Holocene insect fossils from two sites at Ennadai Lake, Keewatin, Northwest Territories, Canada     

Scott A. Elias 《Quaternary Research》1982,17(3):371-390

Ennadai Lake, in the forest-tundra ecotonal region of Keewatin, Northwest Territories, Canada, has been the subject of several paleoecological investigations (palynology, plant macrofossils, fossil soils). This study concerns Holocene insect fossils at Ennadai, a new approach in a region shown to be sensitive to climatic change. The Ennadai I site yielded 53 taxa, representing 13 families of Coleoptera and 7 families of other insects and arachnids, including abundant ants. These fossils range in age from about 6300 to 630 yr B.P. The Ennadai II site produced fossils of 58 taxa, including 13 beetle families and 15 families of other arthropods, ranging in age from 4700 to 870 yr B.P. The insect evidence suggests the presence of trees in the Ennadai region from 6000 to 2200 yr B.P. A conifer pollen decline from 4800 to 4500 yr B.P. at Ennadai has previously been interpreted as an opening up or retreat of forest in response to climatic cooling, but the insect fossils reveal the continued presence of trees during this interval. Both insect assemblages suggest trends of forest retreat and tundra expansion between about 2200 and 1500 yr B.P., presumably due to climatic cooling, with a return of woodland by about 1000 yr B.P.  相似文献   

North American farmland protection strategies in retrospect     

C. R. Bryant  Prof. Dr. L. H. Russwurm 《GeoJournal》1982,6(6):501-511

The arenas in which farmland protection strategies have developed in North America vary in terms of perceptions of the farmland resource and the role of planning, and in terms of administrative structures. Administratively, farmland protection strategies have developed in a variety of structures, ranging from the very decentralized ones of many US states to the more centralized, though still mixed, ones found in some Canadian provinces. Farmland protection strategies can thus be investigated in terms of how they address a variety of fundamental issues. Difficult questions are raised by policy evaluation, e.g. are objectives coherent, how do objectives relate to goals and objectives for other land uses and what would have happened in the absence of the program? It is argued that, while it is essential to encourage more analyses of how results, e.g. farmland removal rates, relate to stated objectives, it is equally important to study the decision-making process of implementation to establish both stated and implied objectives and therefore how farmland protection strategies relate to the broader land use planning and management context for other land uses.  相似文献   

Hydrodynamic dispersion during absorption of water by soil: 2. Immobile water model     

M.J.L. Robin  K.B. Laryea  D.E. Elrick 《Journal of Hydrology》1983,65(4):333-348

The assumptions and analysis of Part 1 are extended to the three model soil-water profiles having different immobile-water contents up to 0.08 m³ m^?3. Concentration profiles in the mobile zone obtained with a constant dispersion coefficient are compared with those calculated with the same dispersion coefficient and no immobile water. The average concentration profiles were calculated from the concentration of the solution in both the mobile and immobile phases. Increasing the immobile-water content decreased and shifted the average concentration profiles further into the soil. The values of the dispersion coefficient calculated with the immobile-water fraction ignored, were found to be water content dependent and many times greater than that of the input dispersion coefficient.  相似文献   

Identification of a magma chamber in the Ghoubbet-Asal rift (Djibouti) from a magnetotelluric experiment     

Daniele Boyer  Jean-Louis Le Mouël  Vincent Courtillot 《Earth and Planetary Science Letters》1981,52(2):372-380

A very broad band (10^?3 to 10⁴ Hz) magnetotelluric investigation of the axial zone of the Ghoubbet-Asal rift (Djibouti) has revealed a shallow (2–4 km) magma chamber which can be mapped in some detail. The suggested roof of the chamber is shallowest very close to the Ardoukoba volcano which was built during the November 1978 rifting episode.  相似文献   

Invertebrate fossils (Insecta: Trichoptera,Diptera, Coleoptera) from the Pleistocene Scarborough Formation at Toronto,Ontario, and their paleoenvironmental significance     

Nancy E. Williams  John A. Westgate  D. Dudley Williams  Anne Morgan  Alan V. Morgan 《Quaternary Research》1981,16(2):146-166

Larval caddisfly, chironomid, and beetle remains have been recovered from the Pleistocene Scarborough Formation in the Toronto region of southern Ontario. Three stratigraphic levels were sampled at the northeastern end of the Scarborough Bluffs; the youngest horizon yielded 16 chironomid taxa, 33 caddisfly taxa, and 28 beetle taxa, whereas the two older levels yielded somewhat less diverse assemblages. Only one taxon in each of the caddisfly and chironomid groups was identified from the presumed correlative beds at Woodbridge, Ontario, but numerous beetle fragments were recovered, several of which have been specifically identified and match species found previously in the upper part of the Scarborough Formation. The youngest sampled assemblage in the Scarborough Formation at the northeastern end of the Scarborough Bluffs is interpreted as indicating cool climatic conditions in a boreal forest environment, given the present-day distributions and feeding habits of these river, lake, and terrestrial taxa. The mean July temperature at this time was probably about 15°C, as compared to the present-day value of 20.5°C. The forest was poorer in deciduous species during deposition of the older part of the formation as preserved here. These results agree well with previous interpretations based on plant remains. We suggest that both aquatic and terrestrial insects are good indicators of macroclimate.  相似文献   

An Early Paleozoic Tectonic Mélange at the Western Margin of West Cathaysia: Constraints from Organic-walled Microfossils     

WANG Lijun  ZHANG Kexin  HE Weihong  YIN Leiming  Shoufa LIN 《《地质学报》英文版》2020,94(4):1060-1070

The Jiangshan-Shaoxing-Pingxiang Fault(JSP Fault) is traditionally considered as the boundary between the Yangtze and Cathaysia blocks in South China. Whether the previously defined Shenshan and Kuli formations located along the JSP fault and near the Xinyu City, Jiangxi Province, are continuous strata or parts of a tectonic mélange is important for understanding the geological history of South China. A carbonaceous phyllite from the area, previously considered as part of the Neoproterozoic Shenshan and Kuli formations, is analyzed palynologically in this study. The AsteridiumComasphaeridium acritarch assemblage found in the slate can be correlated with the basal Cambrian AsteridiumHeliosphaeridium-Comasphaeridium(AHC) acritarch assemblage in Tarim and the Yangtze Block. The early Cambrian biostratigraphical age assignment for the carbonaceous phyllite indicates the presence of both Neoproterozoic and Cambrian rocks in the sedimentary package, and supports that the package is a part of tectonic mélange rather than a continuous Neoproterozoic strata. The Cambrian slate is the youngest known lithology in the mélange at present.  相似文献   

Surface analysis of particles in mine tailings by time-of-flight laser-ionization mass spectrometry (TOF-LIMS)     

C. J. Martin  T. A. Al  L. J. Cabri 《Environmental Geology》1997,32(2):107-113

  Time-of-flight laser-ionization mass spectrometry was applied to study the chemical composition of mineral particle surfaces in a sulphide-rich mine-tailings impoundment. This surface-sensitive technique provides chemical information from surfaces of irregularly shaped mineral particles (both conductive and insulators) less than 100 μm in diameter, which are considered to be representative of particle surface coatings in the tailings pile (after drying). In addition, depth profiles in the mineral particles were obtained. The combination of speed of analysis (1 min), small beam-diameter (2–4 μm), surface sensitivity (2–10 nm), trace-element sensitivity, and capability to analyze rough surfaces makes this method useful as a complement to studies of pore-water geochemistry and tailings mineralogy. As an example, the behavior of Pb and As in the Kidd Creek tailings dam near Timmins, Ontario, Canada, was studied, using a combination of surface analyses, and pore-water geochemical data. Received: 22 February 1995 / Accepted: 6 January 1996  相似文献   

The macrobenthos of Lake Ontario during 1964 to 1966, and subsequent changes in the deepwater community   总被引：1，自引：0，他引：1  

David R. Barton  Bradley Anholt 《Aquatic Sciences - Research Across Boundaries》1997,59(2):158-175

From January 1964 through January 1966, Dr. F.P. Ide and colleagues at the University of Toronto Great Lakes Institute (GLI) collected benthic macroinvertebrates from up to 63 stations during each of 16 cruises on Lake Ontario. This intensive survey was conducted at a time of rapidly increasing anthropogenic impact. Total invertebrate abundance decreased with increasing depth; this distribution was bimodal on the northern side of the lake, with peaks at ca. 35 and 80 m. Oligochaeta were more abundant along the southern than on the northern side of the lake, except in Humber Bay. The amphipodDiporeia was rarely collected at most stations near the mouth of the Niagara River. Chironomidae were most abundant in the Kingston Basin but were common throughout the lake at depths less than 50 m. Sphaeriidae were confined to water <100 m deep and were most abundant along the southern shore. When compared with the results of subsequent surveys of the deepwater zone, the GLI data provide evidence of two major shifts in the abundance of benthic animals. Numbers of Oligochaeta decreased by about 40% during 1965 and remained at the lower levels through 1990. The abundance ofDiporeia changed little from 1964 through 1977, but increased sharply between 1977 and 1981. These shifts do not appear to reflect implementation of controls on the discharge of phosphorus, or direct predation by fish. Changes in fish and zooplankton communities and inputs of toxic contaminants seem equally likely to be responsible for the shifts in the deepwater benthic community. We have proposed several predictions which could test the relative importance of biotic interactions or chemical stressors.  相似文献   

Acid neutralization mechanisms and metal release in mine tailings: a laboratory column experiment   总被引：1，自引：0，他引：1  

Jasna Jurjovec  Carol J. Ptacek  David W. Blowes 《Geochimica et cosmochimica acta》2002,66(9):1511-1523

Mining and milling of base metal ore deposits can result in the release of metals to the environment. When sulfide minerals contained in mine tailings are exposed to oxygen and water, they oxidize and dissolve. Two principal antagonistic geochemical processes affect the migration of dissolved metals in tailings impoundments: sulfide oxidation and acid neutralization. This study focuses on acid neutralization reactions occurring in the saturated zone of tailings impoundments. To simulate conditions prevailing in many tailings impoundments, 0.1 mol/L sulfuric acid was passed continuously through columns containing fresh, unoxidized tailings, collected at Kidd Creek metallurgical site. The results of this column experiment represent a detailed temporal observation of pH, Eh, and metal concentrations. The results are consistent with previous field observations, which suggest that a series of mineral dissolution-precipitation reactions control pH and metal mobility. Typically, the series consists of carbonate minerals, Al and Fe(III) hydroxides, and aluminosilicates. In the case of Kidd Creek tailings, the dissolution series consists of ankerite-dolomite, siderite, gibbsite, and aluminosilicates. In the column experiment, three distinct pH plateaus were observed: 5.7, 4.0, and 1.3. The releases of trace elements such as Cd, Co, Cr, Cu, Li, Ni, Pb, V, and Zn were observed to be related to the pH buffering zones. High concentrations of Zn, Ni, and Co were observed at the first pH plateau (pH 5.7), whereas Cd, Cr, Pb, As, V, and Al were released as the pH of the pore water decreased to 4.0 or less.  相似文献   

Risk-Based Engineering Design for a Landfill Leachate Collection and Liner System   总被引：1，自引：0，他引：1  

Gordon B. Murray  Edward A. McBean  Jonathan F. Sykes 《Ground Water Monitoring & Remediation》1996,16(2):139-146

A methodology is used to identify the tradeoffs between costs and exposure risk associated with landfill leachate collection and low permeable systems. The results are useful in demonstrating the point at which additional levels of sophistication in design of a leachate/liner system do not produce significant reductions of exposure risk. The case study application to the Durham Regional landfill demonstrates that clay liner hydraulic conductivity is the parameter with the largest influence on the risk of exceedance at the point of compliance. When the underlying clay is more permeable, there is a significant merit associated with use of a QA/QC program.  相似文献