Late Hesperian plains formation and degradation in a low sedimentation zone of the northern lowlands of Mars     

José Alexis Palmero Rodríguez  Kenneth L. Tanaka  Jeffrey S. Kargel 《Icarus》2010,210(1):116-134

The plains materials that form the martian northern lowlands suggest large-scale sedimentation in this part of the planet. The general view is that these sedimentary materials were transported from zones of highland erosion via outflow channels and other fluvial systems. The study region, the northern circum-polar plains south of Gemini Scopuli on Planum Boreum, comprises the only extensive zone in the martian northern lowlands that does not include sub-basin floors nor is downstream from outflow channel systems. Therefore, within this zone, the ponding of fluids and fluidized sediments associated with outflow channel discharges is less likely to have taken place relative to sub-basin areas that form the other northern circum-polar plains surrounding Planum Boreum. Our findings indicate that during the Late Hesperian sedimentary deposits produced by the erosion of an ancient cratered landscape, as well as via sedimentary volcanism, were regionally emplaced to form extensive plains materials within the study region. The distribution and magnitude of surface degradation suggest that groundwater emergence from an aquifer that extended from the Arabia Terra cratered highlands to the northern lowlands took place non-catastrophically and regionally within the study region through faulted upper crustal materials. In our model the margin of the Utopia basin adjacent to the study region may have acted as a boundary to this aquifer. Partial destruction and dehydration of these Late Hesperian plains, perhaps induced by high thermal anomalies resulting from the low thermal conductivity of these materials, led to the formation of extensive knobby fields and pedestal craters. During the Early Amazonian, the rates of regional resurfacing within the study region decreased significantly; perhaps because the knobby ridges forming the eroded impact crater rims and contractional ridges consisted of thermally conductive indurated materials, thereby inducing freezing of the tectonically controlled waterways associated with these features. This hypothesis would explain why these features were not completely destroyed. During the Late Amazonian, high-obliquity conditions may have led to the removal of large volumes of volatiles and sediments being eroded from Planum Boreum, which then may have been re-deposited as thick, circum-polar plains. Transition into low obliquity ∼5 myr ago may have led to progressive destabilization of these materials leading to collapse and pedestal crater formation. Our model does not contraindicate possible large-scale ponding of fluids in the northern lowlands, such as for example the formation of water and/or mud oceans. In fact, it provides a complementary mechanism involving large-scale groundwater discharges within the northern lowlands for the emplacement of fluids and sediments, which could have potentially contributed to the formation of these bodies. Nevertheless, our model would spatially restrict to surrounding parts of the northern plain either the distribution of the oceans or the zones within these where significant sedimentary accumulation would have taken place.  相似文献   

Lava flow simulations using discharge rates from thermal infrared satellite imagery during the 2006 Etna eruption   总被引：1，自引：0，他引：1  

Annamaria?VicariEmail author  Alessia?Ciraudo  Ciro?Del?Negro  Alexis?Herault  Luigi?Fortuna 《Natural Hazards》2009,50(3):539-550

Techniques capable of measuring lava discharge rates during an eruption are important for hazard prediction, warning, and mitigation. To this end, we developed an automated system that uses thermal infrared satellite MODIS data to estimate time-averaged discharge rate. MODIS-derived time-varying discharge rates were used to drive lava flow simulations calculated using the MAGFLOW cellular automata model, allowing us to simulate the discharge rate-dependent spread of lava as a function of time. During the July 2006 eruption of Mount Etna (Sicily, Italy), discharge rates were estimated at regular intervals (i.e., up to 2 times/day) using the MODIS data. The eruption lasted 10 days and produced a ~3-km-long lava flow field. Time-averaged discharge rates extracted from 13 MODIS images were utilized to produce a detailed chronology of lava flow emplacement, demonstrating how infrared satellite data can be used to drive numerical simulations of lava flow paths during an ongoing eruptive event. The good agreement between simulated and mapped flow areas indicates that model-based inundation predictions, driven by time-varying discharge rate data, provide an excellent means for assessing the hazard posed by ongoing effusive eruptions.  相似文献   

Observations Of The Turbulence Structure Within Two Stratocumulus-Topped, Marine Boundary Layers     

Pierre Durand  Thomas Bourcy 《Boundary-Layer Meteorology》2001,99(1):105-125

Two situations observed during the second Aerosol Characterization Experiment (ACE-2) are analysed from aircraft measurements in the broken stratocumulus (Sc)-topped marine boundary layer. The first one (26 June 1997), characterized by a non-polluted, oceanic air mass, presents a decoupling between the Sc layer (1400–1520 m) and the turbulent mixed layer, this latter extending from the surface up to 580 m. In contrast, the second case (9 July 1997), during which continental air had been advected over the experimental area, presents a well-coupled layer extending from the surface up to the top of the Sc layer(910 m). This coupling, uncommon in this area in the middle of the day, isrelated to the relative shallowness of the boundary layer. For both situations,it is shown that the turbulent fluxes can be computed with reasonably goodaccuracy (better than 10 %), taking into account both the random and thesystematic errors involved in the eddy-correlation technique. Estimationof random error is based on the computation of the integral scale of thecovariance, and systematic error is estimated from the parameterizationof Mann and Lenschow. The fluxes show that the buoyancy, as a sourceof turbulence, is due to latent heat flux rather than sensible heat flux,with values comparable to previous experiments in the Azores-Canariesbasin. In addition, we propose a method to analyse, for coupled situations,the relationship between the fractional cloudiness and the organization ofthe turbulent field below the clouds. This method is based on a conditionalsampling technique. It is shown that this organization cannot be deducedfrom the analysis of the velocity signal, which is dominated by turbulence.However, when the signals are conditionally sampled according to thepresence or absence of clouds, a weak cloud-related organization can beshown, and the cloud-related transports quantified; the values found areof the order of 10 % of the total transfers, i.e. the same order of magnitude asthe errors on the total flux computation. The method developed is thereforepromising, provided that the uncertainties can be reduced by analyzing a highamount of data.  相似文献   

Geochimie et teneurs isotopiques des systèmes saisonniers de dissolution de la calcite dans un sol sur craie     

L. Dever  R. Durand  J.Ch. Fontes  P. Vachier 《Geochimica et cosmochimica acta》1982,46(10):1947-1956

In a soil developed on the Cretaceous chalk of the Eastern Paris basin, calcite dissolution begins at the surface. The soil water is rapidly saturated in calcite. Calcite dissolution follows two different pathways according to seasonal pedoclimatic conditions.During winter: the soil is only partly saturated in water and the CO₂ partial pressure is low (Ca 10^?3 atm.). As a consequence total inorganic dissolved carbon (TIDC) is a hundred times the carbon content of the gaseous phase. Equilibrium is usually observed between the two phases. It is a closed system. The measured carbon 14 activity (87,5%) and ¹³C content ($\text{δ}{}_{\mathrm{tidc}}{}^{13}\text{C = ?12,2\%0}$) of the drainage water are very close to theoretical values calculated for an ideal mixing system between gaseous and mineral phases (respectively characterized by the following isotopic values: $\text{δ}{}_{\mathrm{G}}{}^{13}\text{C = ?21,5\%0}$; $\text{A}{}_{\mathrm{G}}{}^{14}\text{C = 118\%}$; $\text{δ}{}_{\mathrm{M}}{}^{13}\text{C = +2,9\%0}$; $\text{A}{}_{\mathrm{M}}{}^{14}\text{C = 28\%}$).During spring and summer: the soil moisture decreases, the input of biogenic CO₂ induces an increase of the soil CO₂ partial pressure (Ca from 3.10^?3 atm to 7.10^?3 atm). The carbon content of the gaseous phase is higher by an order of magnitude compared to winter conditions. Therefore the aqueous phase is undersaturated in CO₂ with respect to the latter. This disequilibrium occurs as a result of unbalanced rates of CO₂ dissolution and CO₂ effusion toward atmosphère. It is an open system. The carbon isotopic ratio of the aqueous phase is regulated by that of the gaseous phase, as demonstrated by the agreement between measured and calculated isotopic compositions (respectively δ_{L mes} = from ?9,4%0 to ?11,5%0, δ_{l calc} = from ?9,8%0 to ?13,9%0 A_{L mes} = 119%, A_{L calc} = from 119% to 125%).The solutions originating from both systems (open and closed) move downwards without significant mixing together. It has also been observed that no significant variation of the TIDC isotopic composition occurs during precipitation of secondary calcite.  相似文献   

Molecular parameters of maturation in the Toarcian shales,Paris Basin,France—I. Changes in the configurations of acyclic isoprenoid alkanes,steranes and triterpanes     

A.S. Mackenzie  R.L. Patience  J.R. Maxwell  M. Vandenbroucke  B. Durand 《Geochimica et cosmochimica acta》1980,44(11):1709-1721

The changes in configuration at a number of chiral centres in certain acyclic isoprenoid alkanes, steranes, rearranged steranes and triterpanes of the hopane type in a suite of fourteen Toarcian shales (Paris Basin) have been determined by gas chromatography and combined gas chromatography-mass spectrometry. A sequence of changes in the ratios of various stereoisomers occurs both with increasing maximum depth of burial and in a North-South direction for shallow samples (maximum burial depth < 1000m). These changes cover the full range of maturity shown by the samples. The presence of 5α(H), 14β(H), 17β(H)-steranes in immature samples indicates the presence of a reworked component. The extent of epimerisation at a number of the chiral centres suggests that it relates to the extent of steric hindrance at the centres.  相似文献   

Geochemical studies on the organic matter from the Douala Basin (Cameroon)—II. Evolution of kerogen     

B. Durand  J. Espitalié 《Geochimica et cosmochimica acta》1976,40(7):801-808

Optical examinations, elemental analysis, i.r. spectroscopy and thermogravimetric analysis have been used to characterize the kerogens from the Logbaba (Upper Cretaceous) cores from the Douala Basin (Cameroon). It is shown that those kerogens are derived from the same type of organic matter, having mainly a land-plant origin. This conclusion fits very well that obtained from the examination of the soluble organic matter (see Part I). Thus the evolution of the properties of kerogens during burial is not due to a change in the nature of organic matter and can be related mainly to catagenesis. Owing to the existence of a high geothermal gradient in the basin and a sampling along a 4000 m thick sedimentary column, this evolution can be followed over a large range and correlated to the formation of petroleum and gas.  相似文献   

L'essai de torsion et la résistance au cisaillement des roches     

Durand  E. 《Rock Mechanics and Rock Engineering》1975,7(4):199-230

Rock Mechanics and Rock Engineering - Cette étude présente un appareillage de torsion mis au point au laboratoire de Mécanique des Roches d'Electricité de France. Les...  相似文献   

利用MODIS光学厚度遥感产品研究北京及周边地区的大气污染   总被引：53，自引：2，他引：53  

李成才  毛节泰  刘启汉  刘晓阳  刘桂青  朱爱华 《大气科学》2003,27(5):869-880

对2001年在北京地区利用太阳光度计观测的气溶胶光学厚度和NASA发布的MODIS气溶胶产品进行了比较,验证了这一卫星遥感产品的可靠性;比较了2001年MODIS气溶胶光学厚度(AOD)产品和由空气污染指数(API)计算的每日平均可吸入颗粒物(PM10)浓度,得到了比较高的相关系数,证实该气溶胶产品可用于污染分析.将北京地区AOD与气象能见度观测资料进行比较,得到了不同季节的气溶胶"标高".利用统计的不同季节的气溶胶标高,从光学厚度的季节分布得到了能见度(能见距离)的季节分布.气溶胶光学厚度图像的个例分析表明,除局地排放外,周边区域(主要为西南和南向)的输送对北京市区的空气污染贡献份额较大.卫星遥感气溶胶可以比较直观地再现污染物的区域分布和输送,不仅为研究全球气候变化也为研究区域环境的空气质量提供了一种有效手段.  相似文献   

Experimental investigation of atmospheric boundary layer turbulence     

Aimé Druilhet  Pierre Durand 《Atmospheric Research》1997,43(4):345-388

This paper describes how to measure turbulence in the atmospheric boundary layer (ABL) in order to address certain problems in modern atmospheric physics. These problems mainly relate to the Earth's energy budget (including the hydrological cycle) and biogeochemical cycles. Starting from the main characteristic numbers and the basic equations of atmospheric turbulent flow, we show what turbulence parameters are important to measure. Special attention is given to the various methods used to compute the turbulent fluxes. We analyse the range of scales which has to be measured to properly capture the eddies contributing to the turbulent transfers. This range of scales determines what sensors can be used in the atmospheric surface layer and in the ABL. We describe the most widely used instruments and their performances. The principal platforms used to deploy these instruments are examined. Aircraft are described in more details, because they allow a thorough exploration of the ABL. In the last section, some examples of ABL turbulence signals measured in various conditions are presented. These examples illustrate horizontally homogeneous turbulence as well as inhomogeneous signals for which standard analysis techniques cannot be used. We show how some recent techniques, like wavelet transforms, can help to investigate this kind of signal. At the end, we present what would be interesting to do in the near future for the study of ABL turbulence.  相似文献   

A mesoscale shear convective cell observed during the C.O.A.S.T. experiment: Acoustic sounder measurements     

A. Weill  F. Baudin  C. Mazaudier  G. Desbraux  C. Klapisz  A. G. M. Driedonks  J. P. Goutorbe  A. Druilhet  P. Durand 《Boundary-Layer Meteorology》1988,44(4):359-371

A mesoscale shear convective cell was observed with a Doppler sodar and a minisodar on May 22, 1983 near the Netherland Coast. Boundary-layer modifications associated with fair weather precipitating clouds were observed and a separation is undertaken between the different scales of the perturbations. There is difficulty in estimating the turbulent dissipation rate by the inertial method in the presence of mesoscale perturbations, which suggests the need for independent computation of spatial structure functions of velocity fluctuations and spectral density of velocity fluctuations as functions of frequency to observe the relationship between wave lengths and frequencies.C.O.A.S.T.: Cooperative Experiment with Acoustic Sounding Techniques.  相似文献