Predicting landscape-scale erosion rates using digital elevation models

Functional relationships between erosion rates and topography are central to understanding controls on global sediment flux and interactions among tectonics, climate, and erosion in shaping topography. Based on such relations digital elevation models (DEMs) allow predicting landscape-scale erosion rates to the degree that process models can be calibrated and to the extent that such processes reflect elevation, drainage area, and aspect, or their derivatives such as slope and curvature. Digital elevation models allow investigating the influence of erosional processes on landscape form and evolution through generalized quantitative expressions often referred to as ‘erosion laws’. The analytical forms of such expressions are derived from physical principles, but only limited data are available to guide calibration to particular landscapes. In addition, few studies have addressed how different transport laws interact to set landscape-scale erosion rates in different environments. Conventionally, landscape-scale sediment flux is considered to be linearly related to slope or relief, but recent analyses point toward non-linear relations for steep terrain in which changes in the frequency of landsliding accommodate increased rates of rock uplift. In such situations, landscape-scale erosion rates are more closely tied to erosion potential predicted by models of bedrock river incision. Consequently, I propose that using DEMs to predict absolute or relative erosion rates at the landscape-scale counter-intuitively involves the rate of fluvial processes as governing the sediment flux from steep landscapes, and rates of hillslope processes as governing sediment flux from low-gradient landscapes. To cite this article: D.R. Montgomery, C. R. Geoscience 335 (2003).     

东西科学文化碰撞的火花--纪念德日进神父(1881～1955年)来中国工作80周年

文章试图通过德日进神父自己的记述、与亲友的通信以及人们的回忆寻找他对中国科学做出贡献的发生发展过程,追踪德日进在其事业不同阶段的经历,了解他是如何在极端困难和复杂的条件下取得如此崇高的、科学和哲学的统一.德日进神父(1881～1955年),法国人,1923年来到中国.从在宁夏银川的水洞沟黄土层中发现了旧石器时起,1929年担任中国地质调查所新生代研究室顾问,指导了周口店的发掘研究,经历了第二次世界大战的困难时期,完成了他的名著<智慧圈>及<人的现象>.直至1946年离开中国,他在中国前后生活了23年(1923～1946年).在这23年中,他对中国的地质、古生物科学、考古科学等许多方面进行了大量的调查和研究,培养了人才,撰写了许多科学论文和专著,以及重要的哲学著作.德日进神父在中国受到人们的尊敬和爱戴,被称为中国古脊椎动物学的奠基者和领路人.一个人成就的伟大,往往不在于他意料之中,而是在于出乎他的意想之外.德日进神父是中西科学文化交流历史上、20世纪这一旋回中,连接西方和东方之路的无声的开拓者.他是把自然科学和哲学完美联结在一起的一座看不见的桥梁.文章按时间顺序分别描述德日进神父对东方的印象和思考,包括:1)对东方的憧憬--童年和<马可@波罗游记>;2)对东方的企盼--浪漫主义的东方;3)对东方的失望--长城边上的落日;4)对东方的希望--他们将自己站稳;5)对东方的升华--"智慧圈"和<人的现象>.谨以此文纪念80年前德日进神父来华所开辟的东西方科学交流之道路,和科学与哲学的结合.     

德日进"亚洲干极"理论的现实意义

"亚洲干极"是德日进总结中国北方中生代以来不断干旱化得出的观点.构造运动驱动气候变干是其主导思想.德日进关于中国新生代古地理演化的基本框架至今仍然适用,当代研究补充和深化了"亚洲干极"的理论,老第三纪行星风系的干热气候逐渐在新第三纪被季风气候取代,代表干旱气候的粉尘沉积逐步扩大空间范围,湖相沉积则逐渐收缩.22MaB.P.,8.5MaB.P.,3.6MaB.P.和1.2MaB.P.是"亚洲于极"逐步加强的关键时段.     

Le domaine Tariquide (arc de Gibraltar,Espagne et Maroc) : succession et hiatus de la sédimentation du Jurassique supérieur au Paléocène

The originality of the Malm–Cretaceous series of the Tariquides (Gibraltar arc), as compared to those of the Rifian–Betic ‘Dorsale’ (Alboran domain), and especially with the Penibetic (Iberia) domain, is emphasized. In the Los Pastores Group, near Algeciras, Upper Tithonian nodular limestones directly lie on the Dogger and are followed by Aptychus-bearing limestones (Late Berriasian to Barremian). In the Musa Group, Rif, radiolarites are followed by siliceous limestones (Kimmeridgian–Tithonian), then by karst and massflow breccias connected to a Berriasian tectonics, by Aptychus-bearing marly limestones, then by karst filled by Turonian limestones, and finally by Maastrichtian–Palaeocene polychrome pelites, whose micropalaeontological and mineral compositions (clay minerals, FeMn nodules) refer to a deep-sea, probably infra-CCD, sedimentation. To cite this article: M. Durand-Delga et al., C. R. Geoscience 337 (2005).     

Steady-state vertical distribution of cohesive sediments in a flow

Settling velocity of diluted suspended aggregates is examined under steady-state conditions. It is shown that if the local settling velocity of the suspended mass of sediments at the bottom is gamma distributed, then, the vertical variation of the local mean settling velocity $\overline{W}$ is proportional to a power $1/r$ of the local concentration C, where r is the gamma distribution parameter. That is a consequence of the suspended-sediment sorting produced by the vertical dynamics. The parameter r characterizes the range of settling velocity values for all the aggregates simultaneously in suspension. To cite this article: M. Sánchez et al., C. R. Geoscience 337 (2005).     

Carbonic fluid inclusions in ultrahigh-temperature granitoids from southern India

The granite plutons of Vattamalai (VT), Gangaikondan (GK) and Pathanapuram (PT) intruding granulite facies rocks in southern India were emplaced during the Late Neoproterozoic tectonothermal event. Feldspar thermometry of mesoperthites from the granites yield temperatures of 800–1000?°C indicating high- to ultrahigh-temperature conditions, comparable to similar estimates derived from some of the host granulite facies rocks in the region. This study reports results from a detailed investigation of fluid inclusions in the three granite plutons. Carbonic inclusions characterize the major fluid species in all the cases and their unique abundance in some of these plutons indicates up to 1 wt.% CO₂. In most of the cases, the inclusions show a near-pure CO₂ composition as deduced from melting temperatures which cluster close to $?56.6°$C, and as confirmed by laser Raman spectroscopy. The VT granite preserves the highest density CO₂ fluids among all the three plutons with a density up to 0.912 g?cm^?3 (molar volume of 48.25 cm³?mol^?1). A combination of CO₂ isochores, feldspar thermometry data and dehydration melting curves, and liquidus for water-undersaturated granitic systems clearly bring out a genetic link between these granites and granulitic lower crust. The ultimate origin of the CO₂-rich fluids is linked to sub-lithospheric mantle sources through tectonic processes associated with the assembly of the Gondwana supercontinent. To cite this article: M. Santosh et al., C. R. Geoscience 337 (2005).     

Tenseurs de perméabilité équivalente d'un domaine hétérogène fini

In an earlier paper, it has been shown that for a heterogeneous block of finite size, under linear boundary pressure conditions, a symmetric and positive definite tensor, denoted here by ${\mathbf{K}}^{\mathrm{p}}$, exists, which relates the mean flux to the mean gradient of pressure in the block. In this paper, the conditions of constant boundary flux are first defined. Then it is shown that, under these conditions also, a symmetric and positive definite tensor, denoted ${\mathbf{K}}^{\mathrm{q}}$, exists, which relates the mean flux to the mean pressure gradient. It is then shown that ${\mathbf{K}}^{\mathrm{q}}$ and ${\mathbf{K}}^{\mathrm{p}}$ respectively give the equivalent permeability in the direction of mean gradient and of mean flux. The directional permeability values given by ${\mathbf{K}}^{\mathrm{q}}$ are shown to be smaller than ${\mathbf{K}}^{\mathrm{p}}$. To cite this article: A. Pouya, C. R. Geoscience 337 (2005).     

Estimation de la température maximale d'enfouissement du Toarcien et du Callovo-Oxfordien au centre du bassin de Paris par les marqueurs organiques

The thermal history of the central part of the Paris basin is reconstructed using C₃₁ hopane $\mathrm{S}/\mathrm{R}$ isomerisation ratios and organic matter transformation ratios measured on Lower Toarcian and Callovo-Oxfordian samples. Maximum burial palaeotemperatures range between 90 and 115?°C for the Toarcian shales, and between 75 and 95?°C for the Callovo-Oxfordian samples, from the East to the centre of the basin, respectively. The amount of Late Cretaceous erosion was evaluated to be between ca. 400 to 600 m in the eastern part of the studied area and 100 to 300 m in the centre of the basin. To cite this article: C. Ménétrier et al., C. R. Geoscience 337 (2005).     

A possible satellite of (146) Lucina

This paper reports on an observation of the appulse of (146) Lucina with AGK3 + 17° 1309 made on April 18, 1982, at the Meudon Observatory in France. During this observation a secondary event occurred and was recorded. A Nocticon camera mounted on the 1-m telescope and video equipment was used. This equipment is well adapted to these observations primarily because astrometric and photometric reductions are possible. Furthermore no diaphragm is necessary in contrast to classical photometry, and this reduces the possibility of generating artifacts. The Meudon observation is described. Observational data from other sites have been collected, and have confirmed that the short extinction observed at Meudon was not due to the asteroid itself. A possible interpretation is the existence of a faint satellite in the neighborhood of (146) Lucina. The observation leads to a diameter of at least 5.7 km and a projected distance of 1600 km from the primary.     

A comparison between two simultaneous sets of current measurements in the Straint of Juan de Fuca

A comparison is made between a set of current measurements in a section across the Strait of Juan de Fuca and those recorded further upstream at Race Rocks at a single depth. No outstanding common qualitative features are noted. Cross spectra reveal a low correlation for the subtidal current and suggest an intensification of the diurnal modulation of the flow at Race Rocks. The high correlation in the tidal bands allows to calculate this portion of the tidal current at Race Rocks which is coherent with the one sensed across the section.