The significance of rock structure,lithology and pre‐glacial deep weathering for the shape of intermediate‐scale glacial erosional landforms

The main landforms within the glacially scoured Precambrian rocks of the Swedish west coast are closely connected to the principal structural pattern and have lately been explained as mainly a result of etch processes, probably during the Mesozoic and with a possible second period of etching during the Neogene. To explore the effect of multiple glacial erosion on the rock surfaces, an island with two different lithologies and with striae from different directions was selected for a detailed study, focusing on the shape of roches moutonnées. Air‐photo interpretation of bedrock lineaments and roches moutonnées combined with detailed field mapping and striae measurements are used to interpret the structural and lithological control on the resulting shape. The study reveals a significant difference in shape between roches moutonnées in augen‐granite and orthogneiss. Low elongated and streamlined roches moutonnées occur in the gneiss area, striated by a Late Weichselian ice flow from the NE. This ice flow is subparallel with both the local dominant trend of topographically well‐expressed joints and the schistosity of the gneiss. Frequently, there are no signs of quarrying on the lee‐sides of the gneiss roches moutonnées and hence they resemble the shape of whalebacks, or ruwares, as typically associated with the exposed basal weathering surface found in tropical areas. The granite roches moutonnées were formed by an older ice flow from the ESE, which closely followed the etched WNW–ESE joint system of the granite. Late Weichselian ice flow from the NE caused only minor changes of the landforms. On the contrary, marks of the early ESE ice flow are poorly preserved in the gneiss area, where it probably never had any large effect as the flow was perpendicular to both schistosity and structures and, accordingly, also to the pre‐glacial relief. The study demonstrates that coincidence between ice flow direction and pre‐glacially etched structures is most likely to determine the effects of glacial erosion. Copyright © 2002 John Wiley & Sons, Ltd.     

两个冰期-间冰期旋回的黄土记录及其古气候意义

北京邻区枣沟、斋堂和赤峰黄土－古土壤剖面粒度和磁化率变化在幅度和相位上都有明显的差异。在两个冰期－间冰期旋回，磁化率记录具有冰量变化模式，而粒度记录具有轨道周期特点，粒度和磁化率之间的相位关系在从冰期向间冰期转换和冰期向间冰期过渡的过程中，既有滞后也有超前的表现，很难单纯以成土作用来解释。由于黄土粒度主要反映粉尘源区环境和古风场强度的变化，而磁化率主要记录的是沉积区的成壤作用，反映夏季风的强度变化，因此剖面粒度和磁化率变化的不协调说明古风场和粉尘源区变化与粉尘沉积区气候变化之间不统一。这可能意味着控制夏季风强度变化和控制冬季风强度变化的机制存在差异。     

西安翠华山山崩地质遗迹资源保护

文论述了西安翠华山山崩地质遗迹资源保护的目的，进行了保护分区，将其分为核心保护区、缓冲区和视域保护区三个区，重点分析了核心保护区的保护现状，并在此基础上提出了相应的保护内容和对策，以实现山崩地质遗迹资源的可持续利用和发展。     

Response of the cladoceran community to trophic state change in Lake Apopka, Florida

A paleolimnological evaluation of cladoceran microfossils was initiated to study limnological changes in Lake Apopka, a large (125 km²), shallow (mean depth = 1.6 m), warm, polymictic lake in central Florida. The lake switched from macrophyte to algal dominance in the late 1940s, creating a Sediment Discontinuity Layer (SDL) that can be visually used to separate sediments derived from macrophytes and phytoplankton. Cladoceran microfossils were enumerated as a means of corroborating extant eutrophication data from the sediment record. Inferences about the timing and trajectory of eutrophication were made using the cladoceran-based paleo-reconstruction. The cladoceran community of Lake Apopka began to change abruptly in both total abundance and relative percent abundance just before the lake shifted from macrophyte to algal dominance. Alona affinis, a mud-vegetation associated cladoceran, disappeared before the SDL was formed. Planktonic and benthic species also began to increase below the SDL, indicating an increase in production of both planktonic and benthic species. Chydorus cf. sphaericus, an indicator of nutrient loading, increased relative to all other cladocerans beginning in the layer below the SDL and continuing upcore. Changes in the transitional sediment layer formed before the lake switched to phytoplankton dominance, including an increase in total phosphorus concentration, suggest a more gradual eutrophication process than previously reported. Data from this study supported conclusions from other paleolimnological studies that suggested anthropogenic phosphorus loading was the key factor in the hypereutrophication of Lake Apopka.     

Glacial Lake Outburst Floods in the Nepal Himalaya: A Manageable Hazard?

Within the past fifteen years, glacial lake outburst floods have become an activetopic of discussion within the development community focused on Nepal. Suchfloods endanger thousands of people, hundreds of villages, and basic infrastructuresuch as trails and bridges. The flood risk is also a major impediment to hydroelectricdevelopment in several river basins. Unlike most other mountain hazards in Nepal,reducing the possibility of outburst floods is technically feasible. The first attemptwithin Nepal to reduce the hazard of one lake by artificially lowering its water levelwas partially completed in June 2000. Completing this task and beginning work onother hazardous lakes will require difficult decisions about risk by downstream residentsand substantial investment from the international aid community.     

The postglacial history of three Picea species in New England, USA

Given the difficulty of separating the three Picea species—P. glauca, P. mariana, and P. rubens (white, black, and red spruce)—in the pollen record, little is known about their unique histories in eastern North America following deglaciation. Here we report the first use of a classification tree analysis (CART) to distinguish pollen grains of these species. It was successfully applied to fossil pollen from eight sites in Maine and one in Massachusetts. We focused on the late glacial/early Holocene (14,000 to 8000 cal yr B.P.) and the late Holocene (1400 cal yr B.P. to present)—the two key periods since deglaciation when Picea has been abundant in the region. The result shows a shift from a Picea forest of P. glauca and P. mariana in the late glacial to a forest of P. rubens and P. mariana in the late Holocene. The small number of P. rubens grains identified from the late glacial/early Holocene samples (<5%) suggests that that species was either absent or rare at most of the sites. The occurrence and distribution of the three species do not reveal any geographic or temporal trend during late glacial time, but the data suggest that they were distributed in local patches on the landscape. The results of this study indicate that the recent population expansion of Picea (1000 to 500 cal yr B.P.) was likely the first time since deglaciation that P. rubens was abundant in the region.     

马鞍山的古冰川地貌

马鞍山是四川盆地西南边缘第一高山。此山存在第四纪冰川地貌。它是我国东部一处典型的古冰川地貌，时代属末次冰期与新冰期。     

The onset of Pleistocene glaciation in the Barents Sea: implications for glacial isostatic adjustment

In this paper the effect of a delayed onset of glaciation in the Barents Sea on glacial isostatic adjustment is investigated. The model calculations solve the sea-level equation governing the total mass redistributions associated with the last glaciation cycle on a spherically symmetric, linear, Maxwell viscoelastic earth for two different scenarios for the growth phase of the Barents Sea ice sheet. In the first ice model a linear growing history is used for the Barents Sea ice sheet, which closely relates its development to the build-up of other major Late Pleistocene ice sheets. In the second ice model the accumulation of the Barents Sea ice sheet is restricted to the last 6 ka prior to the last glacial maximum.
The calculations predict relative sea levels, present-day radial velocities, and gravity anomalies for the area formerly covered by the Weichselian ice sheet. The results show that observed relative sea levels in the Barents Sea are appropriate for distinguishing between the different glaciation histories. In particular, present-day observables such as the free-air gravity anomaly over the Barents Sea, and the present-day radial velocities are sensitive to changes in the glaciation history on this scale.
A palaeobathymetry derived from relative sea-level predictions before the last glacial maximum based on the second ice model essentially agrees with a palaeobathymetry derived by Lambeck (1995). The additional emerged areas provide centres for the build-up of an ice sheet and thus support the theory of Hald, Danielsen & Lorentzen (1990) and Mangerud et al. (1992) that the Barents Sea was an essentially marine environment shortly before the last glacial maximum.     

Electrokinetic remediation of metal contaminated glacial tills

This paper presents the results of an experimental investigation which studied the feasibility of using the electrokinetic process to remediate contaminated clays of glacial origin, otherwise known as glacial tills. An overview of the electrokinetic phenomena, as well as previously performed laboratory and field investigations, is first presented. The methodology of the electrokinetic experiments which were conducted to investigate the removal of metals from a glacial till is then described. A total of 16 experiments were conducted using glacial till samples obtained from a project site near Chicago. Sodium and calcium were used as the surrogate cationic metallic contaminants. These experiments demonstrated that ion transport during the electrokinetic process occurs due to both electro-osmosis and electromigration, but that due to electromigration is significantly higher than that due to electro-osmosis. Unlike other clays such as kaolinite, the glacial till used for this investigation possessed high buffering capacity because of its high carbonate content which prevented the acid front migration from the anode to the cathode during the electrokinetic process. The ion removal efficiency of the electrokinetic process was found to increase when: (1) the voltage gradient applied to the soil was increased, (2) the initial concentration of the contaminants was increased, and (3) the duration of the treatment process was increased. The ion removal efficiency was also greater for smaller ions which possess less ionic charge and when the ions existed independently in the soil as compared to when they coexisted. This investigation suggests that the electrokinetic process has significant potential for remediating glacial tills contaminated with metals. However, the properties of Na and Ca are not representative of contaminants, such as heavy metals, so further investigations are needed.