Browsing by Author "Bilardello, Dario"
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Item Data for "Late Paleozoic depositional environments and sediment transport directions of the Itararé Group rocks from the state of São Paulo, Brazil, determined from rock magnetism and magnetic anisotropy" collected at the University of Sao Paulo and the University of Minnesota between 2012 and 2020.(2020-12-22) Bilardello, Dario; dario@umn.edu; Bilardello, Dario; University of Minnesota Institute for Rock MagnetismItem Data for "Simulation of natural alteration of iron oxides in soil: conversion of synthetic ferrihydrite to hematite without artificial dopants, observed with magnetic methods" collected at the University of Minnesota between 2016 and 2020(2020-03-12) Bilardello, Dario; Banerjee, Subir K; Volk, Michael; Soltis, Jennifer A; Penn, R. Lee; dario@umn.edu; Bilardello, Dario; University of Minnesota Institute for Rock MagnetismWe present the results of a new study on the conversion of pure, undoped synthetic ferrihydrite, wet-annealed at pH 6.56 and 90 ℃ without stabilizing ligands, to nanophase goethite, hematite and an intermediate magnetic phase, likely to be nanophase maghemite. Our analysis included magnetic field and temperature dependent properties and characterization by powder x-ray diffraction, Mössbauer spectra and high-resolution transmission electron microscopy. Unlike most other studies of ferrihydrite alteration we sampled alteration products after 0.5 hours, and then in a geometric progression to 32 hours, yielding an extremely detailed examination of the earliest alteration phases. There are many similarities to the latest studies of pure ferrihydrite alteration but with a significant difference: we observe very early appearance of oriented nanophase goethite along with a soft magnetic contribution, while rhombohedral hematite crystals are formed later, as reported in the previous studies. Our observations attest to the non-uniqueness of the magnetic enhancement process and to its strong dependence on environmental conditions, with important implications for the proposed hematite/goethite ratio as a reliable proxy for paleoprecipitation intensity.Item Estimating the abundance of iron sulfide minerals in Minnesota freshwater sediments in relation to pore water and sediment chemistry and wild rice growth(2013-10) Cheah, Darren; Myrbo, Amy; Bilardello, Dario; Feinberg, JoshuaEmpirical observations of growth of wild rice (Zizania sp.) in wetlands, lakes, and rivers appear to indicate that higher sulfate concentrations lead to a growth deficiency in wild rice. Many growth locations of wild rice in Northern Minnesota freshwater systems have been affected by sulfate leakage, and are within the vicinity of the Mesabi and Cuyuna Iron Ranges (historic and current iron mining) and the Duluth Complex (proposed copper and nickel mining). The dissolved sulfate is reduced to sulfide by microbes in the sediment, and may be sequestered as iron sulfide minerals (e.g., greigite, Fe3S4, and pyrite, FeS2). These minerals are likely to be concentrated where iron is common in local terrestrial geology; pore water pH, as well as organic matter and water content of bottom sediments, are probably also significant. Samples were collected from over 100 research sites spread widely across Minnesota, including water bodies that are naturally high and low in sulfate and iron, as well as water bodies that display recent sulfate increases due to local mine drainage. Petrographic microscopy was used to identify and qualitatively estimate pyrite abundance, while scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS) was employed to determine sediment mineralogy at high magnification. Environmental magnetic analyses were conducted on samples selected based on qualitative abundance of pyrite. Preliminary results reveal that samples associated with mining drainage have elevated magnetic grain concentrations with a larger proportion of high-coercivity minerals (e.g., hematite, Fe2O3, and goethite, FeO(OH)) than those from non-mining sites. These minerals are common products of acid mine drainage, and are formed as Fe-bearing silicate minerals are hydrolyzed during acid leaching. The grain size distributions of magnetic minerals were similar for mining and non-mining sites, although lake samples with higher sulfate concentrations appear to correlate with coarser magnetic minerals. Results from this investigation and previously determined chemical analyses data were statistically compared through simple regression analysis, correlation matrix analysis, and Pearson correlation coefficient calculations.Item Evidence for widespread Remagnetizations in South America, case study of the Itararé Group rocks of Brazil(2019-06) Bilardello, Dario; Callebert, William, C; Davis, Joshua, RPaleomagnetism of South American Jurassic/Cretaceous rocks has been troubled by elongated distributions of poles which has led to contrasting interpretations. Moreover, many discordant paleomagnetic poles from the Carboniferous to the Triassic have also been recognized and systematically explained by a variety of processes, but this portion of the South American apparent polar wonder path (APWP) still remains problematic. We have conducted a paleomagnetic study of the sedimentary Permo-Carboniferous Itararé Group rocks and three intruding mafic sills of likely Cretaceous age within the state of São Paulo, Brazil. The site-mean VGP distributions obtained from the sedimentary rocks define elongations that include the VGPs of the mafic intrusions. We interpret these distributions as remagnetization paths toward the directions characteristic of the sills. Careful analysis of the paleomagnetic data of the Itararé sedimentary rocks enables isolation of a primary VGP distribution that is consistent with the reference Carboniferous pole position. The paleomagnetic directions of the sills are partially overprinted by the present time averaged and current Earth’s magnetic field. Combined rock- and paleomagnetic data suggest that interacting SD grains carry a very recent magnetic overprint that is visco-chemical in origin and cannot be fully erased. The dominant distribution of PSD-MD grains carries the high-temperature component, which is either a primary magnetization coincidentally close to the time averaged dipole field direction, or a secondary thermo-viscous magnetization. Extending our study to other Carboniferous to Triassic South American paleomagnetic records reveals that the majority of these data are elongated, similarly to the Itararé Group rocks. Regardless of the age of the rocks, the elongations systematically intersect at the location of the Late Cretaceous reference pole, and at a long- recognized problematic location (“X”) observed in certain Jurassic and Cretaceous rock formations. We interpret the elongated VGP distributions to reflect remagnetizations from the primary VGP positions toward Jurassic-Cretaceous and “X” pole locations, which occurred as a result of the widespread magmatic events associated with the opening of the South Atlantic. The extent of the remagnetizations is formation-specific and other rock-formations should be carefully re-evaluated.Item IRM Quarterly, Volume 23, Number 1 (Spring 2013). Cover article: The Second Summer School for Rock Magnetism Held at the IRM(University of Minnesota. Institute for Rock Magnetism, 2013) Bilardello, DarioItem IRM Quarterly, Volume 23, Number 2 (Summer 2013). Cover article: Some Like it Hot! A new high temperature MFM comes online at the IRM(University of Minnesota. Institute for Rock Magnetism, 2013) Bilardello, Dario; Jackson, MikeItem IRM Quarterly, Volume 23, Number 3 (Fall 2013). Cover article: What do the Mumpsies do?(University of Minnesota. Institute for Rock Magnetism, 2013) Bilardello, Dario; Jackson, MikeItem IRM Quarterly, Volume 24, Number 1 (Spring 2014). Cover article: The Tenth Santa Fe3+ Conference on Rock-Magnetism(University of Minnesota. Institute for Rock Magnetism, 2014) Bilardello, Dario; Jackson, MikeItem IRM Quarterly, Volume 24, Number 3 (Fall 2014). Cover article: A long review from a curt peer: a peek into the peer review system(University of Minnesota. Institute for Rock Magnetism, 2014) Bilardello, DarioItem IRM Quarterly, Volume 25, Number 1 (Spring 2015). Cover article: The Third Summer School for Rock Magnetism Held at the IRM(University of Minnesota. Institute for Rock Magnetism, 2015-07) Bilardello, DarioItem IRM Quarterly, Volume 25, Number 2 (Summer 2015). Cover article: One Move to Rule The Mall: Big Changes in Store for the IRM(University of Minnesota. Institute for Rock Magnetism, 2016-02) Bilardello, DarioItem IRM Quarterly, Volume 25, Number 3 (Fall 2015). Cover article: The IRM at 25: A Quarter Century of Community-Based Research and Education(University of Minnesota. Institute for Rock Magnetism, 2016-03) Moskowitz, Bruce; Banerjee, Subir; Feinberg, Joshua; Jackson, Mike; Solheid, Peat; Bilardello, DarioItem IRM Quarterly, Volume 26, Number 3 (Fall 2016). Cover article: The do's and don'ts of inclination shallowing corrections(University of Minnesota. Institute for Rock Magnetism, 2016-11) Bilardello, DarioItem IRM Quarterly, Volume 27, Number 4 (Winter 2017). Cover article: Magnetic tests and characterization protocols: mineralogy and grain size / domain state Part I: isothermal strong field tests(University of Minnesota. Institute for Rock Magnetism, 2018-02) Volk, Michael; Jackson, Mike; Bilardello, DarioItem IRM Quarterly, Volume 27, Number 2 (Summer 2017). Cover article: The New Deal- transitioning from a disordered to an ordered state(University of Minnesota. Institute for Rock Magnetism, 2017-09) Bilardello, DarioItem IRM Quarterly, Volume 28, Number 1 (Spring 2018). Cover article: The 2018 Summer School in Rock Magnetism(University of Minnesota. Institute for Rock Magnetism, 2018-06) Bilardello, DarioItem IRM Quarterly, Volume 28, Number 2 (Summer 2018). Cover article: Magnetic tests and characterization protocols: mineralogy and grain size / domain state Part II: isothermal weak field tests(University of Minnesota. Institute for Rock Magnetism, 2018-08) Volk, Michael; Bilardello, Dario; Jackson, MikeItem IRM Quarterly, Volume 28, Number 3 (Fall 2018). Cover article: Commonly used experimental parameters for acquisition of anhysteretic remanent magnetization (ARM) and its anisotropy (AARM): Results and recommendations from a rock magnetic community survey(University of Minnesota. Institute for Rock Magnetism, 2018-11) Biedermann, Andrea; Bilardello, Dario; Jackson, Mike; Chadima, Martin; Feinberg, JoshuaItem IRM Quarterly, Volume 28, Number 4 (Winter 2018-2019). Cover article: Civilized magnetist's deadly sins(University of Minnesota. Institute for Rock Magnetism, 2019-02) Bilardello, DarioItem IRM Quarterly, Volume 29, Number 1 (Spring 2019). Cover article: The 11th Santa Fe Conference on Rock Magnetism(University of Minnesota. Institute for Rock Magnetism, 2019-07) Bilardello, Dario