23 results on '"Ramon Egli"'
Search Results
2. Palaeomagnetic and mineral magnetic analyses of the Deckenschotter of northern Switzerland and southern Germany
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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.
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- 2023
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3. Multiscale Brazil nut effects in bioturbated sediment
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Tatiana Savranskaia, Ramon Egli, and Jean-Pierre Valet
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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.
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- 2022
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4. Influence of Seasonal Post‐Depositional Processes on the Remanent Magnetization in Varved Sediments From Glacial Lake Ojibway (Canada)
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Édouard G. H. Philippe, Guillaume St‐Onge, Jean‐Pierre Valet, Pierre‐Marc Godbout, Ramon Egli, Pierre Francus, and Martin Roy
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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
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5. Understanding magnetic interactions and reversal mechanisms in a spinodally decomposed cobalt ferrite using first order reversal curves
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Suraj V. Mullurkara, Ramon Egli, B. C. Dodrill, Susheng Tan, and P. R. Ohodnicki Jr.
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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
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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
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- 2021
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8. Impact of turbulence on magnetic alignment in sediments
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Édouard G. H. Philippe, Jean-Pierre Valet, Guillaume St-Onge, and Ramon Egli
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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.
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- 2022
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9. Magnetotactic advantage in stable sediment by long-term observations of magnetotactic bacteria in Earth’s field, zero field and alternating field
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Xuegang Mao, Ramon Egli, Xiuming Liu, and Lijuan Zhao
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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.
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- 2022
10. Microbially assisted recording of the Earth’s magnetic field in sediment
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Xiangyu Zhao, Ramon Egli, Stuart A. Gilder, and Sebastian Müller
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Science - Abstract
Sediments record variations of the Earth’s magnetic field via the alignment of magnetic grains during and after deposition, yet the role of post-depositional processes remains unclear. Here, the authors present experiments showing how microbially-induced bioturbation controls the alignment process.
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- 2016
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11. Magneto-chemotaxis in sediment: first insights.
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Xuegang Mao, Ramon Egli, Nikolai Petersen, Marianne Hanzlik, and Xiuming Liu
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Medicine ,Science - Abstract
Magnetotactic bacteria (MTB) use passive alignment with the Earth magnetic field as a mean to increase their navigation efficiency in horizontally stratified environments through what is known as magneto-aerotaxis (M-A). Current M-A models have been derived from MTB observations in aqueous environments, where a >80% alignment with inclined magnetic field lines produces a one-dimensional search for optimal living conditions. However, the mean magnetic alignment of MTB in their most widespread living environment, i.e. sediment, has been recently found to be
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- 2014
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12. Effects of Alzheimer’s disease and formalin fixation on the different mineralised-iron forms in the human brain
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Ramon Egli, A. J. E. Lefering, Louise van der Weerd, L. Bossoni, and Andrew G. Webb
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0301 basic medicine ,Male ,Pathology ,Maghemite ,lcsh:Medicine ,Disease ,Ferric Compounds ,0302 clinical medicine ,lcsh:Science ,Aged, 80 and over ,Multidisciplinary ,biology ,Chemistry ,Brain ,Human brain ,Middle Aged ,Alzheimer's disease ,medicine.anatomical_structure ,Female ,medicine.medical_specialty ,Iron ,Hemosiderin ,engineering.material ,Article ,03 medical and health sciences ,Ferrihydrite ,Alzheimer Disease ,Magnetic properties and materials ,Formaldehyde ,medicine ,Humans ,In patient ,Frozen tissue ,Aged ,Nanoscale biophysics ,lcsh:R ,Case-control study ,medicine.disease ,Ferrosoferric Oxide ,Ferritin ,030104 developmental biology ,Case-Control Studies ,Ferritins ,biology.protein ,engineering ,Nanoparticles ,lcsh:Q ,030217 neurology & neurosurgery - Abstract
Iron accumulation in the brain is a phenomenon common to many neurodegenerative diseases, perhaps most notably Alzheimer’s disease (AD).We present here magnetic analyses of post-mortem brain tissue of patients who had severe Alzheimer’s disease, and compare the results with those from healthy controls. Isothermal remanent magnetization experiments were performed to assess the extent to which different magnetic carriers are affected by AD pathology and formalin fixation.While Alzheimer’s brain material did not show higher levels of magnetite/maghemite nanoparticles than corresponding controls, the ferrihydrite mineral, known to be found within the core of ferritin proteins and hemosiderin aggregates, almost doubled in concentration in patients with Alzheimer’s pathology, strengthening the conclusions of our previous studies. As part of this study, we also investigated the effects of sample preparation, by performing experiments on frozen tissue as well as tissue which had been fixed in formalin for a period of five months. Our results showed that the two different preparations did not critically affect the concentration of magnetic carriers in brain tissue, as observable by SQUID magnetometry.
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- 2020
13. Key Signatures of Magnetofossils Elucidated by Mutant Magnetotactic Bacteria and Micromagnetic Calculations
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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.
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- 2022
14. Disentangling magnetic and environmental signatures of sedimentary 10Be/9Be records
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Didier Bourlès, Quentin Simon, Tatiana Savranskaia, Ramon Egli, Nicolas Thouveny, Franck Bassinot, Laure Meynadier, Jean-Pierre Valet, Institut de Physique du Globe de Paris (IPGP (UMR_7154)), Institut national des sciences de l'Univers (INSU - CNRS)-Université de La Réunion (UR)-Institut de Physique du Globe de Paris (IPG Paris)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité), Central Institute for Meteorology and Geodynamics [Vienna] (ZAMG), Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette] (LSCE), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), Paléocéanographie (PALEOCEAN), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), Centre européen de recherche et d'enseignement des géosciences de l'environnement (CEREGE), Institut de Recherche pour le Développement (IRD)-Aix Marseille Université (AMU)-Collège de France (CdF (institution))-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE), European Research Council (ERC)European Commission339899INSU/CNRS, IRDFrench National Research Agency (ANR), ANR-10-EQPX-0024,ASTER-CEREGE,PLATEFORME DE GEOCHIMIE ISOTOPIQUE ASTER/CEREGE(2010), European Project: 246937,EC:FP7:PEOPLE,FP7-PEOPLE-2009-IRSES,SIMTECH(2010), Institut de Physique du Globe de Paris (IPGP), Institut national des sciences de l'Univers (INSU - CNRS)-IPG PARIS-Université de La Réunion (UR)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), and Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)
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010506 paleontology ,Archeology ,010504 meteorology & atmospheric sciences ,[SDU.STU.GP]Sciences of the Universe [physics]/Earth Sciences/Geophysics [physics.geo-ph] ,[SDU.STU]Sciences of the Universe [physics]/Earth Sciences ,Atmospheric sciences ,01 natural sciences ,Authigenic Be-10/Be-9 ratio ,[SDU.STU.GC]Sciences of the Universe [physics]/Earth Sciences/Geochemistry ,Cosmogenic nuclides ,Cosmogenic nuclide ,Ecology, Evolution, Behavior and Systematics ,ComputingMilieux_MISCELLANEOUS ,[SDU.STU.OC]Sciences of the Universe [physics]/Earth Sciences/Oceanography ,Geomagnetic field intensity ,0105 earth and related environmental sciences ,Global and Planetary Change ,Terrigenous sediment ,Sediment ,Geology ,Authigenic ,Moment (mathematics) ,Dipole ,Amplitude ,Earth's magnetic field ,13. Climate action ,Beryllium ,Matuyama-brunhes reversal - Abstract
Reconstructions of the global production rate of the cosmogenic isotope 10Be from sedimentary records of authigenic 10Be/9Be ratios have been successfully used to obtain independent estimates of geomagnetic dipole moment variations caused by field excursions or reversals. In this study, we assess the reliability of 10Be/9Be as a proxy for the cosmogenic 10Be production rate by evaluating two potential biasing sources represented by sediment composition and climatic modulation. For this purpose, we compare five high-resolution 10Be/9Be records of the Matuyama-Brunhes (M-B) field reversal from sediment cores of the Indian, West Pacific, and North Atlantic oceans. Significant increase of 10Be/9Be ratios at ∼ 774 ka is explained in terms of the dominant control of geomagnetic modulation during the M-B reversal. Results do not support the existence of a direct proportionality between measured sedimentary 10Be/9Be ratio and cosmogenic 10Be production rate, as shown by 10Be/9Be records that offset relative to each other during and outside the M-B reversal. Residual differences between offset-corrected rescaled records do not appear to be related to an incomplete correction of variable sediment scavenging efficiencies by 9Be normalization. Instead, these differences can be explained by a common climatic modulation model, assuming a linear relation between 10Be/9Be and the global 10Be production rate with site- and time-dependent additive and multiplicative coefficients. These coefficients are linear functions of a single global climate proxy identified with the benthic δ 18 O record. Additive coefficients are almost constant in time and can represent up to ∼ 60% of the average 10Be/9Be value during periods of stable field polarity. Multiplicative coefficients are also site-specific, with mean values representing the bulk scavenging efficiency of the site, and variations about this mean expressing a multiplicative climatic modulation of the 10Be production rate. The amplitude of this modulation amounts to 10–15% of the maximum variations recorded during the M-B reversal and is sufficiently large to mask minor variations of the dipole moment during stable polarity periods. Reconstructions of the geomagnetic dipole intensity can benefit from the information about climatic modulation effects gained with our modelling approach. Best suited sites for magnetic field reconstructions should be characterized by minimal Be-recycling contributions from ancient 10Be reservoirs and minimal climatic modulation, as far as it can be determined from relative comparisons with other records. These conditions are most likely encountered in open basins at sites (1) with 2.8 km water depth, (2) > 200 km offshore, and (3) located underneath a large current system extending over regions with minimum terrigenous inputs. Scaling all records with respect to a chosen reference enables to produce 10Be/9Be stacks with reduced noise and short-term local environmental effects. Differences between stacks obtained in this manner highlight global climatic effects that need to be considered when generating calibrated reconstructions of the geomagnetic dipole moment.
- Published
- 2021
15. In situ magnetic identification of giant, needle-shaped magnetofossils in Paleocene–Eocene Thermal Maximum sediments
- Author
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Peter C. Lippert, Helen B. Sears, Ioan Lascu, Kenneth J. T. Livi, Ramon Egli, and C. Wagner
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In situ ,Magnetic measurements ,Aquatic Organisms ,Geologic Sediments ,Multidisciplinary ,Magnetotactic bacteria ,Fossils ,Magnetic Phenomena ,Mineralogy ,Sediment ,Coercivity ,Ferrosoferric Oxide ,Physical Phenomena ,Magnetics ,Transmission electron micrograph ,Carbon isotope excursion ,Physical Sciences ,Humans ,Magnetosomes ,Geology ,Magnetofossil - Abstract
Near-shore marine sediments deposited during the Paleocene-Eocene Thermal Maximum at Wilson Lake, NJ, contain abundant conventional and giant magnetofossils. We find that giant, needle-shaped magnetofossils from Wilson Lake produce distinct magnetic signatures in low-noise, high-resolution first-order reversal curve (FORC) measurements. These magnetic measurements on bulk sediment samples identify the presence of giant, needle-shaped magnetofossils. Our results are supported by micromagnetic simulations of giant needle morphologies measured from transmission electron micrographs of magnetic extracts from Wilson Lake sediments. These simulations underscore the single-domain characteristics and the large magnetic coercivity associated with the extreme crystal elongation of giant needles. Giant magnetofossils have so far only been identified in sediments deposited during global hyperthermal events and therefore may serve as magnetic biomarkers of environmental disturbances. Our results show that FORC measurements are a nondestructive method for identifying giant magnetofossil assemblages in bulk sediments, which will help test their ecology and significance with respect to environmental change.
- Published
- 2021
16. Mineral Magnetic Characterization of High-Latitude Sediments From Lake Levinson-Lessing, Siberia
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Ramon Egli, Matthias Lenz, Martin Melles, Stephanie Scheidt, Christian Rolf, and Karl Fabian
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Geophysics ,Mineral ,Magnetic mineralogy ,High latitude ,Geochemistry ,General Earth and Planetary Sciences ,Sediment core ,Geology ,Characterization (materials science) - Abstract
Levinson-Lessing Lake in northern Central Siberia is a sedimentary archive characterized by continuous, widely constant sedimentation at high rates (0.7 m ka−1 for >32 ka). This study provides the first evidence of the suitability of the lake′s sediments for paleomagnetic analyses using the 46-m-long core Co1401. Although the lowermost 8 m are disturbed, the upper 38 m of Co1401 provide the preconditions for an exceptional, high-resolution paleomagnetic record located within the tangent cylinder of the inner core. High-resolution analyses of magnetic susceptibility, anhysteretic remanent magnetization, isothermal remanent magnetization, and hysteresis parameters show largely uniform mineral magnetic properties. First-order reversal curves indicate magnetite particles in pseudo-single domain state are the main remanence carrier, supplemented by single-domain particles, originating likely from magnetotactic bacteria. Above 6.7 m, the bulk magnetic mineralogy is slightly harder than below and initial greigite formation occurs. However, the main remanence carriers are still of detrital origin.
- Published
- 2021
17. Microbially assisted recording of the Earth’s magnetic field in sediment
- Author
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Ramon Egli, Stuart Gilder, Xiangyu Zhao, and Sebastian Muller
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Geologic Sediments ,Rotation ,010504 meteorology & atmospheric sciences ,Earth, Planet ,Science ,General Physics and Astronomy ,010502 geochemistry & geophysics ,01 natural sciences ,Article ,General Biochemistry, Genetics and Molecular Biology ,Sedimentary depositional environment ,0105 earth and related environmental sciences ,Multidisciplinary ,Sediment ,General Chemistry ,Geophysics ,equipment and supplies ,Bacterial Load ,Magnetic field ,Magnetic Fields ,Earth's magnetic field ,Torque ,Remanence ,Dynamo theory ,Bioturbation ,human activities ,Geology - Abstract
Sediments continuously record variations of the Earth's magnetic field and thus provide an important archive for studying the geodynamo. The recording process occurs as magnetic grains partially align with the geomagnetic field during and after sediment deposition, generating a depositional remanent magnetization (DRM) or post-DRM (PDRM). (P)DRM acquisition mechanisms have been investigated for over 50 years, yet many aspects remain unclear. A key issue concerns the controversial role of bioturbation, that is, the mechanical disturbance of sediment by benthic organisms, during PDRM acquisition. A recent theory on bioturbation-driven PDRM appears to solve many inconsistencies between laboratory experiments and palaeomagnetic records, yet it lacks experimental proof. Here we fill this gap by documenting the important role of bioturbation-induced rotational diffusion for (P)DRM acquisition, including the control exerted on the recorded inclination and intensity, as determined by the equilibrium between aligning and perturbing torques acting on magnetic particles., Sediments record variations of the Earth's magnetic field via the alignment of magnetic grains during and after deposition, yet the role of post-depositional processes remains unclear. Here, the authors present experiments showing how microbially-induced bioturbation controls the alignment process.
- Published
- 2016
18. Modelling geomagnetically induced currents in midlatitude Central Europe using a thin-sheet approach
- Author
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I. Schattauer, Alexander Römer, Georg Achleitner, Ramon Egli, Thomas Stefan Halbedl, Ciaran Beggan, Viktor Wesztergom, Roman Leonhardt, and Rachel L. Bailey
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Atmospheric Science ,010504 meteorology & atmospheric sciences ,Space weather ,01 natural sciences ,law.invention ,Physics::Geophysics ,Electric power system ,law ,0103 physical sciences ,Earth and Planetary Sciences (miscellaneous) ,lcsh:Science ,Transformer ,010303 astronomy & astrophysics ,0105 earth and related environmental sciences ,Geomagnetic storm ,lcsh:QC801-809 ,Geology ,Astronomy and Astrophysics ,Geophysics ,Thin sheet ,lcsh:QC1-999 ,Geomagnetically induced current ,lcsh:Geophysics. Cosmic physics ,Earth's magnetic field ,Space and Planetary Science ,Middle latitudes ,Physics::Space Physics ,lcsh:Q ,lcsh:Physics - Abstract
Geomagnetically induced currents (GICs) in power systems, which can lead to transformer damage over the short and the long term, are a result of space weather events and geomagnetic variations. For a long time, only high-latitude areas were considered to be at risk from these currents, but recent studies show that considerable GICs also appear in midlatitude and equatorial countries. In this paper, we present initial results from a GIC model using a thin-sheet approach with detailed surface and subsurface conductivity models to compute the induced geoelectric field. The results are compared to measurements of direct currents in a transformer neutral and show very good agreement for short-period variations such as geomagnetic storms. Long-period signals such as quiet-day diurnal variations are not represented accurately, and we examine the cause of this misfit. The modelling of GICs from regionally varying geoelectric fields is discussed and shown to be an important factor contributing to overall model accuracy. We demonstrate that the Austrian power grid is susceptible to large GICs in the range of tens of amperes, particularly from strong geomagnetic variations in the east–west direction.
- Published
- 2018
19. A modified least-squares collocation method for the determination of crustal deformation: first results in the Swiss Alps
- Author
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Hans-Gert Kahle, Ramon Egli, Alain Geiger, and A. Wiget
- Subjects
Covariance function ,Alps ,least-squares collocation ,levelling ,recent crustal movements ,Geodetic datum ,Geodesy ,Collocation (remote sensing) ,Synthetic data ,Physics::Fluid Dynamics ,Geophysics ,Geochemistry and Petrology ,Collocation method ,A priori and a posteriori ,Vector field ,Geology ,Interpolation - Abstract
Geophysical Journal International, 168 (1), ISSN:0956-540X, ISSN:1365-246X
- Published
- 2017
20. Time-resolved 2-million-year-old supernova activity discovered in Earth’s microfossil record
- Author
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Boyana Deneva, Georg Rugel, Karin Hain, Shawn Bishop, Silke Merchel, L. Fimiani, J.M. Gómez-Guzmán, Valentyna Chernenko, Nicolai Famulok, Gunther Korschinek, Thomas Faestermann, Ramon Egli, Marianne Hanzlik, and Peter Ludwig
- Subjects
Solar System ,Pleistocene ,Magnetotactic bacteria ,Extraterrestrial Environment ,Earth, Planet ,Astronomy ,FOS: Physical sciences ,Astrophysics ,010502 geochemistry & geophysics ,01 natural sciences ,chemistry.chemical_compound ,0103 physical sciences ,010303 astronomy & astrophysics ,Solar and Stellar Astrophysics (astro-ph.SR) ,0105 earth and related environmental sciences ,Magnetite ,Earth and Planetary Astrophysics (astro-ph.EP) ,Multidisciplinary ,Fossils ,Ferrosoferric Oxide ,Supernova ,Stars ,Astrophysics - Solar and Stellar Astrophysics ,chemistry ,Physical Sciences ,Geology ,Earth (classical element) ,Astrophysics - Earth and Planetary Astrophysics ,Accelerator mass spectrometry - Abstract
Massive stars, which terminate their evolution as core collapse supernovae, are theoretically predicted to eject more than 1E-5 solar masses of the radioisotope 60Fe. If such an event occurs sufficiently close to our solar system, traces of the supernova debris could be deposited on Earth. Herein, we report a time resolved 60Fe signal residing, at least partially, in a biogenic reservoir. Using accelerator mass spectrometry, this signal was found through the direct detection of live 60Fe atoms contained within secondary iron oxides, among which are magnetofossils, the fossilized chains of magnetite crystals produced by magnetotactic bacteria. The magnetofossils were chemically extracted from two Pacific Ocean sediment drill cores. Our results show that the 60Fe signal onset occurs around 2.6 Ma to 2.8 Ma, near the lower Pleistocene boundary, terminates around 1.7 Ma, and peaks at about 2.2 Ma., Figures from the Supplementary Information are not included due to file size restrictions. Download the, now open access, original article for those details (see doi)
- Published
- 2016
21. Characterization of primary and secondary magnetite in marine sediment by combining chemical and magnetic unmixing techniques
- Author
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Ramon Egli, Georg Rugel, Thomas Frederichs, Peter Ludwig, Silke Merchel, Volodymyr A. Chernenko, María Julia Orgeira, and Shawn Bishop
- Subjects
Global and Planetary Change ,ferrimagnetic minerals ,Magnetism ,Otras Ciencias Naturales y Exactas ,Extraction (chemistry) ,Sediment ,Mineralogy ,Oceanography ,Dilution ,Characterization (materials science) ,Magnetite ,FORC ,radiochemical separation ,Marine sediments ,chemistry.chemical_compound ,chemistry ,Ferrimagnetism ,accelerator mass spectrometry ,supernova ,Carbonate ,CIENCIAS NATURALES Y EXACTAS ,Geology - Abstract
We present a novel technique for quantitative unmixing of primary and secondary ferrimagnetic minerals in sediments. Hysteresis and high-resolution first-order reversal curve (FORC) measurements are performed on sediment samples before and after digestion in a citrate–bicarbonate–dithionite (CBD) solution optimized for maximum selective extraction of secondary fine-grained iron oxides. The difference between magnetic measurements of untreated and CBD-treated sample materials is used to calculate the original magnetic signature of CBD-extractable minerals. A combination of selective chemical extraction and magnetic measurements suited for the detection of single-domain particles provides a cross-check between chemical and magnetic unmixing of primary and secondary iron oxides and resolves the non-uniqueness problem of numerical unmixing methods. A quantitative magnetic characterization of secondary ferrimagnetic minerals in a magnetofossil-rich pelagic carbonate is presented for the first time. It can be used for calibration of recently developed fast magnetic unmixing techniques. CBD-based Fe extraction from sediments with minimal clastic and/or aeolian inputs, such as pelagic carbonates, is particularly suited for the search for cosmogenic 60Fe signatures from supernova explosions, because 60Fe dilution by dissolved primary Fe-bearing minerals is minimized. Fil: Ludwig, P.. Technische Universitat Munchen; Alemania Fil: Egli, R.. Central Institute for Meteorology and Geodynamics; Austria Fil: Bishop, S.. Technische Universitat Munchen; Alemania Fil: Chernenko, V.. Technische Universitat Munchen; Alemania Fil: Frederichs, T.. Universitat Bremen; Alemania Fil: Rugel, G.. Helmholtz-Zentrum; Alemania Fil: Merchel, S.. Helmholtz-Zentrum; Alemania Fil: Orgeira, Maria Julia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Basicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Basicas, Aplicadas y Ambientales de Buenos Aires; Argentina
- Published
- 2013
22. The lacustrine deposits of Fornaci di Ranica (late Early Pleistocene, Italian Pre-Alps): stratigraphy, palaeoenvironment and geological evolution
- Author
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Roberta Pini, Sergio Chiesa, Cesare Ravazzi, Federico Confortini, Ramon Egli, Marzia Breda, Edoardo Martinetto, and Giovanni Muttoni
- Subjects
Palynology ,geology ,Early Pleistocene ,Pollen zone ,Pleistocene ,biology ,palaeontology ,stratigraphy ,Macrofossil ,580 Plants (Botany) ,biology.organism_classification ,Fornaci di Ranica (Bergamo) ,Paleontology ,late Early Pleistocene ,Cervalces latifrons ,Glacial period ,Quaternary ,Geology ,Earth-Surface Processes - Abstract
An interdisciplinary investigation of the Pleistocene clay succession of Fornaci di Ranica (Italian Pre-Alps) aimed to reconstruct the palaeoenvironmental history and its chronostratigraphic position and to consider the implications for the Quaternary evolution of the southern alpine borderland near the Early/Middle Pleistocene transition. A detailed survey of Quaternary deposits in boreholes and exposed sections provided a complete record of the basin. The most complete core was analyzed for palynology and magnetic properties. Plant macrofossils were obtained by flotation. Pollen and spectrometric analysis allowed a precise stratigraphic placement of a moose antler and braincase kept in museum collections. The basin originated from fluviatile obstruction of a tributary valley cut into bedrock. The basal deposits formed as a terrestrial hydromorphic soil under a dense Tsuga-forest (zone RNC 1). The overlying palustrine gyttja shows a marked forest withdrawal with a climatic signature (zone RNC 3), followed by a re-establishment of mixed conifer forests (zones RNC 4-6). The occurrences of pollen of cold-adapted taxa (Saxifraga oppositifolia type, Saxifraga stellaris type, Larix), are the oldest so far known south of the Alps and suggest that mean summer temperature was near or even below the thermic tree limit. High herb diversity, partially represented by tall forbs, characterizes this zone. A further increase of the water table can be assumed in zones RNC 4 and RNC 5, since pollen of aquatic plants increases. The find of Larix decidua L. cones demonstrates the existence of the European larch in the Early Pleistocene of the Alps, previously not identified at the species level. After the Serio river had reached the maximum Quaternary aggradation, the lake was rapidly filled up with turbiditic sediments. The identification of Cervalces latifrons (Johnson, 1874) by Azzaroli (Palaeantogr. Italica 71(1979) 48) was confirmed. Pollen spectra obtained from clay fragments preserved in the braincase allowed us to constrain the stratigraphic position of these fossil remains in the lower palustrine portion of the sequence. Pollen and moose palaeoecology corroborate the reconstruction of a boreal landscape. The succession of Fornaci di Ranica is attributed to the late Early Pleistocene on the basis of the following elements: (i) the occurrence of an acme pollen zone of Tsuga, with Carya and Pteroearya; (ii) the low representation of Cedrus; (iii) the biochronology of Cervalces latifrons; (iv) normal fossil magnetic polarity, interpreted as part of the Jaramillo subchron on the basis of correlations with other studied sections from the same region, and, finally, (v) indications from the regional geological evolution. The basin deposits spanned the final stage of a temperate period and the subsequent transition to a cold phase during the Jaramillo subchron or the Cobb cryptochron. The basin originated by fluvioglacial aggradation, triggered by glaciation in the northern part of the Serio river catchement. The lake succession may represent an episode of marked increase of polar ice volume related to MIS (36) 30, or 28. The correlation with the Leffe sequence also suggests that cold climate conditions inferred for pollen zone RNC 3 did not occur earlier in the Early Pleistocene of this region. (C) 2004 Elsevier Ltd and INQUA. All rights reserved.
- Published
- 2005
23. Records of paleomagnetic field intensity in sediments : Crossover approach between relative paleointensity and cosmogenic ¹ºBe
- Author
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Tatiana Savranskaia, Institut de Physique du Globe de Paris (IPGP), Institut national des sciences de l'Univers (INSU - CNRS)-IPG PARIS-Université de La Réunion (UR)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP), Université de Paris, Jean-Pierre Valet, Ramon Egli, and STAR, ABES
- Subjects
Magnetic field ,Granular convection ,[SDU.STU] Sciences of the Universe [physics]/Earth Sciences ,Cosmogenic isotopes ,Champ magnétique ,[SDU.STU]Sciences of the Universe [physics]/Earth Sciences ,¹⁰Be ,Convection granulaire ,PDRM - Abstract
The direction and strength of geomagnetic field had been evolving continuously in the past. One of the few means of obtaining continuous reconstructions of this evolution relies on sedimentary records. The latter are therefore important for understanding the geodynamo and the underlying evolution of the Earth’s interior, as well as providing an important dating tool through magnetostratigraphy. Sedimentary records of geomagnetic field variations rely on two main recording mechanisms: the alignment of magnetic particles, which underlies continuous records of relative paleointensity (RPI), and the archivation of cosmogenic isotopes, in particular ¹⁰Be, whose production by cosmic ray spallation is modulated by the screening action of the dipole component of the Earth’s field. Previous studies reported similarities as well as significant differences between RPI and cosmogenic ¹⁰Be (expressed as ¹⁰Be/⁹Be) records. While a perfect match of the two records is not expected due to environmental contaminations present in both records, the similar changes during the periods characterised by significant decrease of the dipole moment are suggested owning to global field strength control of ¹⁰Be production and attenuation of non-dipolar features in RPI records measured within the sediments with the low sedimentation rates (, La direction et l’intensité du champ géomagnétique ont continuellement évolué dans le passé. L’un des rares moyens d’obtenir des reconstitutions continues de cette évolution repose sur les enregistrements sédimentaires. Ces dernières sont donc importants pour comprendre la géodynamo et l’évolution sous-jacente de l’intérieur de la Terre, ainsi que pour fournir un outil de datation important grâce à la magnétostratigraphie. Les enregistrements sédimentaires des variations du champ géomagnétique reposent sur deux mécanismes d’enregistrement principaux: l’alignement des particules magnétiques, qui sous-tend les enregistrements continus de la paléointensité relative (RPI), et l’archivage des isotopes cosmogéniques, en particulier le ¹⁰Be. Bien que l’on ne s’attende pas à une concordance parfaite des deux enregistrements, les changements similaires au cours des périodes caractérisées par une diminution significative du moment dipolaire sont suggérés grâce au contrôle global du champ de production de ¹⁰Be et à l’atténuation des caractéristiques non dipolaires dans les enregistrements RPI mesurés dans les sédiments avec les faibles taux de sédimentation. L’objectif du présent travail était d’améliorer nos connaissances actuelles sur les mécanismes d’enregistrement dans le cas des sédiments marins, en particulier :1. Les facteurs environnementaux responsables du transport et du retrait du 10Be de lacolonne d’eau et l’effet de la distribution des sources sur l’approvisionnement en ⁹Be.2. L’effet des processus post-dépôt, en particulier celui du mélange des sédiments, sur le10Be et les enregistrements RPI.3. Le mécanisme par lequel une magnétisation post-déposition est acquise près du fond dela couche mélangée en surface.4. Les causes d’un décalage systématique entre les enregistrements ¹⁰Be et RPI et lesfacteurs environnementaux affectant le RPI.Afin de démêler l’apport environnemental et magnétique dans les couches sédimentaires de ¹⁰Be/⁹Be, nous avons analysé cinq enregistrements, couvrant la dernière inversion géomagnétique. Les différentes caractéristiques d’enregistrement sur les cinq sites ont été décrites en termes de modulations climatiques additives et multiplicatives, qui dépendent essentiellement de la profondeur de l’eau, de la localisation le long des grands systèmes de courants océaniques, et de la distance à la côte. Les enregistrements RPI sont fortement affectés par les processus post-dépôt, en particulier le mélange des sédiments, qui est entièrement responsable de l’aimantation rémanente naturelle (NRM) acquise par les sédiments bioturbés, et son retard par rapport aux enregistrements ¹⁰Be. Un nouveau modèle de bioturbation a été développé pour expliquer la NRM sédimentaire dans les sédiments bioturbés. Ce modèle inclut un phénomène récemment découvert de ségrégation de taille dans la couche mélangée de surface (SML), analogue à l’effet bien connu de la noix du Brésil (Brazilian-nut). La ségrégation de taille est responsable de la plus longue permanence des grandes particules dans la SML, jusqu’au cas limite des nodules de ferromanganèse. Nous avons démontré l’effet de noix du Brésil sur les particules de microtektite, qui consiste en une ségrégation des fragments en fonction de leur taille. Le modèle de ségrégation par taille permet d’estimer la profondeur réelle du mélange sédimentaire dû à la bioturbation, une fois prise en compte la composante supplémentaire de vitesse liée à la migration des plus grosses particules vers le haut de la colonne sédimentaire.Les résultats de cette recherche ont une importance significative non seulement pour la caractérisation de la réponse au mélange des sédiments et la reconstruction des enregistrements affectés des processus de bioturbation (par exemple ¹⁰Be /⁹Be), mais aussi pour l’évaluation de la validité des modèles d’âge qui sont limités par les âges des traceurs conservateurs.
- Published
- 2020
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