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991.
Ben De Mol Max Kozachenko Andy Wheeler Hugo Alvares Jean-Pierre Henriet Karine Olu-Le Roy 《International Journal of Earth Sciences》2007,96(1):103-120
High-resolution seismic profiles, swath bathymetry, side-scan sonar data and video imageries are analysed in this detailed
study of five carbonate mounds from the Belgica mound province with special emphasis on the well-surveyed Thérèse Mound. The
selected mounds are located in the deepest part of the Belgica mound province at water depths of 950 m. Seismic data illustrate
that the underlying geology is characterised by drift sedimentation in a general northerly flowing current regime. Sigmoidal
sediment bodies create local slope breaks on the most recent local erosional surface, which act as the mound base. No preferential
mound substratum is observed, neither is there any indication for deep geological controls on coral bank development. Seismic
evidence suggests that the start-up of the coral bank development was shortly after a major erosional event of Late Pliocene–Quaternary
age. The coral bank geometry has been clearly affected by the local topography of this erosional base and the prevailing current
regime. The summits of the coral banks are relatively flat and the flanks are steepest on their upper slopes. Deposition of
the encased drift sequence has been influenced by the coral bank topography. Sediment waves are formed besides the coral banks
and are the most pronounced bedforms. These seabed structures are probably induced by bottom current up to 1 m/s. Large sediment
waves are colonised by living corals and might represent the initial phase of coral bank development. The biological facies
distribution of the coral banks illustrate a living coral cap on the summit and upper slope and a decline of living coral
populations toward the lower flanks. The data suggest that the development of the coral banks in this area is clearly an interaction
between biological growth processes and drift deposition both influenced by the local topography and current regime. 相似文献
992.
Out of administrative control: Absentee owners, resident elk and the shifting nature of wildlife management in southwestern Montana 总被引:1,自引:0,他引:1
This paper describes the historical roots of an ongoing wildlife management dilemma involving decreasing opportunities for elk management via public hunting on private land in the context of an expanding elk presence on private land in southwest Montana. Our main focus is on the role of private ranchland in elk ecology, and the ability of land owners to set elk migration in new directions through cumulative decisions about hunting and tolerating elk. This takes elk management, traditionally the purview of the state, out of administrative control. We document connections between the region’s historical and emerging land tenure patterns, and analyze associated changes in hunter access. Elk numbers expanded rapidly in the Upper Yellowstone Valley at a moment of significant transition in ranchland tenure. New owners more interested in natural amenities than in livestock production encouraged the elk and discouraged hunting. This reinforced the spread of elk, and further weakened the ability of the state and other ranchers to manage elk (which interfere with livestock production in numerous ways). Though elk and cattle use the landscape in similar ways, elk became more effective agents of landscape change in a reflexive relationship with ideas of land that stress natural amenities over production. 相似文献
993.
Robert J. Diaz Donald C. Rhoads James A. Blake Roy K. Kropp Kenneth E. Keay 《Estuaries and Coasts》2008,31(6):1184-1197
A combination of methods (infaunal grabs and sediment profile cameras) were used to monitor the response of Boston Harbor
benthic habitats to reductions in wastewater associated with movement of the outfalls to the mouth of the harbor and then
offshore. From 1992 to 2006, there was strong evidence that benthic habitats within Boston Harbor have shifted from a more
anaerobic state to a more aerobic state and that these changes are directly related to changes in carbon loading associated
with outfall placement and improvements in wastewater treatment. Over the period of 1992 to 2000, when the ocean outfall started
to operate, there was >90% reduction in organic loadings to Boston Harbor from 11,400 to 1,200 t C per year. There were also
corresponding decreases in primary production due to reduced nutrient loadings. The most apparent change in harbor benthos
was the widespread increase in 1992 and subsequent decline by 2005 in Ampelisca spp. tube mats. The long-term increase in thickness of the apparent color redox potential discontinuity layer was consistent
with reductions in organic loading and increases in bioturbation. The optimal organic loading for maintaining large areas
of amphipod tube mats and high bioturbation rates was around 500 g C per square meter per year. Above and below this level,
the area of tube mats in Boston Harbor declined. 相似文献
994.
995.
996.
Since its formation in earliest Cambrian time, the St-Honoré alkaline complex has fractured into large subhorizontal slabs under the effect of magmatic pulsations and thermal contraction. These slabs were rapidly segmented and cracked by the same stresses. The secondary permeability resulting from these fractures first aided the circulation of the rare earth mineralizing hydrothermal fluids in the center of the complex, and then, after the unroofing of the complex, instigated the development of a karstic drainage system within the carbonatites of the complex. The accumulated sediments in the karstic caverns derive from the periodic inwashing of the insoluble residues built up on the surface of erosion, were indurated after the sealing of the karstic openings with calcareous muds during the Ordovician transgression, and were faulted with their cover when the Saguenay graben formed. The last event, marked by low temperature regional mineralizating circulation (barite and calcite crystals coating geodes at NIOBEC), permitted the establishment of a new subterrean drainage system. 相似文献
997.
The radioactive fission product, 137Cs, has been observed to mobilize from bottom sediments of two South Carolina reservoirs during summer thermal stratification and hypolimnetic anoxia. Mobilization is attributed to ion-exchange displacement of 137Cs from sediments by cations such as NH+4, Fe+2 and Mn+2 released under anaerobic conditions.Three types of 137Cs binding sites to sediment clay minerals are identified: 1) surface and planar sites from which 137Cs is generally exchangeable by all cations studied (Na+, NH+4, H+, Cs+, Ca+2, Mg+2, Fe+2, and Mn+2); 2) wedge sites where 137Cs exchange is sterically limited to cations of similar size and charge (NH+4, Cs+, K+, and perhaps H3O+); 3) interlayer sites from which 137Cs is not readily exchanged. More than 15 years after final 137Cs inputs, the reservoir sediments we studied showed the following percentage distribution of sites: 2 to 9% surface sites, 6 to 13% wedge sites, and 78 to 85% interlayer sites. In contrast, lake and stream sediments near Oak Ridge, Tennessee receiving 137Cs inputs more than 20 years earlier had greater than 99% of their 137Cs associated with non-exchangeable interlayer sites. The difference is attributed to the paucity in the South Carolina sediments of weathered micaceous clay minerals with their abundant interlayer sites. Such interlayer deficient clays are dominant in the Atlantic and Gulf coastal plains of the United States and elsewhere. This suggests that 137Cs will be physically and chemically more mobile in such areas as well as more biologically available. Mobility will be enhanced in regimes where cation inputs favoring 137Cs exchange occur. Subsurface waste disposal sites where anaerobic conditions develop with NH+4 production and Fe+2 and Mn+2 release might be such a regime. 相似文献
998.
Emanuel Mazor Robert O. van Everdingen H.Roy Krouse 《Geochimica et cosmochimica acta》1983,47(6):1111-1115
Geothermally heated fluids are identified as a component in warm (up to 54°C) springs in the southern Canadian Rocky Mountains. High concentrations of radiogenic He (10?3 ccSTP/cc gas) and atmospheric Ne, Ar, Kr and Xe in the gases that vigorously bubble at the Fairmont Hot Spring, assign the latter to be a “drowned” fumarole, fed by geothermal steam. Up to 75% depletions in the atmospheric noble gases in several warm springs indicate contributions of residual geothermal water. On the other hand, in a few cases noble gases were found in excess (W) over the expected concentrations in airequilibrated recharge water. The observed “reversed” pattern of wnc >WAr >Wkr >Wxe is interpreted as excess air, incorporated during recharge through karstic conduits. The mixing ratios of geothermal and karstic waters can be deduced. 相似文献
999.
K. K. Roy 《Pure and Applied Geophysics》1973,102(1):105-119
Summary The rotating nature of telluric field is simulated in an electrolytic model tank. Variations of this rotating field due to the presence of a few two and three dimensional geological models, simulated in the tank, are studied. The telluric ellipses, recorded on a C.R.O. Screen, are found to be useful for qualitative and quantitative interpretation of the non-linearly polarised telluric field data. Relative usefulnesses of the various parameters, e.g., (i)M=ratio of the semimajor and semiminor axis, (ii)K = square root of normalized surface areas, (iii) = linear eccentricity ((a
2/b
2-1) and (iv)e = conventional eccentricity ((1-b
2/a
2)), of a telluric ellipse are tested. Linear eccentricity appears to be the most sensitive parameter. Methods for determining depth and horizontal extent of a structure from a telluric map are suggested. Near surface inhomogeneities, as revealed from the experiment are unlikely to affect the telluric map due to a basement structure. 相似文献
1000.
Thermo-elastic interactions in an infinite elastic solid due to a concentrated transient heat source
Snehanshu Kumar Roy Choudhuri 《Pure and Applied Geophysics》1972,97(1):57-69
Summary The present paper is concerned with the determination of thermo-elastic stress and temperature distribution in an infinite elastic solid when it is subjected to a concentrated transient heat source taking into account the effect of coupling. The fundamental partial differential equation for the thermo-elastic potential is solved by means of the operational method. The solutions are obtained for small values of time in terms of known functions such as complementary error functions and associated complementary error functions and have the form of power series with respect to the parameter of coupling . Since this parameter is generally very small for most of the metals, the expressions for stress and temperature distribution have been obtained by considering terms upto linear . 相似文献