Geoarchaeology
Encyclopedia
Geoarchaeology is a multi-disciplinary approach which uses the techniques and subject matter of geography
, geology
and other Earth science
s to examine topics which inform archaeological
knowledge and thought. Geoarchaeologists study the natural physical processes that affect archaeological site
s 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, geographic information systems (GIS) and digital elevation models
(DEM) in combination with disciplines from human and social sciences and earth sciences.
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.
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.
The relationship between iron and burning means that magnetic susceptibility is often used for:
The relationship between soil formation and magnetic susceptibility means that it can also be used to:
Whatever the method of getting the phosphorus from the soil into solution, the method of detecting it is usually the same. This uses the ‘molybdate blue’ reaction, where the depth of the colour is proportional to phosphorus concentration. In the lab, this is measured using a colorimeter, where light shining through a standard cell produces an electrical current proportional to the light attenuation. In the field, the same reaction is used on detector sticks, which are compared to a colour chart.
Phosphate concentrations can be plotted on archaeological plans to show former activity areas, and is also used to prospect for sites in the wider landscape.
or sediment
were deposited. Particle sizes are generally separated by means of dry or wet sieving (coarse samples such as till
, gravel
and sand
s, sometimes coarser silt
s) or by measuring the changes of the density of a dispersed solution (in sodiumpyrophosphate, for example))of the sample (finer silts, clay
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.
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.
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.
Geography
Geography is the science that studies the lands, features, inhabitants, and phenomena of Earth. A literal translation would be "to describe or write about the Earth". The first person to use the word "geography" was Eratosthenes...
, geology
Geology
Geology is the science comprising the study of solid Earth, the rocks of which it is composed, and the processes by which it evolves. Geology gives insight into the history of the Earth, as it provides the primary evidence for plate tectonics, the evolutionary history of life, and past climates...
and other Earth science
Earth science
Earth 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. There are both reductionist and holistic approaches to Earth sciences...
s to examine topics which inform archaeological
Archaeology
Archaeology, or archeology , is the study of human society, primarily through the recovery and analysis of the material culture and environmental data that they have left behind, which includes artifacts, architecture, biofacts and cultural landscapes...
knowledge and thought. Geoarchaeologists study the natural physical processes that affect archaeological site
Archaeological site
An 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 record.Beyond this, the definition and geographical extent of a 'site' can vary widely,...
s such as geomorphology
Geomorphology
Geomorphology 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 artifacts
Artifact (archaeology)
An artifact or artefact is "something made or given shape by man, such as a tool or a work of art, esp an object of archaeological interest"...
post-deposition. Geoarchaeologists' work frequently involves studying soil
Soil
Soil 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...
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, geographic information systems (GIS) and digital elevation models
Digital elevation model
A digital elevation model is a digital model or 3-D representation of a terrain's surface — commonly for a planet , moon, or asteroid — created from terrain elevation data....
(DEM) in combination with disciplines from human and social sciences and earth sciences.
Column sampling
Column sampling is a technique of collecting samples from a sectionArchaeological section
In 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
Soil 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...
organic
Soil organic matter
Organic 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...
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
Archaeological section
In 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 .
- 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 spectrophotometry
Phosphate in man-made soils derives from people, their animals, rubbish and bones. 100 people excrete about 62 kg of phosphate annually, with about the same from their rubbish. Their animals excrete even more. A human body contains about 650g of PO4,(500g-80% in the skeleton), which results in elevated levels in burial sites. Most is quickly immobilised on the clay of the soil and ‘fixed’, where it can persist for thousands of years. For a 1 ha site this corresponds to about 150 kg PO4 ha-1yr-1 about 0.5% to 10% of that already present in most soils. Therefore it doesn’t take long for human occupation to make orders of magnitude differences to the phosphate concentration in soil. Phosphorus exist in different ‘pools’ in the soil 1) organic (available), 2) occluded (adsorbed), 3) bound (chemically bound). Each of these pools can be extracted using progressively more aggressive chemicals. Some workers (Eidt especially), think that the ratios between these pools can give information about past land use, and perhaps even dating.Whatever the method of getting the phosphorus from the soil into solution, the method of detecting it is usually the same. This uses the ‘molybdate blue’ reaction, where the depth of the colour is proportional to phosphorus concentration. In the lab, this is measured using a colorimeter, where light shining through a standard cell produces an electrical current proportional to the light attenuation. In the field, the same reaction is used on detector sticks, which are compared to a colour chart.
Phosphate concentrations can be plotted on archaeological plans to show former activity areas, and is also used to prospect for sites in the wider landscape.
Particle size analysis
The particle size distribution of a soil sample may indicate the conditions under which the strataStratum
In geology and related fields, a stratum is a layer of sedimentary rock or soil with internally consistent characteristics that distinguish it from other layers...
or sediment
Sediment
Sediment is naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of fluids such as wind, water, or ice, and/or by the force of gravity acting on the particle itself....
were deposited. Particle sizes are generally separated by means of dry or wet sieving (coarse samples such as till
Till
thumb|right|Closeup of glacial till. Note that the larger grains in the till are completely surrounded by the matrix of finer material , and this characteristic, known as matrix support, is diagnostic of till....
, gravel
Gravel
Gravel is composed of unconsolidated rock fragments that have a general particle size range and include size classes from granule- to boulder-sized fragments. Gravel can be sub-categorized into granule and cobble...
and sand
Sand
Sand is a naturally occurring granular material composed of finely divided rock and mineral particles.The composition of sand is highly variable, depending on the local rock sources and conditions, but the most common constituent of sand in inland continental settings and non-tropical coastal...
s, sometimes coarser silt
Silt
Silt is granular material of a size somewhere between sand and clay whose mineral origin is quartz and feldspar. 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, clay
Clay
Clay is a general term including many combinations of one or more clay minerals with traces of metal oxides and organic matter. Geologic clay deposits are mostly composed of phyllosilicate minerals containing variable amounts of water trapped in the mineral structure.- Formation :Clay minerals...
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.Ostracod analysis
Naturally occurring Ostracods in freshwater bodies are impacted by changes in salinity and pH due to human activities. Analysis of Ostracod shells in sediment columns show the changes brought about by farming and habitation activities. This record can be correlated with age dating techniques to help identify changes in human habitation patterns and population migrations.Archaeological geology
Archaeological geology is a term coined by Werner Kasig in 1980. It is a sub-field of geologyGeology
Geology is the science comprising the study of solid Earth, the rocks of which it is composed, and the processes by which it evolves. Geology gives insight into the history of the Earth, as it provides the primary evidence for plate tectonics, the evolutionary history of life, and past climates...
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.
External links
- Marine geoarchaeology projects at the Centre for Maritime Archaeology, University of Ulster, Coleraine
- The Laboratory of Geoarchaeology, Kazakhstan Information about Geoarchaeological work in Central Asia
- SASSA (Soil Analysis Support System for Archaeologists)