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791.
792.
Development and Application of Oxygen and Carbon Isotopic Measurements of Biogenic Carbonates by Ion Microprobe 总被引:1,自引:0,他引:1
Claire Rollion-Bard Denis Mangin Michel Champenois 《Geostandards and Geoanalytical Research》2007,31(1):39-50
The analytical capabilities of the ims 1270 ion microprobe (SIMS) in determining O and C isotope compositions in biogenic carbonate samples have been tested. Results indicated that, with a spot size of ≊ 30 μm, the average reproducibility at the 1s level was 0.3‰ for oxygen isotopes and 0.6‰ for carbon isotopes. Nevertheless, this reproducibility can reach 0.2‰ for oxygen isotope determinations during some sessions. These reproducibilities allowed us to perform analyses on biogenic carbonate samples for environmental studies. In this paper, examples of oxygen and carbon isotope measurements are presented for a modern coral and the Holocene scleractinian coral, Porites lutea. 相似文献
793.
Ginette Saracco Frédérique Moreau Pierre-Etienne Mathé Daniel Hermitte Jean-Marie Michel 《Geophysical Journal International》2007,171(1):87-103
We have previously developed a method for characterizing and localizing 'homogeneous' buried sources, from the measure of potential anomalies at a fixed height above ground (magnetic, electric and gravity). This method is based on potential theory and uses the properties of the Poisson kernel (real by definition) and the continuous wavelet theory. Here, we relax the assumption on sources and introduce a method that we call the 'multiscale tomography'. Our approach is based on the harmonic extension of the observed magnetic field to produce a complex source by use of a complex Poisson kernel solution of the Laplace equation for complex potential field. A phase and modulus are defined. We show that the phase provides additional information on the total magnetic inclination and the structure of sources, while the modulus allows us to characterize its spatial location, depth and 'effective degree'. This method is compared to the 'complex dipolar tomography', extension of the Patella method that we previously developed. We applied both methods and a classical electrical resistivity tomography to detect and localize buried archaeological structures like antique ovens from magnetic measurements on the Fox-Amphoux site (France). The estimates are then compared with the results of excavations. 相似文献
794.
The excellent topographic condition of the limestone canyons for dam construction may be rejected if they are karstified.
Karst features cause the reservoir not to be impermeable enough to permit the water to fill it and leakage occurs and often
increases with time. Moreover, karst features may involve the stability of the dam itself. A few operated dam sites at the
Zagros Zone encountered a leakage problem. Furthermore, more than 30 dams are presently under study for construction in the
Zagros Zone. Karst conditions and leakage potential were investigated at an under-study site (Khersan 3 Dam) for assessing
the general methodology for the study of leakage potentials. Conventional methods for studying karst features, geological
mapping, geomorphology and extensive borings were applied before the dam was constructed. These methods are not efficient
enough to precisely reveal the karst structure, especially hidden and paleokarst, nor the hydrological behaviour of the karst
structure in different settings of groundwater flow. Based on the present case study and previous applied approaches by other
authors, this paper introduces a methodology by means of karst structure and functioning approaches at local and regional
scales that cover the conventional methods and overcome their shortages. The proposed methodology should be applied before
construction of a dam and should include three steps (a) recognition of geological and hydrogeological settings, (b) delineation
and functioning of the karst system related to the future reservoir, and (c) assessment of the leakage potentials. Following
this methodology, the most probable leakage zone(s) and path(s) at the dam site can be highlighted. 相似文献
795.
Wu XiaoPing Hu XiongLin Michel Bouchon Huang Yong Hu JiaFu Xie ChaoDi Wang ShaoJin Hu YiLi 《中国科学D辑(英文版)》2007,50(11):1655-1662
The spatiotemporal evolution patterns of complete Coulomb stress changes caused by 1988 Ms7.6 earthquake in Lancang-Gengma,Yunnan,are calculated and studied.And the triggering problems of Ms7.2 Gengma shock occurring 13 minutes after the main shock and of Ms5.0―6.9 aftershocks within 24 days after the main shock are discussed.The results show that the spatial distribution patterns of complete Coulomb stress changes of the Ms7.6 main shock are strongly asymmetric.The areas of positive dynamic and static Coulomb stress are both coincident well with the strong aftershocks' locations.The Ms7.2 Gengma shock and most of strong aftershocks are subjected to the triggering effect of dynamic and static Coulomb stresses induced by the Ms7.6 Lancang earthquake. 相似文献
796.
Robert J. Ryan Michel C. Boufadel 《Stochastic Environmental Research and Risk Assessment (SERRA)》2007,21(4):309-316
It has long been understood that streambed hydraulic conductivity plays an important role in surface-subsurface solute exchange.
Using a portable falling head permeameter in situ, we estimated the horizontal hydraulic conductivity, K, of the near-surface streambed sediments at a total of 85 locations encompassing two depth intervals: 7.5–10 and 10–12.5 cm.
The measurements were conducted in an 80 m reach of Indian Creek, a small urban stream in Philadelphia, PA, USA. We found
that the ln K data within each sediment layer were Gaussian, but the combined data set was not. The results indicated that while the mean
hydraulic conductivity decreased with depth, horizontal heterogeneity (e.g. the variance) increased with depth. This strong
contrast between layers suggests that they should be treated as separated entities in modeling studies. Variogram analyses
across the stream suggested symmetry with respect to the thalweg in the upper layer and fractality in the lower layer. The
variograms along the streams suggested that the K data are random. 相似文献
797.
798.
The oceanic substratum of Northern Luzon: Evidence from xenoliths within Monglo adakite (the Philippines) 总被引:2,自引:0,他引:2
Betchaida D. Payot Sebastien Jego Rene C. Maury Mireille Polve Michel Gregoire Georges Ceuleneer Rodolfo A. Tamayo Jr Graciano P. Yumul Jr Herve Bellon Joseph Cotten 《Island Arc》2007,16(2):276-290
Abstract A 8.65 Ma adakitic intrusive sheet exposed near Monglo village in the Baguio District of Northern Luzon contains a suite of ultramafic and mafic xenoliths including in order of abundance: spinel dunites showing typical mantle-related textures, mineral and bulk rock compositions, and serpentinites derived from them; amphibole-rich gabbros displaying incompatible element patterns similar to those of flat or moderately enriched back-arc basin basalt magmas; and amphibolites derived from metabasalts and/or metagabbros of identical affinity. A single quartz diorite xenolith carrying a similar subduction-related geochemical signature has also been sampled. One amphibolite xenolith provided a whole-rock K–Ar age of 115.6 Ma (Barremian). We attribute the origin of this suite to the sampling by ascending adakitic magmas of a Lower Cretaceous ophiolitic complex located at a depth within the 30–35 km thick Luzon crust. It could represent an equivalent of the Isabela-Aurora and Pugo-Lepanto ophiolitic massifs exposed in Northern Luzon. 相似文献
799.
Summary. A geothermal and hydrochemical anomaly was observed in the Lower Triassic sandstone aquifer in the Vittel region (Vosges, France). This anomaly was attributed to a hydrothermal spring under sedimentary cover. In order to localize the hot spring and to quantify more precisely its flow rate and temperature, it is necessary to consider the 3-D thermal problem by taking into account the complex geometry of the domain and the flow rate in the aquifer. A 3-D numerical model of thermal conductive and forced convective transfer, developed for hydrological problems including approximate geometrical and topographical effects, is used which (i) can be directly applied to geologic strata (aquifers) with varying thickness and top and base slope; and (ii) allows calculation of heat flux anomalies associated with fluid flow in such geologically realistic aquifers.
The heat transfer equation is formulated in an orthogonal curvilinear coordinate system. As most geometries dealing with geothermal phenomena in sedimentary basins are nearly horizontal, this formulation can be simplified, leading readily to numerical solution with a finite difference method. The application of the 3-D model to the Vittel aquifer gives temperature results in agreement with measurements. These results provide evidence for the importance of associated forced convection and topographical effects for ground temperature distribution, and show clearly that heat flow in many basins is interpretable only if careful hydrological and thermal studies are made. 相似文献
The heat transfer equation is formulated in an orthogonal curvilinear coordinate system. As most geometries dealing with geothermal phenomena in sedimentary basins are nearly horizontal, this formulation can be simplified, leading readily to numerical solution with a finite difference method. The application of the 3-D model to the Vittel aquifer gives temperature results in agreement with measurements. These results provide evidence for the importance of associated forced convection and topographical effects for ground temperature distribution, and show clearly that heat flow in many basins is interpretable only if careful hydrological and thermal studies are made. 相似文献
800.
Hurley K Cline T Mazets E Aptekar R Golenetskii S Frederiks D Frail D Kulkarni S Trombka J McClanahan T Starr R Goldsten J 《The Astrophysical journal》2000,534(1):L23-L25
The extremely energetic ( approximately 10-4 ergs cm-2) gamma-ray burst (GRB) of 1999 December 8 was triangulated to an approximately 14 arcmin2 error box approximately 1.8 days after its arrival at Earth with the third interplanetary network (IPN), which consists of the Ulysses, Near-Earth Asteroid Rendezvous, and Wind spacecraft. Radio observations with the Very Large Array approximately 2.7 days after the burst revealed a bright fading counterpart whose position is consistent with that of an optical transient source with a redshift of 0.707. We present the time history, peak flux, fluence, and refined 1.3 arcmin2 error box of this event and discuss its energetics. This is the first time that a counterpart has been found for a GRB localized only by the IPN. 相似文献