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391.
A hydrogeological study was conducted in northwestern New Brunswick, Canada, to improve the predictability of fracture-dominated groundwater flow within folded bedrock composed of fine-grained turbidites. Borehole televiewer logging and outcrop mapping, integrated with hydraulic packer tests revealed enhanced hydraulic conductivity associated with northeasterly striking bedding-plane fractures formed during folding and flexural slip. These fractures impart azimuthal anisotropy to the aquifer because of moderately dipping fold limbs. High-angle fractures form a well-developed non-stratabound network, comprising two open fracture sets striking NNE parallel to the current direction of principal stress, and WNW parallel to the direction of principal stress that dominated during the Acadian orogeny. The subset of fractures showing significant oxidation, deemed most important to the groundwater flow system, is dominated by bedding-plane and high-angle fractures striking near-parallel to the maximum principal stress direction, resulting in extensional opening and enhanced hydraulic conductivities. An equivalent porous media model, incorporating anisotropy and varying hydraulic conductivity with depth, indicates that horizontal flow dominates the aquifer with relatively minor exchange between different model layers. These findings have implications for understanding flow directions in the Black Brook Watershed and elsewhere in the Matapédia Basin where fractures formed under similar stress conditions. 相似文献
392.
Roger G. Young Aaron J. Quarterman Rebekah F. Eyles Robert A. Smith William B. Bowden 《新西兰海洋与淡水研究杂志》2013,47(4):803-825
We examined the effects of land use, geology, and longitudinal position within the river network on water quality and thermal regime at 23 sites within the Motueka River catchment. The concentrations of suspended solids, nitrate nitrogen, total nitrogen, Escherichia coli, and Campylobacter were higher at sites draining pastoral and horticultural land than in similar‐sized native or plantation forest streams. Average daily mean temperature and minimum temperature in summer and maximum winter temperature were higher in unshaded pastoral and horticultural streams than at native forest sites. Differences in water quality and thermal regime were also observed among sites with contrasting geology. Conductivity, pH, and minimum winter temperatures were highest at sites draining marble terrain. In contrast, longitudinal patterns in water quality and temperature regime along the 120‐km length of the river were relatively weak, although longitudinal patterns in amplitude of daily temperature fluctuation matched theoretical predictions. In this study, differences in land use appeared to have the strongest influence on most water quality and thermal variables examined. However, geology was an important factor explaining variation in certain variables (e.g., pH and conductivity). Longitudinal patterns in water quality and temperature were relatively weak and in many instances were linked with longitudinal patterns in land use and geology rather than catchment location alone. 相似文献
393.
Craig L. Hebert Alan J. Kaufman Sarah C. Penniston-Dorland Aaron J. Martin 《Precambrian Research》2010
Radiometric constraints on mid-Ediacaran Period glaciation (Gaskiers) in Newfoundland narrowed the known temporal gap between widespread ice ages and the evolution of complex metazoans to several million years. To further evaluate this claim we studied an Ediacaran glacial diamictite at the base of the Fauquier Formation of northern Virginia, and discovered a conformable relationship between the post-glacial cap carbonate and overlying volcanic rocks of the Catoctin Formation. U/Pb zircon age constraints for the rift-related volcanic flows suggest initial emplacement around 571 million years ago. Application of the Catoctin age to the Fauquier succession indicates the occurrence of an ice age about 10 million years younger than the 582 Ma Gaskiers event, supporting the view of multiple Ediacaran Period glaciations. Furthermore, the age constraint from eastern Laurentia falls within radiometric uncertainty of fossiliferous strata in Avalonia, indicating that the Fauquier glaciation was coincident with early metazoan evolution. 相似文献
394.
Lattice diffusion coefficients have been determined for 19 elements (Li, Be, Na, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Y,
Zr, Eu, Gd, Lu and Hf) in a single crystal of San Carlos olivine as a function of crystallographic orientation, at 1,300°C,
1 bar and fO2 = 10−8.3 bars, by equilibration with a synthetic silicate melt. Results for Li, Na, V, Cr, Fe and Zn are from diffusion of these elements
out of the olivine, starting from their indigenous concentrations; those for all other elements are from diffusion into the
olivine, from the silicate melt reservoir. Our 25-day experiment produced diffusion profiles 50 to > 700 μm in length, which
are sufficiently long that precise analyses could be achieved by scanning laser ablation inductively coupled plasma mass spectrometry,
even at concentration levels well below 1 μg g−1. For the divalent cations Ca, Mn, Fe and Ni, profiles were also obtained by electron microprobe analysis. The results of
the two methods agree well with each other, and are consistent with divalent cation diffusion coefficients previously determined
using different experimental methodologies. Olivine/melt partition coefficients retrieved from the data are also consistent
with other published partitioning data, indicating that element incorporation and transport in olivine in our experiment occurred
via mechanisms appropriate to natural conditions. Most of the examined trace elements diffuse through olivine at similar rates
to the major octahedral cations Fe and Mg, showing that cation charge and radius have little direct influence on diffusion
rates. Aluminium and P remain low and constant in the olivine, implying negligible transport at our analytical scale, hence
Al and P diffusion rates that are at least two orders of magnitude slower than the other cations studied here. All determined
element diffusivities are anisotropic, with diffusion fastest along the [001] axis, except Y and the REEs, which diffuse isotropically.
The results suggest that element diffusivity in olivine is largely controlled by cation site preference, charge balance mechanisms
and point-defect concentrations. Elements that are present on multiple cation sites in olivine (e.g. Be and Ti) and trivalent
elements that are charge-balanced by octahedral site vacancies tend to diffuse at relatively fast rates. 相似文献
395.
Scott A. Rush Jill A. Olin Aaron T. Fisk Mark S. Woodrey Robert J. Cooper 《Estuaries and Coasts》2010,33(4):963-970
Much of North America’s tidal marsh habitat has been significantly altered by both natural and man-made processes. Thus, there
is a need to understand the trophic ecology of organisms endemic to these ecosystems. We applied carbon (δ
13C) and nitrogen (δ
15N) stable isotope analysis, along with isotope mixing models, to egg yolk, liver, and muscle tissues of clapper rails (Rallus longirostris) and their likely prey items. This analysis enabled us to explore variation in trophic niche and diet composition in this
important marsh bird in two northern Gulf of Mexico tidal marshes that are river and ocean-dominated. For the river-associated
estuary, δ
13C and δ
15N of egg yolks, liver, and pectoral muscle tissue samples provided evidence that clapper rails maintained a similar diet during
both the winter and the breeding season. A trophic link between C3 primary productivity and the clapper rail’s diet was also indicated as the δ
13C of clapper rail egg yolks related negatively with the aerial cover of C3 macrophytes. Clapper rails from the ocean-dominated estuary had a narrower trophic niche and appeared to be utilizing marine
resources, particularly, based on modeling of liver stable isotope values. Variation in stable isotope values between egg
yolk and liver/muscle in both systems suggests that endogenous resources are important for egg production in clapper rails.
These results demonstrate that diet composition, prey source, and niche width of clapper rails can vary significantly across
different estuaries and appear to be influenced by hydrological conditions. 相似文献
396.
Iron isotope compositions of carbonatites record melt generation, crystallization, and late-stage volatile-transport processes 总被引:2,自引:0,他引:2
Clark M. Johnson Keith Bell Brian L. Beard Aaron I. Shultis 《Mineralogy and Petrology》2010,98(1-4):91-110
Carbonatites define the largest range in Fe isotope compositions yet measured for igneous rocks, recording significant isotopic fractionations between carbonate, oxide, and silicate minerals during generation in the mantle and subsequent differentiation. In contrast to the relatively restricted range in δ56Fe values for mantle-derived basaltic magmas (δ56Fe?=?0.0?±?0.1‰), calcite from carbonatites have δ56Fe values between ?1.0 and +0.8‰, similar to the range defined by whole-rock samples of carbonatites. Based on expected carbonate-silicate fractionation factors at igneous or mantle temperatures, carbonatite magmas that have modestly negative δ56Fe values of ~ ?0.3‰ or lower can be explained by equilibrium with a silicate mantle. More negative δ56Fe values were probably produced by differentiation processes, including crystal fractionation and liquid immiscibility. Positive δ56Fe values for carbonatites are, however, unexpected, and such values seem to likely reflect interaction between low-Fe carbonates and Fe3+-rich fluids at igneous or near-igneous temperatures; the expected δ56Fe values for Fe2+-bearing fluids are too low to produced the observed positive δ56Fe values of some carbonatites, indicating that Fe isotopes may be a valuable tracer of redox conditions in carbonatite complexes. Further evidence for fluid-rock or fluid-magma interactions comes from the common occurrence of Fe isotope disequilibrium among carbonate, oxide, silicate, and sulfide minerals in the majority of the carbonatites studied. The common occurrence of Fe isotope disequilibrium among minerals in carbonatites may also indicate mixing of phenocyrsts from distinct magmas. Expulsion of Fe3+-rich brines into metasomatic aureols that surround carbonatite complexes are expected to produce high-δ56Fe fenites, but this has yet to be tested. 相似文献