Observing artificially induced strain: implications for subglacial deformation

By analysing a series of four successive thin‐sections from a ceramic clay that was subjected to uniaxial compression, we were able to monitor the development of microstructures in a fine‐grained sediment. The artificially induced microstructures, such as unidirectional clay reorientations and linear and circular grain arrangements, are identical to features that have been observed in thin‐sections of subglacially deformed tills, and therefore may be used as representative analogues. We argue that the structures, reflecting slip, planar shear displacements as well as rotational movements, can be explained by assuming a Coulomb‐plastic response to imposed shear. We conclude that sediments subjected to subglacial deformation behave as Coulomb materials, at least during the final stages of the deformation. The present study bridges the gap between field studies, experimental studies and theoretical modelling. The microscopic observations assist in visualising inferred subglacial processes and facilitate up‐ and downscaling between diverse methodological approaches. Copyright © 2003 John Wiley & Sons, Ltd.     

Classification of artificial (man-made) ground

The legacy inherited from anthropogenic processes needs to be addressed in order to provide reliable and up-to-date ground information relevant to development and regeneration in the urban environment. The legacy includes voids as well as anthropogenic deposits (artificial ground). Their characteristics derive from former quarrying and mining activities industrial processes creating derelict ground, variably consolidated made ground, and contaminated groundwater and soils. All need to be systematically assessed to inform the planning process and provide the basis for engineering solutions. Site-specific investigation needs to be conducted on the back of good quality geoscientific data. This comes from ‘field’ survey, remotely sensed data interpretation, historical maps, soil geochemical sampling, and geotechnical investigation. Three-dimensional and, in the future, four dimensional, characterization of superficial deposits is required to reach an understanding of the potential spatial lithological variability of artificial ground and the geometry of important surfaces, i.e. the boundary conditions. The classification scheme for artificial ground outlined in this paper and adopted by the British Geological Survey, will help in achieving this understanding.     

Sediment Phosphorus Chemistry and Microbial Biomass along a Lowland New Zealand Stream

An evaluation of the distribution of P concentrations in streamflow, P fractions andthe microbial biomass P pool was made of bed and bank sediments along a lowlandstream in New Zealand. Agricultural intensification increased downstream. However,most P fractions decreased downstream (total P decreased from c. 400 to 250 mg kg^-1) in bed sediments, while P in streamflow remained relatively constant (generally < 0.005 mg l^-1) and sediment microbial P increased from 2 to 8 mg kg^-1. An investigation of P release from dried and rewetted sediments showed that solution P (CaCl2-P) increased, on average > 300%, and proportional to the size of the microbial biomass P pool before drying, except in sediments with much organic carbon (OC). When supplied with a P source (1 mg l^-1) and then simultaneously with a C source (glucose, 100 mg l^-1), all sediment behaved similarly and biotic sorption accounted for, on average, 27 and 34% of the total sediment uptake, respectively (maximum of 58%). The quantity of P taken up was related to the initial size of the microbial biomass P pool, and the availability of P as influenced by organic P complexes and OC. The sediment microbial biomass represents a transient, but small store of P could be useful to indicate bioavailable P inputs.     

Water-quality trends in White Rock Creek Basin from 1912-1994 identified using sediment cores from White Rock Lake reservoir, Dallas, Texas

Historical trends in selected water-quality variables from 1912 to 1994 in White Rock Creek Basin were identified by dated sediment cores from White Rock Lake. White Rock Lake is a 4.4-km² reservoir filled in 1912 and located on the north side of Dallas, Texas, with a drainage area of 259 km². Agriculture dominated land use in White Rock Creek Basin before about 1950. By 1990, 72% of the basin was urban. Sediment cores were dated using cesium-137 and core lithology. Major element concentrations changed, and sedimentation rates and percentage of clay-sized particles in sediments decreased beginning in about 1952 in response to the change in land use. Lead concentrations, normalized with respect to aluminum, were six times larger in sediment deposited in about 1978 than in pre-1952 sediment. Following the introduction of unleaded gasoline in the 1970s, normalized lead concentrations in sediment declined and stabilized at about two and one-half times the pre-1952 level. Normalized zinc and arsenic concentrations increased 66 and 76%, respectively, from before 1952 to 1994. No organochlorine compounds were detected in sediments deposited prior to about 1940. Concentrations of polychlorinated biphenyls (PCB) and DDE (a metabolite of DDT) increased rapidly beginning in the 1940s and peaked in the 1960s at 21 and 20 µg kg^-1, respectively, which is coincident with their peak use in the United States. Concentrations of both declined about an order of magnitude from the 1960s to the 1990s to 3.0 and 2.0 µg kg^-1, respectively. Chlordane and dieldrin concentrations increased during the 1970s and 1980s. The largest chlordane concentration was 8.0 µg kg^-1 and occurred in a sediment sample deposited in about 1990. The largest dieldrin concentration was 0.7 µg kg^-1 and occurred in the most recent sample deposited in the early 1990s. Agricultural use of chlordane and dieldrin was restricted in the 1970s; however, both were used as termiticides, and urban use of chlordane continued at least until 1990. Recent use of dieldrin and aldrin, which degrades to dieldrin, has not been reported; however, increasing trends in dieldrin since the 1970s suggest recent urban use could have occurred.     

天山北坡降水对河流水沙情势影响

以天山北坡头屯河流域为例，在对山区不同海拔的降水特征、侵蚀产沙情势以及河流水沙运移特点分析的基础上，详尽就山区降水对河流水沙情势的年际变化、年内变化以及月变化的影响进行了分析研究，并就降水对不同海拔的河流水沙情势的影响强度及相互关系作了探讨．     

辽东湾北部浅海区泥沙输送及其沉积特征

根据实测资料，本文定量分析了辽东湾北部泥沙输送及其分布，并对辽河三角洲沉积区划作了初步讨论。研究表明本区泥沙以纵向搬运为特征。双台子河以西来沙和辽河西水道入海泥沙是区域东部拦门沙体和浅滩发育的主导因素。汛季大潮期，泥沙自西向东运移落淤在河口及毗邻浅水域；小潮期，泥沙除向东扩散外，大部泥沙向海方搬运。调查区可划分六个现代沉积作用区，即潮坪沉积区、辽河水下三角洲细粒沉积区、河口沙洲沉积区、波浪潮流冲蚀沉积区、河口冲积沉积区以及潮汐水道沉积区。     

液压传感间接测量水位计的研制及其应用

压力式水位计在水文自动测报系统中很难推广的主要原因是泥沙对传感器的影响,泥沙不但会使传感器测量精度达不到测验要求,而且由于泥沙淤积还会给水位计的日常维护带来很大不便。目前进口传感器测量精度高、稳定性能好,但仍避免不了泥沙的影响。针对这一问题,提出了一种新型压力式水位计———液压传感间接测量水位计,该水位计解决了泥沙对压力式水位计的影响,是一种具有很大发展前景的水位测量仪器。     

栖霞组沉积地球化学特征及其环境意义

沉积环境的古氧相特征是沉积环境和古海洋特征恢复的重要内容。岩石地球化学特征是判断其形成环境氧化还原条件的重要手段之一。本文以来宾地区铁桥面为重点．通过对栖霞组灰岩的地球化学分析，结合沉积学、古生态学特征．认为栖霞组沉积于贫氧的沉{只背景．是在海水深度和海域的局限程度等沉积条件发生周期性变化的情况下形成的。古氧相地球化学指标V(V十Ni)、Cc/La、U／Th值都适用于该组以钙质沉积为主的沉积物。黄铁矿矿化程度(DOP值)变。化较大．眨映该区多变的古氧相特征。     

三峡大坝建成后长江输沙量的减少及其对长江三角洲的影响

三峡大坝建成之后,大量泥沙滞留于库区,出库泥沙量减少,坝下河床冲刷而提供相当数量的泥沙,支流湖泊供沙也发生变化,这将使进入河口地区的泥沙有所减少。三峡大坝以上长江干流和支流建设新的大坝,南水北调、封山育林、退耕还林以及减少水土流失都将进一步减少长江进入河口地区的泥沙。由此估计,三峡大坝建成后的百年内长江输入河口地区的泥沙约为2.0×10⁸～2.5×10⁸t/a;冰后期长江三角洲形成和发育期间的长江年均输沙量为1.84×10⁸～2.28×10⁸t。二者的数值相当接近,然而与近50年的观测(4.33×10⁸t/a)相差甚远,长江流域的气候变化和人类活动可能是造成这一现象的原因。文章着重说明中国和长江上游人口的增长、种植作物的改变可能是水土流失、长江泥沙量增长的主要原因。     

Inferring the mass fraction of floc-deposited mud: application to fine-grained turbidites

Fine sediment deposition in the ocean is complicated by the cohesive nature of muds and their tendency to flocculate. The result is disaggregated inorganic grain size (DIGS) distributions of bottom sediment that are influenced by single‐grain and floc deposition. This study outlines a parametric model that characterizes bottom sediment DIGS distributions. Modelled parameters are then used to infer depositional conditions that account for the regional variation in the grain sizes deposited by turbidity currents on the Laurentian Fan–Sohm Abyssal Plain, offshore south‐eastern Canada. Results indicate that, on the channellized Laurentian Fan, the mass fraction of floc‐deposited mud increases only slightly downslope. The small evolution in this fraction arises because sediment concentration and turbulent energy are associated in turbidity currents. On the Sohm Abyssal Plain, however, the mass fraction of floc‐deposited mud decreases, probably as a result of lower sediment concentration at this source‐distal site. Estimates of the mass fraction of mud deposited as flocs suggest that floc deposition is the dominant mode by which sediment is lost from suspension, although single‐grain deposition contributes more to the depositional flux in proximal areas where high energy breaks flocs and in distal areas where low sediment concentration limits floc formation. It is concluded that, throughout the dispersal system, changes in the fraction of flocculated mud deposited from turbidity currents reflect changes in sediment concentration and energy downslope.