Geoarchaeology

Geoarchaeology is a sub-field of archaeology which uses the techniques and subject matter of Geography, 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.

Geoarchaeology is a recent field of research that uses the computer cartography, the Geographic Information System (GIS) and the Digital Elevation Models (D.E.M.) in combination with disciplines from Human and Social Sciences and Earth Sciences.

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.

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.

Trace Element Geochemistry
Trace element geochemistry is the study of the abundances of elements in geological materials that do not occur in a large quantity in these materials. Because these trace elements concentration are determined by a large number of particular situations under which a certain geological material is formed, they are usually unique between two locations which contain the same type of rock or other geological material.

Geoarchaeologists use this uniqueness in trace element geochemistry to trace ancient patterns of resource-acquisition and trade. For example, researchers can look at the trace element composition of obsidian artifacts in order to "fingerprint" those artifacts. They can then study the trace element composition of obsidian outcrops in order to determine the original source of the raw material used to make the artifact.

Clay mineralogy analysis
Geoarchaeologists study the mineralogical characteristics of pots through macroscopic and microscopic analyses. They can use these characteristics to understand the various manufacturing techniques used to make the pots, and through this, to know which production centers likely made these pots. They can also use the mineralogy to trace the raw materials used to make the pots to specific clay deposits.

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.

Over the last decades, archaeologists and historians have faced the necessity to reconstruct ancient settlement history not only through the study of the material excavated, but also with the use of palaeo-environmental parameters.