Magnetic hysteresis of limestones: facies control?

Of the many petrophysical properties such as acoustic velocity, dielectric constant, electrical resistivity, etc., the widest variation is shown by magnetic responses. Susceptibilities commonly range over 4 orders of magnitude between different lithic samples. Thus, magnetic properties show great potential for the characterization, provenance‐determination, thermal history, and treatment of stone tools and masonry. In order of increasing complexity and decreasing value to the archaeologist, we recommend low‐field susceptibility, saturation remanence, hysteresis ratios, isothermal remanence acquisition, and alternating field demagnetization of a saturation remanence. The natural remanence (NRM) is rarely of any value in characterizing artifacts. The physical basis for this discrimination is the nature of the magnetic minerals, their abundance and distribution through the sample, and, for remanence‐bearing minerals, their domain structure, crystallographic perfection, and grain‐size. These characteristics may be changed in distinctive ways by cultural effects such as percussion or fire, and surface conditions such as frost action, forest fires, or subsequent weathering. © 1998 John Wiley & Sons, Inc.

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“…For example, 0.1% magnetite can swamp the low field susceptibility of clay or carbonate rock (Borradaile, 1988;Borradaile et. al., 1993a).…”

Section: Introductionmentioning

confidence: 99%

Characterizing stone tools by rock-magnetic methods

Borradaile

Stewart

Ross³

1998

Geoarchaeology

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“…The differences between the calibration curves for the pelagic Mediterranean-region limestones and the shallowerwater Lincolnshire Oolite are attributed to magnetic mineralogy controlled by depositional environments. This hypothesis is supported by circumstantial evidence based on comparisons of hysteresis data for different limestones facies that include those discussed here (Borradaile et al, 1993;Borradaile and Hamilton, 2003). The pelagic limestone's properties permit greater resolution for classical historical times, whereas the Jurassic Oolite of Lincolnshire is more precise over a medieval range, corresponding to the respective suitability of their rock magnetic behavior.…”

Section: Discussionmentioning

confidence: 72%

“…The most important factor controlling the relaxation time, at average surface temperatures (20°C or 293°K) is relatively easy to comprehend: grain volume. Moreover, ferromagnetic grain-size may be related to rock type (e.g., clastic vs. pelagic limestone; Borradaile et al, 1993;Borradaile and Hamilton, 2003).…”

Section: Principles Of Viscous Remanent Magnetizationmentioning

confidence: 99%

Installation age of limestone masonry determined from its viscous remagnetization

Borradaile

Almqvist

2005

Geoarchaeology

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Many rocks passively acquire some time-dependent or "viscous" remanent magnetism (VRM) at ambient temperatures, without any extraordinary energetic intervention. This magnetization overprints existing remanent magnetization so that it is effectively a remagnetization subparallel to the contemporary geomagnetic field, averaging the geomagnetic field orientation. Certain limestone masonry remagnetizes viscously over an archaeologically useful interval (100 to 8000 Ka) so that the degree of remagnetization is monotonically (but not linearly) related to the construction age. The laboratory unblocking temperature (T UB ) that removes the viscous magnetization is a simple monotonic measure of relative age. The longer a piece of masonry remained stabilized in a certain orientation, the greater is its viscous remagnetization and the higher is its T UB . Monuments of known age with a similar limestone source permit us to establish a calibration curve of T UB against historical ages. The resulting calibration curve may then be used to predict the ages of otherwise-undated masonry. Viscous remanent magnetism dating provides precision of Ͻ 50a in medieval monuments in England and Ͻ 150a precision for classical to Neolithic monuments in Cyprus; precision depends on the remagnetization rate of the limestone in question. Our calibration curves, for the Jurassic Oolitic Limestone of England and for the LefkaraPakhna Chalks of Cyprus, allowed us to investigate the authenticity of a medieval English synagogue in Lincoln, England, and of a medieval house in Cyprus. Multiple archaeologic VRMs show that masonry was recycled in historical times.

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“…This material is then dispersed by bottom currents throughout ocean basins and the MS of the sediments increases accordingly. This hypothesis is that most commonly cited to explain MS variations (Borradaile et al 1993, Robinson 1993, English 1999, Ellwood et al 2000, Stage 2001. Other mechanisms, also related to sea level change, can be responsible for increase of magnetic materials in sedimentary basins during lowering sea level.…”

Section: Discussionmentioning

confidence: 81%

“…A few studies proposed a link between MS and depositional environment (Borradaile et al 1993, Da Silva & Boulvain 2006, Da Silva et al 2009a. These studies presented different MS/depositional environment responses in different platform types, suggesting that sealevel changes leading to variation in detrital input are not the only parameter controlling average MS values.…”

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confidence: 99%

Sedimentology and magnetic susceptibility of Mississippian (Tournaisian) carbonate sections in Belgium

Bertola¹,

Boulvain²,

Silva³

et al. 2012

Bull. Geosci.

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Magnetic susceptibility (MS) and biostratigraphy have been used to correlate better the reference sections of the Belgian Tournaisian, the Rivage road and railway sections and the Gendron-Celles railway section. These 200 m thick time-equivalent sections are about sixty kilometres apart and belong to two different sedimentation areas: a shallow ramp setting for Rivage (Condroz Sedimentation Area) and a subsiding area for Gendron (Dinant Sedimentation Area). The sedimentological model shows that both sections are characterized by a carbonate-dominated sedimentation (crinoids-peloids-algae assemblages), interrupted by more argillaceous facies related to rapid sea-level rises (crinoids-brachiopods-bryozoans assemblages). Accommodation space was significantly higher in the DSA and allowed the development of Waulsortian buildups during the Ivorian. Variations of magnetic susceptibility (MS) seem to be related to fluctuations in detrital input and carbonate productivity. MS evolution with palaeogeography can be integrated in the previously published model for the Devonian ramp system: external ramp settings have low carbonate productivity, low water agitation and high MS, whereas more proximal environments are characterized by higher carbonate productivity, higher water agitation and lower MS. MS curves are in general agreements with the 3 rd -order sequence interpretation. Lowstand system tracts (LST) show the highest MS values while transgressive system tracts (TST) are characterized by decreasing values and highstand system tracts/falling stage system tracts (HST/FSST) by the lowest values.•

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Magnetic hysteresis of limestones: facies control?

Cited by 35 publications

References 23 publications

Characterizing stone tools by rock-magnetic methods

Characterizing stone tools by rock-magnetic methods

Installation age of limestone masonry determined from its viscous remagnetization

Sedimentology and magnetic susceptibility of Mississippian (Tournaisian) carbonate sections in Belgium

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