Biogenic magnetite, detrital hematite, and relative paleointensity in Quaternary sediments from the Southwest Iberian Margin

Channell, James E T; Hodell, David A; Margari, Vasiliki; Skinner, Luke C; Tzedakis, Polychronis C.; Kesler, Michael S.

doi:10.1016/j.epsl.2013.06.026

Cited by 43 publications

(51 citation statements)

References 66 publications

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“…[] reported NRM/ARM ratios that are 2–4 times higher for biogenic magnetite with respect to a detrital component, while Channell et al . [] did not report significant differences between the two components.…”

Section: Discussionmentioning

confidence: 87%

Natural remanent magnetization acquisition in bioturbated sediment: General theory and implications for relative paleointensity reconstructions

Egli

Zhao

2015

Geochem Geophys Geosyst

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We present a general theory for the acquisition of natural remanent magnetizations (NRM) in sediment under the influence of (a) magnetic torques, (b) randomizing torques, and (c) torques resulting from interaction forces. Dynamic equilibrium between (a) and (b) in the water column and at the sedimentwater interface generates a detrital remanent magnetization (DRM), while much stronger randomizing torques may be provided by bioturbation inside the mixed layer. These generate a so-called mixed remanent magnetization (MRM), which is stabilized by mechanical interaction forces. During the time required to cross the surface mixed layer, DRM is lost and MRM is acquired at a rate that depends on bioturbation intensity. Both processes are governed by a MRM lock-in function. The final NRM intensity is controlled mainly by a single parameter c that is defined as the product of rotational diffusion and mixed-layer thickness, divided by sedimentation rate. This parameter defines three regimes: (1) slow mixing (c < 0.2) leading to DRM preservation and insignificant MRM acquisition, (2) fast mixing (c > 10) with MRM acquisition and full DRM randomization, and (3) intermediate mixing. Because the acquisition efficiency of DRM is larger than that of MRM, NRM intensity is particularly sensitive to c in case of mixed regimes, generating variable NRM acquisition efficiencies. This model explains (1) lock-in delays that can be matched with empirical reconstructions from paleomagnetic records, (2) the existence of small lock-in depths that lead to DRM preservation, (3) specific NRM acquisition efficiencies of magnetofossil-rich sediments, and (4) some relative paleointensity artifacts.

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Section: Discussionmentioning

confidence: 87%

Natural remanent magnetization acquisition in bioturbated sediment: General theory and implications for relative paleointensity reconstructions

Egli

Zhao

2015

Geochem Geophys Geosyst

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“…Similarly, Channell et al (2013) detected hematite in marine sediments by rock magnetic characterization but did not observe hematite in magnetic extracts collected by a peristaltic pump-driven magnetic extraction system. The results described here suggest that these weaker magnetic minerals may be efficiently analyzed through the characterization of residue portions after primary extraction is complete.…”

Section: Broader Impactsmentioning

confidence: 89%

“…For example, pelagic marine carbonates contain biogenic magnetic minerals that may provide clues to the types of ocean environments in which they were formed (Roberts et al 2013). By magnetically separating the biogenic magnetic minerals from these sediments and analyzing by TEM, researchers have been able to interpret magnetic mineral morphologies as evidence of certain magnetotactic bacteria, which may serve as a proxy for environmental conditions at time of deposition Roberts et al 2012;Channell et al 2013). More specifically, studies of the magnetic mineral assemblages within carbonaterich marine sediments across the , 55 Ma Paleocene-Eocene Thermal Maximum, one of the largest and least understood periods of climate variability, have been used to create environmental paleothermometers (Schumann et al 2008) and to infer a possible cometary impact as a trigger (Kent et al 2003).…”

Section: Broader Impactsmentioning

confidence: 98%

Simple and Efficient Separation of Magnetic Minerals From Speleothems and Other Carbonates

Strehlau

Hegner

Strauss

et al. 2014

Journal of Sedimentary Research

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Trace concentrations of iron oxide minerals in carbonate sediments can preserve fine details about Earth processes, from high-resolution recordings of the Earth's ancient magnetic field to microscopic remnants of extraterrestrial impacts. This paper presents a novel flask extraction method which uses a neodymium magnet and an orbital shaker for simple and efficient separation of magnetic minerals from carbonate sediments. A mineral assemblage of magnetic standards (titanomagnetite, magnetite, goethite, and hematite) combined with other mineral standards (kaolinite, quartz, and nanoscale TiO 2 ) was subjected to the extraction procedure and compared to a natural speleothem sample. Exposure of the magnetic standards to a mildly acidic acetate buffer (pH , 4) did not cause physical or chemical alteration. The strongly magnetic minerals were reproducibly extracted, with greater than 90% efficiency (by mass), from mixtures of the mineral standards. XRD and low-temperature magnetic characterization demonstrated phase purity of the extracts. Quantitative comparison with two commonly used literature methods showed that the flask extraction method was more reproducible and efficient. The addition of surfactant (Na(PO 3 ) 6 ) did not significantly improve extraction efficiency. Sequential dissolution and flask extraction of a simulated speleothem containing magnetic particles resulted in consistent extraction efficiencies for samples containing large (. 1 mm) strongly magnetic grains, but a reduction in efficiency was observed for smaller (, 1 mm) grain sizes. No method successfully extracted the weakly magnetic goethite and hematite. However, unprecedented, representative characterization of these minerals was possible through quantitative analysis of the remainder after the collection of the magnetic extract. This approach may facilitate detailed characterization of a wide range of carbonates, such as pelagic limestone, dolostone, unlithified carbonate ooze, speleothems, and freshwater and pedogenic carbonates. Such mineral extractions can lead to new insights into paleoenvironmental processes as well as an improved understanding of the recording of the Earth's magnetic field.

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“…An apparent RPI minimum at ~13 ka appears in some individual RPI records, as a notch in RPI stacks (Figure ), and in virtual axial dipole moment (VADM) proxies from 10 Be flux in Greenland ice cores (Channell et al, ). In one core from the Iberian Margin (MD01‐2444), a pronounced RPI minimum at ~13 ka is associated with a directional magnetic excursion (Channell et al, ). The apparent RPI minimum at ~13 ka in core MD01‐2444 coincides with the old‐end of the 0‐14 ka Holocene paleointensity model of Pavón‐Carrasco et al ().…”

Section: The Geomagnetic Fieldmentioning

confidence: 99%

The Role of Geomagnetic Field Intensity in Late Quaternary Evolution of Humans and Large Mammals

Channell

Vigliotti

2019

Reviews of Geophysics

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It has long been speculated that biological evolution was influenced by ultraviolet radiation (UVR) reaching the Earth's surface, despite imprecise knowledge of the timing of both UVR flux and evolutionary events. The past strength of Earth's dipole field provides a proxy for UVR flux because of its role in maintaining stratospheric ozone. The timing of Quaternary evolutionary events has become better constrained by fossil finds, improved radiometric dating, use of dung fungi as proxies for herbivore populations, and improved ages for nodes in human phylogeny from human mitochondrial DNA and Y chromosomes. The demise of Neanderthals at ~41 ka can now be closely tied to the intensity minimum associated with the Laschamp magnetic excursion, and the survival of anatomically modern humans can be attributed to differences in the aryl hydrocarbon receptor that has a key role in the evolutionary response to UVR flux. Fossil occurrences and dung‐fungal proxies in Australia indicate that episodes of Late Quaternary extinction of mammalian megafauna occurred close to the Laschamp and Blake magnetic excursions. Fossil and dung fungal evidence for the age of the Late Quaternary extinction in North America (and Europe) coincide with a prominent decline in geomagnetic field intensity at ~13 ka. Over the last ~200 kyr, phylogeny based on mitochondrial DNA and Y chromosomes in modern humans yields nodes and bifurcations in evolution corresponding to geomagnetic intensity minima, which supports the proposition that UVR reaching Earth's surface influenced mammalian evolution with the loci of extinction controlled by the geometry of stratospheric ozone depletion.

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Biogenic magnetite, detrital hematite, and relative paleointensity in Quaternary sediments from the Southwest Iberian Margin

Cited by 43 publications

References 66 publications

Natural remanent magnetization acquisition in bioturbated sediment: General theory and implications for relative paleointensity reconstructions

Natural remanent magnetization acquisition in bioturbated sediment: General theory and implications for relative paleointensity reconstructions

Simple and Efficient Separation of Magnetic Minerals From Speleothems and Other Carbonates

The Role of Geomagnetic Field Intensity in Late Quaternary Evolution of Humans and Large Mammals

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