Examinando por Materia "geochemistry"

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    Distribución de Allanita en el Stock de Mariquita y su posible origen
    (Universidad EAFIT, 2022) Romero Muñoz, Katherin; Bustamante Londoño, Camilo
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    Do geochemical estimates of sediment focusing pass the sediment test in the equatorial Pacific?
    (AMER GEOPHYSICAL UNION, 2005-01-28) Lyle, M; Mitchell, N; Pisias, N; Mix, A; Martinez, JI; Paytan, A; Universidad EAFIT. Departamento de Geología; Ciencias del Mar
    The paleoceanographic recording fidelity of pelagic sediments is limited by chemical diagenesis and physical mixing (bioturbation and horizontal sediment transport). Diagenesis and bioturbation are relatively well-studied, but the effects of physical sedimentation have been largely ignored. Modeling U series isotopes (e.g., 230Th) can potentially quantify horizontal sediment movement, but model horizontal sediment focusing often equals or exceeds the vertical particle rain. We find no evidence of this level of sediment focusing in the equatorial Pacific from geophysical data or sediment core comparisons. The overestimate of sediment focusing by 230Th is probably caused by poor model assumptions: that sediment does not fractionate (does not sort according to size during transport) and that 230Th cannot leak from slowly accumulating sediments. Both assumptions are weak. U series methods do hold promise to quantify sediment focusing if properly calibrated. With calibration the trade-offs between seeking high sedimentation rates for better time resolution and the blurring by horizontal sediment focusing can be better assessed. Copyright 2005 by the American Geophysical Union.
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    Magnetic biomonitoring as a tool for assessment of air pollution patterns in a tropical valley using Tillandsia sp.
    (MDPI AG, 2018-07-01) Mejía-Echeverry, D.; Chaparro, M.A.E.; Duque-Trujillo, J.F.; Chaparro, M.A.E.; Miranda, A.G.C.; Mejía-Echeverry, D.; Chaparro, M.A.E.; Duque-Trujillo, J.F.; Chaparro, M.A.E.; Miranda, A.G.C.; Universidad EAFIT. Departamento de Ciencias; Geología Ambiental y Tectónica
    Recently, air pollution alerts were issued in the Metropolitan Area of Aburrá Valley (AVMA) due to the highest recorded levels of particulate matter (PM2.5 and PM10) ever measured. We propose a novel methodology based on magnetic parameters and an epiphytic biomonitor of air pollution in order to improve the air pollution monitoring network at low cost. This methodology relies on environmental magnetism along with chemical methods on 185 Tillandsia recurvata specimens collected along the valley (290 km2). The highest magnetic particle concentrations were found at the bottom of the valley, where most human activities are concentrated. Mass-specific magnetic susceptibility (?) reaches mean (and s.d.) values of 93.5 (81.0) and 100.8 (64.9) × 10-8 m3 kg-1 in areas with high vehicular traffic and industrial activity, while lower ? values of 27.3 (21.0) × 10-8 m3 kg-1 were found at residential areas. Most magnetite particles are breathable in size (0.2-5 µm), and can host potentially toxic elements. The calculated pollution load index (PLI, based on potentially toxic elements) shows significant correlations with the concentration-dependent magnetic parameters (R = 0.88-0.93; p < 0.01), allowing us to validate the magnetic biomonitoring methodology in high-precipitation tropical cities and identify the most polluted areas in the AVMA. © 2018 by the authors.