Minh Tran  Thi Phuong Quynh Le  Thuy Thi Duong  Didier Orange  Jean Louis Janeau  Thomas Pommier  Emma Rochelle-Newall 《Aquatic Sciences - Research Across Boundaries》2016,78(2):367-379

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Twentieth century changes in montane vegetation in the eastern Free State,South Africa,derived from palynology of hyrax dung middens     

Jose S. Carrin  Louis Scott  John C. Vogel 《第四纪科学杂志》1999,14(1):1-16

The dating and pollen analysis of a hyrax dung deposit in a mountain rock shelter (Rooiberg Shelter II) are compared with that in a previous study from the same mountain range at the rural town Clarens, in South Africa. Calibration of radiocarbon measurements from the dung deposit provides different possibilities for the age of the sequence. Unlikely dates can be eliminated on the basis of pollen stratigraphy, comparisons with a previously studied accumulation from the last 30 yr, artificially increased radiocarbon levels in the upper samples as result of nuclear arms testing after 1954, the presence of historically introduced exotic elements, and the assumption of a relatively constant rate of dung accumulation. According to these considerations we suggest that the dung started accumulating at the beginning of the twentieth century. The pollen contents show marked changes in composition, indicating mainly open grass vegetation with fynbos in the first half of this century and woody vegetation in the second half. A first marked increase of the woody component is estimated to have occurred around 1950, but it only became permanent in the 1960s. The fluctuating pollen sequence can best be interpreted in terms of the combined effects of rainfall changes, fire and stock grazing, the latter of which increased together with town expansion in the area during the course of this century. Considering historical events recorded in the area and the region in general, the results suggest that pollen in hyrax dung is a good recorder of vegetation change. Copyright © 1999 John Wiley & Sons, Ltd.  相似文献   

PPAPI: A Program for Groundwater Modeling Tasks in Distributed Parallel Computing Environments          下载免费PDF全文

Jens Schumacher  Kevin Hayley  Louis‐Charles Boutin  Emma White 《Ground water》2018,56(2):248-250

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Mechanisms of lateral and linear extension of gullies (dongas) in a subhumid grassland of South Africa     

Pascal Podwojewski  Jean Louis Janeau  Sandrine Caquineau  Jeffrey Hughes 《地球表面变化过程与地形》2020,45(13):3202-3215

The formation of deep gullies (called ‘dongas’ locally) in rangeland in KwaZulu-Natal Province in South Africa is a natural phenomenon. These U-shaped, very wide gullies have considerable lateral expansion due to the episodic collapse of sidewalls. The dongas have developed in duplex soils such as Luvisols and Lixisols formed on Permian sedimentary rocks or unconsolidated Quaternary colluvium. This study combined morphological, mineralogical and chemical characterization with measurements of grain-size content, structural stability and the complete shrinkage curve to detect changes in soil properties of the different horizons located in the gully banks. The different soil horizons present clear and sharp differences in physical and mineralogical properties. The topsoil with complete grass cover is very resistant to soil detachment. However, the leached E horizon and the BC horizon have low structural stability. The soil profile down to and including the Bt horizon contains exclusively illite in the clay fraction, while the BC colluvial layer and the C horizon (mudstone) contain expandable interstratified illite–smectite. The Bt horizon has a high water content at saturation and high shrinkage, while the BC and C horizons have a high residual shrinkage and a very low water content at saturation. Because this type of gully expansion is not significantly linked to slope value or the stream power index (SPI) at the gully head, to land-use change, high rainfall intensities or the threshold of concentrated runoff being exceeded at the gully head, other causes were investigated. It was concluded that the heterogeneity between horizons with different mineralogical properties and structural stabilities, soil types and parent material, anisotropic water-saturation and shrink-swell properties are of major importance. This heterogeneity between different soil horizon morphologies and their physical properties can explain why the relationship between the critical slope and the drainage area for gully initiation showed a threshold for gullying much lower than that found elsewhere. © 2020 John Wiley & Sons, Ltd.  相似文献   

High-resolution Observations of H$\alpha$ Spectra with a Subtractive Double Pass     

C. Beck  R. Rezaei  D. P. Choudhary  S. Gosain  A. Tritschler  R. E. Louis 《Solar physics》2018,293(2):36

High-resolution imaging spectroscopy in solar physics has relied on Fabry–Pérot interferometers (FPIs) in recent years. FPI systems, however, become technically challenging and expensive for telescopes larger than the 1 m class. A conventional slit spectrograph with a diffraction-limited performance over a large field of view (FOV) can be built at much lower cost and effort. It can be converted into an imaging spectro(polari)meter using the concept of a subtractive double pass (SDP). We demonstrate that an SDP system can reach a similar performance as FPI-based systems with a high spatial and moderate spectral resolution across a FOV of \(100^{\prime\prime} \times100^{\prime \prime}\) with a spectral coverage of 1 nm. We use H\(\alpha\) spectra taken with an SDP system at the Dunn Solar Telescope and complementary full-disc data to infer the properties of small-scale superpenumbral filaments. We find that the majority of all filaments end in patches of opposite-polarity fields. The internal fine-structure in the line-core intensity of H\(\alpha\) at spatial scales of about 0\(.\!\!^{\prime \prime }\)5 exceeds that in other parameters such as the line width, indicating small-scale opacity effects in a larger-scale structure with common properties. We conclude that SDP systems in combination with (multi-conjugate) adaptive optics are a valid alternative to FPI systems when high spatial resolution and a large FOV are required. They can also reach a cadence that is comparable to that of FPI systems, while providing a much larger spectral range and a simultaneous multi-line capability.  相似文献   

Hillslope water tracks in the High Arctic: Seasonal flow dynamics with changing water sources in preferential flow paths          下载免费PDF全文

Michel Paquette  Daniel Fortier  Warwick F. Vincent 《水文研究》2018,32(8):1077-1089

Preferential subsurface flow paths known as water tracks are often the principal hydrological pathways of headwater catchments in permafrost areas, exerting an influence on slope physical and biogeochemical processes. In polar deserts, where water resources depend on snow redistribution, water tracks are mostly found in hydrologically active areas downslope from snowdrifts. Here, we measured the flow through seeping water track networks and at the front of a perennial snowdrift, at Ward Hunt Island in the Canadian High Arctic. We also used stable isotope analysis to determine the origin of this water, which ultimately discharges into Ward Hunt Lake. These measurements of water track hydrology indicated a glacio‐nival run‐off regime, with flow production mechanisms that included saturation overland flow (return flow) in a low sloping area, throughflow or pipe‐like flow in most seepage locations, and infiltration excess overland flow at the front of the snowdrift. Each mechanism delivered varying proportions of snowmelt and ground water, and isotopic compositions evolved during the melting season. Unaltered snowmelt water contributed to >90% of total flow from water track networks early in the season, and these values fell to <5% towards the end of the melting season. In contrast, infiltration excess overland flow from snowdrift consisted of a steady percentage of snowmelt water in July (mean of 69%) and August (71%). The water seeping at locations where no snow was left in August 2015 was isotopically enriched, indicating a contribution of the upper, ice‐rich layer of permafrost to late summer discharge during warmer years. Air temperature was the main driver of snowmelt, but the effect of slope aspect on solar radiation best explained the diurnal discharge variation at all sites. The water tracks in this polar desert are part of a patterned ground network, which increases connectivity between the principal water sources (snowdrifts) and the bottom of the slope. This would reduce soil–water interactions and solute release, thereby favouring the low nutrient status of the lake.  相似文献