Some Aspects of Resource Uncertainty and Their Economic Consequences in Assessment of the 1002 Area of the Arctic National Wildlife Refuge

Natural Resources Research - Exploration ventures in frontier areas have high risks. Before committing to them, firms prepare regional resource assessments to evaluate the potential payoffs. With...     

A method to reduce the influence of ice-rafted debris on a grain size record from northern Fram Strait, Arctic Ocean

The granulometric composition of terrigenous deep-sea sediments provides information on current speed if certain frame conditions are fulfilled. These include that current transport is the only transport process. At high latitudes this type of investigation is impaired due to the influence of ice-rafted debris (IRD) which contaminates the current-sorted grain size fractions. This study presents a new method that addresses this problem by setting the ice-rafted sand in relation to the silt of both current- and ice-transported origin. Deviations from the resulting regression function are then used to determine the behaviour of the silt mean grain size as a function of current speed largely independent from IRD bias. The study is based on sediments from the Yermak Plateau, Arctic Ocean, a region influenced by IRD brought with the south-headed Transpolar Drift and by north-directed bottom currents. The IRD correction results in displaying changes of current speed at much higher clarity; climate forcing of the currents becomes more evident. For example, the 8200 year cold event shows up as a major event in the corrected record whereas it is hardly visible in the original record.     

Inferring erosional resistance of bedrock units in the east Tennessee mountains from digital elevation data

Measures of local relief, regional relief, and slope were calculated from digital elevation models (DEMs) for 50 bedrock units in the Ridge and Valley and Blue Ridge provinces of Tennessee. Each of these measures was normalized and the three were then averaged to produce the erosional resistance index (ERI). Bedrock units with higher ERI values include coarse clastics, intermediate clastics, and metaplutonics. Units with lower values include shales, limestones, limestones plus dolostones, and carbonates plus fine clastics. Dolostones tend to have intermediate values. The calculated ERI values were compared with subjective ratings by a geologist with decades of field experience in east Tennessee. Generally, the agreement between the two ratings was good, the most glaring exception being several shales with improbably high ERI values. These turned out to be thin units cropping out beneath very hard sandstones, allowing them to stand higher and steeper than would otherwise be possible. A systematic method for detecting such erroneously high ERI values is suggested. Inspection of a drainage map superimposed on the geology map shows that in a given area, streams tend to flow on rock units with the lowest ERI values. In addition, statistical analysis shows that bedrock units with the lowest ERI values are, on average, almost three times closer to the nearest stream and six times as likely to have streams flowing on them than are units with highest values. Further, the effect of ERI on stream location is strongest for streams with drainage areas between 1 and 30 km². Thus, small streams appear to be subject to greater lithologic control than are larger streams.     

宁芜地区大平山铜矿、天台山黄铁矿与古火山机构关系的探讨

以大平山铜矿、天台山黄铁矿矿为例，阐述了该区的矿区、矿床地质及火山机构特征，并从成矿时间、空间及成因三个方面论述了矿床成矿与古火山机构的关系。     

Radio identification and continuum spectra of decameter-wavelength sources

The paper describes a method for the radio identification of decameter-wavelength sources based on their continuum spectra and analysis of their coordinates in relatively large error boxes surrounding a specified position on the sky. The distribution of continuum spectra and identifications in other wavelength ranges are analyzed for the resulting radio catalog. Using identifications with the FIRST and NVSS surveys, the statistics of the spectral index-size and spectral index-flux density distributions for steep-spectrum sources have been studied, and a catalog of ultrasteep-spectrum (α相似文献   

Capture of Helium and Other Volatiles during the Growth of Olivine Phenocrysts in Picritic Basalts from the Juan Fernandez Islands

Olivine crystals in basalt contain helium that can be extractedfor isotopic analysis. Helium-bearing olivine phenocrysts inpicritic tholeiites from the Juan Fernandez Islands, SE Pacific,crystallized from moderately differentiated liquids. None arexenocrysts of mantle peridotite. The helium occurs in cavitiesor bubbles in inclusions best seen at high magnification inthe olivine. The olivine grew around spinel, sulfide, and bubblesthat preferentially nucleated on crystal surfaces. Inclusionswithin these phases range from large cavities to tiny, facetedpits arranged in rows. Many crystals contain curving trainsof inclusions along annealed features. The inclusions formedduring mixing between cooler differentiated magma and hotterolivine-charged magma, which accelerated vesiculation. Bubblesnucleated on the olivine as they do on ice when stirred in carbonatedwater. Mixing also induced thermal stress fracturing, like thecracking of ice dropped into water. Cracking, irregular extinction,and subgrain formation occurred when faceted crystals collidedwith each other or with conduit walls. Boundary layer meltsand bubbles were drawn quickly into the fractures. Thus fewinclusions contain equilibrium proportions of minerals and vapor.Mantle-derived helium clearly permeated into shallow storagereservoirs, including rift zones where magmatic differentiation,mixing, and vapor exsolution were fairly extensive. KEY WORDS: Juan Fernandez; volatiles; inclusions; olivine; picrite     

Atomistic simulation of the structure and elastic properties of pyrite (FeS2) as a function of pressure

Interatomic potential parameters have been derived at simulated temperatures of 0 K and 300 K to model pyrite FeS₂. The predicted pyrite structures are within 1% of those determined experimentally, while the calculated bulk modulus is within 7%. The model is also able to simulate the properties of marcasite, even though no data for this phase were included in the fitting procedure. There is almost no difference in results obtained for pyrite using the two potential sets; however, when used to model FeS₂ marcasite, the potential fitted at 0 K performs better. The potentials have also been used to study the high-pressure behaviour of pyrite up to 44 GPa. The calculated equation of state gives good agreement with experiment and shows that the Fe–S bonds shorten more rapidly that the S–S dimer bonds. The behaviour of marcasite at high pressure is found to be similar to that of pyrite.