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41.
Whether or not there are extensional detachment faults in the Alboran basement can be tested directly because a part of the Alboran Basin is now emerged. These detachments, related to crustal thinning beneath the Alboran Basin, occurred from the Aquitanian to Tortonian. The resulting extensional geometries can be described in general terms. During the Serravalian a considerable southwest extension of the basin took place, accompanied by south-southeast extension in the northern Gibraltar Arc. Other detachments affected by Serravalian extension can be found. The spreading of the Alboran was nearly coeval with roughly westward migration of the Gibraltar mountain front. 相似文献
42.
Knowledge of marine geological environments in which shallow gas is accumulating is becoming increasingly important in global
studies of climate change because a measurable proportion of the total methane source comes from continental margins. Previous
studies have revealed that coastal environments represent important geological environments where microbial methane is being
generated, is accumulating, and is being released. In the Ría de Pontevedra, at least 4.5 km2 of seafloor in the innermost part of the ría is underlain by sediments containing natural gas. Seismic interpretation contributes
new findings for the definition of periods and geological environments in which the gas could have been generated, and is
accumulating and released in the Ría de Pontevedra. Groundtruthing the seismic data (facies, environments) makes it possible
to identify favourable geological environments for gas generation in the sedimentary infill of the Ría de Pontevedra. Sequence
stratigraphy based on high-resolution seismic profiles and post-Last Glacial Maximum sea-level records makes it possible to
establish the stratigraphic architecture of the ría and to define the periods in which gas could have been generated. The
results of this study show that the sedimentary infill is composed of a fifth-order sequence developed since the Last Glacial
Maximum. Within this sequence, gas appears to have accumulated in the Holocene deposits associated with the latest transgressive
and highstand system tracts. Seismic analysis shows that gas could have been generated in different geological environments
in the Ría de Pontevedra. If coastal environments at times of lower sea level were similar to those of the present, organic-rich
mud deposits (deposited mainly in lakes, estuaries and floodplains) could have survived transgression and remained buried
as potential gas sources in the inner part of the ría. 相似文献
43.
Background signal of the scintillation detector routinely used for atmospheric Kr-85 counting follows fluctuations, and their connection with cosmic ray variations is searched for. A strong correlation between the 27-day moving average of sunspot numbers and the background is obtained from the 1988 data. 相似文献
44.
Zdeněk Švestka 《Solar physics》1989,121(1-2):399-417
One has to distinguish between two kinds of the gradual phase of flares: (1) a gradual phase during which no energy is released so that we see only cooling after the impulsive phase (a confined flare), and (2) a gradual phase during which energy release continues (a dynamic flare).The simplest case of (1) is a single-loop flare which might provide an excellent opportunity for the study of cooling processes in coronal loops. But most confined flares are far more complicated: they may consist of sets of unresolved elementary loops, of conglomerates of loops, or they form arcades the components of which may be excited sequentially. Accelerated particles as well as hot and cold plasma can be ejected from the flare site (coronal tongues, flaring arches, sprays, bright and dark surges) and these ejecta may cool more slowly than the source flare itself.However, the most important flares on the Sun are flares of type (2) in which a magnetic field opening is followed by subsequent reconnection of fieldlines that may continue for many hours after the impulsive phase. Therefore, the main attention in this review is paid to the gradual phase of this category of long-decay flares. The following items are discussed in particular: The wide energy range of dynamic flares: from eruptions of quiescent filaments to most powerful cosmic-ray flares. Energy release at the reconnection site and modelling of the reconnection process. The post-flare loops: evidence for reconnection; observations at different wavelengths; energy deposit in the chromosphere, chromospheric ablation, and velocity fields; loops in emission; shrinking loops; magnetic modelling. The gradual phase in X-rays and on radio waves. Post-flare X-ray arches: observations, interpretation, and modelling; relation to metric radio events and mass ejections, multiple-ribbon flares and anomalous events, hybrid events, possible relations between confined and dynamic flares. 相似文献
45.
Spin rate estimation of sounding rockets using GPS wind-up 总被引:2,自引:1,他引:1
Carrier phase wind-up is a well-known effect that arises from the relative rotation between a transmitting and receiving antenna.
In GPS measurements at L1 frequency, this effect translates into an error of 19.029 cm per full relative rotation of antennas.
Since this effect is independent of the satellite elevation for pure rotation about the antenna boresight axis, it is usually
absorbed by the clock estimation in navigation algorithms. Therefore, the impact of wind-up is usually neglected for applications
that do not require accuracies to the cm level like RTK. However, in receiving platforms with high rotation rate, the accumulated
wind-up value can be important and actually be larger than receiver noise or even ionospheric variations. Therefore, in such
scenarios, the wind-up contribution can be isolated and used as a source of information to compute the spin rate of such platforms
using an appropriate combination of GPS observables. This work shows some results of a coarse, yet simple, approach to monitor
the rotation angle and spin-rate of spin stabilized sounding rockets flown by DLR. 相似文献
46.
The Karalar galena-barite deposits are typical examples of the carbonate-hosted barite-galena deposits widely occurring in
the Central Tauride Belt. These deposits are located in Permian limestones as ore veins along fault zones that are discordant
to the bedding planes and as thin veinlets within hardly brecciated bottom zones of Permian limestones. The ore deposits contain
mainly barite and galena and small amounts of sphalerite, pyrite, fahlore, limonite, quartz, and calcite. Barites occur during
the earlier episode of mineralization and were mylonitized before the formation of galena. Galena and other minerals occur
epigenetically with barite along porous zones between brecciated barite crystals and are especially abundant in the hardly
mylonitized zones. Fluid inclusion studies indicate that the ore deposits of the area were developed by hydrothermal fluids
with following characteristics: they contained NaCl, CaCl2, and MgCl2; the salinity of the fluids was relatively high and their temperature was low during the crystallization of barites in the
earlier episode of mineralization; and the salinity of the fluids decreased and their temperature increased during the crystallization
of sulfide minerals through the later episode of mineralization. δ18O and the δD results indicate that the water in the mineralizing fluid was of meteoric origin. The deposits were formed by
deep meteoric water circulating through marine sediments. Shallow circulating and slightly warmed fluids dissolved Ba and
sulfate from marine sediments of the basement and transported them to the mineralization environment during the early episode,
while deep circulating and more heated fluids dissolved Pb, Zn, and other elements from the basement and reached the environment
during the later episode of mineralization.
The text was submitted by the authors in English. 相似文献
47.
We simulate direct current (DC) borehole resistivity measurements acquired in steel-cased deviated wells for the assessment
of rock formation properties. The assumed data acquisition configuration considers one current (emitter) and three voltage
(collector) electrodes that are utilized to measure the second difference of the electric potential along the well trajectory.
We assume a homogeneous, 1.27-cm-thick steel casing with resistivity equal to 10 − 5 Ω· m. Simulations are performed with two different numerical methodologies. The first one is based on transferring two-dimensional
(2D) axisymmetric optimal grids to a three-dimensional (3D) simulation software. The second one automatically produces optimal
3D grids yielded by a 3D self-adaptive goal-oriented algorithm. Both methodologies utilize high-order finite elements (FE)
that are specially well-suited for problems with high-contrast coefficients and rapid spatial variations of the electric field,
as it occurs in simulations that involve steel-cased wells. The method based on transferring 2D-optimal grids is efficient
in terms of CPU time (few seconds per logging position). Unfortunately, it may produce inaccurate 3D simulations in deviated
wells, even though the error remains below 1% for the axisymmetric (vertical) well. The method based on optimal 3D grids,
although less efficient in terms of CPU time (few hours per logging position), produces more accurate results that are validated
by a built-in a posteriori error estimator. This paper provides the first existing simulations of through-casing resistivity
measurements in deviated wells. Simulated resistivity measurements indicate that, for a 30° deviated well, measurements in
conductive layers 0.01 Ω· m) are similar to those obtained in vertical wells. However, in resistive layers (10,000 Ω· m),
we observe 100% larger readings in the 30° deviated well. This difference becomes 3,000% for the case of a 60° deviated well.
For this highly-deviated well, readings corresponding to the conductive formation layer are about 30% smaller in magnitude
than those in a vertical well. Shoulder effects significantly vary in deviated wells. 相似文献
48.
The playa-lakes of the Monegros desert in north-east Spain are saline wetlands in an arid environment, a rare phenomenon in Europe. These extremely valuable habitats are threatened by changes associated with agricultural expansion and incorporation of new irrigated areas. An understanding of the present hydrologic regime will enable changes to be identified, particularly those brought about by flooding and pollution caused by irrigation surplus. This study sets out to show the results of applying a daily water balance in three selected playa-lakes. The balance was in two parts and consisted of: (1) the average balance for all the endorheic basin using the BALAN_11 program, and (2) the water balance in some playa-lakes, applying discharge flows obtained from the previous balance. The resulting volumes of water were converted to water depths and contrasted with reference volumes taken from field and Landsat images. The model was calibrated by applying various hypotheses of function which enabled the results to be adjusted. The proposed balance is an acceptable reproduction of field water measurements during this period, and underlines the consistency of the conceptual model. The methodology used is appropriate for understanding the playa-lakes function and for monitoring them for conservation purposes. 相似文献
49.
The region known as Pampa Plain, in Argentina, is a vast area characterized by slopes of less than 0.05%. The surface sediment is silty sand, mainly Aeolian, referred to as Pampean Loess, which is a phreatic aquifer unit of utmost importance for the water supply of the region. On account of the slight gradient, hydrogeological analyses using only hydraulic measurements are difficult to perform, often leading to confusing results. Thus, the study presented relies on hydrochemical modeling and isotopic determinations as well. The study area comprises three catchments in the inter-mountainous area corresponding to El Moro, Tamangueyú and Seco creeks, and covering 2,570 km2 in the province of Buenos Aires. Measurements of piezometric levels and samples of groundwater, surface water and rainwater were carried out between January and March 2005. Major ion results were analyzed by means of hydrochemical graphs and hydrogeochemical modelling using NETPATH. The resulting data show that it is possible to identify local changes in recharge, flow direction and stream/groundwater relationship by using hydrochemical and isotopic information, which may become a useful and more precise tool for the study of particularly flat landscapes. 相似文献
50.