Geoarchaeology is a multi disciplinary approach rather than a discipline and uses the techniques and subject matter of
GeographyGeography is the study of the Earth and its lands, features, inhabitants, and phenomena. A literal translation would be "to describe or write about the Earth". The first person to use the word "geography" was Eratosthenes...
,
geologyGeology is the science and study of the solid and liquid matter that constitutes the Earth. The field of geology encompasses the study of the composition, structure, physical properties, dynamics, and history of Earth materials, and the processes by which they are formed, moved, and changed...
and other
earth scienceEarth science , is an all-embracing term for the sciences related to the planet Earth. It is arguably a special case in planetary science, the Earth being the only known life-bearing planet...
s to examine topics which inform
archaeologicalArchaeology or archeology is the science that studies human cultures through the recovery, documentation, analysis, and interpretation of material culture and environmental data, including architecture, artifacts, biofacts, and landscapes...
knowledge and thought.
Geoarchaeologists study the natural physical processes that affect
archaeological siteAn archaeological site is a place in which evidence of past activity is preserved , and which has been, or may be, investigated using the discipline of archaeology and represents a part of the archaeological recordBeyond this, the definition and geographical extent of a 'site' can vary widely,...
s such as
geomorphologyGeomorphology is the scientific study of landforms and the processes that shape them...
, the formation of sites through geological processes and the effects on buried sites and
artifactsAn artifact or artefact is any object made or modified by a human. In archaeology, an artifact is an object recovered by some archaeological endeavor, which may have a cultural interest. Examples include stone tools such as projectile points, pottery vessels, metal objects such as buttons or guns,...
post-deposition.
Geoarchaeologists' work frequently involves studying
soilSoil is a natural body consisting of layers of mineral constituents of variable thicknesses, which differ from the parent materials in their morphological, physical, chemical, and mineralogical characteristics. It is composed of particles of broken rock that have been altered by chemical and...
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
sectionIn archaeology a section is a view in part of the archaeological sequence showing it in the vertical plane, as a cross section, and thereby illustrating its profile and stratigraphy. This may make it easier to view and interpret as it developed over time....
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
soilSoil is a natural body consisting of layers of mineral constituents of variable thicknesses, which differ from the parent materials in their morphological, physical, chemical, and mineralogical characteristics. It is composed of particles of broken rock that have been altered by chemical and...
organicOrganic matter is matter that has come from a once-living organism; is capable of decay, or the product of decay; or is composed of organic compounds. The definition of organic matter varies upon the subject it is being used for....
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
sectionIn archaeology a section is a view in part of the archaeological sequence showing it in the vertical plane, as a cross section, and thereby illustrating its profile and stratigraphy. This may make it easier to view and interpret as it developed over time....
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
strataIn geology and related fields, a stratum is a layer of rock or soil with internally consistent characteristics that distinguishes it from contiguous layers. Each layer is generally one of a number of parallel layers that lie one upon another, laid down by natural forces. They may extend over...
or
sedimentSediment is any particulate matter that can be transported by fluid flow, and which eventually is deposited.Sediments are most often transported by water transported by wind and glaciers...
were deposited. Particle sizes are generally separated by means of dry or wet sieving (coarse samples such as
tillthumb|right|Glacial till with tufts of grassTill is unsorted glacial sediment. Glacial drift is a general term for the coarsely graded and extremely heterogeneous sediments of glacial origin. Glacial till is that part of glacial drift which was deposited directly by the glacier. It may vary from...
,
gravelGravel is rock that is of a specific particle size range. Specifically, it is any loose rock that is larger than two millimeters in its smallest dimension and no more than . The next smaller size class in geology is sand, which is > in size. The next larger size is cobble, which is >. Gravel can...
and
sandSand is a naturally occurring granular material composed of finely divided rock and mineral particles.As the term is used by geologists, sand particles range in diameter from 0.0625 to 2 millimeters. An individual particle in this range size is termed a sand grain...
s, sometimes coarser
siltSilt is soil or rock derived granular material of a grain size between sand and clay. Silt may occur as a soil or as suspended sediment in a surface water body...
s) or by measuring the changes of the density of a dispersed solution (in sodiumpyrophosphate, for example))of the sample (finer silts,
clayClay is a naturally occurring material composed primarily of fine-grained minerals, which show plasticity through a variable range of water content, and which can be hardened when dried and/or fired...
s). 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
geologyGeology is the science and study of the solid and liquid matter that constitutes the Earth. The field of geology encompasses the study of the composition, structure, physical properties, dynamics, and history of Earth materials, and the processes by which they are formed, moved, and changed...
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.
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