Hydrofracturing in response to the development of an overpressurised subglacial meltwater system during drumlin formation: an example from Anglesey,NW Wales     

Emrys Phillips  Leanne Hughes 《Proceedings of the Geologists' Association. Geologists' Association》2014

This paper presents the results of a detailed study of a complex hydrofracture system and host diamictons exposed within a longitudinal section through an elongate drumlin located to the west of Cemlyn Bay, Anglesey, NW Wales. This complex, laterally extensive sand, silt and clay filled hydrofracture system was active over a prolonged period and is thought to have developed beneath the Late Devensian (Weichselian) Irish Sea Ice Stream as it overrode this part of NW Anglesey. The sediment-fill to the hydrofracture system is deformed with kinematic indicators (folds, thrusts, augen) recording a SW-directed sense of shear, consistent with the regional ice flow direction across this part of the island. The lack of any geomorphological evidence for active retreat of the Irish Sea ice across Anglesey has led to the conclusion that hydrofracturing at the Cemlyn Bay site occurred within the bed of the Irish Sea Ice Stream whilst this relatively faster flowing corridor of ice was actively overriding the island. Shear imposed by the overriding ice led to the development of a subglacial shear zone which facilitated the propagation of the hydrofracture system with the laterally extensive feeder sills occurring parallel to Y-type Riedel shears. Although a subglacial setting beneath the active Irish Sea Ice Stream can be argued for the Cemlyn Bay hydrofracture system, its relationship to the formation of the ‘host’ drumlin remains uncertain. However, evidence presented here suggests that hydrofracturing may have occurred during the later stages or post landform development in response to the migration of overpressurised meltwater within the bed of the Irish Sea ice; possibly accompanying the local thinning and shutdown of the Irish Sea Ice Stream on Anglesey.  相似文献   

Distribution of trace metals in stream sediments along the Trans-Amazonian Federal Highway,Pará State,Brazil     

《Journal of South American Earth Sciences》2014

A total of 64 sediment samples were collected along a stretch of about 988 km of the Trans-Amazonian Federal Highway, between Marabá and Itaituba, Pará State, in order to characterize the distribution of metals and trace elements. Due to the lithological and geological diversity along this stretch of the Amazon, the study region was divided in three distinct tracks. Statistical data analysis (Spearman correlation and Principal Factor Analysis) shows strong signature and predominance of regional rocks chemistry, such as mafic-ultramafic-bearing elements (Ni and Cr) and hydrothermalism-bearing elements such as Cu and Pb. Enrichment factors were calculated for three different normalizer agents: 1) Fe and Mn, representing the Fe and Mn (hydr)oxides, 2) Al representing clay minerals, and 3) organic matter (OM). The Fe and Mn (hydr)oxides showed to be the most proficient metal carrier among the geological matrices, likely due to the larger lithological diversity. On the other hand, OM positively correlated to trace element distribution.  相似文献   

Geochemistry and behavior of REE in stream sediments close to an old Sn-W mine,Ribeira, Northeast Portugal     

《Chemie der Erde / Geochemistry》2014,74(4):545-555

The abandoned Sn-W Ribeira mine, northeast of Portugal, contained quartz veins with cassiterite, wolframite, scheelite, pyrite, arsenopyrite, sphalerite, chalcopyrite, manganocolumbite, bismuthinite, native bismuth, phosphates and carbonates. The exploration took place on the northern slope of the Viveiros stream, which is an affluent of the Sabor River. The waste-rock dumps and tailings were deposited on the hillside, close to the mine and are nowadays exposed to significant weathering and erosion, as they are not vegetated. The eroded material is transported by the Viveiros stream toward the Sabor River. A seasonal stream drains the tailings. The stream sediments samples were collected along the Viveiros stream, in the seasonal stream, in a seasonal spring at the bottom of the tailings, in the Sabor River and in other streams not affected by mine workings, following the mine influence along the Viveiros stream and in the Sabor River (1.2 km away from the mine workings). The data show that the degree of pollution increases along the Viveiros stream, especially in winter. The highest degree of pollution is for As, In, W, Sn and Bi. The sediments from the drainage of the main tailings are particularly polluted during winter, by Bi, In and Sn. The sedimentary precipitate from the spring is polluted in Cu, As, In, Sn, Ta, W, Bi, Zn, Nb, Ag, Sb and Ta. The sediments from the Sabor River are significantly polluted by As, Ag, In, Sn, W and Bi. The sediments from the regional streams, Viveiros stream and Sabor River have similar REE (NASC normalized) patterns (ΣREE = 131.7–185.9 mg/kg, La_N/Lu_N = 1.23–1.42 and Eu/Eu* = 1.02), while those from the seasonal stream, crossing the main tailings, are enriched in REE (ΣREE = 250.3–283.6 mg/kg, La_N/Lu_N = 1.6–2.09 and Eu/Eu* = 0.96). The general decrease in La_N/Lu_N values with increase in total Fe₂O₃ can be explained by the partitioning of HREE to the solid Fe-oxides phase. The sedimentary precipitate and coatings, which are mainly formed by Fe-oxy-hydroxides, but also contain jarosite, are impoverished in all REE. The impoverishment can be explained by the release of REE from the surface of the Fe-oxy-hydroxides, which occurs due to a local lowering of pH, caused by jarosite dissolution. During successive alternate cycles of wet and dry conditions, takes place the formation of Fe-oxy-hydroxides and jarosite in the sedimentary precipitate and coatings. The subsequent dissolution of jarosite releases acidity, thus promoting de-sorption of REE from the Fe-oxy-hydroxides mineral phases.  相似文献   

A benchmark comparison of numerical methods for infinite Prandtl number thermal convection in two-dimensional Cartesian geometry     

B. J. Travis  C. Anderson  J. Baumgardner  C. W. Gable  B. H. Hager  R. J. O'Connell 《地球物理与天体物理流体动力学》2013,107(3-4):137-160

Abstract

A comparison is made between seven different numerical methods for calculating two-dimensional thermal convection in an infinite Prandtl number fluid. Among the seven methods are finite difference and finite element techniques that have been used to model thermal convection in the Earth's mantle. We evaluate the performance of each method using a suite of four benchmark problems, ranging from steady-state convection to intrinsically time-dependent convection with recurring thermal boundary layer instabilities. These results can be used to determine the accuracy of other computational methods, and to assist in the development of new ones.  相似文献   

辽宁金杖子地区水系沉积物地球化学特征          下载免费PDF全文

秦丹鹤  李昊璐  王志民  刘博  黄晨承 《地质找矿论丛》2023,38(2):225-230

金杖子地区位于冀东-辽西金成矿带,区内矿产资源丰富,成矿地质条件优越。本文在1∶25000水系沉积物测量工作的基础上,结合该区地质特征和成矿地质条件,对该地区10种元素的地球化学特征、离散程度及综合异常特征进行研究,圈定综合异常3处,为进一步的地质勘查工作提供了依据。  相似文献   

The connection between Labrador Sea buoyancy loss, deep western boundary current strength, and Gulf Stream path in an ocean circulation model     

Stephen G. Yeager  Markus Jochum 《Ocean Modelling》2009,30(2-3):207-224

The sensitivity of the North Atlantic gyre circulation to high latitude buoyancy forcing is explored in a global, non-eddy resolving ocean general circulation model. Increased buoyancy forcing strengthens the deep western boundary current, the northern recirculation gyre, and the North Atlantic Current, which leads to a more realistic Gulf Stream path. High latitude density fluxes and surface water mass transformation are strongly dependent on the choice of sea ice and salinity restoring boundary conditions. Coupling the ocean model to a prognostic sea ice model results in much greater buoyancy loss in the Labrador Sea compared to simulations in which the ocean is forced by prescribed sea ice boundary conditions. A comparison of bulk flux forced hindcast simulations which differ only in their sea ice and salinity restoring forcings reveals the effects of a mixed thermohaline boundary condition transport feedback whereby small, positive temperature and salinity anomalies in subpolar regions are amplified when the gyre spins up as a result of increased buoyancy loss and convection. The primary buoyancy flux effects of the sea ice which cause the simulations to diverge are ice melt, which is less physical in the diagnostic sea ice model, and insulation of the ocean, which is less physical with the prognostic sea ice model. Increased salinity restoring ensures a more realistic net winter buoyancy loss in the Labrador Sea, but it is found that improvements in the Gulf Stream simulation can only be achieved with the excessive buoyancy loss associated with weak salinity restoring.  相似文献   

Cartographic techniques for mapping the geochemical data of stream sediments: the “Sample Catchment Basin” approach     

M.?SpadoniEmail author  G.?Cavarretta  A.?Patera 《Environmental Geology》2004,45(5):593-599

The Sample Catchment Basin (SCB) mapping technique extends the representativeness of the geochemical features of stream sediments to the surface of the whole upstream drainage basin. SCB boundaries clash with the water divides traced from each sampling point and are limited upstream by the presence of further SCBs. They are also assumed to represent the elementary map unit. The rank of SCBs can be defined counting the number of upstream SCBs along the branches of a fluvial network. The presence of low rank SCBs minimizes the statistical redundancy of measures. The SCB technique is particularly suitable for the geochemical mapping of mountainous or hilly areas and to correctly display the information into a morphological context. This approach can be also valuable in the case of low sampling density, inhomogeneous sampling schemes, and especially when very accurate evaluations of the spatial distribution of chemicals (with natural or anthropogenic origin) are required.  相似文献   

On different types of adjustment usable to calculate the parameters of the stream power law     

Alain Demoulin  Arnaud BeckersBenoît Bovy 《Geomorphology》2012,138(1):203-208

Model parameterization through adjustment to field data is a crucial step in the modeling and the understanding of the drainage network response to tectonic or climatic perturbations. Using as a test case a data set of 18 knickpoints that materialize the migration of a 0.7-Ma-old erosion wave in the Ourthe catchment of northern Ardennes (western Europe), we explore the impact of various data fitting on the calibration of the stream power model of river incision, from which a simple knickpoint celerity equation is derived. Our results show that statistical least squares adjustments (or misfit functions) based either on the stream-wise distances between observed and modeled knickpoint positions at time t or on differences between observed and modeled time at the actual knickpoint locations yield significantly different values for the m and K parameters of the model. As there is no physical reason to prefer one of these approaches, an intermediate least-rectangles adjustment might at first glance appear as the best compromise. However, the statistics of the analysis of 200 sets of synthetic knickpoints generated in the Ourthe catchment indicate that the time-based adjustment is the most capable of getting close to the true parameter values. Moreover, this fitting method leads in all cases to an m value lower than that obtained from the classical distance adjustment (for example, 0.75 against 0.86 for the real case of the Ourthe catchment), corresponding to an increase in the non-linear character of the dependence of knickpoint celerity on discharge.  相似文献   

有限区域流函数和速度势的计算及其在台风中应用   总被引：1，自引：1，他引：0  

黎爱兵  张立凤  臧增亮  张云 《气象科学》2012,32(1):1-8

在Endlich提出求解旋转风和辐散风基础上,本文给出了直接利用风场迭代计算流函数和速度势的方法,该方法不但能求解流函数和速度势,还可将原始风场直接分解为旋转风和辐散风。此方法在有限区域中,能大大降低边界条件对计算结果的影响,不仅能计算准确的涡度和散度,还能很好的重建原始风场。采用此方法,对"0808"号台风"凤凰"进行了诊断分析,得到了台风不同时期的流函数和速度势、旋转风和辐散风。结果发现在台风的不同时期,流函数与高度场相似,可用其低值中心来分析台风移动路径和强度的变化,速度势存在高值区,其中心与高度场低值中心不吻合;旋转风的涡旋中心也可用来反映台风中心,台风南侧辐散风较大,故可用来反映南方水汽供应对台风发展、成熟、衰退的影响。  相似文献   

Impact of mining activities on soils and sediments at the historical mining area in Podljubelj,NW Slovenia     

Tamara Teršič  Mateja Gosar  Robert Šajn 《Journal of Geochemical Exploration》2009

The abandoned Hg mine in Podljubelj was in operation with interceptions from 1557 to 1902. The entire operating period yielded about 110 000 tons of ore, from which 360 tons of Hg was produced. The objective of the research project was to establish the contents and spatial distribution of Hg in soils and stream sediments in the vicinity of the mine. On an area of 88 ha the soil was sampled in a 100 × 100 m grid. Two soil horizons (0–5 cm and 20–30 cm) were sampled in order to distinguish between geogenic and anthropogenic Hg sources. It was established that on an area of about 9 ha Hg content in soil exceeds The New Dutchlist action value for Hg (10 mg/kg). Total Hg concentrations in soil samples vary between 0.17 and 719 mg/kg, with a mean of 3.0 mg/kg. Mercury contents in stream sediments range from 0.065 to 1.4 mg/kg, with a mean of 0.64 mg/kg. The highest determined value in soils was found in the area around the former roasting furnace, where the ore was processed. Increased Hg concentrations were also found on the mine waste dump (108 mg/kg). Mercury contents in soils generally decrease with soil profile depth and with the distance from the mine and from the roasting furnace location. Mercury also appears in higher concentrations along the road that runs through the valley, which results from the use of Hg-bearing ore residues in road construction. The average enrichment factor (EF) of Hg in topsoil with respect to subsoil is 3.3. Calculated enrichment factors show higher values also for Cd (3.2), Pb (2.7), Ca (2.4) and P (1.9). The average enrichment factor of Hg in topsoil with regard to the established Slovenian soil averages (EF_slo) is 19. EF_slo of other determined chemical elements do not exceed 3.0.  相似文献