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91.
Adrian C. Armstrong 《水文研究》1988,2(4):383-389
Linear system theory can be used to model and predict watertable responses to precipitation inputs in an artificially drained field. The response function is mathematically equivalent to the Unit Hydrograph concept familiar to hydrologists. This paper shows that it is possible to derive such response functions, and comments on the problems encountered in their derivation. Response functions for two contrasted sites are presented, and the possibilities for their use discussed. 相似文献
92.
Adrian J. Brearley 《Meteoritics & planetary science》1993,28(4):590-595
Abstract— Rare, ultrafine-grained Ti oxides (Ti3O5 and the Magnéli phases, Ti5O9 and Ti8O15) have been identified by transmission electron microscopy in the CM2 carbonaceous chondrite, Bells and a carbonaceous chondrite matrix clast from the Nilpena polymict ureilite. In both meteorites the Ti oxides occur in the matrix as isolated grains and clusters of two or more grains. They are euhedral in shape and have grain sizes of 0.05–0.3 μm. Magnéli phases have been recently shown to be a common component in some interplanetary dust particles, but this is the first reported occurrence in a meteorite. The morphological properties and grain size of the Ti oxides are consistent with formation by vapor phase condensation either within the solar nebula or possibly in a presolar environment. 相似文献
93.
Adrian Gilli Flavio S. Anselmetti Daniel Ariztegui† Milan Beres† Judith A. McKenzie Vera Markgraf‡ 《Sedimentology》2005,52(1):1-23
The results of a seismic stratigraphic analysis of a closed lake basin, Lago Cardiel, in southernmost South America are reported. Very few high-resolution, continental records spanning the Late Quaternary have been obtained from this region. Seismic sequence stratigraphic analysis allows a reconstruction of lake level variations. Two major hiatuses of unknown age occurred during the early evolution of the basin with the deposition of an alluvial fan in a restricted area in the intervening time period. Following the development of a relatively shallow lake during the late Pleistocene and a short desiccation pulse around 11 220 14C yr BP, a transgression of over 135 m occurred at the beginning of the Holocene. The transgression was associated with the formation of beach ridges preserved in the lake stratigraphy on the floor of the modern Lago Cardiel at four different elevations. The preservation of largely unreworked beach ridges indicates a stepwise rise in the lake level. There is no seismic evidence of a major lowering of the lake below modern level during the entire Holocene. Deposition since the mid-Holocene is marked by strong lateral differences in sediment accumulation with a depocentre slightly to the north of the basin midpoint and a pronounced mounded distribution. Seismic reflection geometries, as well as sedimentological characteristics indicate a lacustrine contourite drift covering an area of 80–100 km2. As Lago Cardiel is under the influence of westerly winds, these most likely drove lake circulation. The identification of drowned beach ridges and of contourite drifts illustrates that high-resolution seismic stratigraphy is not only a powerful tool in reconstructing past lake level elevations for closed lake basins, but it can also provide information about the rate of lake level changes and the presence and strength of lake currents. 相似文献
94.
The TerraSAR-X (TSX) synthetic aperture radar (SAR) marks the recent emergence of a new generation of spaceborne radar sensors
that can for the first time lay claim to localization accuracies in the sub-meter range. The TSX platform’s extremely high
orbital stability and the sensor’s hardware timing accuracy combine to enable direct measurements of atmospheric refraction
and solid Earth movements. By modeling these effects for individual TSX acquisitions, absolute pixel geolocation accuracy
on the order of several centimeters can be achieved without need for even a single tiepoint. A 16-month time series of images
was obtained over a fixed test site, making it possible to validate both an atmospheric refraction and a solid Earth tide
model, while at the same time establishing the instrument’s long-term stability. These related goals were achieved by placing
trihedral corner reflectors (CRs) at the test site and estimating their phase centers with centimeter-level accuracy using
differential GPS (DGPS). Oriented in pairs toward a given satellite track, the CRs could be seen as bright “points” in the
images, providing a geometric reference set. SAR images from the high-resolution spotlight (HS) mode were obtained in alternating
ascending and descending orbit configurations. The highest-resolution products were selected for their small sample dimensions,
as positions can be more precisely determined. Based on the delivered product annotations, the CR image positions were predicted,
and these predictions were compared with their measured image positions both before and after compensation for atmospheric refraction and systematic solid Earth deviations. It was possible to show that when the atmospheric
distortion and Earth tides are taken into account, the TSX HS products have geolocation accuracies far exceeding the specified
requirements. Furthermore, this accuracy was maintained for the duration of the 16-month test period. It could be demonstrated
that with a correctly calibrated sensor, and after accounting for atmospheric and tidal effects, tiepoint-free geolocation
is possible with TSX with an absolute product accuracy of about 5 cm. 相似文献
95.
96.
97.
Matrix micrites are a commonly used carbonate archive for the reconstruction of past environmental parameters, but one that is submitted to known limitations. Main reasons for the often ambiguous value of many micrite-based isotope data sets are the unknown origin of the micrite components and their poorly resolved diagenetic history. Here we present carbon and oxygen-isotope data retrieved from Oxfordian to Tithonian Ammonitico Rosso nodular micrites sampled from three sections in the Betic Cordillera (Southern Spain). All three sections were correlated and sampled using a rigorous biostratigraphic framework. A noteworthy feature is that analyzed matrix micrites are more conservative in terms of their isotopic composition than other carbonate materials commonly considered to resist diagenetic alteration under favourable circumstances. Remarkably, this refers not only to δ13C ratios, which reflect the typical Late Jurassic global trend, but also to δ18O ratios that range around 0.3‰. The 18O-enriched oxygen-isotope ratios are considered to represent diagenetic stabilization of carbonate ooze under the influence of marine porewaters within the sediment–water interphase (i.e., the immature sedimentary section, usually submitted to biogenic activity). This interpretation agrees with the very early lithification of micrite nodules with cements precipitated from marine porewaters, enriched by the dissolution of aragonite skeletals (i.e., ammonite shells). According to the model proposed, low sedimentation rates as well as rapid early marine differential cementation, under the influence of currents and seawater pumping, affected the sediment–water interphase of epioceanic swells where deposition resulted in early lithified Ammonitico Rosso facies. The data obtained show that special care must be taken to prevent oversimplified interpretations of carbonate archives, particularly in the context of epioceanic settings. 相似文献
98.
Spatial geochemistry of a Carboniferous platform-margin-to-basin transect: Balancing environmental and diagenetic factors 总被引:1,自引:0,他引:1
Bram van der Kooij Adrian Immenhauser Anita Csoma Juan Bahamonde Thomas Steuber 《Sedimentary Geology》2009,219(1-4):136-150
Conventional (one-dimensional) chemostratigraphy of marine carbonates assesses the chemical archive of individual stratigraphic sections and their correlation in space and time. Whereas this approach has shown to be of value when linking isobathymetric domains, usually characterised by similar facies, more caution is needed when correlations are extended across different physiographic settings and hence different facies belts. Here, the spatial geochemical record of Pennsylvanian platform-margin-to-basin transects across a bathymetric range of about 800 m is documented and discussed in a process-oriented context. Particularly, the presence of layered palaeo-water masses and their potential control on slope facies distribution and geochemical properties requires attention. Whereas Carboniferous thermo- and/or chemo-clines most likely affected depth-related slope facies zonation, it was facies change and hence, variances in porosity–permeability properties, that controlled differential early burial diagenetic alteration. Specifically, the lower-slope related breccia facies is characterised by higher volumes of early burial carbonate cements. This implies that these sediments entered the shallow-burial domain with a considerable open pore space and gave way to an increased rock:fluid ratio. Whereas the δ13C record is invariant with bathymetry, the more diagenesis-sensitive δ18O proxy, records pronounced shifts observed across major facies boundaries. From this it is concluded that although the primary controlling factor of slope facies distribution with depth is probably palaeoceanographic in nature, it is differential rock:fluid ratios that control the first-order, spatial shifts in δ18O composition. These findings show that one-dimensional chemostratigraphy will severely underestimate the complexity of three-dimensional (bathymetric) data sets across platform margins. This is of relevance for the interpretation of the geochemical archive of fossil carbonate platforms in general. 相似文献
99.
100.
Hamed Ketabchi Davood Mahmoodzadeh Behzad Ataie‐Ashtiani Adrian D. Werner Craig T. Simmons 《水文研究》2014,28(24):5938-5953
The fresh groundwater lenses (FGLs) of small islands can be highly vulnerable to climate change impacts, including sea‐level rise (SLR). Many real cases of atoll or sandy islands involve two‐layer hydrogeological conceptualizations. In this paper, the influential factors that affect FGLs in two‐layer small islands subject to SLR are investigated. An analytical solution describing FGLs in circular islands, composed of two geological layers, is developed for the simplified case of steady‐state and sharp‐interface conditions. An application of the developed model is demonstrated to estimate the FGL thickness of some real‐world islands by comparison with existing FGL thickness data. Furthermore, numerical modelling is applied to extend the analysis to consider dispersion effects and to confirm comparable results for both cases. Sensitivity analyses are used to assess the importance of land‐surface inundation caused by SLR, relative to other parameters (i.e. thickness of aquifer layers, hydraulic conductivity, recharge rate and land‐surface slope) that influence the FGL. Dimensionless parameters are used to generalize the findings. The results demonstrate that land‐surface inundation has a considerable impact on a FGL influenced by SLR, as expected, although the FGL volume is more sensitive to recharge, aquifer thickness and hydraulic conductivity than SLR impacts, considering typical parameter ranges. The methodology presented in this study provides water resource managers with a rapid‐assessment tool for evaluating the likely impacts of SLR and accompanying LSI on FGLs. 相似文献