A new map of glacigenic features and glacial landsystems in central mainland Nunavut,Canada

A new digital map of glacial geomorphic features and interpreted glacial landsystems was produced for an area covering ~415 000 km² in the Keewatin Sector of the Laurentide Ice Sheet (LIS) in Nunavut. The map integrates information from previous surficial geology maps and >14 000 field stations, and is significantly improved by the detailed inventory of ~152 000 glacigenic features using high-resolution ArcticDEM data and Landsat 8 imagery. From this, we identify and map coherent patterns of landform development (landsystems) between the Manitoba border and the Arctic coast, many of which are entirely new and others that are significantly modified or updated. In particular, we recognize six separate ice streams, including one probable remnant ice stream, and we delineate numerous palimpsest streamlined landscapes with associated ice-flow trends and relative ages. A continuum of relict terrains with varying basal ice thermal conditions is mapped for the first time in the ice divide migration zone between Baker Lake and Wager Bay. In addition, deglacial cold-based retreat terrains and preserved warm-based landscapes unaffected by younger glacial events have been identified. These new georeferenced, multi-scale data sets and interpreted glacial landsystems provide a comprehensive framework to strengthen reconstructions of the glacial history and dynamics of one of the largest ice domes of the LIS, identify distinct glacial sediment transport paths for applications to mineral exploration, and test numerical modelling of the LIS in support of climate change studies and long-term evolution of modern ice sheets.     

Effect of the environment on the hydrochemical characteristics of an alluvial aquifer following an exceptional multiyear drought (Mediterranean Seashore,Hérault,France): Part II—Climatology and agronomy

The hydrochemical evolution of an alluvial groundwater located along the Mediterranean seashore is analyzed with respect to its agricultural and climatic environment, including degree of saturation of the soil; types of cultures, chemical fertilizers and phytosanitary treatments; selective irrigations of the cultivated areas; precipitations. It is shown that the environmental effect on the groundwater's vulnerability depends on two groups of factors:

1. Transfers from surface to groundwater of nitrates, chlorides, sulfates, and potassium, which are governed by: (a) the climatic conditions before the agricultural activities begin, (b) the kinds of agricultural activities and their distribution in time with respect to a given climatic context. Phenomena of retention of and/or rapid diffusion are related to the sedimentary heterogeneities of the reservoir and to the differences of temperatures between irrigation waters and precipitations.
2. Cationic exchanges related to the presence of clays of Montmorillonite-Kaolinite type.

     

Gold dispersion in a tropical rainforest weathering profile at Dondo Mobi, Gabon

At Dondo Mobi in the gold district of Eteke, south Gabon, gold mineralization was studied in a tropical forest setting. The mineralization occurs in quartz veins within amphibolites of an Archaean gneiss-amphibolite series. Gold distribution patterns were studied in the different horizons of the weathering profile and in the different grain-size fractions of the materials sampled from three pits sunk in the weathered zone: upslope (pit P1), directly overlying (pit P2) and downslope (pit P3) of the mineralization.The weathering profile consists of an upper, thick, loose sandy argillaceous horizon (H1), an irregular nodular horizon with laterite nodules or blocks (H2) and a saprolite layer (H3) up to 70 m thick. In each pit, the specific geochemical signature of the bedrock is recognized in the three horizons of the weathering profile. Some groups of elements, e.g., Cr-Ni or Ba-V-P₂O₃, characterize amphibolite or black shale, respectively. Signal attenuations in the upper horizon can be explained by a homogenization effect. That can be related to a mushroom supergene dispersion, simultaneously inducing vertical decrease and lateral enrichment in element contents. Gold also mushrooms extensively in the different horizons of the weathering profile. The dispersion pattern is somewhat anisotropic, a strong enlargement being observed in the upper (H1) and intermediate nodular (H2) horizons alike. However, the evolution of Au distribution is not the same for all grain-size fractions: (a) in the finest fraction, Au is regularly distributed in the weathering profile at the anomalous top and tends to preserve an equivalent level of concentration laterally; (b) in the coarsest fraction, the maximum Au content is found in the upper horizon just above the mineralized structure; it is rapidly decreases laterally, in the surface halo.The Au geochemical dispersion halo consists mainly of fine-grained gold developed from rather coarse-grained mineralization. Its characteristics suggest that Au dispersion was produced as a result of Au dissolution together with collapse of the weathering profile causing gold migration over short distances.The minimal volumetric reduction of saprolite in the upper horizon can be estimated to be in the range of 60%, on the basis of the content of the different grain-size fractions and the density variations in the various horizons.In exploration, geochemical techniques, even using wide sample spacing, are proving quite adequate to prospect for Au in tropical rainforest weathering environment. Indeed, significant, well-contrasted dispersion haloes facilitate detection of rather confined mineralization.     

A Syringe and Cartridge Method for Down-Hole Sampling for Trace Organics in Ground Water

A newly developed technique which allows the down-hole sampling and subsequent analysis of ground water for trace organic contaminants was tested during an investigation of contaminant migration at an inactive landfill site in Burlington, Ontario, Canada. The sampling device, which is lowered down piezometers with a tube, consists of a small cylindrical cartridge of sorbent material attached to a syringe. Vacuum or pressure applied at the surface controls the movement of the plunger in the syringe. The volume of the syringe determines the volume of sample water that passes through the cartridge. The cartridge is removed from the syringe at the surface. One cartridge is used for each sampling; the syringe is reusable. The residual water in the cartridge is removed in the laboratory, and the cartridge is desorbed to a fused silica capillary column for analysis by gas chromatography (GC). The analyses discussed here were performed on a GC/mass spectrometer/data system (GC/MS/DS). Of the many organic compounds that were identified in the samples, three compounds were clearly landfill-related: 1,1,1-trichloroethane, chlorobenzene, and para-dichlorobenzene. The three compounds were found at levels substantially above blank levels in 9, 5, and 5 piezometers, respectively. The average concentrations were 14., 5.3, and 0.88μg/1 (ppb), respectively. The pooled coefficients of variation for the analyses for the three compounds were 27., 6.9, and 6.4%, respectively. The volatility of 1,1,1-trichloroethane was probably the cause of the greater variability in its analytical data. The main advantages of the technique over most conventional sampling methods include: (1) down-hole sampling in a manner which minimizes the potential for volatilization losses; (2) avoidance of passage of the sample through long sections of tubing that may contaminate the sample or cause adsorptive losses; (3) convenience of sample handling, storage, and shipping; and (4) high sensitivity.     

Coseismic and post-seismic signatures of the Sumatra 2004 December and 2005 March earthquakes in GRACE satellite gravity

The GRACE satellite mission has been measuring the Earth's gravity field and its temporal variations since 2002 April. Although these variations are mainly due to mass transfer within the geofluid envelops, they also result from mass displacements associated with phenomena including glacial isostatic adjustment and earthquakes. However, these last contributions are difficult to isolate because of the presence of noise and of geofluid signals, and because of GRACE's coarse spatial resolution (>400 km half-wavelength). In this paper, we show that a wavelet analysis on the sphere helps to retrieve earthquake signatures from GRACE geoid products. Using a wavelet analysis of GRACE geoids products, we show that the geoid variations caused by the 2004 December ( M _w= 9.2) and 2005 March ( M _w= 8.7) Sumatra earthquakes can be detected. At GRACE resolution, the 2004 December earthquake produced a strong coseismic decrease of the gravity field in the Andaman Sea, followed by relaxation in the area affected by both the Andaman 2004 and the Nias 2005 earthquakes. We find two characteristic timescales for the relaxation, with a fast variation occurring in the vicinity of the Central Andaman ridge. We discuss our coseismic observations in terms of density changes of crustal and upper-mantle rocks, and of the vertical displacements in the Andaman Sea. We interpret the post-seismic signal in terms of the viscoelastic response of the Earth's mantle. The transient component of the relaxation may indicate the presence of hot, viscous material beneath the active Central Andaman Basin.     

XMCD at Fe L<Subscript>2,3</Subscript> edges,Fe and S K edges on Fe<Subscript>7</Subscript>S<Subscript>8</Subscript>

Pyrrhotite (Fe₇S₈) is a natural iron sulphide that can participate in rock magnetisation. Its electronic structure is not yet surely described. X-ray magnetic circular dichroism (XMCD) at Fe L_2,3 edges on Fe₇S₈, coupled with multiplet calculations, shows that iron is present only as Fe²⁺ in this magnetic iron sulphide. It reveals a strong magnetic orbital moment. XMCD at Fe and S K edges shows the quite strong polarization of both Fe and S in Fe₇S₈.     

The junction of Fensch and Moselle rivers,France; mineralogy and composition of river materials

The Moselle river flows in the north-east of France, from Vosges Mountains to neighboring countries Luxembourg and Germany. One of its tributaries, the Fensch river, drains a highly industrialized watershed, strongly impacted by mining, smelting and surfacing activities. The objective of this work, part of a general research program on Moselle watershed (Zone Atelier Moselle) was to assess the impact of the polluted Fensch river on the global quality of the Moselle river. For that purpose, water, sediments and suspended particulate matter were sampled in both rivers, upstream and downstream the junction. Four main sampling campaigns were carried out, in winter during a flood event and in spring at low water level. On a first step, mineralogical analyses (XRD and FTIR) and chemical analyses (ICP-MS, ICP-AES), were performed on sediments, suspended particulate matters and filtered waters. Major and trace elements concentrations were obtained on two different granulometric fractions (0–2 mm and 0–50 μm) revealing the enrichment in heavy metals of fine particles. From one collecting campaign to another, seasonal variations could be evidenced on suspended matter composition even though major minerals (calcite, quartz and kaolinite) were always present. Furthermore, spatial variations were evidenced for Fensch and Moselle downstream sediments. Thus, very fine-grained sediments, poorly crystallized, displaying at the same time higher metal concentrations and higher organic matter content than in Fensch river material, were collected downstream, in a low hydrodynamic conditions zone, assumed as a preferential sedimentary zone or even as a placer. Strong correlations could be revealed between iron content and contaminant concentrations, confirming the origin of polluted material.