Geomagnetic Events and Relative Paleointensity Records — Clues to High-Resolution Paleomagnetic Chronostratigraphies of Late Quaternary Marine Sediments?

Bleil, Ulrich; Dobeneck, Tilo von

doi:10.1007/978-3-642-58646-0_26

Cited by 33 publications

(38 citation statements)

References 39 publications

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“…The remanence acquisition process in sediments, however, is only partly known. Gradual lock-in over a long time period can lead to smoothing of the geomagnetic field record (Hyodo 1984;Langereis et al 1992;Bleil and Dobeneck 1999) and to a biased paleointensity distribution (Mazaud 1996). Therefore, sedimentary records are generally considered to be less reliable than volcanic records.…”

Section: Paleomagnetic Data and Its Interpretationmentioning

confidence: 99%

Polarity Reversals from Paleomagnetic Observations and Numerical Dynamo Simulations

2010

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Recent advances in the study of geomagnetic field reversals are reviewed. These include studies of the transitional field during the last geomagnetic reversal and the last geomagnetic excursion based on paleomagnetic observations, and analysis of reversals in self-consistent 3D numerical dynamo simulations. Field models inferred from observations estimate reversal duration in the range of 1-10 kyr (depending on site location). The transitional fields during both the Matuyama/Brunhes reversal and the Laschamp excursion are characterized by low-latitude reversed flux formation and subsequent poleward migration. During both events the dipole as well as the non-dipole field energies decrease. However, while the non-dipole energy dominates the dipole energy for a period of 2 kyr in the reversal, the non-dipole energy merely exceeds the dipole energy for a very brief period during the excursion. Numerical dynamo simulations show that stronger convection, slower rotation, and lower electrical conductivity provide more favorable conditions for reversals. A nondimensional number that depends on the typical length scale of the flow and represents the relative importance of inertial effects, termed the local Rossby number, seems to determine whether a dynamo will reverse or not. Stable polarity periods in numerical dynamos may last about 1 Myr, whereas reversals may last about 10 kyr. Numerical dynamo reversals often involve prolonged dipole collapse followed by shorter directional instability of the dipole axis, with advective processes governing the field variation. Magnetic upwellings from the equatorial inner-core boundary that produce reversed flux patches at low-latitudes of the core-mantle boundary could be significant in triggering reversals. Inferences from the observational and modeling sides are compared. We summarize with an outlook on some open questions and future prospects.H. Amit ( )

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Section: Paleomagnetic Data and Its Interpretationmentioning

confidence: 99%

Polarity Reversals from Paleomagnetic Observations and Numerical Dynamo Simulations

2010

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“…Verosub 1997). The lock-in depth is related to sedimentation rate and composition (Bleil & von Dobeneck 1999), and is generally considered to be around 10 cm depth (e.g. Roberts & Winklhofer 2004).…”

Section: Introductionmentioning

confidence: 99%

New directional archeomagnetic data of burned cave sediments from Switzerland and geomagnetic field variations in Central Europe

Kapper¹,

Donadini²,

Mauvilly

et al. 2014

Geophysical Journal International

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S U M M A R YThis paper presents new directional archaeomagnetic data from nine Meso-/Neolithic fireplaces, sampled in a cave shelter, at Arconciel, in western Switzerland. Rock magnetic measurements indicate a homogenous magnetic mineralogy in all fireplaces, with magnetite as the main magnetic carrier. The remanent magnetization is stable and generally shows one characteristic directional component. Nine new directions, which were obtained from Arconciel, are combined with 356 other archaeomagnetic data from a circular area with a radius of 700 km around this site, to obtain a penalized least square spline fit for the past 9000 yr. We found in general good agreement with other local compilations, such as the Balkan curve, the regional SCHA.DIF.8k model and with lake sediments from UK, Fennoscandia and Switzerland. Nevertheless, a time lag of several centuries is observed for a declination maximum between the archaeomagnetic spline fit and the other European data records around 5900 BC. This time lag is also observed in the Swiss lake sediment record; therefore we interpret this shift as a local feature of the Earth's magnetic field.

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“…The effects of remanence smoothing on paleomagnetic records can be constrained by numerical modelling of post-depositional remanent magnetization (PDRM) acquisition (e.g., Bleil and von Dobeneck, 1999;Roberts and Winklhofer, 2004). The PDRM lock-in depth would have to be unrealistically large to cause significant smoothing of paleomagnetic records at estimated sedimentation rates in the range from 0.8 to 2 m/k.y.…”

Section: Are Recording Artefacts Likely To Have Compromised the Paleomentioning

confidence: 99%

“…PDRM smoothing is therefore extremely unlikely in the present record. A more serious concern is that variations in sediment grain size or lithology could have also led to large variations in magnetic grain size, which can cause variable lock-in efficiency (e.g., Bleil and von Dobeneck, 1999). This possibility can be investigated with rock magnetic data, such as the FORC diagrams that are shown for the studied transition interval from CRP-2 in Fig.…”

Section: Are Recording Artefacts Likely To Have Compromised the Paleomentioning

confidence: 99%

High-resolution evidence for dynamic transitional geomagnetic field behaviour from a Miocene reversal, McMurdo Sound, Ross Sea, Antarctica

et al. 2007

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We report a high-resolution record of a Miocene polarity transition (probably the Chron C6r-C6n transition) from glacimarine sediments in McMurdo Sound, Ross Sea, Antarctica, which is the first transition record reported from high southern latitudes. The transition is recorded in two parallel cores through a 10.7 m stratigraphic thickness. The sediments are interpreted as having been deposited in a marine environment under the influence of floating ice or seaward of a glacier terminus from which a large sediment load was delivered to the drill site. The core was recovered using rotary drilling, which precludes azimuthal orientation of the core and determination of a vector record of the field during the transition. However, constraints on transitional field behaviour are provided by the exceptional resolution of this record. Large-scale paleomagnetic inclination fluctuations in the two cores can be independently correlated with each other using magnetic susceptibility data, which suggests that the sediments are reliable recorders of geomagnetic field variations. Agreement between the two parallel transition records provides evidence for highly dynamic field behaviour, as suggested by numerous large-scale inclination changes (∼90• ) throughout the transition. These large-scale changes occur across stratigraphically narrow intervals, which is consistent with the suggestion of rapid field changes during transitions. In one intact portion of the core, where there is no apparent relative core rotation between samples, declinations and inclinations are consistent with the presence of a stable cluster of virtual geomagnetic poles within the transition (although the possibility that this cluster represents a rapid depositional event cannot be precluded). These observations are consistent with those from other high-resolution records and provide a rare detailed view of transitional field behaviour compared to most sedimentary records, which are not as thick and which appear to have been smoothed by sedimentary remanence acquisition processes.

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Geomagnetic Events and Relative Paleointensity Records — Clues to High-Resolution Paleomagnetic Chronostratigraphies of Late Quaternary Marine Sediments?

Cited by 33 publications

References 39 publications

Polarity Reversals from Paleomagnetic Observations and Numerical Dynamo Simulations

Polarity Reversals from Paleomagnetic Observations and Numerical Dynamo Simulations

New directional archeomagnetic data of burned cave sediments from Switzerland and geomagnetic field variations in Central Europe

High-resolution evidence for dynamic transitional geomagnetic field behaviour from a Miocene reversal, McMurdo Sound, Ross Sea, Antarctica

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