Grain‐size dependence of the rock magnetic properties for a natural maghemite

Boer, Cor B. de; Dekkers, Mark J.

doi:10.1029/96gl00781

Cited by 62 publications

(44 citation statements)

References 18 publications

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“…B cr was 22 š 1 mT, slightly lower than that of magnetite but comparable to literature values (e.g. natural maghemite ¾23 mT [33]). …”

Section: Magnetic Analysis Of Maghemite Samplessupporting

confidence: 51%

“…Comparable temperature ranges have been reported in the literature (e.g. 510º-660ºC [30], ¾650ºC [33]). The results indicate -like in the case of magnetite -that the seemingly similar conditions under which the two batches were synthesised do not rule out the possibility of differences in magnetic or structural characteristics of the samples.…”

Section: Magnetic Analysis Of Maghemite Samplesmentioning

confidence: 55%

“…5) [33]). After heating to 700ºC, the remaining magnetisation at room temperature was approximately 1-3 A m 2 kg 1 .…”

Section: Magnetic Analysis Of Maghemite Samplesmentioning

confidence: 99%

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Dissolution behaviour of fine-grained magnetite and maghemite in the citrate–bicarbonate–dithionite extraction method

Oorschot

Dekkers

1999

Earth and Planetary Science Letters

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Mineral magnetic properties of soils and sediments are increasingly used as proxy parameters for environmental and palaeoclimate analysis. To investigate which magnetic minerals contribute to the environmental signal in the samples, chemical techniques such as the citrate-bicarbonate-dithionite (CBD) extraction method have been introduced in environmental magnetism studies. This technique is assumed to distinguish lithogenic (magnetite) from pedogenic (maghemite) mineral content in soils and sediments. Unfortunately, interpretation of the CBD extractions is not straightforward because the procedure is sometimes more suitable for distinction between grain size than for distinction between minerals. The procedure of the CBD extraction technique was investigated to determine the influence of extraction temperature and iron oxide concentration on the dissolution behaviour of the samples. Synthetic samples were extracted at three different temperatures (60º, 70º and 80ºC) at similar iron oxide concentration (5 wt%), and for three different concentrations (0.1 wt%, 1 wt% and 5 wt%) at the same temperature (60ºC). Our results show that a lower extraction temperature reduces the dissolution rate for all samples, while decrease in iron oxide concentration increases the dissolution rate. Thus, the parameters in the CBD procedure have a major influence on the dissolution behaviour of the samples. In practice this means that when natural samples of differing iron oxide concentration are extracted with this technique, the results of the extractions cannot be compared. Therefore, the outcome of this type of extraction experiment can only be accurately interpreted when the effect of the procedure on the dissolution behaviour is taken into account.

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“…B cr was 22 š 1 mT, slightly lower than that of magnetite but comparable to literature values (e.g. natural maghemite ¾23 mT [33]). …”

Section: Magnetic Analysis Of Maghemite Samplessupporting

confidence: 51%

Section: Magnetic Analysis Of Maghemite Samplesmentioning

confidence: 55%

See 1 more Smart Citation

Dissolution behaviour of fine-grained magnetite and maghemite in the citrate–bicarbonate–dithionite extraction method

Oorschot

Dekkers

1999

Earth and Planetary Science Letters

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“…• C (Özdemir & Banerjee 1984;Özdemir 1990;de Boer & Dekkers 1996;Dunlop &Özdemir 1997;de Boer et al 2001). Moreover, the high degree of reversibility of the curve at high temperatures suggests that this ash underwent the highest heating temperature.…”

Section: Susceptibility Variations At Temperatures Up To 700mentioning

confidence: 99%

Rock-magnetic analyses as a tool to investigate archaeological fired sediments: a case study of Mirador cave (Sierra de Atapuerca, Spain)

Carrancho

Villalaín

Angelucci

et al. 2009

Geophysical Journal International

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S U M M A R YHere we report a detailed mineral magnetic study of Neolithic burnt levels in the Mirador Cave (Sierra de Atapuerca, Burgos, Spain) to reconstruct the burning history and to investigate their suitability for archaeomagnetic purposes. As a consequence of the ancient burning, a characteristic facies sequence was developed along the Holocene stratigraphy. From top to bottom it includes: (i) 2-10 cm ash layers, (ii) ∼2 cm underlying rubefied layers and (iii) clay, mainly unburnt and of variable thickness. In some cases a thermally altered facies (2-6 cm) with a heterogeneous texture was identified (facies TF), usually between rubefactions and the unburnt levels. 126 oriented samples from 4 units (MIR12, 15, 18 and 21) and a 2 m section, all comprised between units MIR21 (6380 ± 40 14 C BP) and MIR9 (5090 ± 40 14 C BP) were analysed with rock magnetic methods. In addition, bulk sediment from each facies that comprise the Neolithic sequence was investigated. Measurements included: stepwise alternating field and thermal demagnetization of natural remanent magnetization (NRM), viscosity experiments, determination of the anisotropy of the magnetic susceptibility (AMS), the susceptibility frequency dependence at room temperature and determination of the temperature dependence of the susceptibility. Additional experiments consisted in the determination of the behaviour of anhysteretic and isothermal (IRM) remanences, magnetic hysteresis loops, first-order-reversal-curve diagrams, and thermal demagnetization of threeaxial IRM. It appeared that the facies all show a fairly similar magnetic mineralogy and grain size dominated by low-titanium magnetite that is often partially maghaemitized. Main differences constitute the amount of superparamagnetic particles that is higher in unburnt strata concurring with a less well-defined NRM behaviour. The magnetic mineral concentration is notably higher in ashes. This homogeneity strongly suggests that similar sources and burial conditions prevailed during Neolithic times. Agreeing with archaeological observations and favoured by rapid burial conditions, very limited alterations have been deduced. AMS data revealed the absence of fluid flow in the ash lenses sampled. Demagnetization revealed a stable single NRM component in ashes, a single or two-component NRM in rubefactions and less stable multicomponent behaviour in clays. In ashes, magnetic minerals are likely secondary in origin formed by low-temperature oxidization soon after burning. Although this thermochemical nature of the NRM invalidates the use of these sediments for palaeointensity studies, archaeomagnetic (directional) data can be successfully obtained because the burning and oxidation are closely confined in time.

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“…Those parameters also indicate an upward decrease in grain size of the ferrimagnetic minerals between 215 and 170 mbsf at Site 1115 and 320 and 280 mbsf at Site 1109. De Boer and Dekkers (1996) showed that the grain-size dependence of rock magnetic parameters for PSD maghemite is less prominent than for magnetite. Variations in the rock magnetic parameters for our samples may therefore mainly reflect the grain-size changes in magnetite.…”

Section: Discussionmentioning

confidence: 99%

Magnetic properties of sediments from Ocean Drilling Program sites 1109, 1115, and 1118 (Leg 180), Woodlark Basin (Papua New Guinea)

Ishikawa

Frost

2014

Earth Planet Sp

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Latest Miocene-Pleistocene synrift sediments at Ocean Drilling Program sites 1109, 1115, and 1118 (Leg 180), located on the hanging wall margin north of the Moresby fault in the Woodlark Basin, showed variations in magnetic parameters carried by magnetite and maghemite related to sedimentation process in the basin. At sites 1109 and 1115, an increase in the sedimentation rate at 3.8 Ma was accompanied by the deposition of sediments with low ferrimagnetic mineral concentrations. An increase in the ferrimagnetic mineral concentrations occurred between 3.4 Ma and 3.2 Ma at the three sites. The onset age of the change became younger with distance from the subsidence center of the basin near the Moresby fault: 3.4 Ma at Site 1118, 3.3 Ma at Site 1109, and 3.2 Ma at Site 1115, which implies a northward onlapping of sediments with high ferrimagnetic mineral concentration. Sediments with finer-grained ferrimagnetic minerals were deposited between 2.3 and 2.0 Ma at sites 1118 and 1109 and later, 2.8 Ma at Site 1115 during a period of a low sedimentation rate. The upper parts of sites 1109 and 1115 had a diamagnetic contribution, which is attributed to relatively high concentrations of diamagnetic pelagic materials at a low sedimentation rate associated with the low frequency of turbidites.

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Grain‐size dependence of the rock magnetic properties for a natural maghemite

Cited by 62 publications

References 18 publications

Dissolution behaviour of fine-grained magnetite and maghemite in the citrate–bicarbonate–dithionite extraction method

Dissolution behaviour of fine-grained magnetite and maghemite in the citrate–bicarbonate–dithionite extraction method

Rock-magnetic analyses as a tool to investigate archaeological fired sediments: a case study of Mirador cave (Sierra de Atapuerca, Spain)

Magnetic properties of sediments from Ocean Drilling Program sites 1109, 1115, and 1118 (Leg 180), Woodlark Basin (Papua New Guinea)

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