15 results on '"Ramon Egli"'
Search Results
2. Palaeomagnetic and mineral magnetic analyses of the Deckenschotter of northern Switzerland and southern Germany
- Author
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Stephanie Scheidt, Marius W. Buechi, Ramon Egli, Andrea R. Biedermann, and Gaudenz Deplazes
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Magnetic polarity stratigraphy ,Tiefere Deckenschotter ,Höhere Deckenschotter ,Sediment ,Switzerland ,Germany ,Geology ,QE1-996.5 - Abstract
Abstract The Deckenschotter is a fluvial to glaciofluvial gravel unit in northern Switzerland and southern Germany. The deposits are considered the oldest preserved glacial to interglacial Quaternary deposits in the northern Alpine foreland and are thus important geomorphological markers for landscape evolution. Nevertheless, the age of the deposits is only approximately known and subject to controversial debates. This study presents the results of an extensive palaeomagnetic investigation carried out on intercalated fine-grained sediments at 11 sites of the Höhere Deckenschotter (HDS) and at 5 sites of the Tiefere Deckenschotter (TDS). The HDS show reversed and normal magnetisations, indicating deposition > 0.773 Ma, while the TDS exhibit only normal directions. Age constraints for the different sites are discussed in the light of evidence from other studies. The study therefore clearly supports the efforts to determine the age of the Deckenschotter. As data from previous palaeomagnetic studies on the HDS and TDS have not been published or preserved, this is in fact the only data-based palaeomagnetic study available.
- Published
- 2023
- Full Text
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3. Multiscale Brazil nut effects in bioturbated sediment
- Author
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Tatiana Savranskaia, Ramon Egli, and Jean-Pierre Valet
- Subjects
Medicine ,Science - Abstract
Abstract Size segregation in granular materials is a universal phenomenon popularly known as the Brazil nut effect (BNE), from the tendency of larger nuts to end on the top of a shaken container. In nature, fast granular flows bear many similarities with well-studied mixing processes. Instead, much slower phenomena, such as the accumulation of ferromanganese nodules (FN) on the seafloor, have been attributed to the BNE but remain essentially unexplained. Here we document, for the first time, the BNE on sub-millimetre particles in pelagic sediment and propose a size segregation model for the surface mixed layer of bioturbated sediments. Our model explains the size distribution of FN seeds, pointing to a uniform segregation mechanism over sizes ranging from 1 cm, which does not depend on selective ingestion by feeding organisms. In addition to explaining FN nucleation, our model has important implications for microfossil dating and the mechanism underlying sedimentary records of the Earth’s magnetic field.
- Published
- 2022
- Full Text
- View/download PDF
4. Influence of Seasonal Post‐Depositional Processes on the Remanent Magnetization in Varved Sediments From Glacial Lake Ojibway (Canada)
- Author
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Édouard G. H. Philippe, Guillaume St‐Onge, Jean‐Pierre Valet, Pierre‐Marc Godbout, Ramon Egli, Pierre Francus, and Martin Roy
- Subjects
natural remanent magnetization ,detrital remanent magnetization ,varve ,inclination shallowing ,paleointensity ,paleomagnetism ,Geophysics. Cosmic physics ,QC801-809 ,Geology ,QE1-996.5 - Abstract
Abstract The natural remanent magnetization (NRM) of high sedimentation rate sediments provides significant information about paleomagnetic secular variation of the Earth's magnetic field and can also potentially be used for stratigraphy. However, NRM acquisition depends on conditions inherent to the depositional environment. In addition to recording a precise annual chronology, varved sediments reflect marked annual sedimentary changes. The Earth's magnetic field does not vary significantly over such a short period, so magnetic changes recorded by varves are expected to reflect the influence of depositional parameters on the recording process. We focus here on a sequence of 27 ± 1 varves from the former proglacial Lake Ojibway (∼8.5 ka cal BP) from which individual cm‐thick summer and winter beds were sampled. Paleomagnetic, granulometric and geochemical analyses were conducted on each bed. A mean inclination shallowing of 24.3° is observed in winter beds, along with an 11.3° shallowing in summer beds. Magnetic declinations follow, on average, the expected field direction, but differences of up to 20° occur between successive beds. Summer beds are thicker than winter beds and have stronger magnetic susceptibility, higher Ca/Fe ratios and coarser sedimentary and magnetic grains. This grain size pattern reflects the input of coarser detrital particles during summer, while the finer fraction remained in suspension until it was deposited in winter. A combination of differential compaction between the winter and summer beds, seasonally varying physical and magnetic properties of sediments, and delayed NRM acquisition explains the variable and coercivity‐dependent inclination shallowing.
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- 2023
- Full Text
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5. Understanding magnetic interactions and reversal mechanisms in a spinodally decomposed cobalt ferrite using first order reversal curves
- Author
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Suraj V. Mullurkara, Ramon Egli, B. C. Dodrill, Susheng Tan, and P. R. Ohodnicki Jr.
- Subjects
Physics ,QC1-999 - Abstract
Cobalt ferrites exhibit widely varied magnetic behaviour due to the presence of a miscibility gap leading to the formation of periodic self-assembled nanostructures via spinodal decomposition. Periodicity and amplitude of the compositional fluctuations can be controlled by thermodynamic and kinetic processing parameters which allows for careful tuning of the magnetic properties. Although reports have shown evidence of spinodal decomposition, there is a lack of detailed characterization of the magnetic interactions and reversal mechanisms in these materials. In this work we use high-resolution first order reversal curves (FORC) measurements to understand the underlying magnetic processes occurring in a cobalt ferrite with a nominal composition of Co1.8Fe1.2O4 before (calcined) and after spinodal decomposition (annealed). Additionally, FORC measurements with preconditioning fields were conducted to separate the interaction signatures at low coercive fields by biasing the sample in positive and negative mean fields. Microstructural characterization using TEM combined with EDS showed uniform chemistry in the calcined sample and the presence of Fe rich and Co rich regions in the annealed sample, due to spinodal decomposition. Signs of positive exchange interactions were observed in both calcined and annealed samples. This work presents the first detailed magnetic characterization of magnetic interactions in a nanostructured cobalt ferrite, and provides an example of magnetic characterization of nanostructured ferrites using FORC.
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- 2023
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6. Rapid light carbon releases and increased aridity linked to Karoo–Ferrar magmatism during the early Toarcian oceanic anoxic event
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Eric Font, Luís Vítor Duarte, Mark J. Dekkers, Celine Remazeilles, Ramon Egli, Jorge E. Spangenberg, Alicia Fantasia, Joana Ribeiro, Elsa Gomes, José Mirão, and Thierry Adatte
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Medicine ,Science - Abstract
Abstract Large-scale release of isotopically light carbon is responsible for the carbon isotope excursion (CIE) of the Toarcian Oceanic Anoxic Event during the Lower Jurassic. Proposed sources include methane hydrate dissociation, volcanogenic outgassing of carbon dioxide and/or thermogenic methane release from the Karoo‐Ferrar magmatic province (southern Africa). Distinct small-scale shifts superimposed on the long-term CIE have been interpreted as rapid methane pulses linked to astronomically forced climate changes. In the Peniche reference section (Portugal), these small-scale shifts correspond to distinct brownish marly layers featuring markedly high mercury (Hg) and magnetic mineral concentration. Total organic carbon and Hg increase are uncorrelated, which suggests input of Hg into the atmosphere, possibly released after the intrusion of the Karoo-Ferrar sills into organic-rich sediments. Enhanced magnetic properties are associated with the presence of martite, washed-in oxidized magnetite, inferred to be due to increased aridity on the continental hinterland. This study provides strong evidence for a direct link between the Karoo-Ferrar magmatism, the carbon-isotope shifts and the resulting environmental changes.
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- 2022
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7. Intermediate field directions recorded in Pliocene basalts in Styria (Austria): evidence for cryptochron C2r.2r-1
- Author
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Elisabeth Schnepp, Patrick Arneitz, Morgan Ganerød, Robert Scholger, Ingomar Fritz, Ramon Egli, and Roman Leonhardt
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Paleomagnetism ,Paleointensity ,Transitional field configuration ,Cryptochron C2r.2r-1 ,39Ar/40Ar dating ,Styria (Austria) ,Geography. Anthropology. Recreation ,Geodesy ,QB275-343 ,Geology ,QE1-996.5 - Abstract
Abstract Pliocene volcanic rocks from south-east Austria were paleomagnetically investigated. Samples were taken from 28 sites located on eight different volcanoes. Rock magnetic investigations revealed that magnetic carriers are Ti-rich or Ti-poor titanomagnetites with mainly pseudo-single-domain characteristics. Characteristic remanent magnetization directions were obtained from alternating field as well as from thermal demagnetization. Four localities give reversed directions agreeing with the expected direction from secular variation. Another four localities of the Klöch–Königsberg volcanic complex (3) and the Neuhaus volcano (1) have reversed directions with shallow inclinations and declinations of about 240° while the locality Steinberg yields a positive inclination of about 30° and 200° declination. These aberrant directions cannot be explained by local or regional tectonic movements. All virtual geomagnetic pole positions are located on the southern hemisphere. Four virtual geomagnetic poles lie close to the geographic pole, while all others are concentrated in a narrow longitude sector offshore South America (310°–355°) with low virtual geomagnetic pole latitudes ranging from − 15° to − 70°. The hypothesis that a transitional geomagnetic field configuration was recorded during the short volcanic activity of these five localities is supported by 9 paleointensity results and 39Ar/40Ar dating. Virtual geomagnetic dipole moments range from 1.1 to 2.9·1022 Am2 for sites with low VGP latitudes below about 60° and from 3.0 to 9.3·1022 Am2 for sites with higher virtual geomagnetic pole latitudes. The new 39Ar/40Ar ages of 2.51 ± 0.27 Ma for Klöch and 2.39 ± 0.03 Ma for Steinberg allow for the correlation of the Styrian transitional directions with cryptochron C2r.2r-1 of the geomagnetic polarity time scale. Graphic abstract
- Published
- 2021
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8. Impact of turbulence on magnetic alignment in sediments
- Author
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Édouard G. H. Philippe, Jean-Pierre Valet, Guillaume St-Onge, and Ramon Egli
- Subjects
natural remanent magnetisation ,turbidite ,hyperpycnite ,sediment ,detrital remanent magnetization ,depositional remanence ,Science - Abstract
Rapidly deposited layers (RDL) such as turbidites or hyperpycnites are mostly studied for their sedimentological properties, but are carefully avoided in paleomagnetic studies due to the disturbances caused by such sudden and rapid sediment accumulation. Therefore, these layers can also be seen as potential indicators of sediment parameters susceptible of affecting the alignment of magnetic grains and ultimately the acquisition of the natural remanent magnetization (NRM). We have compiled 13 Holocene rapidly deposited layers from core MD99-2222 in the Saguenay Fjord, eastern Canada (St-Onge and al., 2004) with varying thicknesses (from 7.1 cm to 1,510 cm) and 4 Quaternary turbidites of different origins, to document the influence of sedimentary and magnetic parameters on natural remanent magnetization acquisition. We found a logarithmic relationship between rapidly deposited layers thickness on the one hand, and the amplitude of inclination changes and magnetic grain sizes on the other. Inclination and magnetic grain sizes are themselves correlated to each other by a logarithmic law. As there is no relationship between inclination deviation and stratigraphic depth, compaction alone cannot account for such large effects on inclination. Flocculation is grain size sensitive, but it is expected to affect mainly the natural remanent magnetization intensity, rather than its direction. Turbulence that prevails during the rapid deposition of sediments during such events is most likely the dominant factor.
- Published
- 2022
- Full Text
- View/download PDF
9. Magnetotactic advantage in stable sediment by long-term observations of magnetotactic bacteria in Earth’s field, zero field and alternating field
- Author
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Xuegang Mao, Ramon Egli, Xiuming Liu, and Lijuan Zhao
- Subjects
Medicine ,Science - Abstract
Magnetotactic bacteria (MTB) rely on magnetotaxis to effectively reach their preferred living habitats, whereas experimental investigation of magnetotactic advantage in stable sediment is currently lacking. We studied two wild type MTB (cocci and rod-shaped M. bavaricum) in sedimentary environment under exposure to geomagnetic field in the laboratory, zero field and an alternating field whose polarity was switched every 24 hours. The mean concentration of M. bavaricum dropped by ~50% during 6 months in zero field, with no clear temporal trend suggesting an extinction. Cell numbers recovered to initial values within ~1.5 months after the Earth’s field was reset. Cocci displayed a larger temporal variability with no evident population changes in zero field. The alternating field experiment produced a moderate decrease of M. bavaricum concentrations and nearby extinction of cocci, confirming the active role of magnetotaxis in sediment and might point to a different magnetotactic mechanism for M. bavaricum which possibly benefited them to survive field reversals in geological periods. Our findings provide a first quantification of magnetotaxis advantage in sedimentary environment.
- Published
- 2022
10. Extracting Magnetic Dipole field variations from cosmogenic 10Be records
- Author
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Tatiana Savranskaia, Ramon Egli, Sanja Panovska, and Monika Korte
- Abstract
Sedimentary records of the Earth’s magnetic field often contain unwanted climatic overprints, distorting the reconstruction of paleomagnetic field intensity variations. In case of field reconstructions based on the cosmogenic isotope 10Be, whose production is modulated by the solar activity and the dipolar component of the geomagnetic field, environmental overprints arise from climatic modulations of the source distribution, transport, and sediment scavenging efficiencies. Although the lithological dependence of the scavenging efficiency is supposed to be removed by normalizing 10Be with the stable isotope 9Be, this normalization can introduce its own environmental effects, caused by changes in source, distribution and transport of two isotopes. These processes lead to inter-sites differences observed between 10Be/9Be and corresponding relative paleointensity records, limiting use for global magnetic field models constructions. Principal component analysis (PCA) and independent component analysis (ICA) of four 10Be/9Be records from West Pacific and North Atlantic Ocean sites, characterized by different environmental settings, allowed us to extract the common pattern controlled by the evolution of the dipole field. These observations are made on records covering the last 380 ka, including seven geomagnetic excursions.While the first component of cosmogenic 10Be records clearly reflects geomagnetic dipole changes, it seems that the second and third components are dominated by 100- and 23-ka periodic oscillations respectively, corresponding to Earth’s orbital forcing. PCA and ICA methods are shown to be a powerful tool for disentangling and assessing different components of cosmogenic beryllium records. The geomagnetic component can serve to better understand the long-term geomagnetic field evolution, thus improving our knowledge of driving mechanisms sustaining the geodynamo.
- Published
- 2023
11. Key Signatures of Magnetofossils Elucidated by Mutant Magnetotactic Bacteria and Micromagnetic Calculations
- Author
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Matthieu Amor, Juan Wan, Ramon Egli, Julie Carlut, Christophe Gatel, Ingrid Marie Andersen, Etienne Snoeck, Arash Komeili, Interférométrie, In situ et Instrumentation pour la Microscopie Electronique (CEMES-I3EM), Centre d'élaboration de matériaux et d'études structurales (CEMES), Institut National des Sciences Appliquées - Toulouse (INSA Toulouse), Institut National des Sciences Appliquées (INSA)-Université Fédérale Toulouse Midi-Pyrénées-Institut National des Sciences Appliquées (INSA)-Université Fédérale Toulouse Midi-Pyrénées-Institut de Chimie de Toulouse (ICT-FR 2599), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS)-Institut National Polytechnique (Toulouse) (Toulouse INP), Université Fédérale Toulouse Midi-Pyrénées-Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS)-Institut National Polytechnique (Toulouse) (Toulouse INP), Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut National des Sciences Appliquées - Toulouse (INSA Toulouse), Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS), Department of Plant and Microbial Biology [Berkeley], University of California [Berkeley] (UC Berkeley), University of California (UC)-University of California (UC), Institut de Biosciences et Biotechnologies d'Aix-Marseille (ex-IBEB) (BIAM), Aix Marseille Université (AMU)-Centre National de la Recherche Scientifique (CNRS)-Direction de Recherche Fondamentale (CEA) (DRF (CEA)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA), Zentralanstalt für Meteorologie und Geodynamik [Vienna] (ZAMG), Institut de Physique du Globe de Paris (IPG Paris), Institut National des Sciences Appliquées (INSA)-Université de Toulouse (UT)-Institut National des Sciences Appliquées (INSA)-Université de Toulouse (UT)-Institut de Chimie de Toulouse (ICT), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS)-Institut National Polytechnique (Toulouse) (Toulouse INP), Université de Toulouse (UT)-Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS)-Institut National Polytechnique (Toulouse) (Toulouse INP), Université de Toulouse (UT)-Centre National de la Recherche Scientifique (CNRS), Université de Toulouse (UT), Department of Molecular and Cell Biology, ANR-10-EQPX-0038,MIMETIS,Microscopie Interférométrique et Microscopie Electronique en Transmission In Situ(2010), and European Project: 823717,ESTEEM3
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Geophysics ,[SDU]Sciences of the Universe [physics] ,Space and Planetary Science ,Geochemistry and Petrology ,[PHYS.COND.CM-GEN]Physics [physics]/Condensed Matter [cond-mat]/Other [cond-mat.other] ,Earth and Planetary Sciences (miscellaneous) ,[CHIM.CRIS]Chemical Sciences/Cristallography ,[PHYS.COND.CM-MS]Physics [physics]/Condensed Matter [cond-mat]/Materials Science [cond-mat.mtrl-sci] ,[PHYS.PHYS.PHYS-INS-DET]Physics [physics]/Physics [physics]/Instrumentation and Detectors [physics.ins-det] ,ComputingMilieux_MISCELLANEOUS - Abstract
International audience; Magnetotactic bacteria (MTB) produce single-stranded or multi-stranded chains of magnetic nanoparticles that contribute to the magnetization of sediments and rocks. Their magnetic fingerprint can be detected in ancient geological samples and serve as a unique biosignature of microbial life. However, some fossilized assemblages bear contradictory signatures pointing to magnetic components that have distinct origin(s). Here, using micromagnetic simulations and mutant MTB producing looped magnetosome chains, we demonstrate that the observed magnetofossil fingerprints are produced by a mixture of single-stranded and multi-stranded chains, and that diagenetically induced chain collapse, if occurring, must preserve the strong uniaxial anisotropy of native chains. This anisotropy is the key factor for distinguishing magnetofossils from other populations of natural magnetite particles, including those with similar individual crystal characteristics. Furthermore, the detailed properties of magnetofossil signatures depend on the proportion of equant and elongated magnetosomes, as well as on the relative abundances of single-stranded and multi-stranded chains. This work has important paleoclimatic, paleontological, and phylogenetic implications, as it provides reference data to differentiate distinct MTB lineages according to their chain and magnetosome morphologies, which will enable the tracking of the evolution of some of the most ancient biomineralizing organisms in a time-resolved manner. It also enables a more accurate discrimination of different sources of magnetite particles, which is pivotal for gaining better environmental and relative paleointensity reconstructions from sedimentary records.
- Published
- 2022
12. Reentrant phenomenon in the diffuse ferroelectric BaSn0.15Ti0.85O3 : Local structural insights and first-order reversal curves study
- Author
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Carlo Meneghini, Akash Surampalli, Deepak Prajapat, Ramon Egli, and V. Raghavendra Reddy
- Subjects
Materials science ,Reentrancy ,Condensed matter physics ,First order ,Ferroelectricity - Published
- 2021
13. Dipole and Nondipole Evolution of the Historical Geomagnetic Field From Instrumental, Archeomagnetic, and Volcanic Data
- Author
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Karl Fabian, Ramon Egli, Patrick Arneitz, and Roman Leonhardt
- Subjects
Dipole ,geography ,Geophysics ,geography.geographical_feature_category ,Earth's magnetic field ,Volcano ,Space and Planetary Science ,Geochemistry and Petrology ,Earth and Planetary Sciences (miscellaneous) ,Historical record ,Geology ,South Atlantic Anomaly - Published
- 2021
14. Magnetotactic advantage in stable sediment by long-term observations of magnetotactic bacteria in Earth's field, zero field and alternating field
- Author
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Xuegang Mao, Ramon Egli, Xiuming Liu, and Lijuan Zhao
- Subjects
Geologic Sediments ,Magnetics ,Multidisciplinary ,Earth, Planet ,RNA, Ribosomal, 16S ,Gram-Negative Bacteria ,Magnetosomes ,Bacterial Physiological Phenomena ,Ecosystem ,Phylogeny - Abstract
Magnetotactic bacteria (MTB) rely on magnetotaxis to effectively reach their preferred living habitats, whereas experimental investigation of magnetotactic advantage in stable sediment is currently lacking. We studied two wild type MTB (cocci and rod-shaped M. bavaricum) in sedimentary environment under exposure to geomagnetic field in the laboratory, zero field and an alternating field whose polarity was switched every 24 hours. The mean concentration of M. bavaricum dropped by ~50% during 6 months in zero field, with no clear temporal trend suggesting an extinction. Cell numbers recovered to initial values within ~1.5 months after the Earth’s field was reset. Cocci displayed a larger temporal variability with no evident population changes in zero field. The alternating field experiment produced a moderate decrease of M. bavaricum concentrations and nearby extinction of cocci, confirming the active role of magnetotaxis in sediment and might point to a different magnetotactic mechanism for M. bavaricum which possibly benefited them to survive field reversals in geological periods. Our findings provide a first quantification of magnetotaxis advantage in sedimentary environment.
- Published
- 2021
15. Unlocking information about fine magnetic particle assemblages from first-order reversal curve diagrams: Recent advances
- Author
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Andrew P. Roberts, David Heslop, Xiang Zhao, Hirokuni Oda, Ramon Egli, Richard J. Harrison, Pengxiang Hu, Adrian R. Muxworthy, and Tetsuro Sato
- Subjects
General Earth and Planetary Sciences - Published
- 2022
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