A nepheline-alkali feldspar geothermometer

A nepheline-alkali feldspar geothermometer has been developed which is based on the thermodynamics of an Na—K exchange reaction between nepheline and alkali feldspar. The activities are formulated in terms of site occupancies, and the regular solution model is used to represent non-ideal mixing of the cations on each site. The distribution of Na and K on the alkali sites in nepheline is calculated from published nepheline-brine ion-exchange data. The standard Gibbs energy of the geothermometer reaction is calculated from experimental data on coexisting nephelines and alkali feldspars (Hamilton and MacKenzie, 1960, 1965). The geothermometer is applied to nepheline syenites from the Precambrian Igdlerfigssalik intrusion, S.W. Greenland, and gives temperatures which suggest that nepheline and alkali feldspar continue to equilibrate with cooling after they crystallise from the magma.     

Precambrian microfossils from the McArthur River lead-zinc-silver deposit northern territory,Australia

Structurally preserved insoluble organic cellular matter is intimately associated with Precambrian lead-zinc-silver ore in the McArthur River deposit, Australia. The ore is essentially a non-metamorphosed mineralized bituminous dolomitic shale of marine volcanic association and has some similarities with the Mt. Isa and Broken Hill deposits.     

Microbial nitrogen removal in a developing suburban estuary along the South Carolina coast

The conversion of undisturbed coastal regions to commercial and suburban developments may pose a threat to surface and groundwater quality by introducing nitrate-nitrogen (NO₃ ^?-N) from runoff of land-applied wastewater and fertilizers. Microbial denitrification is an important NO₃ ^?-N removal mechanism in coastal sediments. The objective of this study was to compare denitrification and nitrate conversion rates in coastal sediments from a golf course, suburban site, undeveloped marsh, and nonmarsh area near rapidly developing Hilton Head Island, South Carolina. Nitrous oxide was measured using gas chromatography and nitrate and ammonium concentrations were measured using a flow injection autoanalyzer in microcosms spiked, with 50 μg NO₃ ^?-N gdw^?1. The two marsh sites had the greatest ammonium production, which was correlated with fine sediment particle size and higher background sediment nitrate and surface water sulfate concentrations. The golf course swale had greatest denitrification rates, which were correlated with higher total carbon and organic nitrogen in sediments. Nitrate was consumed in golf course sediments to a greater extent than in the undeveloped marsh and upland freshwater sites, suggesting that the undeveloped sites and receiving estuaries may be more susceptible to nitrate contamination than the golf course swale and marsh under nonstorm conditions. Construction of swales and vegetated buffers using sediments with high organic carbon content as best management practices may aid in removing nitrate and other contaminants from runoff prior to its transport to the receiving marsh and estuary.     

Landscape: a wasted legacy

Summary This paper explores the way in which the rehabilitation within geography of 'landscape' has been partial and unbalanced. Landscape history, arguably the most geographically relevant aspect of landscape study, has been marginalized–though it has demonstrated a remarkable capacity to flourish in an interdisciplinary context. It is argued that the neglect of landscape history is not in the best interests of geography, and that its reintegration would allow a more balanced perspective on landscape to be developed.     

The rôle of aquaculture in the industrial regions of the temperate zone

The prosperous industrial areas of North America and Europe support a diverse and vigorous aquaculture industry. Although climatic restrictions of temperature, photosynthetic energy and exposure may limit the potential, the relatively intensive forms of production of the area are supported by good and expanding market demand. Thus, many forms of production are technically sophisticated. Capital and operating cost levels are generally high and technically difficult. Poorly marketable products are not economically viable. The bulk of production is therefore concentrated on three fish groups: rainbow trout, Atlantic and Pacific salmon, channel catfish, and two mollusc groups: oysters and mussels. The potential for growth and development of the industry is good but is increasingly controlled by market expansion rather than by technical innovation.     

Editorial 2003

2002 was a highly successful year. The most recent (2001) ISIImpact Factors for journal citations confirm that Journal ofPetrology remains the premier journal in the field of petrology(Journal of Petrology—3.283; Earth & Planetary ScienceLetters—2.700; Geochimica Cosmochimica Acta—2.614;Contributions to Mineralogy & Petrology     

A kinematic hardening constitutive model for sands: the multiaxial formulation

This paper explores the possibility of using well-accepted concepts—Mohr-Coulomb-like strength criterion, critical state, existence of a small strain elastic region, hyperbolic relationship for representing global plastic stress–strain behaviour, dependence of strength on state parameter and flow rules derived from the Cam-Clay Model—to represent the general multiaxial stress–strain behaviour of granular materials over the full range of void ratios and stress level (neglecting grain crushing). The result is a simple model based on bounding surface and kinematic hardening plasticity, which is based on a single set of constitutive parameters, namely two for the elastic behaviour plus eight for the plastic behaviour, which all have a clear and easily understandable physical meaning. In order to assist the convenience of the numerical implementation, the model is defined in a ‘normalized’ stress space in which the stress–strain behaviour does not undergo any strain softening and so certain potential numerical difficulties are avoided. In the first part the multiaxial formulation of the model is described in detail, using appropriate mixed invariants, which rationally combine stress history and stress. The model simulations are compared with some experimental results for tests on granular soils along stress paths lying outside the triaxial plane over a wide range of densities and mean stresses, using constitutive parameters calibrated using triaxial tests. Furthermore, the study is extended to the analysis of the effects induced by the different shapes of the yield and bounding surfaces, revealing the different role played by the size and the curvature of the bounding surface on the simulated behaviour of completely stress- and partly strain-driven tests. Copyright © 1999 John Wiley & Sons, Ltd.