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1.
Analyses of platinum-group elements (PGE) in rocks collected from the Voikar-Syninsky ophiolite in the Polar Urals suggest that the distribution and geochemistry of PGE in this Paleozoic ophiolite are similar to those in Mesozoic ophiolites from elsewhere. Chondrite-normalized PGE patterns for chromitite, the tectonite unit, and ultramafic and mafic cumulate unit have negative slopes. These results are similar to those found for chromitites from other ophiolites; stratiform chromities show positive slopes. If the magmas that form both types of chromitite originate from similar mantle source material with respect to PGE content, the processes involved must be quite different. However, the distinct chondrite-normalized PGE patterns may reflect differing source materials. 相似文献
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《Applied Geochemistry》1986,1(4):463-468
In the mountainous areas of Siberia intensive destruction of ore deposits occurs as a result of Pleistocene mountain glaciation and, as a consequence, element dispersion trains form in the eroded material and in the stream sediments. In these areas, cirques and glaciated valleys are incised as much as 250–600 m into ore deposits. Geochemical anomalies in the stream sediments in the glaciated valleys form as water washes through the till and lacustrine sediments. The surface erosion processes result in the removal of fine gold from talus-covered cirque walls from where it is deposited in channels and lakes. Secondary dispersion halos may either be localized entirely within cirques, or they may be found in the drift within the outwash or glaciolacustrine environments downstream of the cirques. Intermittent accumulations of gold are specifically concentrated in glacially-fed stream sediments in those glaciated valleys characterized by smooth, flat bottoms and abundant lakes: gold in such cases tends to be concentrated in the lake muds. After the lakes have silted up, gold will be found in the fluvial deposits. In general, the complete elemental composition of the ore under discussion (Au, Ag, Pb and Zn) is reflected in only short dispersion trains within the fluvial and lacustrine deposits. Gold anomalies, on the other hand, are extensive (up to 6 km) in the stream sediments within the glaciated valleys and will occur sorbed onto hydrous iron oxides and clays, as well as in the form of flattened (thin) gold particles. In the glaciated valleys, the gold geochemical anomalies in moraine, lacustrine and stream sediments properly reflect the mineralization in the drainage basin. 相似文献
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A fine exposure of perennially frozen ice-rich silt and associated flora and vertebrate fauna of late-Quaternary age exists at Mamontova Gora along the Aldan River in central Yakutia, Siberia, U.S.S.R. The silt deposit caps a 50-m-high terrace and consists of three units. An upper layer 1–2 m thick overlies a 10–15-m-thick brownish to black silt layer. The lower silt layer is greenish to gray and about 15 m thick. All the silt is well sorted with 60% of the particles falling between 0.005 and 0.5 mm in diameter and is generally chemically and mineralogically homogeneous. The middle unit contains may extinct vertebrate mammal remains and ice wedges. The lower unit contains little vegetation and no ice wedges. The silt is widespread and exists as a loamy blanket on terraces at various elevations on both sides of the lower Aldan River. The origin of the silt blanket of late-Quaternary age in central Yakutia has long been controversial. Various hypotheses have been suggested, including lacustrine and alluvial, as well as frost-action origins. It is sometimes referred to as loess-like loam. Péwé believes the silt at Mamontova Gora is loess, some of which has been retransported very short distances by water. The silt probably was blown from wide, braided, unvegetated flood plains of rivers draining nearby glaciers. The silt deposits are late Quaternary in age and probably associated with the Maximum glaciation (Samarov) and Sartan and Syryan glaciations of Wisconsinan age. On the basis of biostratigraphy, 10 radiocarbon dates, and their relation to the nearby glacial record, it is felt that the upper unit at Mamontova Gora is Holocene and the middle unit is Wisconsinan. The youngest date available from the middle unit at this particular location is 26,000 years. Dates greater than 56,000 years were obtained in the lower part of the middle unit. The lower unit is definitely beyond the range of radiocarbon dating and probably is older than the last interglacial. The sediment, fauna, ice wedges, stratigraphy, and age of perennially frozen slit deposits in central Alaska are remarkably similar to those of the deposits exposed in central Yakutia. Both areas consist of unglaciated rolling lowlands and river terraces surrounded by high mountains that were extensively glaciated in Pleistocene time. The glaciers extended from the high mountains to the edges of the ranges. In both regions, extensively braided, silt-charged rivers drained the mountains and flowed through the lowlands on their way to the sea. It follows that there should be a similar late-Quaternary history. 相似文献
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Steven D. Machemer Julia S. Reynolds Leslie S. Laudon Thomas R. Wildeman 《Applied Geochemistry》1993,8(6)
The wetland constructed at the Big Five Tunnel in Idaho Springs, Colorado was designed to remove, passively, heavy metals from acid mine drainage. In optimizing the design of such a wetland, an improved understanding of the chemical processes operating there was required, particularly SO42− reduction and sulfide precipitation. For this purpose, field and laboratory data were collected to study the balance of S in the system. Field data collected included water analyses of the mine drainage and wetland effluents and measurements of H2S gas emissions from the wetland. The concentration of sulfide in the wetland effluent ranged from 10−4 to 10−3 mol/l. The average rates of H2S emission from the surface of the substrate were 150 nmol/cm2/d in the summer and 0.17 and 0.35 nmol/cm2/d in the winter. This maximum estimated loss of sulfide was not significant in reducing the amount of sulfide available for precipitation with metals. Sequential extraction experiments for S on wetland substrates showed that acid volatile sulfides (AVS) increased with time in the wetland substrate. A serum bottle experiment was conducted to study the S balance in the Big Five wetland by quantitatively measuring the amount of S in different phases as microbial SO42− reduction progressed. The increase in AVS reasonably balanced the decrease in SO42− concentration in the experiment, suggesting that the decrease in SO42− concentration represented the amount of SO42− reduced and that nearly all of the sulfide produced was precipitated as AVS. Sulfide precipitation was determined to be the primary metal removal process in the wetland system and amorphous FeS is the primary iron sulfide formed in the substrate. 相似文献
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S.B. Lavrov M.K. Bandman K.P. Kosmachev G.V. Sdasyuk S.S. Artobolevsky L.M. Shevchenko 《Geoforum》1979,10(3):333-344
A major field of research since the 1920s has been methods and theories of economic regionalization. The territorial-production complex is now recognized as a key developmental tool within the framework of economic-planning regions. Recently, there has been a more marked growth of study into problems of natural-resource development, social progress and change in the U.S.S.R. as well as into the spatial structure of other nations, particularly other socialist countries and non-socialist developing countries. 相似文献
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《International Geology Review》2012,54(5):884-888
Tufa occurs widely in the Tatar A.S.S.R. and adjacent republics. It is associated with springs escaping from aquifers in deposits of Permian age. No tufa deposits were observed in the region where Jurassic and later deposits are developed. Tufa deposits occur because of a breakdown of calcium bicarbonate to CaCO3, water and CO2. The presence of organic matter and phosphorous inhibits this reaction, accounting in part for the lack of tufa deposition in the other regions. It appears also that tufa deposition is favored by 1) increase of water surface, hence increased evaporation and CaCO3 concentration and 2) slopes where argillaceous material is present.—J.J. Finney 相似文献
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STUART D. LUDLAM 《Sedimentology》1981,28(1):85-96
In Fayetteville Green Lake, past sedimentation rates can be accurately and precisely estimated by separating annual couplets or varves in dried sediment samples. Two measures were used, which serve as upper and lower limits on estimated sedimentation rate. They agree within 5 % with average annual sedimentation rate in couplets for recent years. Between 3 and 5 replicate samples are needed to reduce the half-width of 95 % confidence intervals on individual couplet sedimentation rates to 30 g m?2 yr?1 about 5 % of average recent rates. In the late 1800s sedimentation rate averaged 392 g m?2 yr?1 and ranged between 324 and 466 g m?2 yr?1, while in the 1970s the rate averaged 581 g m?2 yr?1 by the same measure, and ranged between 384 and 646 g m?2 yr?1. Sedimentation rate averaged for 13 years does not vary over short distances in the profundal zone, but lateral variation in sedimentation rate can be detected for individual years over the same distance. Not all this variation was associated with the non-uniform distribution of dark sublaminae and thin turbidites which cannot be separated from the annual layers. This indicates that although precise estimates of sedimentation rates can be made at different points in the lake, estimates will have to be made at numerous points before annual sedimentation rates for the lake as a whole can be accurately assessed. 相似文献
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《International Geology Review》2012,54(8):1387-1396
A very interesting and informative paper on widespread occurrence of a thermal hydrosphere. Geothermal power uses are discussed. Distribution of heated waters, some up to 150° C is discussed in considerable detail, especially with reference to possible power utilization of the geothermal energy. Seven hydrothermal regions of the U.S.S.R. are discussed and delineated. Chemical quality of waters is referred to. There is a summary listing of locations in the U.S.S.R. where thermal waters could be utilized for generation of electric power. — B. N. Cooper. 相似文献
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In 1983 water quality monitoring was conducted on peat deposits in Highlands County, Florida, U.S.A. The monitoring objective was to provide initial data on the water quality in the area in order to identify potential problems with environmental licensing of peat harvesting operations on these deposits. The investigation included sampling for in situ and laboratory water analyses, peat core analyses, elutriate tests, and interstitial water quality analyses. The general trends evident from the data are that BOD and COD (and the resulting DO) may change from the control and harvest peatlands, but not consistently. In addition, total suspended solids, organic color, total nitrogen, and total phosphorus concentrations appear to be elevated under disturbed conditions. For metals, the major cations (Ca, Mg, K, Fe) may show an increase under disturbed conditions vs. control. For the remaining metals, some increases may occur, but the changes are essentially unpredictable. 相似文献
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《Applied Geochemistry》1988,3(5):517-521
Iodine and Cl are enriched in soils in the vicinity of the Magmont and Buick lead mines near Bixby, southeastern Missouri. The enrichments, up to 5.6 ppm I and 305 ppm Cl, are against regional background of 1.26 ppm I and 41 ppm Cl. The area of highest I and Cl is thought to reflect a zone of base metal sulphide mineralization occurring about 400 m below the surface. Iodine and Cl are also enriched in soils immediately adjacent to a tailings pond, hence these elements would appear to be leached from this source. A zone of enhanced I values (up to 2.65 ppm I) to the north of a lead smelter is superimposed on a much larger zone of lead enrichment (up to 12,000 ppm Pb) and is thought to represent I released from sulphide ores on smelting. 相似文献
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湖南郴县华塘地区的长兴阶 总被引：2，自引：0，他引：2
<正> 湖南南部郴县、桂阳交界的华圹地区,晚二叠世晚期地层发育良好。在东西长6公里,南北宽1.3公里的华塘向斜范围内(图1),岩相变化很大,既有以硅质岩为主含菊石的“大隆组”,又有以厚层白云质灰岩为主,含筵类、菊石、腕足类等的“长兴组”。笔者在采集化石、测制剖面进行生物地层工作的同时,对上述两种岩相的变化关系进行了追索和研究,现将我们的认识概述如下。 (一)郴县华塘公社三合小学剖面 相似文献
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E. Sherbon Hills 《International Journal of Earth Sciences》1959,47(2):543-561
The structure and history of several Devonian cauldron-subsidences and related granitic intrusions showing evidence of sub-surface ring-fracturing in South Eastern Australia are discussed. The Marysville Igneous Complex includes fish and plant bearing beds in the Acheron Cauldron, which has a diameter of 15 miles, and contains 6000 ft. of acid lavas, with subordinate andesites and basalts. Most of the occurrences are consanguineous. The parent magma is intermediate, close to the hypersthene dacites of the region, and is believed to have been injected as a magma wedge from the east. 相似文献
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Bryan Shuman Anna K. Henderson Steven M. Colman Jeffery R. Stone Sherilyn C. Fritz Lora R. Stevens Mitchell J. Power Cathy Whitlock 《Quaternary Science Reviews》2009,28(19-20):1861-1879
The availability of water shapes life in the western United States, and much of the water in the region originates in the Rocky Mountains. Few studies, however, have explicitly examined the history of water levels in the Rocky Mountains during the Holocene. Here, we examine the past levels of three lakes near the Continental Divide in Montana and Colorado to reconstruct Holocene moisture trends. Using transects of sediment cores and sub-surface geophysical profiles from each lake, we find that mid-Holocene shorelines in the small lakes (4–110 ha) were as much as 10 m below the modern lake surfaces. Our results are consistent with existing evidence from other lakes and show that a wide range of settings in the region were much drier than today before 3000–2000 years ago. We also discuss evidence for millennial-scale moisture variation, including an abruptly-initiated and -terminated wet period in Colorado from 4400 to 3700 cal yr BP, and find only limited evidence for low-lake stands during the past millennium. The extent of low-water levels during the mid-Holocene, which were most severe and widespread ca 7000–4500 cal yr BP, is consistent with the extent of insolation-induced aridity in previously published regional climate model simulations. Like the simulations, the lake data provide no evidence for enhanced zonal flow during the mid-Holocene, which has been invoked to explain enhanced mid-continent aridity at the time. The data, including widespread evidence for large changes on orbital time scales and for more limited changes during the last millennium, confirm the ability of large boundary-condition changes to push western water supplies beyond the range of recent natural variability. 相似文献