thumb|right|A geoarchaeologist analyzes the stratigraphy on the route of the LGV Est high-speed railway line.

thumb|geoarchaeologist at work on column sample

Geoarchaeology is a multidisciplinary field of study that applies the theories and techniques of the geosciences to archaeology. It draws on techniques and approaches from geomorphology, sedimentology, pedology, stratigraphy, and geochronology to interpret sediments, soils, and landforms in archaeological investigations to inform archaeological and chronological knowledge and thought. Geoarchaeologists study the natural physical processes that affect archaeological sites such as geomorphology, for example, and their effects on buried sites and artifacts post-deposition.

Geoarchaeologists' work frequently involves studying the soils and sediments of archaeological sites and the surrounding region to inform archaeological research. Geoarchaeologists also frequently use tools such as computer cartography, geographic information systems (GIS), and digital elevation models (DEM) in combination with disciplines from human and social sciences and earth sciences to inform their investigations and interpretations of sites.

Geoarchaeology is important because it informs archaeologists about the geology of the site, including the geomorphology of the soil and sediment. It also places artifacts and landforms present in the site into relative and absolute temporal context to better inform archaeological interpretations.

The application of stratigraphic principles to archaeological sites stems from the work of Niels Stenson (aka Nicolas Steno) in 1669 and James Hutton in 1788. In archaeological contexts, GIS is mainly used for managing information and for spatial analysis. Spatial analysis is its most common application in archaeology, followed closely by heritage management.

  • 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 and their animals, rubbish, and bones. One hundred people excrete about 62 kg of phosphate annually, with about the same amount from their rubbish. Their animals excrete even more. The human body contains about 650 g of (500g, or 80%, in the skeleton), resulting 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 ha-1yr-1, about 0.5% to 10% of that already present in most soils. Therefore, it doesn't take long for human activity to make orders-of-magnitude differences in the phosphate concentration in soil. Phosphorus exists 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 method is used to get the phosphorus from the soil into solution, the process 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, in which light passing through a standard cell produces an electric current proportional to the light attenuation. In the field, the same reaction is used on detector sticks compared to a colour chart.

Phosphate concentrations can be plotted on archaeological plans to show former activity areas and are also used to prospect for sites on the broader landscape.

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 using dry or wet sieving (coarse samples such as till, gravel, and sands, sometimes coarser silts) or by measuring the changes in the density of a dispersed solution (in sodium pyrophosphate, for example) of the sample (finer silts, clays). A rotating clock glass with a very fine-grained dispersed sample under a heat lamp helps separate particles.

The results are plotted as curves that can be analyzed using statistical methods to characterize particle distribution and other parameters.

The fractions received can be further investigated for cultural indicators, macrofossils and microfossils, and other interesting features, so particle size analysis is the first step in handling these samples.

Trace element geochemistry

Trace element geochemistry studies the abundance of elements in geological materials that do not occur in large amounts. Because these trace element concentrations are determined by many factors that govern the conditions under which a specific geological material is formed, they are usually unique between two locations containing 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 examine the trace element composition of obsidian artifacts to "fingerprint" them. They can then study the trace element composition of obsidian outcrops 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 them. They can also use mineralogy to trace the raw materials used to make the pots to specific clay deposits.

Ostracod Analysis

Naturally occurring Ostracods in freshwater bodies are Affected by changes in salinity and pH due to human activities. Analysis of Ostracod shells in sediment columns reveals 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 subfield of geology that emphasises the value of earth constituents for human life.

See also

  • Deposit model

Notes

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
  • 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.
  • The Laboratory of Geoarchaeology, Kazakhstan Information about Geoarchaeological work in Central Asia
  • SASSA (Soil Analysis Support System for Archaeologists)