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  • 1
    Electronic Resource
    Electronic Resource
    Mössbauer and molecular orbital study of chlorites (2000)
    Springer
    Physics and chemistry of minerals 27 (2000), S. 258-269 
    Details
    ISSN: 1432-2021
    Keywords: Key words Chlorites ; Iron lattice sites ; Mössbauer spectroscopy ; Molecular orbital calculations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract  The different Fe2+ lattice sites in iron-rich chlorites have been characterized by Mössbauer spectroscopy and molecular orbital calculations in local density approximation. The Mössbauer measurements were recorded at 77 K within a small velocity range (±3.5 mm s−1) to provide high energy resolution. Additionally, measurements were recorded in a wider velocity range (±10.5 mm s−1) at temperatures of 140, 200, and 250 K in an applied field (7 T) parallel to the γ-beam. The zero-field spectra were analyzed with discrete Lorentzian-shaped quadrupole doublets to account for the Fe2+ sites M1, M2, and M3 and with a quadrupole distribution for Fe3+ sites. Such a procedure is justified by the results obtained from MO calculations, which reveal that different anion (OH−) distributions in the first coordination sphere of M1, M2, and M3 positions have more influence on the Fe2+ quadrupole splitting than cationic disorder. The spectra recorded in applied field were analyzed in the spin-Hamiltonian approximation, yielding a negative sign for the electric field gradient (efg) of Fe2+ in the M1, M2, and M3 positions. The results of the MO calculations are in quantitative agreement with experiment and reveal that differences in the quadrupole splittings (ΔE Q ), their temperature dependence and in the isomer shifts (δ) of Fe2+ in M1, M2, and M3 positions can theoretically by justified. Therefore, the combined Mössbauer and MO investigation shows that the three Fe2+ lattice sites in the chlorites investigated here can be discriminated according to their ΔE Q -δ parameter pairs. With the calculated average iron-oxygen bond strength, the MO study provides an explanation for the observed trend that the population of the three lattice sites by Fe2+ increases according to the relation M1 〈 M2 〈 M3.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002690050255
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Studies of iron in deep-sea sediments by Mössbauer spectroscopy (1998)
    Springer
    Hyperfine interactions 117 (1998), S. 383-403 
    Details
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The distribution of the forms of Fe in the solid phases in core samples of sediments from the Peru Basin has been investigated by Mössbauer spectroscopy with special attention to the cause of the sharp color transition between an upper green colored and a lower tan colored part. An important part of sample handling includes strict exclusion of oxygen during preparation of absorbers and measurements at cryogenic temperatures. The measurement strategy includes measurements between 77 K and 300 mK in zero external magnetic field, supplemented by measurements in external magnetic fields at 4.2 and 300 mK (up to 6.2 and 1 T, respectively). The temperature scans allow detection, identification and quantification of superparamagnetic iron oxides (goethite and hematite). The oxides are only present in samples from the upper tan-colored part of the core. The major part of the Fe(II) and Fe(III) (〉80%) is present in a magnetic structure similar to that of layer silicates. The relative Fe(II) content of the layer silicates is practically identical to that determined from the paramagnetic components measured at liquid nitrogen temperature. This shows that the color transition in the sediment coincides with a change in the relative Fe(II) content in layer silicates from 11 to 37%. The color change can thus be explained by an increase in occurrence of Fe(II)–Fe(III) pairs exhibiting absorption bands due to intervalence electron transfer.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1012678907127
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  • 3
    Electronic Resource
    Electronic Resource
    Mössbauer, magnetic, X‐ray fluorescence and transmission electron microscopy study of natural magnetic materials from speleothems: haematite and the Morin transition (2000)
    Springer
    Hyperfine interactions 128 (2000), S. 353-373 
    Details
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Detrital magnetic materials within cave stalagmitic formations, e.g., haematite or magnetite, carry remanence whose vector is of value in dating. Magnetometry measurements on a particular haematite‐bearing sample reveal that remanence was substantially restored and/or conserved on rewarming after cooling below the Morin transition temperature. Mössbauer measurements indicate the presence of two types of haematite, distinguished primarily by particle size. The majority is small in size, partially exhibiting superparamagnetism, and does not undergo a Morin transition above liquid nitrogen temperature. Superparamagnetic goethite is the second major component. Mine haematite samples of surface location with different color and mineralogical composition have also been studied. Possible relations between the mineralogical composition of the mine samples and detrital stalagmitic magnetic material, the modifications and the origin of this mineralization are discussed. Special attention is paid to the “irreversible” Morin transition in large enough (〉20 nm) haematite particles and the possible loss of natural remanent magnetization and hence of palaeomagnetic records.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1012668623559
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  • 4
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    Mössbauer and molecular orbital study of chlorites (2000)
    Springer
    Details
    Publication Date: 2000-03-21
    Print ISSN: 0342-1791
    Electronic ISSN: 1432-2021
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Published by Springer
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    PAPER CURRENT
  • 5
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    Iron oxidation in sediment cores (Site 1062) during six months of storage in the Ocean Drilling Program archive (2000)
    In:  Proceedings of the Ocean Drilling Program: Scientific Results, 172 . Chapter 2.
    Details
    Publication Date: 2017-07-27
    Description: Changes in bulk sediment Fe(II)/Fe(III) ratio and in the distribution of iron among different minerals as a result of Ocean Drilling Program archive storage in the Bremen Core Repository were investigated using Mössbauer spectroscopy. Massive Fe(II) to Fe(III) oxidation, which involved between 24% and 45% of the initial Fe(II), occurred within only 6 months of refrigerated storage. Prior to archive storage, 〉95% of the Fe(II) in the sediment samples under investigation was structural iron in silicate minerals. Hence, virtually the entire oxidation process took place within silicate mineral lattices, and the sediment mineral assemblage was not changed in this case. Nevertheless, the observed oxidation of the comparatively shielded silicate lattice Fe(II) suggests that Fe(II) bound in authigenic carbonates, phosphates, or sulfides—such as that found in many marine sediments—would likely be oxidized at least as fast. Those minerals, however, would be replaced by Fe(III)-bearing oxides and oxyhydroxides, which implies a change of sediment composition, and thus, of various sediment properties, including the magnetic signal, within a few months of storage. Furthermore, changes in the silicate lattice Fe(II)/Fe(III) ratio during storage, such as those reported here, also signify loss of information. This is because oxidation of the structural Fe(II) upon contact with atmospheric oxygen may occur only inasmuch as the inverse Fe(III)–Fe(II) redox transition has taken place in the seabed. Therefore, the reversible shift, if it were measured under controlled reoxidation in the laboratory, may suggest the chemical stress that was suffered by the iron oxide minerals at the ocean bottom. Concerning Site 1062, this process might help to judge both the authenticity of magnetic field excursion records and the lithostratigraphic value of red lutites at given sediment depths. Although the nature and extent of information loss or alteration during storage depend on sediment type, the reported observations emphasize the need for special sample protection with respect to properties that might be affected.
    Type: Article , NonPeerReviewed
    Format: text
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    PAPER (OCEANREP)
  • 6
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    A geochemical model of the Peru Basin deep-sea floor and the response of the system to technical impacts (2001)
    Pergamon Press
    In:  Deep Sea Research Part II: Topical Studies in Oceanography, 48 . pp. 3737-3756.
    Details
    Publication Date: 2020-08-05
    Description: A geochemical model of the Peru Basin deep-sea floor, based on an extensive set of field data as well as on numerical simulations, is presented. The model takes into account the vertical oscillations of the redox zonation that occur in response to both long-term (glacial/interglacial) and short-term (El Niño Southern Oscillation (ENSO) time scale) variations in the depositional flux of organic matter. Field evidence of reaction between the pore water NO3− and an oxidizable fraction of the structural Fe(II) in the clay mineral content of the deep-sea sediments is provided. The conditions of formation and destruction of reactive clay Fe(II) layers in the sea floor are defined, whereby a new paleo-redox proxy is established. Transitional NO3− profile shapes are explained by periodic contractions and expansions of the oxic zone (ocean bottom respiration) on the ENSO time scale. The near-surface oscillations of the oxic–suboxic boundary constitute a redox pump mechanism of major importance with respect to diagenetic trace metal enrichments and manganese nodule formation, which may account for the particularly high nodule growth rates in this ocean basin. These conditions are due to the similar depth ranges of both the O2 penetration in the sea floor and the bioturbated high reactivity surface layer (HRSL), all against the background of ENSO-related large variations in depositional Corg flux. Removal of the HRSL in the course of deep-sea mining would result in a massive expansion of the oxic surface layer and, thus, the shut down of the near-surface redox pump for centuries, which is demonstrated by numerical modeling.
    Type: Article , PeerReviewed
    Format: text
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    PAPER (OCEANREP)
  • 7
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    (Table T1-2) Proportion of ferrous and ferric iron in ODP Hole 172-1062A sediments (2000)
    PANGAEA
    In:  Supplement to: König, Iris; Lougear, A; Bruns, P; Gruetzner, Jens; Trautwein, Alfred X; Dullo, Wolf-Christian (2000): Iron oxidation in sediment cores (Site 1062) during six months of storage in the Ocean Drilling Program archive. In: Keigwin, LD; Rio, D; Acton, GD; Arnold, E (eds.) Proceedings of the Ocean Drilling Program, Scientific Results, College Station, TX (Ocean Drilling Program), 172, 1-11, https://doi.org/10.2973/odp.proc.sr.172.214.2000
    Details
    Publication Date: 2024-01-09
    Description: Changes in bulk sediment Fe(II)/Fe(III) ratio and in the distribution of iron among different minerals as a result of Ocean Drilling Program archive storage in the Bremen Core Repository were investigated using Mössbauer spectroscopy. Massive Fe(II) to Fe(III) oxidation, which involved between 24% and 45% of the initial Fe(II), occurred within only 6 months of refrigerated storage. Prior to archive storage, 〉95% of the Fe(II) in the sediment samples under investigation was structural iron in silicate minerals. Hence, virtually the entire oxidation process took place within silicate mineral lattices, and the sediment mineral assemblage was not changed in this case. Nevertheless, the observed oxidation of the comparatively shielded silicate lattice Fe(II) suggests that Fe(II) bound in authigenic carbonates, phosphates, or sulfides - such as that found in many marine sediments - would likely be oxidized at least as fast. Those minerals, however, would be replaced by Fe(III)-bearing oxides and oxyhydroxides, which implies a change of sediment composition, and thus, of various sediment properties, including the magnetic signal, within a few months of storage. Furthermore, changes in the silicate lattice Fe(II)/Fe(III) ratio during storage, such as those reported here, also signify loss of information. This is because oxidation of the structural Fe(II) upon contact with atmospheric oxygen may occur only inasmuch as the inverse Fe(III)-Fe(II) redox transition has taken place in the seabed. Therefore, the reversible shift, if it were measured under controlled reoxidation in the laboratory, may suggest the chemical stress that was suffered by the iron oxide minerals at the ocean bottom. Concerning Site 1062, this process might help to judge both the authenticity of magnetic field excursion records and the lithostratigraphic value of red lutites at given sediment depths. Although the nature and extent of information loss or alteration during storage depend on sediment type, the reported observations emphasize the need for special sample protection with respect to properties that might be affected.
    Keywords: 172-1062A; Age model; Blake-Bahama Outer Ridge, North Atlantic Ocean; DEPTH, sediment/rock; DRILL; Drilling/drill rig; DSDP/ODP/IODP sample designation; Iron II, ferrous iron; Iron III, ferric iron; Joides Resolution; Leg172; Ocean Drilling Program; ODP; Sample code/label; Sample comment
    Type: Dataset
    Format: text/tab-separated-values, 144 data points
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    DATA PANGAEA
  • 8
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    Iron oxidation in sediment cores (Site 1062) during six months of storage in the Ocean Drilling Program archive (2000)
    In:  EPIC3In Keigwin, L.D., Rio, D., Acton, G.D, and Arnold, E. (Eds.), Proc. ODP, Sci. Results, 172, pp. 1-11
    Details
    Publication Date: 2019-07-17
    Repository Name: EPIC Alfred Wegener Institut
    Type: Inbook , peerRev
    Format: application/pdf
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    PAPER (OA)
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