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71.
High-Resolution Seismic Reflection Evidence for Middle Holocene Environmental Change, Owasco Lake, New York 总被引:2,自引:0,他引:2
Approximately 70 km of new decimeter-resolution seismic reflection profile data from Owasco Lake, New York define a middle Holocene (4600 14C yr B.P.) erosion surface in the north end of the lake at water depths as great as 26 m. Beneath the lake, post-glacial sediments are up to 9 m thick and represent about 10% of the total sediment fill. Early to middle Holocene sediments, 6 m thick, contain biogenic gas at the south end of the basin and a large (4 km×300 m×15 m) subaqueous slide deposit along the east-central portion of the lake. Late Holocene sediments are thinner or absent, particularly at the north end of the lake. The middle Holocene erosion surface may have been produced by a drop in lake level. Alternatively, it may represent a change in climate during the transition between the relatively warm Holocene hypsithermal and cool neoglacial. At this time (4600 14C yr B.P.) circulation in Owasco Lake appears to have evolved from sluggish to active. The increased circulation, which persists today, probably resulted from atmospheric cold fronts with strong southwesterly winds that piled up water at the north end of the lake. The increased water circulation may have been ultimately driven by decreasing insolation, which produced an increased pole-to-equator thermal gradient and, thus, stronger global winds that began at the transition between the hypsithermal and neoglacial. 相似文献
72.
73.
Summary We document a rare case of micron-sized gold inclusions in Ir–Os alloy and overgrowth rims on Pt–Fe alloy from an alluvial
Au-PGE placer derived from an Uralian/Alaskan type intrusion in Primorye, Russia. The gold inclusions occasionally form complex
aggregates with cooperite [PtS] or tolovkite [IrSbS], and replace magmatic inclusions of Ir-rich Pt–Fe alloy which exsolved
from the Ir–Os–Pt matrix. Gold has a relatively constant composition (>90 wt.% Au, a few wt.% Ag, and up to 8 wt.% Pt).
The gold rims form superfine (3–5 μm) discontinuous films on the Pt–Fe alloy crystals often followed by cooperite overgrowth.
Both gold textures suggest an electrochemical control of gold precipitation via selective Pt–Fe leaching during low-temperature
overprint and/or weathering of PGE alloy. 相似文献
74.
Henry Rishbeth 《Astronomy& Geophysics》2007,48(3):3.37-3.37
Associate of the RAS, pioneer in ionospheric incoherent scatter theory and observation, practical manager and leader, not least of EISCAT. 相似文献
75.
76.
John T. Lehmann Robert Foy Donna A. Lehman 《Aquatic Sciences - Research Across Boundaries》2001,63(2):168-181
Physiological data indicate that a 3-compartment model appropriately represents ingestion, assimilation, and accumulation of somatic and reproductive tissue by an aquatic invertebrate predator. A secondary production model calibrated to growth and respiration data is used to constrain the model equations. Inverse solution methods are used to estimate rate constants for digestion and for net accrual of tissue by growing animals at different temperatures. Predicted time to 50% maximum digestion matches well with the empirical rate of digestion of prey enzymes in the predator gut. Model-derived digestion rates are consistent with the assimilation rate constant obtained by independent radiotracer methods, and with experimental detection time for prey enzymes. The model approach permits parameter estimation within a complex system of equations so that results can be compared with experimental data. 相似文献
77.
Summary
The feasibility and safety of a mining project or the choice among alternative mining methods could depend on the joint densities
and orientations within the rock mass. The accurate determination of the orientation of all joints is technically difficult
and often economically unrealistic. This study presents a new approach in classifying joints found in exploration boreholes
as joint sets, whose statistical distribution is determined from a few hundred oriented joints in boreholes. Each non-oriented
joint is classified as belonging to a set based on its “a posteriori” probability of membership in a Bayesian framework. The
theoretical rate of success of the classification can be computed for each possible borehole orientation and plotted on a
stereonet to determine the optimal orientation of new boreholes. The performance and limitations of this approach are investigated.
An application example at the Mont Porphyre's large scale block-caving project at Gaspé Mines, Quebec, Canada, is studied. 相似文献
78.
Structure and evolution of the backstop in the eastern Nankai Trough area (Japan): Implications for the soon-to-come Tokai earthquake 总被引:1,自引:0,他引:1
Abstract We present data showing that the intra-oceanic shortening now occurring south of the eastern Nankai Trough that has produced the Zenisu Ridge has also been responsible for the formation of a previous ridge now buried below the continental margin. This ridge, that we refer to as Paleo-Zenisu, is presently adjacent to the backstop and its location coincides with the outer limit of the seismogenic decollement. The subduction of the paleo-Zenisu ridge below the wedge has led to its complete reorganization and has given its identity to the Great Tokai earthquake rupture zone. The formation of paleo-Zenisu and its consequent subduction has induced the tilting of the backstop toward the northwest since ca 2 Ma. This model suggests that the backstop and possibly the wedge are dextrally sheared because they are extruded southwestward in relation to the collision of the Izu-Bonin Ridge with Japan. We use the finite motion from Zenisu to paleo-Zenisu to derive both the subduction vectors along the Nankai Trough and the shortening vectors within Zenisu-Izu. The amount of shortening absorbed within Zenisu-Izu increases toward the northeast. The corresponding subduction vectors of the Zenisu platelet below the wedge decrease accordingly to the northeast from 50 to less than 20 mm/year and the Zenisu body rotates clockwise with a pole near 36° North, 139° East. This might explain the apparent longer repetition time of great earthquakes in the Tokai area. On the other hand, the 25-35 mm/year obtained for the rate of shortening along the Zenisu thrust indicates a high seismic potential there. 相似文献
79.
Maxime Le Goff Bernard Henry Lucien Daly 《Physics of the Earth and Planetary Interiors》1992,70(3-4):201-204
A statistical method is proposed for the smoothing of polar wander paths and for giving their confidence limits by the mean of successive ellipses. The method is fully parametrical and is based on the relations between the inertia matrix and the parameters of the Fisher distribution, from which a bivariate form is deduced. An elementary tensorial calculation gives the parameters of the confidence ellipse around a vectorial weighted mean, for any unimodal set of vectors. This model can also be used for other statistical tests, wherever the rotational symmetry hypothesis is not consistent (i.e. the fold test). 相似文献
80.
Bernard Henry 《Physics of the Earth and Planetary Interiors》1992,70(3-4):214-218
We present a model that is applicable to the relatively frequent case of rocks in which the magnetic fabric is dominated by uniaxial paramagnetic minerals, and in which the deformation (pure shear) corresponds to the March-Fernandez model. Borradaile et al.'s procedure for the isolation of the magnetic fabric of monocrystals of anisotropic components allows us to obtain the magnetic properties equivalent to those of all the component minerals if they should be artificially aligned. In the case of real component minerals with similar shape parameters, χ (dependent on dimension ratio), these properties will correspond to those of a theoretical equivalent mineral. Therefore, finite strain and orientation tensors may be determined from magnetic fabric measurements of such polymineralic rocks. 相似文献