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981.
This paper records sedimentary data which indicate that at least part of the Wilsons River floodplain, on the margins of the subtropical rainforest known as the 'Big Scrub', has a long and certainly pre-European history of relative treelessness. Despite a general presumption that this lowland subtropical region was completely forested prior to European settlement, recent historical research has indicated that certain areas were naturally open. While the historical information is clear, the data reported here-a fossil pollen record and one radiocarbon date- reinforces that information for one type of locality, providing an initial indication of time depth. 相似文献
982.
Conservative tracers are necessary to obtain groundwater transport velocities at the field scale. Deuterated water is an
effective tracer for this purpose due to its similarity to water, chemical stability, non-reactivity, ease of handling and
sampling, relatively neutral buoyancy, and reasonable price. Reliable detection limits of 0.1 mg deuterium/L may be obtained
in field tests. A field example is presented in which deuterated water, bromide, and pentafluorobenzoic acid are used as groundwater
tracers. Deuterated water appeared to be transported conservatively, producing almost identical breakthrough curves as that
of other soluble tracers.
Electronic Publication 相似文献
983.
Measurements of 226Ra and 210Pb in barite samples separated from different depths of a piston core from the eastern equatorial Pacific are reported. 226Ra is enriched in the barite as would be expected from the chemistries of Ra and Ba; the ratio centers around 1.5 · 1014 atoms/mole. The results suggest that barite is concentrating Ra at a rate comparable to its decay rate, viz. 5.78 · 10?3 yr?1. The gross 210Pb depletion with respect to 226Ra is indicative of 222Rn loss due to the smallness of the barite crystals. 相似文献
984.
B.?ForesEmail authorView authors OrcID profile C.?Champollion N.?Le?Moigne J.?Chery 《Journal of Geodesy》2017,91(3):269-277
In this paper, we investigate the impact of ambient temperature changes on the gravity reading of spring-based relative gravimeters. Controlled heating experiments using two Scintrex CG5 gravimeters allowed us to determine a linear correlation (R \(^{2}>\) 0.9) between ambient temperature and gravity variations. The relation is stable and constant for the two CG5 we used: ?5 nm/s\(^{2}/^\circ \)C. A linear relation is also seen between gravity and residual sensor temperature variations (R \(^{2}>\) 0.75), but contrary to ambient temperature, this relation is neither constant over time nor similar between the two instruments. The linear correction of ambient temperature on the controlled heating time series reduced the standard deviation at least by a factor of 2, to less than 10 nm/s\(^{2}\). The laboratory results allowed for reprocessing the data gathered on a field survey that originally aimed to characterize local hydrological heterogeneities on a karstic area. The correction of two years of monthly CG5 measurements from ambient temperature variations halved the standard deviation (from 62 to 32 nm/s\(^{2}\)) and led us to a better hydrological interpretation. Although the origin of this effect is uncertain, we suggest that an imperfect control of the sensor temperature may be involved, as well as a change of the properties of an electronic component. 相似文献
985.
To predict future river flows, empirical trend projection (ETP) analyses and extends historic trends, while hydroclimatic modelling (HCM) incorporates regional downscaling from global circulation model (GCM) outputs. We applied both approaches to the extensively allocated Oldman River Basin that drains the North American Rocky Mountains and provides an international focus for water sharing. For ETP, we analysed monthly discharges from 1912 to 2008 with non‐parametric regression, and extrapolated changes to 2055. For modelling, we refined the physical models MTCLIM and SNOPAC to provide water inputs into RIVRQ (river discharge), a model that assesses the streamflow regime as involving dynamic peaks superimposed on stable baseflow. After parameterization with 1960–1989 data, we assessed climate forecasts from six GCMs: CGCM1‐A, HadCM3, NCAR‐CCM3, ECHAM4 and 5 and GCM2. Modelling reasonably reconstructed monthly hydrographs (R2 about 0·7), and averaging over three decades closely reconstructed the monthly pattern (R2 = 0·94). When applied to the GCM forecasts, the model predicted that summer flows would decline considerably, while winter and early spring flows would increase, producing a slight decline in the annual discharge (?3%, 2005–2055). The ETP predicted similarly decreased summer flows but slight change in winter flows and greater annual flow reduction (?9%). The partial convergence of the seasonal flow projections increases confidence in a composite analysis and we thus predict further declines in summer (about ? 15%) and annual flows (about ? 5%). This composite projection indicates a more modest change than had been anticipated based on earlier GCM analyses or trend projections that considered only three or four decades. For other river basins, we recommend the utilization of ETP based on the longest available streamflow records, and HCM with multiple GCMs. The degree of correspondence from these two independent approaches would provide a basis for assessing the confidence in projections for future river flows and surface water supplies. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
986.
Studying seismic wave propagation across rock masses and the induced ground motion is an important topic, which receives considerable attention in design and construction of underground cavern/tunnel constructions and mining activities. The current study investigates wave propagation across a rock mass with one fault and the induced ground motion using a recursive approach. The rocks beside the fault are assumed as viscoelastic media with seismic quality factors, Qp and Qs. Two kinds of interactions between stress waves and a discontinuity and between stress waves and a free surface are analyzed, respectively. As the result of the wave superposition, the mathematical expressions for induced ground vibration are deduced. The proposed approach is then compared with the existing analysis for special cases. Finally, parametric studies are carried out, which includes the influences of fault stiffness, incident angle, and frequency of incident waves on the peak particle velocities of the ground motions. 相似文献
987.
Patterns of Nd and Sr isotopic ratios produced by magmatic and post-magmatic processes in the Shiant Isles Main Sill, Scotland 总被引:3,自引:0,他引:3
K. A. Foland F. G. F. Gibb C. M. B. Henderson 《Contributions to Mineralogy and Petrology》2000,139(6):655-671
The Shiant Isles Main Sill of the British Tertiary Igneous Province is a classic example of a differentiated, alkaline basic
sill. Four separate intrusions, each emplaced internally in rapid succession, form a 165-m-thick sill hosted by Lower Jurassic
sedimentary rocks. Extensive Nd and Sr isotopic studies were conducted on samples from a vertical section through the sill
where the relationships of samples to one another are well defined. The results illuminate patterns of modification of isotopic
ratios and clarify the petrogenesis (magma sources, crustal contamination), magmatic processes (bulk mixing, interstitial
liquid mixing), and post-magmatic alteration (hydrothermal effects on Sr and Nd). Overall, the whole-rock initial 87Sr/86Sr ratios range from ∼0.7037 to 0.7061 while initial 143Nd/144Nd ratios vary from ∼0.51243 to 0.51286 (ɛNd∼−0.7 to +5.7) – values that contrast markedly with those of the country rock. Acid leaching (HCl) of the whole-rock samples
that removes analcime indicates that most of the scatter in the 87Sr/86Sr is caused by the ubiquitous sub-solidus, aqueous alteration during which more-radiogenic Sr was introduced into the sill,
especially along the margins, and also reveals magmatic isotopic ratios. In contrast, Nd was immobile during fluid interaction
so that the sill 143Nd/144Nd ratios were not affected, even <1 m from the country-rock contact. Using leached rock values, 87Sr/86Sr and 143Nd/144Nd ratios are inversely correlated from magmatic processes. Magmas with two distinct isotopic compositions were involved:
a more primitive one with 143Nd/144Nd ∼0.51285 and 87Sr/86Sr ∼0.7035 that produced the first two intrusions and a more evolved one (with 0.51252 and 0.7048) that produced the third
intrusion. Mixing of the two magmas was very limited, restricted to near contacts between units, and apparently occurred by
interstitial melt migration. The more evolved crinanitic magma was probably produced from a batch of the more primitive picritic
melt by a small degree of crustal contamination and crystal fractionation during a short crustal residence prior to ascent
and emplacement.
Received: 20 December 1999 / Accepted: 5 May 2000 相似文献
988.
B. CHARLOTTE SCHREIBER GERALD M. FRIEDMAN† ARVEDO DECIMA‡ EDWARD SCHREIBER 《Sedimentology》1976,23(6):729-760
In Sicily, Messinian evaporitic sedimentary deposits are developed under a wide variety of hypersaline conditions and in environments ranging from continental margin (subaerial), to basin-margin supratidal, to intertidal, to subtidal and out into the hypersaline basin proper. The actual water depth at the time of deposition is indeterminate; however, relative terms such as ‘wave base’ and ‘photic zone’ are utilized. The inter-fingering relationships of specific evaporitic facies having clear and recognizable physical characteristics are presented. These include sub-aerial deposits of nodular calcium sulphate formed displacively within clastic sediments; gypsiferous rudites, arenites and arenitic marls, all of which are reworked sediments and are mixed in varying degrees with other clastic materials (subaerial, supratidal, and intertidal to deep basinal deposits). Laminated calcium sulphate alternating with very thin carbonate interlaminae and having two different aspects; one being even and continuous and the other of a wavy, irregular appearance (subtidal, intertidal, and supratidal deposits). Nodular calcium sulphate beds, usually associated with wavy, irregular laminated beds (supratidal, sabkha deposits); very coarsely crystalline gypsum beds (selenite), associated with more even, laminated beds (subaqueous, intertidal to subtidal deposits); wavy anastomozing gypsum beds, composed of very fine, often broken crystals (subaqueous, current-swept deposits); halite having hopper and chevron structures (supratidal to intertidal); and halite, potash salts, etc. having continuous laminated structure (subaqueous, possibly basinal). Evidence for diagenetic changes is observed in the calcium sulphate deposits which apparently formed by tectonic stress and also by migrating hypersaline waters. These observations suggest that the common, massive form of alabastrine gypsum (or anhydrite, in the subsurface) may not always be ascribed to original depositional features, to syndiagenesis or to early diagenesis but may be the result of late diagenesis. 相似文献
989.
990.
S. V. Kalenskii S. Kurtz V. I. Slysh P. Hofner C. M. Walmsley L. E. B. Johansson P. Bergman 《Astronomy Reports》2010,54(10):932-939
We present the results of VLA observations of a maser candidate in the low-mass star formation region L1157 in the 70-61 A + transition at 44 GHz. The line is emitted by a compact, undoubtedly maser source associated with clump B0a, which is seen in maps of L1157 in thermal lines of methanol and other molecules. A much weaker compact source is associated with clump B1a, which is brighter than B0a in thermal methanol lines. The newly detected masers may form in thin layers of turbulent post-shock gas. In this case, the maser emission may be beamed, so that only an observer located in or near the planes of the layers can observe strong masers. On the other hand, the maser lines are double with a “red” asymmetry, indicating that the masers may form in collapsing clumps. A detailed analysis of collapsing-cloud maser models and their applicability to the masers in L1157 will be developed in subsequent papers. 相似文献