Global trace metal cycles and predictions     

Fred T. Mackenzie  Ronald J. Lantzy  Virginia Paterson 《Mathematical Geology》1979,11(2):99-142

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Climate-mediated changes in small lakes inferred from midge assemblages: the influence of thermal regime and lake depth     

Roberto Quinlan  Michael J. Paterson  John P. Smol 《Journal of Paleolimnology》2012,48(2):297-310

Subfossil midge (Chironomidae and Chaoboridae) assemblages were examined in the surficial sediments (0?C1?cm) from small inland lakes in the Experimental Lakes Area (ELA) of northwestern Ontario, Canada. In these boreal lakes, maximum depth (Z_max), alkalinity, Secchi depth and chlorophyll-a concentrations explained significant amounts of variation in the subfossil assemblages. Constrained ordinations (redundancy analysis) indicated that the relationship between Z_max (as sqrt Z_max) and assemblage composition was strong enough to develop a paleolimnological inference model. Model statistics suggested that a robust model was generated (r ²?=?0.78, RMSEP?=?0.533, max bias?=?0.674); however, when the model was applied to a subfossil stratigraphy from an ELA lake sediment core, results suggested that the inference model had produced an unrealistically shallow Z_max inference. Further analyses indicated that thermal regime had a strong influence on assemblage composition; when the influence of thermal regime was partialled out, there was a much weaker relationship between Z_max and assemblage composition, particularly for stratified lakes. A thermal regime inference model was subsequently developed, which, when applied to the lake sediment core stratigraphy, indicated that the shallow Z_max inference may have been the result of a period of increased mixing or polymixis in this stratified lake. Water column mixing may increase due to hypolimnetic warming and increased water clarity resulting from declines in dissolved organic carbon. In a training set where there are strong correlations between lake depth and assemblage composition, this relationship is not necessarily a strict function of lake depth, but of some other highly correlated variable, likely thermal conditions.  相似文献   

The importance of model choice on pH inferences from scaled chrysophyte assemblages in North America     

Andrew M. Paterson  Brian F. Cumming  Sushil S. Dixit  John P. Smol 《Journal of Paleolimnology》2002,27(3):379-391

The selection of a reliable inference model is a crucial step in developing ecologically sound reconstructions of environmental variables in the past. We compared intra- and inter-regional regression-based models, and an inter-regional Modern Analogue Technique (MAT) model in their ability to infer lakewater pH from scaled chrysophyte assemblages. The performance of each model was assessed by examining cross-validated coefficients of determination and prediction errors, and through reconstructing the pH of 50 modern and fossil samples in south-central Ontario, Canada. Using the intra- and inter-regional data sets, we found little difference in the ability of the regression-based models to infer present-day pH. Partial Least Squares (PLS) regression, Weighted Averaging (WA), and Weighted Averaging Partial Least Squares (WA-PLS) inference models showed similar values for jack-knifed coefficients of determination (r² _jack), root mean squared errors of prediction (RMSEP_jack), and mean and maximum biases. Based on an analogue matching approach, the inferred values from 48 fossil sediment samples suggested that the intra-regional model did not provide reliable reconstructions for approximately half of the fossil samples. However, inferences from the inter-regional MAT and regression-based models were found to have appropriate analogues and thus considered to be more reliable.  相似文献   

Zr–LREE rich minerals in residual peraluminous granulites, another factor in the origin of low Zr–LREE granitic melts?     

C. Villaseca  D. Orejana  B.A. Paterson 《Lithos》2007,96(3-4):375-386

There is a significant enrichment in some trace elements in the major residual minerals of peraluminous granulite xenoliths from the lower crust. Those trace elements are released from the breakdown of accessory phases at high-T granulite-facies conditions (> 850 °C). Around 10–35% of Zr is hosted in granulite rutile and garnet, whereas, the entire LREE–Eu budget is controlled by feldspar. The Zr- and REE-compatible behaviour of the major granulite phases, combined with the scarcity of accessory phases, which are mostly included in major granulite minerals, leads to a disequilibrium in accessory dissolution in the peraluminous partial melts. Thus the melt extracts less Zr and LREE and, consequently, generates the false impression of having lower-T when applying current accessory phase dissolution models.  相似文献   

Pro-poor sanitation technologies   总被引：1，自引：0，他引：1  

Charlotte Paterson  Duncan Mara 《Geoforum》2007,38(5):901-907

It is estimated that at least two billion people have inadequate sanitation. The current situation in water and sanitation services for millions of peri-urban residents is starkly anti-poor and represents a major challenge for the 21st century. By virtue of its cost and water requirements, we would argue that conventional sewerage is an implicitly anti-poor technology. This paper summarises low-cost sanitation technologies that have been developed by engineers from around the world, and seeks to provide evidence that there is such a thing as a pro-poor technology. We argue that simplified sewerage is often the only sanitation technology that is technically feasible and economically appropriate for low income, high-density urban areas. Simplified sewerage will only truly be a pro-poor technology if issues such as lack of investment in sanitation, insufficient cost recovery for sanitation services, conservative technical standards favoured over innovation, low-cost technologies perceived as second class provision, the nature of peri-urban settlements, and lack of engagement with users, are addressed. So often, peri-urban sanitation schemes fail to exist, fail to be sustainable, or fail to be pro-poor. The challenge is for engineers, social scientists and other professionals to work together to make pro-poor sanitation a reality and interdisciplinarity the norm.  相似文献   

Comparing different methods of calculating volume-weighted hypolimnetic oxygen (VWHO) in lakes     

Roberto Quinlan  Andrew M. Paterson  John P. Smol  Marianne S. V. Douglas  Bev J. Clark 《Aquatic Sciences - Research Across Boundaries》2005,67(1):97-103

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Effect of Pressure on Stress-Strain Properties of Materials     

M. S. Paterson 《Geophysical Journal International》1967,14(1-4):13-17

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A high-pressure,high-temperature apparatus for studies of seismic wave dispersion and attenuation     

Ian Jackson  M. S. Paterson 《Pure and Applied Geophysics》1993,141(2-4):445-466

An apparatus is described which provides for the investigation of viscoelasticity/anelasticity in geologic and related materials under conditions of high pressure and temperature. Cylindrical specimens are tested in torsion—a geometry particularly well suited to shear mode observations at the low strain amplitudes of the linear regine. Forced oscillation experiments allow the measurement of disperision and attenuation at the low frequencies of teleseismic wave propagation. The conduct of complementary forced oscillation and creep tests allows recoverble anelastic strains to be distinguished from those of permanent viscous deformation. It has been demonstrated that robust measurements can be made at strain amplitudes below 10^–5 and frequencies of 1 mHz–1 Hz, underP-T conditions to 300 MPa and 1200°C. The prospects for further development of this facility are outlined.  相似文献   

Superplastic flow in finegrained limestone   总被引：1，自引：0，他引：1  

S.M. Schmid  J.N. Boland  M.S. Paterson 《Tectonophysics》1977,43(3-4)

Creep of Solnhofen limestone at temperatures between 600° and 900° C was found to fall into three different flow regimes: regime 1 with an exponential stress-dependence of strain rate, regime 2 with power-law creep and n ~ 4.7 and finally a superplastic regime 3 with n ~ 1.7. Within the superplastic regime the creep behaviour is strongly grain-size dependent, the strain rate increasing markedly with decrease in grain size at a given stress. Microstructural observations indicate that in regimes 1 and 2 intracrystalline plasticity is dominant whereas the superplastic regime is characterized by grain-boundary sliding. The crystallographic preferred orientation within the superplastic regime is weaker and of different geometry when compared with that in flow regimes 1 and 2. In a discussion on the deformation mechanisms it is suggested that flow regimes 1 and 2 are regimes of dis location creep in which the rate controlling step is diffusion assisted; for the superplastic regime existing models of grain-boundary sliding are compared with the observations Finally, the tectonophysical importance of superplasticity is discussed and by extra polating the observed creep behaviour to geological strain rates it is found that super plasticity in rocks is to be expected under a wide range of conditions, particularly at smal grain sizes.  相似文献   

Systematics of zircon crystallisation in the Cretaceous Separation Point Suite, New Zealand, using U/Pb isotopes, REE and Ti geothermometry   总被引：5，自引：3，他引：2  

Robert Bolhar  Steve D. Weaver  J. Michael Palin  Jim W. Cole  Lorraine A. Paterson 《Contributions to Mineralogy and Petrology》2008,156(2):133-160

Plutonic zircons from the Cretaceous Separation Point Suite (SPS) were analysed by LA-ICPMS for U–Pb isotope ratios and trace element concentrations. Pooled ²⁰⁶Pb/²³⁸U ages range from 112 to 124 Ma. Cathodoluminescence imaging reveals minor inheritence and textural evidence of repeated dissolution and re-precipitation of zircon. Core and rim spot analyses, however, document zircon growth during extended periods of time (>2 myr). Protracted crystallisation histories for simple plutonic systems are inconsistent with generalised thermal constraints, which predict cooling below the solidus within <1 myr. Consequently, we conclude that the SPS granitoids sampled in this study were not emplaced rapidly but incrementally over extended time periods. Zircon Th/U and Zr/Hf ratios are positively correlated with crystallisation temperatures, consistent with crystallisation from evolving melts. However, highly variable trace element concentrations, along with temperature reversals are indicative of complex crystallisation histories involving continuous fractional crystallisation repeatedly punctuated by hotter, more mafic magma recharge. Normalised abundances of the redox-sensitive elements Eu and Ce in zircon vary systematically with degrees of whole rock differentiation, pointing to evolutionary trends in magmatic oxidation states coupled with feldspar crystallisation.  相似文献