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Re: soil magnetic susceptibilities
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Newsgroup: sci.archaeology
Posted by:
2007-12-11 08:18:16



Digger schrieb:
> > Thanks for the pointing out the paper by Caggiano et al. Their values
> > (from 8*10^-5 to 185*10^-5) are unambiguous and they look sensible
> > indeed. (The highest values were found next to a road with heavy
> > traffic, the lowest ones in an uncultivated area.)
>
> The values in the Caggiano paper look remarkably low compared to the types
> of readings I've obtained in the field. These would suggest to me that the
> soils are very thin and that there has been little if any prolonged
> occupation in the area. I suspect any agricultural activity has probably
> been fairly recent and I that there has not been much in the way of soil
> enrichment through the addition of organic material.
>
> The types of readings they report are in a similar ball park to the types of
> reading I have obtained off chalk bedrock in the south of England AFTER the
> top soil has been stripped away.

In an earlier post you mentioned readings from "0.16 SI" to "180 SI".
If these are suceptibilities in SI units, all your soils would have
stuck to a conventional permanent magnet - some strongly, some less
so; a value of 180 is in the ballpark of the susceptibilities for
industrial soft iron.

It is known that natural processes often lead to an enrichment of iron
in the topsoil, sometimes to the point that you find more than 50%
iron ore; indeed such deposits were mined for iron production in
historic and prehistoric times (so-called "Raseneisenerz" in Germany).

Iron ores like these will certainly stick to a permanent magnet, but
common soils do not in my experience. I consider it likely that your
readings (as well as the Oxford and Vienna numbers mentioned) include
an unstated negative power of ten as also suspected by JS. What does
the instrument manual say?

Martin.

 

 

 

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