Relative geomagnetic intensity of the field during the last 140 ka

Meynadier, L.; Valet, Jean‐Pierre; Weeks, Robin; Shackleton, Nicholas J; Hagee, V. Lee

doi:10.1016/0012-821x(92)90150-t

Cited by 190 publications

(138 citation statements)

References 20 publications

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“…The record also shows significant agreement with earlier studies from the western equatorial Pacific by Constable and Tauxe (1987) and Tauxe and Wu (1990). Furthermore, Meynadier et al (1992) have obtained a 140-k.y. record from the Somali Basin that closely reproduces features in the Mediterranean record of Trie et al (1992).…”

Section: Introductionsupporting

confidence: 81%

Mineral Magnetic Properties of Middle and Upper Pleistocene Sediments at Sites 883, 884, and 887, North Pacific Ocean

Roberts¹,

Verosub²,

Weeks³

et al. 1995

Proceedings of the Ocean Drilling Program, 145 Scientific Results

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Mineral magnetic studies have been conducted on middle and upper Pleistocene sediments from Holes 883D, 884D, and 887B in the North Pacific Ocean to assess their suitability for determinations of relative paleointensity of the geomagnetic field. Thermomagnetic and high-field hysteresis data suggest that the magnetic mineralogy of the clay-rich sediments at Holes 883D and 884D is dominated by pseudosingle domain magnetite in a narrow grain-size range. The uniform grain size of the magnetic particles in the clay-rich sediment is consistent with sorting and transport by long-distance bottom currents. Coarse-grained magnetic minerals occur in high concentrations in restricted stratigraphic intervals where volcanic ashes occur. Apart from these intervals, the sediments meet the established criteria for relative paleointensity studies. Such studies are now in progress. The sediments at Hole 887B are not suitable for relative paleointensity determinations because of large variations in both grain size and concentration of magnetite. In particular, reductive diagenesis appears to have caused preferential dissolution of fine-grained magnetite in diatomrich intervals in Hole 887B. Significant variation in the magnetic properties of diatom-, clay-, and tephra-rich parts of all the sequences preclude a straightforward interpretation o f tne magnetic susceptibility signal as a paleoclimate proxy as is the case in depositional environments that are dominated by climatically modulated CaCO 3 fluctuations.

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Section: Introductionsupporting

confidence: 81%

Mineral Magnetic Properties of Middle and Upper Pleistocene Sediments at Sites 883, 884, and 887, North Pacific Ocean

Roberts¹,

Verosub²,

Weeks³

et al. 1995

Proceedings of the Ocean Drilling Program, 145 Scientific Results

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“…Parameter S was used to calculate ratio of "soft" minerals to "hard" minerals, Meynadier et al (1992) (Fig. 3(b)).…”

Section: Resultsmentioning

confidence: 99%

Holocene geomagnetic secular variations recorded by sediments from Escondido Lake (south Argentina)

Gogorza

Sinito

Tommaso³

et al. 2014

Earth Planet Sp

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Paleomagnetic and sedimentological studies carried out on two short cores and nine long cores from the bottom sediments from Escondido Lake (south-western Argentina) are described.Rock magnetic analysis suggests that the main carriers of magnetization seems to be ferrimagnetic minerals, predominantly pseudo single domain magnetite. The presence of greigite, as diagenetic euxinic material, is also suggested.Calibrated ages were calculated from radiocarbon dating and a transfer function shortened depth-age is built, which suggests the existence of a hiatus, supported by the suggestion of previous palynological studies about the possible evidence of the younger Dryas cooling event seen in the Antarctic ice cores.The stacked inclination and declination curves and their standard deviations using arithmetical average after chronostratigraphic correlations are made.Inclination data show two well defined periods: a long period (about 7700 years) and a short one (between 2660 and 2900 years). Declination data show two intermediate periods (about 3600 and 2900 years respectively) and a long, although less reliable, period (about 10000 years). The longer periods may be related to dipolar variations, while the shorter periods may be associated to non dipolar variations.

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“…Zheng et al (1995) used the NRM/ARM ratio after thermal demagnetization at 300C to represent the relative paleointensity for paleosol S1 in the Huanxian section, and compared the results with stacked paleointensity records from the Somali Basin and Mediterranean Seas (Meynadier et al, 1992;Tric et al, 1992) remanence records except for that of Pan et al (2001) were published with respect to depth, and have been re-scaled in Figure 5.8 based on the age control points provided in the original papers. Even if one were to stretch and squeeze the records to "tune" features to improve correlations, there is no obvious correspondence among these records, including the normalized remanence record obtained in this study.…”

Section: Comparison Of Normalized Remanences With Those From Other Lomentioning

confidence: 99%

How does Chinese loess become magnetized?

Zhao

Roberts

2010

Earth and Planetary Science Letters

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Thick loess deposits on the Chinese Loess Plateau provide an outstanding archive of paleoclimate, geomagnetic field and paleoenvironmental changes over at least the last 2.6 Ma. Much work on magnetic polarity reversals, pedogenic magnetic enhancement and climatic change has been carried out over the past 30 years. However, questions about how Chinese loess becomes magnetized remain unanswered. In this thesis, I have sought to address key questions concerning magnetization processes in the Chinese loess. To understand magnetization processes, it is important to understand which magnetic minerals are present and the processes that caused them to be present. Magnetic and other analyses of both loess and paleosol samples indicate that pedogenic superparamagnetic and single domain magnetite and hematite can be present. The mass concentration of hematite can exceed 90% of the magnetic particle assemblage. An eolian dust deposition simulator designed for laboratory redeposition experiments was then used to demonstrate that both a depositional remanent magnetization (DRM) and a post-depositional remanent magnetization (PDRM) can be acquired by Chinese loess. Water content significantly affects the efficiency of PDRM acquisition. No significant PDRM was observed when the water content was below a critical threshold of 40%. Published paleomagnetic data from the Chinese loess indicate the widespread occurrence of inclination error. Detailed paleomagnetic studies of U-channel samples from the last loess/paleosol sequence at Yuanbao were made to assess whether the Chinese loess can accurately record geomagnetic relative paleointensity variations. Three normalized remanence records were determined using conventional normalization as well as the pseudo-Thellier method. Strong coherence among the normalized remanence records indicate that the whole range of magnetic minerals has been affected by pedogenesis. Poor similarity among published normalized remanence records from the Chinese loess, as well as with marine relative paleointensity records indicate that the Chinese loess is not suitable for relative paleointensity determinations. The range of magnetic minerals present and their varying distribution within loess and paleosol sediments indicate that the magnetization is due to a mixture of remanence acquisition mechanisms including DRM, PDRM, chemical remanent magnetization (CRM) and viscous remanent magnetizations, which also indicates complexities in remanence acquisition that will complicate attempts to extract relative paleointensity information. This thesis has provided an improved understanding of the mechanisms of Chinese loess magnetization, and re-emphasizes the importance of pedogenic CRM acquisition.

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Relative geomagnetic intensity of the field during the last 140 ka

Cited by 190 publications

References 20 publications

Mineral Magnetic Properties of Middle and Upper Pleistocene Sediments at Sites 883, 884, and 887, North Pacific Ocean

Mineral Magnetic Properties of Middle and Upper Pleistocene Sediments at Sites 883, 884, and 887, North Pacific Ocean

Holocene geomagnetic secular variations recorded by sediments from Escondido Lake (south Argentina)

How does Chinese loess become magnetized?

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