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| Heslop, David; Roberts, Andrew P.. |
| Principal component analysis (PCA) is a well-established technique in paleomagnetism and provides a means to estimate magnetic remanence directions from univectorial segments of stepwise demagnetization data. Derived directions constrain past geomagnetic field behavior and form the foundation of chronological and tectonic reconstructions. PCA of isolated remanence segments relies on estimates of the segment mean and covariance matrix, which can carry large uncertainties given the relatively small number of demagnetization data points used to characterize individual specimens. Traditional PCA does not, however, lend itself to quantification of these uncertainties, and inferences drawn from paleomagnetic reconstructions suffer from an inability to propagate... |
| Tipo: Text |
Palavras-chave: Paleomagnetism; Directional uncertainty; Principal component analysis. |
| Ano: 2016 |
URL: https://archimer.ifremer.fr/doc/00421/53255/54707.pdf |
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| Chang, Liao; Roberts, Andrew P.; Heslop, David; Hayashida, Akira; Li, Jinhua; Zhao, Xiang; Tian, Wei; Huang, Qinghua. |
| Magnetic mineral inclusions occur commonly within other larger mineral phases in igneous rocks and have been demonstrated to preserve important paleomagnetic signals. While the usefulness of magnetic inclusions in igneous rocks has been explored extensively, their presence in sediments has only been speculated upon. The contribution of magnetic inclusions to the magnetization of sediments, therefore, has been elusive. In this study, we use transmission electron microscope (TEM) and magnetic methods to demonstrate the widespread preservation of silicate-hosted magnetic inclusions in marine sedimentary settings. TEM analysis reveals detailed information about the microstructure, chemical composition, grain size, and spatial arrangement of nanoscale magnetic... |
| Tipo: Text |
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| Ano: 2016 |
URL: https://archimer.ifremer.fr/doc/00421/53206/54929.pdf |
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| Heslop, David; Roberts, Andrew P.; Chang, Liao. |
| The central ridge structure of a first-order reversal curve (FORC) distribution is indicative of uni-axial noninteracting single domain magnetic particles, which provides the opportunity to identify and characterize biogenic magnetic mineral remains (magnetofossils) in sediments. Recent studies have shown that magnetofossils are widespread in the geological record and that they carry useful environmental information and contribute to paleomagnetic recording, which makes it essential to quantify how these biogenic components contribute to the magnetic properties of sediments. We present results from six sedimentary sequences whose magnetic mineral assemblages contain a significant magnetofossil contribution. Using principal component analysis, we find that... |
| Tipo: Text |
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| Ano: 2014 |
URL: https://archimer.ifremer.fr/doc/00290/40135/39212.pdf |
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| Chang, Liao; Bolton, Clara T.; Dekkers, Mark J.; Hayashida, Akira; Heslop, David; Krijgsman, Wout; Kodama, Kazuto; Paterson, Greig A.; Roberts, Andrew P.; Rohling, Eelco J.; Yamamoto, Yuhji; Zhao, Xiang. |
| We have identified millennial-scale variations in magnetic mineral diagenesis from Pacific Ocean sediments offshore of Japan that we correlate with changes in organic carbon burial that were likely driven by Asian monsoon fluctuations. The correlation was determined by identifying offsets between the positions of fossil diagenetic fronts and climatically induced variations in organic carbon burial inferred from magnetic and geochemical analyses. Episodes of intense monsoon activity and attendant sediment magnetic mineral diagenesis also appear to correlate with Heinrich events, which supports the existence of climatic telecommunications between Asia and the North Atlantic region. Several lines of evidence support our conclusions: (1) fluctuations in... |
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| Ano: 2016 |
URL: https://archimer.ifremer.fr/doc/00356/46703/47266.pdf |
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| Hong, Hoabin; Chang, Liao; Hayashida, Akira; Roberts, Andrew P.; Heslop, David; Paterson, Greig A.; Kodama, Kazuto; Tauxe, Lisa. |
| Sedimentary relative paleointensity (RPI) records are often carried by complex magnetic mineral mixtures, including detrital and biogenic magnetic minerals. Recent studies have demonstrated that magnetic inclusions within larger detrital silicate particles can make significant contributions to sedimentary paleomagnetic records. However, little is known about the role such inclusions play in sedimentary paleomagnetic signal recording. We analyzed paleomagnetic and mineral magnetic data for marine sediment core MD01‐2421 from the North Pacific Ocean, offshore of central Japan, to assess how magnetic inclusions and other detrital magnetic minerals record sedimentary paleomagnetic signals. Stratigraphic intervals in which abundant magnetic inclusions dominate... |
| Tipo: Text |
Palavras-chave: Magnetic mineral inclusions; Relative paleointensity; Detrital remanent magnetization. |
| Ano: 2019 |
URL: https://archimer.ifremer.fr/doc/00505/61685/65640.pdf |
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| Chang, Liao; Roberts, Andrew P.; Winklhofer, Michael; Heslop, David; Dekkers, Mark J.; Krijgsman, Wout; Gerald, John D. Fitz; Smith, Paul. |
| Biogenic magnetic minerals produced by magnetotactic bacteria occur ubiquitously in natural aquatic environments. Their identification and characterization are important for interpretation of paleomagnetic and environmental magnetic records. We compare two magnetic methods for their identification and characterization in a diverse set of sedimentary environments: ferromagnetic resonance (FMR) spectroscopy and first-order reversal curve (FORC) diagrams, constrained by transmission electron microscope observations. The advantages and limitations of each method are evaluated. FMR analysis provides a strong diagnostic indicator because of its ability to detect the strong shape anisotropy that arises from the biogenic chain architecture, but it can be obscured... |
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| Ano: 2014 |
URL: https://archimer.ifremer.fr/doc/00290/40109/39375.pdf |
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| Govin, Aline; Holzwarth, Ulrike; Heslop, David; Keeling, Lara Ford; Zabel, Matthias; Mulitza, Stefan; Collins, James A.; Chiessi, Cristiano M.. |
| Numerous studies use major element concentrations measured on continental margin sediments to reconstruct terrestrial climate variations. The choice and interpretation of climate proxies however differ from site to site. Here we map the concentrations of major elements (Ca, Fe, Al, Si, Ti, K) in Atlantic surface sediments (36 degrees N-49 degrees S) to assess the factors influencing the geochemistry of Atlantic hemipelagic sediments and the potential of elemental ratios to reconstruct different terrestrial climate regimes. High concentrations of terrigenous elements and low Ca concentrations along the African and South American margins reflect the dominance of terrigenous input in these regions. Single element concentrations and elemental ratios including... |
| Tipo: Text |
Palavras-chave: Atlantic surface sediments; Terrigenous input; Major elements. |
| Ano: 2012 |
URL: https://archimer.ifremer.fr/doc/00214/32550/31035.pdf |
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| Collins, James A.; Govin, A.; Mulitza, Stefan; Heslop, David; Zabel, M.; Hartmann, J.; Rohl, U.; Wefer, Gerold. |
| Relict dune fields that are found at 14° N in the modern-day African Sahel are testament to equatorward expansions of the Sahara desert during the late Pleistocene. However, difficulties of dating dune formation mean that abrupt millennial-scale climate events are not always resolved in these records. High-resolution marine core studies have identified Heinrich Stadials as the dustiest periods of the last glacial, although no studies have mapped the spatio-temporal evolution of dust export from West Africa. We use the major-element composition of four marine sediment cores to reconstruct the spatial extent of Saharan-dust versus river-sediment input to the continental margin from West Africa over the last 60 ka. This allows us to map the position of the... |
| Tipo: Text |
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| Ano: 2013 |
URL: http://archimer.ifremer.fr/doc/00182/29279/27696.pdf |
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