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181.
The physical characteristics of surface sediments from a suite of pristine lakes on Signy Island, maritime Antarctic, were used to develop a quantitative link between catchment ice-extent and lake-sediment response. Percentage dry weight, median particle size, percentage loss-on-ignition and wet density of the lakes' surface sediments were the most significant variables explaining contemporary catchment ice-extent. Two independent reconstruction models – Partial Least Squares (PLS) and a Modern Analog Technique (MAT) – were applied to dated sediment cores at two sites on Signy Island. The validity of the reconstructions was tested against historical information on catchment ice-extent. With sufficiently high sedimentation rates and sampling resolution, the models can predict sub-decadal changes in ice-extent. The model results are best regarded as indicators of erosion resulting from meltwater activity in the catchment. Comparison of results with Twentieth Century climate records affirms the hypothesis that climatic warming is the most likely cause for the ice retreat observed on Signy Island during the last 40 yrs. Similar reconstruction models using these simple sedimentary measures could be developed for analogous locations in the Antarctic and in Arctic and Alpine regions. 相似文献
182.
Four thousand years of atmospheric lead pollution in northern Europe: a summary from Swedish lake sediments 总被引:8,自引:7,他引:8
This paper presents a large palaeolimnological study of the pre-industrial and industrial history of atmospheric lead pollution deposition in Sweden. Both lead concentrations and 206Pb/207Pb ratios have been analysed in 31 lakes covering most of Sweden, plus one lake in north-west Russia. Four of the lakes have varved (annually-laminated) sediments. Isotope analysis is a sensitive and effective method to distinguish pollution lead from natural catchment lead and to detect early pollution influence, because the 206Pb/207Pb ratio in unpolluted background sediments in Sweden was > 1.3, while that of lead from pollution, derived from ores and coal, was < 1.2. The sediments show a consistent picture of past temporal changes in atmospheric lead pollution. These changes include: the first traces of pollution 3,500-3,000 yrs ago; a pollution peak in Greek-Roman Times (about 0 AD); lower lead fall-out between 400 and 900 AD; a significant and permanent increase in atmospheric lead fall-out from about 1000 AD; an increase with the Industrial revolution; a major increase following World War II; the maximum peak in the 1970s; and decreasing fall-out over the last decades. The four varved sediments provide high-resolution records of atmospheric pollution. They reveal pollution peaks about 1200 and 1530 AD which match the history of metal production in Europe. According to the varve records the lead pollution level in the late 1990s had decreased beneath the level of the 1530s. The pollution level 1200 AD was about 35% of the 1980s, when lead pollution was still near its all time high. About 50% of the total accumulated atmospheric lead pollution deposition through time was deposited in the pre-industrial period. The sediments also show a consistent picture of the geographic distribution of atmospheric lead deposition over time, with higher deposition in south Sweden and declining levels to the north, which supports the hypothesis that the main sources of pre-industrial atmospheric lead pollution in Sweden were cultural areas in mainland Europe and Great Britain. 相似文献
183.
The “greatest lake period” means that the lakes are in the stage of their maximum areas. As the paleo lake shorelines are
widely distributed in the lake basins on the Tibetan Plateau, the lake areas during the “greatest lake period” may be inferred
by the last highest lake shorelines. They are several, even tens times larger than that at present. According to the analyses
of tens of lakes on the Plateau, most dating data fell into the range of 40-25 ka BP, some lasted to 20 ka BP. It was corresponded
to the stage 3 of marine isotope and interstitial of last glaciation. The occurrence of maximum areas of lakes marked the
very humid period on the Plateau and was also related to the stronger summer monsoon during that period. 相似文献
184.
The postglacial environmental development of Raffles Sø, East Greenland: inferences from a 10,000 year diatom record 总被引:1,自引:0,他引:1
Holger Cremer Bernd Wagner Martin Melles Hans-Wolfgang Hubberten 《Journal of Paleolimnology》2001,26(1):67-87
A 341 cm long sediment sequence was recovered from the unofficially named Raffles Sø on Raffles Ø, outer Scoresby Sund region, East Greenland. The sediment sequence consists in the upper part (0–230 cm) of a stratified gyttja enriched in organic carbon and biogenic silica whereas the lower core part (235–341 cm) is composed of terrigenous, consolidated glacio-limnic sediments. 14C-AMS measurements indicate that the sediment sequence represents the entire Holocene lake history from 10,030 calibrated radiocarbon years.The geochemical parameters (opal, total organic carbon (TOC), total nitrogen (TN)) and the total diatom concentration show similar developments during the Holocene, and reflect changes in biological production and nutrient input into the lake. These records clearly reveal a broad Holocene TOC-opal-maximum interval between 5200 and 1800 cal. yrs BP.The diatom flora consisted of 66 taxa representing 20 genera but only seven taxa were abundant and, sometimes, these were monospecifically dominant during the Holocene. In the sediment core from Raffles Sø four successive stratigraphical zones can be distinguished. Accumulation of diatom valves began at 9900 cal. yrs BP with a Stephanodiscus minutulus (Kütz.) Cleve and Möller dominated assemblage (stratigraphic zone 1) followed by a diatom flora dominated by Cyclotella pseudostelligera Hustedt and, less frequently, by Diatoma tenuis Agardh (9400 until 5900 cal. yrs BP, zone 2). Cyclotella sp. A, a taxon which belongs to the Cyclotella rossii-comensis-tripartita-complex, was the dominant floral element between 5200 and 1800 cal. yrs BP (zone 3). From 1800 cal. yrs BP, the periphytic taxa Fragilaria capucina var. gracilis (Østr.) Hustedt and F. capucina var. rumpens (Kütz.) Lange-Bertalot attained highest relative abundances, also almost monospecifically (zone 4).The distribution and composition of the diatom assemblages in the sediment record from Raffles Sø probably reflect past variations in the extent of the lake-ice cover during the growing season. More or less ice-free conditions during summer may have prevailed during the early Holocene until ca. 1800 cal. yrs BP, which allowed growth of planktonic diatoms (Cyclotella taxa) in the pelagic lake region. From 1800 cal. yrs BP, colder conditions lead to a perennial lake-ice cover with a small ice-free moat in summer which favored the growth of periphytic, littoral species (Fragilaria capucina varieties). 相似文献
185.
通过地面调查及钻井地质资料分析,对柴达木盆地干柴沟地区第三系湖盆边缘斜坡带沉积体系构成进行分析研究,该体系主要由扇三角洲沉积体系,水下洪积扇-近岸浊流沉积体系,辫状河三角洲沉积体系,常态湖三角洲沉积体系和湖泊沉积体系组成。对其成因地层格架及湖盆充填模式进行了探讨分析。 相似文献
186.
地表复杂地区煤田地震勘探方法及效果 总被引:2,自引:6,他引:2
以宁夏、山东的煤矿地震勘探为例,介绍了复杂地表工区地震勘探的方法与地质效果。 相似文献
187.
Velocity and absorption tomograms are the two most common forms of presentation of radar tomographic data. However, mining personnel, geophysicists included, are often unfamiliar with radar velocity and absorption. In this paper, general formulae are introduced, relating velocity and attenuation coefficient to conductivity and dielectric constant. The formulae are valid for lossy media as well as high-resistivity materials. The transformation of velocity and absorption to conductivity and dielectric constant is illustrated via application of the formulae to radar tomograms from the Hellyer zinc–lead–silver mine, Tasmania, Australia. The resulting conductivity and dielectric constant tomograms constructed at Hellyer demonstrated the potential of radar tomography to delineate sulphide ore zones. 相似文献
188.
The freshwater snail fauna in 51 lakes on the Åland Islands was investigated. By means of cluster analysis it appears that lakes may be divided into four groups on the basis of snail species composition. The lakes of the four groups show a spatial distribution which is related to topographical differences, terrestrial vegetation and land use. Snails may be divided on the basis of water hardness into hard water species and calcium indifferent species or into demanding and modest/indifferent species when clustering is based on presence/absence. 相似文献
189.
The Upper Permian Sedimentary Facies and Its Role in the Dajing Cu-Sn Deposit, Linxi County, Inner Mongolia, China 总被引:3,自引:1,他引:3
Gongjiong QIN Yosuke KAWACHI Liqing ZHAO Yongzheng WANG Qiang OU 《Resource Geology》2001,51(4):293-305
Abstract: Exhaustive investigations were launched for confirming the upper Permian host rocks of the Dajing Cu-Sn Deposit, probing into the possibility that Dajing is a Sedex type deposit during cosedimentation, complementing the deficiency of previous researches and going further into substantiating the role of the upper Permian strata in the control of ore distribution. After more than two years work, we reclassified the sedimentary facies in the Dajing area and its periphery as shallow fresh water lake and delta. Indicative sedimentary structures, such as ripple marks, rain marks, and mud cracks combined with contemporary fossils, were revealed. Having measured the flow directions, performed chemical comparison, and analyzed various sediments from sourceland in the Dajing area by XRF, we consequently redivided the strata into four sedimentary members, among which P2 l1 and P2 l2 were concluded as significant ore-hosted strata. The upper Permian basin was a lateral rift basin. The water and sediments in the basin are much deeper and thicker in the north than those in the south.
The indicators of special sedimentary facies, such as gravity flow, brine pool and synchronogenic stratiform structure of the ore cannot be found in the Dajing area. There was no growth fault, assemblage of sulfide and sulfate, and no zonation as well.
On the basis of study in this area, taking into account the paleosedimentary environment as capriciously flowing shallow lake, which approximated the state of oxidation, we figured that the paleogeography made it prohibitively difficult to form stratiform sulfide deposits which are prone to form in deoxidized environment. It can be ruled out the possibility that the Dajing deposit is a syngenetic deposit during sedimentation. 相似文献
The indicators of special sedimentary facies, such as gravity flow, brine pool and synchronogenic stratiform structure of the ore cannot be found in the Dajing area. There was no growth fault, assemblage of sulfide and sulfate, and no zonation as well.
On the basis of study in this area, taking into account the paleosedimentary environment as capriciously flowing shallow lake, which approximated the state of oxidation, we figured that the paleogeography made it prohibitively difficult to form stratiform sulfide deposits which are prone to form in deoxidized environment. It can be ruled out the possibility that the Dajing deposit is a syngenetic deposit during sedimentation. 相似文献
190.