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  • 1
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    Apparent magnetic polarity reversals due to remagnetization resulting from late diagenetic growth of greigite from siderite (2008)
    Blackwell Publishing
    Details
    Publication Date: 2012-02-03
    Description: A mixed-polarity zone, representing alternations between remagnetized and non-remagnetized strata, has been documented within the lower few metres of the CRP-1 core (Ross Sea, Antarctica). Detailed rock magnetic investigation of this interval indicates that the normal polarity remagnetization is carried by magnetostatically interacting single-domain particles of a ferrimagnetic iron sulphide mineral, while the reversed-polarity magnetization of non-remagnetized strata is carried by magnetite with a broad range of grain sizes and negligible magnetostatic interactions. Scanning electron microscope observations of polished sections indicate that the ferrimagnetic iron sulphide mineral is greigite (Fe3S4). Based on microtextural relationships, it is not possible to determine the relative timing of formation for much of the greigite. However, a significant proportion of the greigite has grown on the surface of authigenic siderite (FeCO3) grains that occur as microconcretions and as cement surrounding detrital matrix grains. In such cases, microtextural relationships indicate that siderite post-dates early diagenetic pyrite and that greigite post-dates the siderite. Siderite usually forms in environments with abundant dissolved iron and carbonate, but without dissolved pore water H2S. This set of geochemical conditions occurs in methanic settings below the sulphate reduction zone (in which early diagenetic pyrite forms).We interpret the observed remagnetization of the lower part of the CRP-1 core as due to a late diagenetic pore water migration event where abundant iron on the surface of siderite grains reacted with fluids containing limited dissolved sulphide, thereby causing precipitation of greigite. The distribution of siderite (and associated greigite) in the lower part of the CRP-1 core is patchy, which accounts for the apparent alternation of polarities. This study is part of a growing catalogue of remagnetizations involving greigite, which suggests that occurrences of greigite should be treated with caution in palaeomagnetic and environmental magnetic studies.
    Description: Published
    Description: 89-100
    Description: 2.2. Laboratorio di paleomagnetismo
    Description: JCR Journal
    Description: reserved
    Keywords: Antarctica ; diagenesis ; greigite ; iron carbonate ; iron sulphide ; remagnetization ; siderite ; 04. Solid Earth::04.05. Geomagnetism::04.05.06. Paleomagnetism ; 04. Solid Earth::04.05. Geomagnetism::04.05.07. Rock magnetism
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 2
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    Magnetostratigraphic chronology of a late Eocene to early Miocene glacimarine succession from the Victoria Land Basin, Ross Sea, Antarctica (2008)
    Elsevier
    Details
    Publication Date: 2017-04-04
    Description: Drilling offshore from Cape Roberts, Antarctica, has enabled recovery of a 1472-m cumulative record of late Eocene–early Miocene history of sedimentary basin development and climate change in the Western Ross Sea. In this paper, we synthesize the results of palaeomagnetic analyses carried out on the CRP-1, CRP-2 and CRP-3 sediment cores, and present a chronology for the recovered Eocene–Miocene succession. Stepwise demagnetization data demonstrate that secondary overprints have been successfully removed and that characteristic remanent magnetizations (ChRMs) have been clearly identified in most of the samples. A close sampling interval has allowed a detailed magnetic polarity stratigraphy to be established for the composite succession. Correlation with the geomagnetic polarity time scale (GPTS) has been constrained by a number of 40Ar/39Ar and 87Sr/86Sr ages, as well as by a recently developed Antarctic siliceous microfossil zonation, and by calcareous nannoplankton biostratigraphy. The basal sediments of the Eocene–Miocene succession rest unconformably on Devonian sandstones of the Beacon Supergroup. A basal sandstone breccia, which probably represents the onset of rifting in the Victoria Land Basin (VLB), is overlain by a succession of sandstones that are interbedded with thin conglomerate beds. These sediments give way to more clearly glacially influenced mudstones and diamictite facies in the mid Oligocene, and, by the Oligocene–Miocene boundary, coincident with the Mi-1 glaciation, a permanent glacial dominance was imprinted on the sedimentary record. Average sediment accumulation rates were initially rapid in the late Eocene–early Oligocene (up to 60 cm/k.y.), but reduced to only a few cm/k.y. in the early Miocene as basin subsidence slowed.
    Description: Published
    Description: 207-236
    Description: 2.2. Laboratorio di paleomagnetismo
    Description: 3.8. Geofisica per l'ambiente
    Description: JCR Journal
    Description: reserved
    Keywords: Antarctica ; Cape Roberts Project ; Cenozoic ; Chronology ; Magnetostratigraphy ; 04. Solid Earth::04.05. Geomagnetism::04.05.06. Paleomagnetism
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 3
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    Paleomagnetic record of basaltic volcanism from Pukaki and Onepoto maar lake cores, Auckland Volcanic Field, New Zealand (2010)
    Royal Society of New Zealand
    Details
    Publication Date: 2017-04-04
    Description: The Auckland Volcanic Field contains several maars that formed after the last interglacial and subsequently filled with sediment. Two of these maars, Pukaki and Onepoto, were recently cored as part of the Auckland Maar Lakes Project. The tephra stratigraphy of the cores indicates that sediment accumulated relatively slowly in both maars until the Holocene when ocean waters breached the craters and they filled up quite rapidly. Using u-channels, we collected 23 m of pre-Holocene lacustrine sediment from the Pukaki 1-01 core and 15 m from the Onepoto core. Paleomagnetic measurements were performed on these at the University of California, Davis. Environmental magnetic records from both cores provide insights in particular about the eruptive history of the Auckland Volcanic Field. The lack of a tephrostratigraphic control in the lower portion of the cores, and the lack of similar trends in the magnetic parameters, prevented a complete core correlation. The main finding is that local basaltic tephra layers visible in the cores show up as spikes in the concentration dependent magnetic parameters, suggesting that other spikes represent tephra layers that are not as easily discerned.
    Description: In press
    Description: 2.2. Laboratorio di paleomagnetismo
    Description: JCR Journal
    Description: open
    Keywords: Environmental magnetism ; Pukaki ; Onepoto ; Auckland Volcanic Field ; maars ; ash deposits ; 04. Solid Earth::04.05. Geomagnetism::04.05.09. Environmental magnetism ; 04. Solid Earth::04.08. Volcanology::04.08.08. Volcanic risk
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 4
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    Geomagnetic field behavior at high latitudes from a paleomagnetic record from Eltanin core 27–21 in the Ross Sea sector, Antarctica (2008)
    Elsevier
    Details
    Publication Date: 2017-04-04
    Description: We present a high-resolution paleomagnetic record from 682 discrete samples from Eltanin 27–21 (69.03°S 179.83°E), a 16-meter long piston core recovered in 1968 at a water depth of 3456 m by the USNS Eltanin as part of Operation Deep Freeze. After removal of a low-coercivity overprint, most samples yield stable characteristic remanent magnetization directions. The downhole variation in the magnetic inclination provides a well-resolved magnetostratigraphy from the Brunhes Chron (0–0.781 Ma), through the Reunion Subchron (2.128–2.148 Ma), and into Chron C2r.2r. The sedimentation rates are sufficiently high that even short-term geomagnetic features, like the Cobb Mountain excursion, are resolved. The record from Eltanin 27–21 provides new insights into the behavior of the geomagnetic field at high latitudes, about which very little is currently known. Using the variability in the inclinations during stable polarity intervals, we estimate that the dispersion in the paleomagnetic pole position over the past ~2 Myr is 30.3°±4.3°, which is significantly greater than observed at low to mid latitude sites. The higher dispersion observed at Eltanin 27–21 is consistent with numerical modeling of the geodynamo. That modeling has shown that polar vortices can develop in the Earth's core within the tangent cylinder, defined as the cylinder coaxial with the Earth's rotation axis and tangent to the inner core/outer core boundary. The polar vortices produce vigorous fluid motion in the core, which creates greater geomagnetic field variability above the tangent cylinder at the surface of the Earth. The tangent cylinder intersects the Earth's surface in the polar regions at 79.1° latitude, which is relatively close to the latitude of Eltanin 27–21.
    Description: Published
    Description: 435-443
    Description: 2.2. Laboratorio di paleomagnetismo
    Description: JCR Journal
    Description: reserved
    Keywords: paleomagnetism ; geomagnetism ; magnetostratigraphy ; Eltanin ; Ross Sea ; Antarctica ; tangent cylinder ; geodynamo ; Cobb Mountain Subchron ; Reunion Subchron ; 04. Solid Earth::04.05. Geomagnetism::04.05.06. Paleomagnetism ; 04. Solid Earth::04.05. Geomagnetism::04.05.07. Rock magnetism
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 5
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    Environmental magnetic record of paleoclimate, unroofing of the Transantarctic Mountains, and volcanism in late Eocene to early Miocene glaci-marine sediments from the Victoria Land Basin, Ross Sea, Antarctica (2013)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: We synthesize environmental magnetic results for sediments from the Victoria Land Basin (VLB), which span a total stratigraphic thickness of 2.6 km and a ~17 Myr age range. We assess how magnetic properties record paleoclimatic, tectonic, and provenance variations or mixtures of signals resulting from these processes. The magnetic properties are dominated by large-scale magnetite concentration variations. In the late Eocene and early Oligocene, magnetite concentration variations coincide with detrital smectite concentration and crystallinity variations, which reflect paleoclimatic control on magnetic properties through influence on weathering regime; high magnetite and smectite concentrations indicate warmer and wetter climates and vice versa. During the early Oligocene, accelerated uplift of the Transantarctic Mountains gave rise to magnetic signatures that reflect progressive erosion of the Precambrian-Mesozoic metamorphic, intrusive, and sedimentary stratigraphic cover succession associated with unroofing of the adjacent Transantarctic Mountains. From the early Oligocene to the early Miocene, a consistent fining upward of magnetite particles through the recovered composite record likely reflects increased physical weathering with glacial grinding contributing to progressively finer grained Ferrar Dolerite-sourced magnetite. After 24 Ma, the magnetic properties of VLB sediments are primarily controlled by the weathering and erosion of McMurdo Volcanic Group rocks; increased volcanic glass contents contribute to the fining upward of magnetite grain size. Overall, long-term magnetic property variations record the first-order geological processes that controlled sedimentation in the VLB, including paleoclimatic, tectonic, provenance, and volcanic influences.
    Description: Published
    Description: 1845–1861
    Description: 2.2. Laboratorio di paleomagnetismo
    Description: JCR Journal
    Description: restricted
    Keywords: environmental magnetism ; Antarctica ; paleoclimate ; volcanism ; Ross Sea ; Cenozoic ; 03. Hydrosphere::03.01. General::03.01.06. Paleoceanography and paleoclimatology ; 04. Solid Earth::04.04. Geology::04.04.08. Sediments: dating, processes, transport ; 04. Solid Earth::04.04. Geology::04.04.10. Stratigraphy ; 04. Solid Earth::04.05. Geomagnetism::04.05.09. Environmental magnetism
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 6
    facet.materialart.
    Unknown
    Paleomagnetic record of basaltic volcanism from Pukaki and Onepoto maar lake cores, Auckland Volcanic Field, New Zealand (2010)
    Details
    Publication Date: 2017-04-04
    Description: The Auckland Volcanic Field contains several maars that formed after the last interglacial and subsequently filled with sediment. Two of these maars, Pukaki and Onepoto, were recently cored as part of the Auckland Maar Lakes Project. The tephra stratigraphy of the cores indicates that sediment accumulated relatively slowly in both maars until the Holocene when ocean waters breached the craters and they filled up quite rapidly. Using u-channels, we collected 23 m of pre-Holocene lacustrine sediment from the Pukaki 1-01 core and 15 m from the Onepoto core. Paleomagnetic measurements were performed on these at the University of California, Davis. Environmental magnetic records from both cores provide insights in particular about the eruptive history of the Auckland Volcanic Field. The lack of a tephrostratigraphic control in the lower portion of the cores, and the lack of similar trends in the magnetic parameters, prevented a complete core correlation. The main finding is that local basaltic tephra layers visible in the cores show up as spikes in the concentration dependent magnetic parameters, suggesting that other spikes represent tephra layers that are not as easily discerned.
    Description: Published
    Description: 71-79
    Description: 2.2. Laboratorio di paleomagnetismo
    Description: JCR Journal
    Description: restricted
    Keywords: Pukaki ; Onepoto ; Auckland Volcanic Field ; maars ; ash deposits ; 04. Solid Earth::04.05. Geomagnetism::04.05.09. Environmental magnetism
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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