Geoarchaeology

Geoarchaeology is a sub-field of archaeology which uses the techniques and subject matter of geology and other earth sciences to examine topics which inform archaeological knowledge and thought.

Geoarchaeologists study the natural physical processes that affect archaeological sites such as geomorphology, the formation of sites through geological processes and the effects on buried sites and artifacts post-deposition.

Geoarchaeologists' work frequently involves studying soil and sediments as well as other geographical concepts to contribute an archaeological study.

Techniques used in geoarchaeology

Column sampling

Column sampling is a technique of collecting samples from a section for analyzing and detecting the buried processes down the profile of the section. Narrow metal tins are bashed into the section in a series to collect the complete profile for study. If more than one tin is needed they are arranged offset and overlapping to one side so the complete profile can be rebuilt offsite in laboratory conditions.

Loss on ignition testing

Loss on ignition testing for soil organic content.- a technique of measuring organic content in soil samples. Samples taken from a known place in the profile collected by column sampling are weighed then placed in a fierce oven which burns off the organic content. The resulting cooked sample is weighed again and the resulting loss in weight is an indicator of organic content in the profile at a certain depth. These readings are often used to detect buried soil horizons. A buried soil's horizons may not be visible in section and this horizon is an indicator of possible occupation levels. Ancient land surfaces especially from the prehistoric era can be difficult to discern so this technique is useful for evaluating an areas potential for prehistoric surfaces and archaeological evidence. Comparative measurements down the profile are made and a sudden rise in organic content at some point in the profile combined with other indicators is strong evidence for buried surfaces.

Magnetic susceptibility analysis

The magnetic susceptibility of a material is a measure of its ability to become magnetised by an external magnetic field (Dearing, 1999). The magnetic susceptibility of a soil reflects the presence of magnetic iron-oxide minerals such as maghaematite; just because a soil contains a lot of iron does not mean that it will have high magnetic susceptibility. Magnetic forms of iron can be formed by burning and microbial activity such as occurs in top soils and some anaerobic deposits. Magnetic iron compounds can also be found in igneous and metamorphic rocks.

The relationship between iron and burning means that magnetic susceptibility is often used for:
* Site prospection, to identify areas of archaeological potential prior to excavation.
* Identifying hearth areas and the presence of burning residues in deposits (Tite and Mullins, 1971).
* Explaining whether areas of reddening are due to burning or other natural processes such as gleying (waterlogging).

The relationship between soil formation and magnetic susceptibility means that it can also be used to:
* Identify buried soils in depositional sequences.
* Identify redeposited soil materials in peat, lake sediments etc.

Phosphate and orthophosphate content with spectrophotometetry

Particle size analysis

The particle size distribution of a soil sample may indicate the conditions under which the strata or sediment were deposited. Particle sizes are generally separated by means of dry or wet sieving (coarse samples such as till, gravel and sands, sometimes coarser silts) or by measuring the changes of the density of a dispersed solution (in sodiumpyrophosphate, for example))of the sample (finer silts, clays). A rotating clock-glass with a very fine-grained dispersed sample under a heat lamp is useful in separating particles.

The results are plotted on curves which can be analyzed with statistical methods for particle distribution and other parameters.

The fractions received can be further investigated for cultural indicators, macro- and microfossils and other interesting features, so particle size analysis is in fact the first thing to do when handling these samples.

Archaeological geology

Archaeological geology (term coined by Werner Kasig, 1980), is a sub-field of geology which emphasises the value of earth constituents for human life.

ee also

*Deposit model

References

* Slinger , A., Janse , H.. and Berends , G. 1980 . Natuursteen in monumenten. Zeist / Baarn Rijksdienst voor de Monumentenzorg.
* Kasig, Werner 1980. Zur Geologie des Aachener Unterkarbons (Linksrheinisches Schiefergebirge, Deutschland) — Stratigraphie, Sedimentologie und Palaeogeographie des Aachener Kohlenkalks und seine Bedeutung fuer die Entwicklung der Kulturlandschaft im Aachener Raum Aachen RWTH Fak Bergbau… "zur Erlangung…" =. Aachen RWTH.
* Jonghe , Sabine de -, Tourneur , Francis, Ducarme , Pierre , Groessens , Eric e.a. 1996 . Pierres à bâtir traditionnelles de la Wallonie - manuel de terrain. Jambes / Louvain la Neuve ucl,chab / dgrne / region wallonne
* Dreesen , Roland , Dusar , M. and Doperé , F., 2001 . Atlas Natuursteen in Limburgse monumentenx- 2nd print 320pp. . LIKONA ISBN 90-74605-18-4
* Dearing, J. (1999) Magnetic susceptibility. In, Environmental magnetism: a practical guide Walden, J., Oldfield, F., Smith, J., (Eds). Technical guide, No. 6. Quaternary Research Association, London, pp. 35-62.
* Tite, M.S., and Mullins, C. (1971) Enhancement of magnetic susceptibility of soils on archaeological sites. Archaeometry,13, 209–19.

External links

* [http://www.science.ulster.ac.uk/cma/ Marine geoarchaeology projects at the Centre for Maritime Archaeology, University of Ulster, Coleraine]
* [http://www.lgakz.org The Laboratory of Geoarchaeology, Kazakhstan] Information about Geoarchaeological work in Central Asia
* [http://www.sassa.org.uk SASSA (Soil Analysis Support System for Archaeologists)]