Geoarchaeology

Last updated
A geoarchaeologist analyzes a stratigraphy on the route of the LGV Est high-speed railway line. Geoarcheologue.JPG
A geoarchaeologist analyzes a stratigraphy on the route of the LGV Est high-speed railway line.
geoarchaeologist at work on column sample Geoarchaeologistatwork.png
geoarchaeologist at work on column sample

Geoarchaeology is a multi-disciplinary approach which uses the techniques and subject matter of geography, geology, geophysics 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. Geoarchaeologists may also use computer cartography, geographic information systems (GIS) and digital elevation models (DEM) in combination with disciplines from human and social sciences and earth sciences. [1] Geoarchaeology is important to society because it informs archaeologists about the geomorphology of the soil, sediment, and rocks on the buried sites and artifacts they are researching. By doing this, scientists are able to locate ancient cities and artifacts and estimate by the quality of soil how "prehistoric" they really are. Geoarchaeology is considered a sub-field of environmental archaeology because soil can be altered by human behavior, which archaeologists are then able to study and reconstruct past landscapes and conditions.

Contents

Techniques used

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 hammered 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 area's 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.

Near-surface geophysical prospection

Geophysical archaeological prospection methods are used to non-destructively explore and investigate possible structures of archaeological interest buried in the subsurface. Commonly used methods are:

Less commonly used geophysical archaeological prospection methods are:

offset column sampling of the soil profile Columns.002.png
offset column sampling of the soil profile

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:

The relationship between soil formation and magnetic susceptibility means that it can also be used to:

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 650 g of PO
4
(500 g–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 PO
4
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 electric 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 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 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 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' concentrations 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. [3]

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. [4]

Archaeological geology

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

See also

Notes

  1. Ghilardi, M. and Desruelles, S. (2008) “Geoarchaeology: where human, social and earth sciences meet with technology”. S.A.P.I.EN.S.1 (2)
  2. Tite, M.S.; Mullins, C. (1971). "Enhancement of magnetic susceptibility of soils on archaeological sites". Archaeometry. 13 (2): 209–219. doi:10.1111/j.1475-4754.1971.tb00043.x.
  3. Druca, I. C. and Q. H. J. Gwynb (1997), From Clay to Pots: A Petrographical Analysis of Ceramic Production in the Callejón de Huaylas, North-Central Andes, Peru, Journal of Archaeological Science, 25, 707-718.
  4. "^ Manuel R. Palacios-Fest, "Nonmarine ostracode shell chemistry from ancient hohokam irrigation canals in central Arizona: A paleohydrochemical tool for the interpretation of prehistoric human occupation in the North American Southwest" Geoarchaeology, Volume 9 Issue 1, Pages 1 – 29, Published Online: 9 Jan 2007" (PDF). Archived from the original (PDF) on 17 July 2011. Retrieved 6 April 2010.

Related Research Articles

<span class="mw-page-title-main">Sedimentary rock</span> Rock formed by the deposition and subsequent cementation of material

Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particles to settle in place. The particles that form a sedimentary rock are called sediment, and may be composed of geological detritus (minerals) or biological detritus. The geological detritus originated from weathering and erosion of existing rocks, or from the solidification of molten lava blobs erupted by volcanoes. The geological detritus is transported to the place of deposition by water, wind, ice or mass movement, which are called agents of denudation. Biological detritus was formed by bodies and parts of dead aquatic organisms, as well as their fecal mass, suspended in water and slowly piling up on the floor of water bodies. Sedimentation may also occur as dissolved minerals precipitate from water solution.

<span class="mw-page-title-main">Archaeological site</span> Place in which evidence of past activity is preserved

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. Sites may range from those with few or no remains visible above ground, to buildings and other structures still in use.

<span class="mw-page-title-main">Geochronology</span> Science of determining the age of rocks, sediments and fossils

Geochronology is the science of determining the age of rocks, fossils, and sediments using signatures inherent in the rocks themselves. Absolute geochronology can be accomplished through radioactive isotopes, whereas relative geochronology is provided by tools such as paleomagnetism and stable isotope ratios. By combining multiple geochronological indicators the precision of the recovered age can be improved.

<span class="mw-page-title-main">Geophysical survey (archaeology)</span> Non-invasive physical sensing techniques used for archaeological imaging or mapping

In archaeology, geophysical survey is ground-based physical sensing techniques used for archaeological imaging or mapping. Remote sensing and marine surveys are also used in archaeology, but are generally considered separate disciplines. Other terms, such as "geophysical prospection" and "archaeological geophysics" are generally synonymous.

<span class="mw-page-title-main">Palynology</span> Study of dust

Palynology is the "study of dust" or of "particles that are strewn". A classic palynologist analyses particulate samples collected from the air, from water, or from deposits including sediments of any age. The condition and identification of those particles, organic and inorganic, give the palynologist clues to the life, environment, and energetic conditions that produced them.

Environmental archaeology is a sub-field of archaeology which emerged in 1970s and is the science of reconstructing the relationships between past societies and the environments they lived in. The field represents an archaeological-palaeoecological approach to studying the palaeoenvironment through the methods of human palaeoecology. Reconstructing past environments and past peoples' relationships and interactions with the landscapes they inhabited provides archaeologists with insights into the origin and evolution of anthropogenic environments, and prehistoric adaptations and economic practices.

<span class="mw-page-title-main">Phosphorite</span> Sedimentary rock containing large amounts of phosphate minerals

Phosphorite, phosphate rock or rock phosphate is a non-detrital sedimentary rock that contains high amounts of phosphate minerals. The phosphate content of phosphorite (or grade of phosphate rock) varies greatly, from 4% to 20% phosphorus pentoxide (P2O5). Marketed phosphate rock is enriched ("beneficiated") to at least 28%, often more than 30% P2O5. This occurs through washing, screening, de-liming, magnetic separation or flotation. By comparison, the average phosphorus content of sedimentary rocks is less than 0.2%. The phosphate is present as fluorapatite Ca5(PO4)3F typically in cryptocrystalline masses (grain sizes < 1 μm) referred to as collophane-sedimentary apatite deposits of uncertain origin. It is also present as hydroxyapatite Ca5(PO4)3OH or Ca10(PO4)6(OH)2, which is often dissolved from vertebrate bones and teeth, whereas fluorapatite can originate from hydrothermal veins. Other sources also include chemically dissolved phosphate minerals from igneous and metamorphic rocks. Phosphorite deposits often occur in extensive layers, which cumulatively cover tens of thousands of square kilometres of the Earth's crust.

<span class="mw-page-title-main">Survey (archaeology)</span> Non-destructive exploration of the archaeological material in a given area

In archaeology, survey or field survey is a type of field research by which archaeologists search for archaeological sites and collect information about the location, distribution and organization of past human cultures across a large area. Archaeologists conduct surveys to search for particular archaeological sites or kinds of sites, to detect patterns in the distribution of material culture over regions, to make generalizations or test hypotheses about past cultures, and to assess the risks that development projects will have adverse impacts on archaeological heritage. The surveys may be: (a) intrusive or non-intrusive, depending on the needs of the survey team and; (b) extensive or intensive, depending on the types of research questions being asked of the landscape in question. Surveys can be a practical way to decide whether or not to carry out an excavation, but may also be ends in themselves, as they produce important information about past human activities in a regional context.

<span class="mw-page-title-main">Gold prospecting</span> Act of searching for new gold deposits

Gold prospecting is the act of searching for new gold deposits. Methods used vary with the type of deposit sought and the resources of the prospector. Although traditionally a commercial activity, in some developed countries placer gold prospecting has also become a popular outdoor recreation.

Exploration geophysics is an applied branch of geophysics and economic geology, which uses physical methods, such as seismic, gravitational, magnetic, electrical and electromagnetic at the surface of the Earth to measure the physical properties of the subsurface, along with the anomalies in those properties. It is most often used to detect or infer the presence and position of economically useful geological deposits, such as ore minerals; fossil fuels and other hydrocarbons; geothermal reservoirs; and groundwater reservoirs.

Luminescence dating refers to a group of methods of determining how long ago mineral grains were last exposed to sunlight or sufficient heating. It is useful to geologists and archaeologists who want to know when such an event occurred. It uses various methods to stimulate and measure luminescence.

Post-excavation analysis constitutes processes that are used to study archaeological materials after an excavation is completed. Since the advent of "New Archaeology" in the 1960s, the use of scientific techniques in archaeology has grown in importance. This trend is directly reflected in the increasing application of the scientific method to post-excavation analysis. The first step in post-excavation analysis should be to determine what one is trying to find out and what techniques can be used to provide answers. Techniques chosen will ultimately depend on what type of artifact(s) one wishes to study. This article outlines processes for analyzing different artifact classes and describes popular techniques used to analyze each class of artifact. Keep in mind that archaeologists frequently alter or add techniques in the process of analysis as observations can alter original research questions.

<span class="mw-page-title-main">Forensic geology</span>

Forensic geology is the study of evidence relating to minerals, oil, petroleum, and other materials found in the Earth, used to answer questions raised by the legal system.

<span class="mw-page-title-main">Magnetic survey (archaeology)</span> Magnetic detection of archaeological artefacts and features

Magnetic surveying is one of a number of methods used in archaeological geophysics. Magnetic surveys record spatial variation in the Earth's magnetic field. In archaeology, magnetic surveys are used to detect and map archaeological artefacts and features. Magnetic surveys are used in both terrestrial and marine archaeology.

The soil biomantle can be described and defined in several ways. Most simply, the soil biomantle is the organic-rich bioturbated upper part of the soil, including the topsoil where most biota live, reproduce, die, and become assimilated. The biomantle is thus the upper zone of soil that is predominantly a product of organic activity and the area where bioturbation is a dominant process.

<span class="mw-page-title-main">Near-surface geophysics</span> Geophysics of first tens of meters below surface

Near-surface geophysics is the use of geophysical methods to investigate small-scale features in the shallow subsurface. It is closely related to applied geophysics or exploration geophysics. Methods used include seismic refraction and reflection, gravity, magnetic, electric, and electromagnetic methods. Many of these methods were developed for oil and mineral exploration but are now used for a great variety of applications, including archaeology, environmental science, forensic science, military intelligence, geotechnical investigation, treasure hunting, and hydrogeology. In addition to the practical applications, near-surface geophysics includes the study of biogeochemical cycles.

Chronological dating, or simply dating, is the process of attributing to an object or event a date in the past, allowing such object or event to be located in a previously established chronology. This usually requires what is commonly known as a "dating method". Several dating methods exist, depending on different criteria and techniques, and some very well known examples of disciplines using such techniques are, for example, history, archaeology, geology, paleontology, astronomy and even forensic science, since in the latter it is sometimes necessary to investigate the moment in the past during which the death of a cadaver occurred. These methods are typically identified as absolute, which involves a specified date or date range, or relative, which refers to dating which places artifacts or events on a timeline relative to other events and/or artifacts. Other markers can help place an artifact or event in a chronology, such as nearby writings and stratigraphic markers.

This page is a glossary of archaeology, the study of the human past from material remains.

The Riadino-5 Site is an archaeological site located on a terrace within the Šešupė River Valley in the Kaliningrad Oblast of the Russian Federation. Unlike most other sites near this area, the Riadino-5 site is one of the first sites of the Middle to Upper Paleolithic transitional period to have been found in the Baltic region, which includes Lithuania, Latvia, Estonia, and areas of the Russian Federation. Even when compared to other sites of similar age, the Riadino-5 site is still one of the northernmost sites to have been occupied in the Central European region. This makes it one of the oldest sites documenting human habitation, dating back all the way to the Marine Isotope Stage 3, approximately ca 57-26 thousand calendar years ago. The site itself was occupied during the Middle to Upper Paleolithic period within that era between 50 to 44 ka. Upon discovery, the site measured 200 meters by 80 meters. The approximate aging of the site was supported by findings of flint artifacts, using luminescence IRSL dating based on potassium-feldspar sample size and Carbon-14 dating of charcoal and ash layers from the site. At the moment, the exact culture and society of the site occupants has yet to be determined, and is currently undergoing comparative analysis to other similarly dated sites in the vicinity to uncover some answers.

Cultural layer is a key concept in archaeology, particularly culture-historical archaeology especially in archaelogical digs or excavations. A cultural layer helps determine an archaeological culture: the remnants of human settlement that can be grouped and identified as coming from approximately the same distinct time period.

References