Origin of Ca in South Indian calcretes developed on metamorphic rocks

Calcrete profiles developed on Precambrian silicate rocks in south peninsular India are studied and compared in terms of mineralogical, chemical and isotopic composition. The aim of this study is to determine the origin of calcium and the processes governing the development of a minor economic deposit in different geomorphic settings. The investigation integrates observations from an outcrop to a microfabric scale and reveals that the origin of calcium is local and linked with the weathering of the minerals of the surrounding rocks. The CaCO₃ precipitation occurs after vertical and lateral translocation in the slope system.     

Anthropogenic Pb accumulation in forest soils from Lake Clair watershed: Duchesnay experimental forest (Québec, Canada)

Mineral soil horizons (Ae, Bhf1, Bhf2, Bf, BC and C) were carefully collected from two podzolic soil profiles in the Lake Clair watershed (Québec) in order to assess anthropogenic trace metal accumulation. Petrographic and selective analyses were performed to establish the soil mineralogy and properties. Furthermore, a complete sequential extraction procedure has been applied to help understanding the complex chemical speciation of Pb in forest soils. Chemical speciation of Pb showed a strong vertical gradient: 85% of this metal is mainly partitioned in refractory minerals in the C-horizon whereas in the upper Bhf1 and Ae-horizons, less than 50% of Pb is associated with this fraction. In the Ae-horizon, for example, 35%, 30% and 12% of total Pb, respectively, is associated with the exchangeable, labile organic matter and amorphous Fe-Mn oxides fractions. The distribution of Pb and Cr in the studied forest soils mainly reflects progressive contamination of the watershed by anthropogenic atmospheric sources. The anthropogenic source is indicated by elevated Cr and Pb concentrations in the topsoil (Bhf and Ae) horizons and by strong negative correlation between ²⁰⁶Pb/²⁰⁷Pb ratios and total Pb concentrations. According to these isotopic values, penetration of anthropogenic Pb does not exceed 10 cm in both soil profiles. Below this depth, both Pb concentrations and isotopic ratios remain nearly constant and similar to values observed in pre-anthropogenic sediments from Lake Clair. These values are interpreted as the natural geochemical backgrounds of the watershed. Based on that behaviour, calculated anthropogenic Pb net inputs amounted to between 1.24 and 1.8 g/m².     

Real-time forecasting of water table depth and soil moisture profiles

We present a method for real-time forecasting of water table depth and soil moisture profiles. The method combines a simple form of data-assimilation with a moving window calibration of a deterministic model describing flow in the unsaturated zone and local as well as regional drainage. The local drainage level is calibrated on-line using a moving window calibration. Assigning more weight to the last available measurements then yields a form of model adaptation that is in between on-line calibration and data-assimilation (i.e. a simplified form of Newtonian nudging). Five-day hydrological forecasts are performed based on 5-day weather forecasts, while on-line observations of phreatic level and soil moisture content are assimilated on a daily basis. Advantages of the proposed method are that it improves the real-time forecasts compared to off-line calibration and ordinary moving window calibration and that it yields physically consistent soil moisture profiles.     

On the effects of petrographic composition on coalbed methane sorption

The effect of petrographic composition on the methane sorption capacity has been determined for a suite of coals and organic-rich shales. Subbituminous and bituminous coals were separated into bright and dull lithotypes by hand-picking. The methane sorption capacities range between 0.5 and 23.9 cm³/g at a pressure of 6 MPa. The low volatile bituminous Canmore coal and the anthracite sample have the highest capacities with the “natural coke” having the lowest. For low-rank coals there is no significant difference between bright and dull samples except for one coal with the dull sample having a greater sorption capacity than its bright equivalent. For higher-rank coals, the bright samples have a greater methane capacity than the dull samples and the difference between sample pairs increases with rank. The boghead coal samples have the highest sorption capacities in the liptinite-rich coals suite and are higher than subbituminous to medium volatile bituminous samples. Pore size distribution indicates that methane is held as solution gas in liptinite-rich coals and by physical sorption in micropores in liptinite-poor coals. These contrasting processes illustrate that liptinite-rich samples need to be independently assessed. The positive relationship between reactive inertinite content and methane sorption capacity occurs within the subbituminous to medium volatile bituminous coals because the reactive inertinite is structurally similar to vitrinite and have a higher microporosity than non-reactive inertinite. Reactivity of inertinite should be assessed in CBM studies of dull coals to provide a better understanding of petrographic composition effects on methane capacity.     

Interaction of tectonics, eustasy, climate and carbonate production on the sedimentary evolution of an early/middle Jurassic extensional basin (Southern Provence Sub-basin, SE France)

This paper describes the evolution of an extensional basin in regard to the nature and sequence stratigraphic arrangement of its carbonate deposits. The purpose of this study is to evaluate the respective effects of tectonism, eustasy, climate and oceanography on a carbonate sedimentary record. The case study is the early to mid‐Jurassic age carbonate succession of the Southern Provence Sub‐basin (SE France), located within the southern part of the extensional Western European Tethyan Margin. This work is based on sedimentologic, biostratigraphic (using ammonites and brachiopods) and sequence stratigraphic analysis of the carbonate facies of the Cherty Reddish Limestone Formation (late Sinemurian to earliest Bajocian). These strata were deposited in shoreface to lower offshore depositional environments. The succession of the various environments together with the recognition of key stratigraphic surfaces allow us to define four second‐order depositional sequences; of late Sinemurian to earliest Pliensbachian, early Pliensbachian to late Pliensbachian, earliest Toarcian to middle Aalenian and late Aalenian to early Bathonian ages. The architecture of the depositional sequences (thickness and facies variations within the systems tracts, wedge‐shaped geometries) reflects a strong tectonic control. The sub‐basin was structured by extensional faults (oriented approximately 070–090/250–270). Sea‐level variations, fluctuations in carbonate production and preservation, and environmental changes were also significant controlling factors of the carbonate deposition. The interplay of the tectonic control with the other factors resulted in five main phases in the sedimentary evolution of the sub‐basin: (1) dominant tectonic control during the initial rifting stage (late Sinemurian to early Pliensbachian); (2) increasing extensional tectonics (mid‐Pliensbachian); (3) global climato‐eustatic sea‐level fall (latest Pliensbachian) and global climato‐eustatic sea‐level rise plus hypoxia/anoxia (early Toarcian); (4) relative sea‐level fall linked to tectonic uplift related to the ‘Mid‐Cimmerian phase’ (mid‐Aalenian) and (5) oceanographic events (upwelling) and reduction in carbonate production (hypoxia/anoxia) plus tectonic downwarping (late Aalenian/earliest Bajocian).     

Remote sensing and GIS for mapping groundwater recharge and discharge areas in salinity prone catchments,southeastern Australia

Identifying groundwater recharge and discharge areas across catchments is critical for implementing effective strategies for salinity mitigation, surface-water and groundwater resource management, and ecosystem protection. In this study, a synergistic approach has been developed, which applies a combination of remote sensing and geographic information system (GIS) techniques to map groundwater recharge and discharge areas. This approach is applied to an unconfined basalt aquifer, in a salinity and drought prone region of southeastern Australia. The basalt aquifer covers ~11,500 km² in an agriculturally intensive region. A review of local hydrogeological processes allowed a series of surface and subsurface indicators of groundwater recharge and discharge areas to be established. Various remote sensing and GIS techniques were then used to map these surface indicators including: terrain analysis, monitoring of vegetation activity, and mapping of infiltration capacity. All regions where groundwater is not discharging to the surface were considered potential recharge areas. This approach, applied systematically across a catchment, provides a framework for mapping recharge and discharge areas. A key component in assigning surface and subsurface indicators is the relevance to the dominant recharge and discharge processes occurring and the use of appropriate remote sensing and GIS techniques with the capacity to identify these processes.

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Résumé Sur un bassin versant, l’identification des zones d’alimentation et des aires d’émergence des eaux souterraines est capitale pour mettre en œuvre des stratégies de réduction de la salinité, de gestion des eaux souterraines et superficielles, et de protection des écosystèmes. Une approche synergique a été développée, sur la base de recherches existantes pour cartographier de manière systématique les zones de recharge et d'émergence. Elle combine des techniques de télédétection et de Systèmes d’Information Géographique, dans le but de cartographier les zones d’alimentation et d’émergence. Ces techniques ont été appliquées à un aquifère basaltique libre, dans un secteur sujet à la sécheresse et à la salinité du Sud-Est australien. L’aquifère considéré couvre environ 11,500 km² d’une région essentiellement agricole. Un inventaire des processus hydrogéologiques locaux a conduit à l’établissement d’une série d’indicateurs superficiels et subsuperficiels des zones d’alimentation et d’émergence. Plusieurs méthodes de télédétection et de SIG furent alors utilisées pour cartographier ces indicateurs de surface, y compris les analyses de terrain, le suivi de l’activité de la végétation et la cartographie des capacités d’infiltration. Toutes les régions en dehors des zones d'émergence sont considérées commes des zones d'alimentation potentielles. Un des composants clés de l’attribution des indicateurs superficiels et subsuperficiels est la concordance avec les processus majeurs d’alimentation et de prélèvement entrant en jeu, et l’utilisation de méthodes de télédétection et SIG adaptées permettant d’identifier ces processus.

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Resumen La identificación de áreas de descarga y recarga de agua subterránea es crítica para la implementación de estrategias efectivas relacionadas con mitigación de salinidad, gestión de recursos de agua subterránea y agua superficial, y protección de ecosistemas. En este estudio se ha desarrollado un enfoque sinérgico apoyándose en investigación existente el cual aplica una combinación de técnicas de sistemas de información geográfico (SIG) y sensores remotos para cartografiar áreas de recarga y descarga de agua subterránea. Este enfoque se aplica a un acuífero de basalto no confinado en una región del sureste de Australia propensa a sequía y salinidad. El acuífero de basalto cubre aproximadamente 11,500 km² en una región con agricultura intensiva. Una revisión de los procesos hidrogeológicos locales permitió el establecimiento de una serie de indicadores superficiales y subterráneos de áreas de recarga y descarga de agua subterránea. Luego se utilizaron varias técnicas de SIG y sensores remotos para cartografiar estos indicadores superficiales incluyendo: análisis del terreno, monitoreo de la actividad de la vegetación, y cartografiado de la capacidad de infiltración. Todas las regiones donde el agua subterránea no descarga en la superficie fueron consideradas áreas potenciales de recarga. Este enfoque que se ha aplicado sistemáticamente a través de la cuenca aporta un marco para la cartografía de áreas de recarga y descarga. Un componente clave en la asignación de indicadores superficiales y subterráneos lo constituye la relevancia a los procesos dominantes de recarga y descarga que ocurren y el uso de técnicas apropiadas de SIG y sensores remotos con la capacidad para identificar esos procesos.

     

Impact of slate quarrying on soil properties in semi-arid Mahendragarh in India

Slate quarrying in Mahendragarh district of Haryana state has resulted in changes in soil properties. Most of the mining area is devoid of vegetation. The soil in and around the mining area (0–1 km) is alkaline (pH 11.2–11.7) but non-saline (electrical conductivity < 4). The alkaline nature of the soil was attributed to the high concentrations of hydroxyl (OH⁻), carbonate (CO₃²⁻) and bicarbonate (HCO₃ ⁻) present in minerals of mined materials. Biotite, limonite, kaolinite, gibbsite, muscovite, geothite, dolomite and so on were the chief minerals added to soil through mining. The physical properties of soil, i.e. porosity, water-holding capacity (WHC), bulk density and particle density represented poor soil health in mining area (34.4, 29.8%, 1.636, 2.496 g/cc, respectively) and they improved with distance away from it (46.4, 38.3%, 1.070, 2.180 g/cc, respectively, at a distance of 1 km). Porosity and WHC were found to be a function of increased organic matter away from the mining area. CO₃²⁻, HCO₃⁻, phosphate (PO₄³⁻), lead (Pb) and iron (Fe) were more in mining area and decreased with distance. On the other hand, sodium (Na⁺), potassium (K⁺), chloride (Cl⁻), sulphate (SO₄²⁻), organic carbon, total Kjeldahl’s nitrogen, cation exchange capacity, chromium (Cr) and cadmium (Cd) increased with distance from mining area. High concentration of heavy metals in mining area was a cause of concern (0.93 μg/g Cd, 22.35 μg/g Cr, 26.25 μg/g Pb, 1,383.75 μg/g Fe). The change in physico-chemical properties could be because of the addition of chemical constituents that are a part of major minerals present in mined material. The soil away from mining area represented comparatively better properties.     

A modified iterative sandwich method for determination of near-solidus partial melt compositions. I. Theoretical considerations

The sandwich technique for determining the composition of partial melts in equilibrium with mantle lithologies may be a particularly powerful method for determining melt compositions at the onset of melting if the method is applied iteratively. However, conventional iterative sandwich experiments, in which the liquid from a preceding experiment is used as the “meat” of the sandwich in the following experiment, may require many iterations before the melts produced can be directly relatable to the melting relations of the target bulk rock composition. A modified iterative sandwich experimental (MISE) technique is proposed that may circumvent many of the problems of more conventional techniques. Consideration of experimental uncertainties, including both random and systematic errors in determination of partial melt compositions as well as the influence of errors in estimates of the solidus temperature of the rock of interest, suggests that the MISE technique may produce robust results even when melt composition errors are significant and that errors in estimation of the solidus location are detectable and therefore avoidable.