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11.
Michael Wagreich Ana-Voica Bojar Reinhard F. Sachsenhofer Stephanie Neuhuber Hans Egger 《Cretaceous Research》2008,29(5-6):965
Ultrahelvetic units of the Eastern Alps were deposited on the distal European continental margin of the (Alpine) Tethys. The Rehkogelgraben section (“Buntmergelserie”, Ultrahelvetic unit, Upper Austria) comprises a 5 m thick succession of upper Cenomanian marl-limestone cycles overlain by a black shale interval composed of three black shale layers and carbonate-free claystones, followed by lower Turonian white to light grey marly limestones with thin marl layers. The main biostratigraphic events in the section are the last occurrence of Rotalipora and the first occurrences of Helvetoglobotruncana helvetica and Quadrum gartneri. The thickest black shale horizon has a TOC content of about 5%, with predominantly marine organic matter of kerogen type II. Vitrinite reflectance and Rock-Eval parameter Tmax (<424 °C) indicate low maturity. HI values range from 261 to 362 mg HC/g TOC. δ13C values of bulk rock carbonates display the well documented positive shift around the black shale interval, allowing correlation of the Rehkogelgraben section with other sections such as the Global Boundary Stratotype Section and Point (GSSP) succession at Pueblo, USA, and reference sections at Eastbourne, UK, and Gubbio, Italy. Sediment accumulation rates at Rehkogelgraben (average 2.5 mm/ka) are significantly lower than those at Pueblo and Eastbourne. 相似文献
12.
Impact of land use covers upon karst processes in a typical Fengcong depression system of Nongla, Guangxi, China 总被引:2,自引:0,他引:2
Cheng Zhang Jianguo Pei Yunqiu Xie Jianhua Cao Lanling Wang 《Environmental Geology》2008,55(8):1621-1626
The direction and intensity of karst processes can be deeply affected by soil physical and chemical variations which were
resulted from land use. Taking Nongla Fengcong depression area, Mashan County, Guangxi as an example, authors discussed the
impact of land use on karst processes based on the data of field limestone tablet. The results showed that the corrosional
rates at varied soil depth are quite different. Corrosional rate in woodland and orchard is mostly bigger than 20 mg/a, which
is much higher than that in tilled land and shrub. Generally, corrosional rate decreased from orchard, woodland, tilled land,
fallow land and shrub successively, in which soil organic matter (OM) and soil pH are two major controlling factors: corrosion
process is controlled remarkably by soil OM in woodland and orchard. The higher the organic matter content is and the less
the pH value is, the higher the corrosional rate is. Owing to lower organic matter content, the corrosional rate is mainly
affected by soil CO2 in tilled land and shrub. 相似文献
13.
Correlations between heavy metals and organic carbon extracted by dry oxidation procedure in urban roadside soils 总被引:1,自引:0,他引:1
Xue Song Wang 《Environmental Geology》2008,54(2):269-273
The organic fraction in soils has a significant influence on heavy metal transport. In this study, the organic carbon content
was measured by dry oxidation procedure from 21 Xuzhou urban roadside soils to assess the relationships between the concentrations
of heavy metals (Pb, Cu, Zn, and Cr) and the amount of organic carbon. The anthropogenic heavy metals (e.g. Pb, Cu, Zn) were
strongly correlated with organic carbon (denoted by Corg−c) extracted by dry oxidation while natural heavy metal (e.g. Cr) showed no correlation to the Corg−c. The anthropogenic heavy metals were also strongly correlated with the amount of the total carbon. These results show that
the anthropogenic heavy metals are mainly enriched in the organic matter in the Xuzhou urban roadside soils. 相似文献
14.
Natural radioactivity in sediment of Wei River,China 总被引:1,自引:0,他引:1
The concentrations of natural radionuclides in sediment of Wei River of China were measured using γ-ray spectrometry with
the aim of estimating the radiation hazard as establishing a database for radioactivity levels of river sediment of China.
The activity concentrations of 226Ra, 232Th and 40K in sediment samples ranged from 10.4 to 39.9 Bq kg−1, 15.3 to 54.8 Bq kg−1 and 514.8 to 1,175.5 Bq kg−1, respectively. The concentrations of these radionuclides were compared with the typical world values and the average activities
of Chinese soil and Shaanxi soil. Radium equivalent activity (Raeq), external hazard index (H
ex) and representative level index (I
γr) were calculated for the samples to assess the radiation hazards arising due to the use of these sediment samples in the
construction of dwellings. All the sediment samples have Raeq lower than the limit of 370 Bq kg−1, H
ex less than unity and I
γr close to 1 Bq kg−1. The overall mean outdoor terrestrial gamma dose rate is 64.8 nGy h−1 and the corresponding outdoor annual effective dose is 0.079 mSv. None of the studied location is considered a radiological
risk and sediment can be safely used in construction. 相似文献
15.
Tensioned foundations are common in civil engineering applications such as transmission towers, harbors, offshore structures, basement slabs under pressure, industrial equipment, etc. Procedures for the design of tensioned foundations are discussed in this paper, including specific recommendations for more common transmission tower foundations. Starting from a distinction between shallow and deep modes of failure, the paper presents the most common failure mechanisms for shallow failure in tension, including procedures for calculation of foundation tensile capacity under vertical and inclined loading. Emphasis is given to the influence of the strength of the compacted backfill compared to the strength of the natural soil, including presentation of results of full-scale loading tests. 相似文献
16.
Variation of infiltration rate through karstic surfaces due to land use changes: A case study in Murgia (SE-Italy) 总被引:1,自引:0,他引:1
Filomena Canora M. Dolores Fidelibus Antonella Sciortino Giuseppe Spilotro 《Engineering Geology》2008,99(3-4):210
Groundwaters of the Murgia carbonate aquifer represent the main groundwater resource of the Apulia region (SE Italy). In the highlands (Alta Murgia) karst crops out in different forms and textures which have been preserved up to the 1970s: little evolved agriculture and sheep rearing produced only a marginal modification of the epikarst while a high degree of division into parcels by drystone walls helped in preserving soils from erosion. In the last years the original scenery of the Alta Murgia changed due to widespread transformations of surface karstic textures for agricultural purposes, with undeniable negative consequences on the hydrogeological balance, concerning both the infiltration and the runoff terms. Stone shattering led to flattening and deep alteration of a large part of the original karstic landscape and to demolition of drystone walls.In a study area of about 139 km2 located in the Alta Murgia, the comparison of aerial photos related to the period 1950–2001 indicated that stone shattering had occurred for about 42% of the area.The hydrological behaviour of the first soil layer of experimental parcels representing both shattered stone and natural karstic surface textures was analysed by using the numerical model Hydrus-2D with the aim of estimating the variation on infiltration rate due to stone shattering. Intensive field and laboratory measurements concerned soil texture, soil water content, pressure head, saturated hydraulic conductivity, pan evaporation and meteorological parameters. 相似文献
17.
Vittorio Zanon Fátima Viveiros Catarina Silva Ana Rita Hipólito Teresa Ferreira 《Natural Hazards》2008,45(1):19-31
A detailed study was carried out on a piece of land that had been struck by lightning during the violent rainstorm that raged
over the Island of S?o Miguel (Azores Archipelago) in late October 2006. Temperature and gas measurements (CO2, CO, H2S and CH4) were performed in four study trenches, dug in an area of ∼3 m2, where an underground fire had been initiated by the impact with a lightning stroke, followed by the emission of a column
of gases and smoke. The soil under study was originally a well-pedogenized about 80 cm thick bed, made of volcanic clayey
to silty tephra fallouts and contained 5.5–9.7% of organic matter. The underground fire was monitored for one week and revealed a peak release of
404 ppm CO and 3.4% CO2 originating from a horizon located about 45 cm under the soil surface. Measurements of temperature, performed one week after
the impact, indicated a maximum value of 326°C inside the soil, while 516.5°C were measured on the surface of a lava block
interred about 20 cm under the surface. Subsequently, a stratigraphic and sedimentologic study proved the role of the grain-size
of the soil and of the organic matter content of the different horizons of the impact area, in determining the ratio between
anoxic/oxidised combustion conditions and in the progress of the process itself. It was also noticed that combustion was not
total all over in the soil bed and that the process had slightly migrated toward SW during the observation period. The combustion
process went on for about ten days, in spite of several other violent rainstorms, until it was artificially extinguished through
the excavations made to obtain study trenches. This particular circumstance evidenced the potential natural hazard represented
by this kind of atmospheric event, especially in a land where the volcanic nature of the soil may easily mislead inexperienced
observers and, consequently, delay proper action. 相似文献
18.
19.
青藏高原西北缘祁漫塔格山中新世快速抬升的磷灰石裂变径迹证据 总被引:2,自引:0,他引:2
对祁漫塔格山体不同海拔高度所取的9个磷灰石样品的裂变径迹分析结果表明,东昆仑西段中新世早中期为主要的隆升期且隆升速率较高,早期隆升速率为111m/Ma,晚期隆升速率为98m/Ma,总体隆升速率为100m/Ma。样品显示出磷灰石裂变径迹长度大致分2类,一类磷灰石裂变径迹长度为(12.21±10.20)-(13.75±0.30)μm,径迹长度分布图基本上为窄而对称的正态分布,反映具有快的剥露冷却速率,未受到后期热事件的干扰。另一类磷灰石裂变径迹长度为(11.88±0.33)~(13.32±0.27)μm,较前一类具有稍慢的剥露冷却速率,并且受到了后期热事件的干扰。 相似文献
20.
庵东浅滩沉积分带和沉积速率 总被引:4,自引:0,他引:4
杭州湾南岸的庵东浅滩具有地貌特征、沉积类型和沉积构造各异的三个沉积相带。垂向沉积带为潮滩沉积体的盖层,以泥滩、粘土质粉砂和薄砂泥交互层为特征;改造带位于中低潮位线附近,以粉砂滩、潮沟系统、粉砂沉积和沙波层理为特征;横向沉积带为潮滩堆积体的基础,以滩坡、粉砂及细砂质粉砂沉积、冲刷-充填构造为特征。据潮汐韵律层的统计,庵东浅滩沉积速率的短周期分量,常态条件下为每半日潮周期0.1~2.0cm,异常条件下可达每半日潮周期4~64cm。沉积速率的长周期分量,据地形对比和~(210)Pb推算,垂向沉积带为2~4.5cm/a;改造带中的粉砂滩为2.1~4.5cm/a,潮沟影响范围内为1~10~1cm/a量级;横向沉积带则以高于50cm/a的高沉积速率和变幅为主。近10年来,该浅滩的年淤积量为6×10~7t/a,其中85%集中于横向沉积带。 相似文献