Geophysical and Geochemical Survey Techniques

Archaeology is an important field that presents people with a way of studying the existence and way of life of people who lived many years ago. Archeological sites are areas where there are preserved indications of activities that took place in the past. These can be activities that happened before recorded history, activities that were recorded in history or events that occurred in the contemporary period. Some of these Archaeological sites may have formed due to anthropogenic factors although they may also be formed through natural or aftermath processes. It is mostly the remnants that have been buried by layers soil and rocks that have higher chances of being preserved. This is because the exposed cultural remnants may be displaced by anthropogenic or environmental factors (Blofeld J. 2004 p.71). The buried remains are usually covered with sediments accretion from water and wind erosion or natural processes such as earthquakes, mud flows and earth quakes. Some old structures may also be buried when new ones are built on top of them.

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The buried remains are effectively explored through geophysical and geochemical prospecting. These methods are efficient in detecting the invisible characteristics of the remains. The devices used in are significant in distinguishing between relics, which is significant in tracing human remains. The two techniques were developed in a bid to increase professionalism in archeology. The use of geophysics is an effective way of detecting deviations in the magnetic field of the earth through the use of magnetometers. These magnetic fields emanate from artifacts of iron metal as well as structures that were made of stone. Together with these techniques, devices that measure electrical resistance of the soil are also used (Bose R. N. 2005 pp.56-57).

 

Techniques used in Archeological Prospecting

Geophysical and geochemical prospecting are two major techniques that have been widely employed. The two techniques are significant in the identification of human activities that exist as remains buried under the earth surface. The characteristics of the remains are analyzed by an expert who establishes whether they represent human activities or natural factors. The archeological site of Apamee was investigated with the use of the two techniques. They have enhanced the understanding of this archeological site. In the United Kingdom, the two techniques have been applied in many archeological surveys (Braithwaite, R. 2001 pp. 121-123).

Fluxgate gradiometers are the most commonly used for surveying due to the fact that they are affordable for many archeologists and also for their swiftness in data acquisition. The Cesium gradiometer has been in use for a long time. The equipment allows production of high quality maps of the urban areas. The archeological maps produced facilitate planning in order to select the best point. They have been used to survey of a large area of archeological sites in Britain. The equipment requires that the prospective areas be burned before surveying can be done (Kailasan 2000 pp.36-41).

Seismic Refraction is a technique that largely makes use of geophysical techniques. The method has been used successfully over many years. Its transferability has been proved to yield perfect results. This technique was mainly adopted for the purpose of obtaining information from deep underground, where it can not be reached with the use of the Ground Probing Radar (GPR). The technique has several advantages due to the fact that it has no complications in data interpretation. Although it is quite slow in acquisition of data, it is advantageous since it is simple. It has been in use for several years in Bradford University’s geophysical surveys (Crowner, M.L. 2000 pp. 18-21).

Magnetic Susceptibility is another technique which involves distinguishing and putting archeology and the geology separately. Geomagnetic methods are usually combined to conduct powerful geophysical assessment. When the magnetic properties of the underlying soil are known, the surveys can be made easier. The components of a site should be analyzed separately in order to acquire a considerable understanding of the archeological site (Robert A. 2005 p.27). The vertical distribution is significant and should be studied correctly. This is because the characteristics of stratification are usually associated with the occupation of humans in a particular area. This stratification represents the different phases of human settlement. It is usually done through investigating the core samples. There are particular devices that are used for recording the response of core samples towards magnetic fields continuously. The susceptibility of various positions within the core is measured by the use of maximum likelihood estimation (Paul, Y.R. Bhanumurthy and M. Jagannathan 1996 pp. 37-41).

Marine magnetic survey has been used to survey archeological sites, for example the Caesarea Maritima in Israel. In this site, it was applied in the identification of structures that were buried in the Roman Harbour since King Herod’s time. Magnetometry is significant in identification of concrete structures that have been buried over a long period of time in marine ecosystems (V. Paoletti, M. Secomandi, M. Piromallo, F.giordano, M. Fedi and A.Rapolla 2005 p. 52). The method was also used in archeological surveys in the Milfield Basin in England. The area is a significant archeological site which holds the Anglian and Neolithic habitation.

In Egypt, magnetic methods have been successfully used for many years. The gradiometer was used to detect archeological aspects of mud and fire bricks in Saqqara, Cairo. This helped in preserving the archeological monuments. However, the equipment has the disadvantages of noisiness due to its sensitivity, errors as well as poor environmental conditions during the field surveys (Hodah, Abdallatif, el-hemalyand, Abd el-all 2005 pp. 57)

Vertical profiling with the use of imaging systems is a technique that provides accurate information obtained through the use of a twin probe with half meter spacing on a grid measuring 1 meter and an electrical imaging system. Varying features emerge from a plan developed from the equipment. These features include the most recent garden features to be developed as well as medieval ditches. The technique was used in the Lower City of Troia, Turkey. It was also used to survey an extensive area of settlement in the Roman city of Ilion as well as the Hellenistic city beginning 1988 (Davies W. & Frude W. 1999 pp.92-93).

The remains of Bronze Age were buried about three meters from the surface. The technique was used in stone buildings and became possible due to a large amount of the element magnetite in the buried cultural remains of the region which provided a significant contrast that facilitated the identification. The fluxgate gradiometer has been constantly used for surveying remains of the upper layers of strata. It is also used for detecting archeological remains on the upper layers of strata. This method works at a high speed and therefore it is popular since it can be used for surveying a large area (Gaffne C. Hughes G. and Gater J. 2005 p.52).

The cesium magnetometer was used to survey the deeper layers of strata. This is because it has a higher sensitivity as well as the ability to produce a clear image of large buildings in Troia. It was also used in KoBulawayo, Zimbabwe. The technique uses the induction of a magnetic field in the soil through electromagnetic energy of low frequency. Soil enhancement is important since the method detects changes in magnetic susceptibility (C.Gaffney G.Hughes and J.Gater 2005 pp.32-34)

The non-invasive electromagnetic methods were used to survey archeological remains in Argentina. The Ground Penetrating Radar helped in detecting the occurrence of adobe walls in the Fortress located along the Atlantic coast with the use of GSSI equipment. Many geophysical methods can be combined in order to produce accurate and precise data. These include; electromagnets, Geo-radar and resistivity (Anstey N. A. 1991 p. 37).

High resolution measurements have been produced through the use of these equipments. The technique was developed for the purpose of facilitating archeological research, especially in the University of Albrechts in Kiel, where the archeometry working group has used them for more than ten years (Rosaire E. 1992 pp 66-68). However, there are limitations due to the costs associated with the excavation of extensive areas.

There are non-destructive methods that can be used to get information from underground which is closely associated with the landscape that surrounds the archeological site. The georadar is used for identification of the remains in peaty soil. In Northern Germany, electromagnetics are largely used for archeological prospecting in Schleswing-Holstein. Fluxgate magnetometers are used for the detection of Celtic and temple grounds. Resistivity and magnetics were also used to detect the remains of Hittite settlements. The interpretation of hillforts has been made easier through the cost effective magnetometry method of geophysical survey. It is usually appropriate where there are no prospects of future excavation (Ramchandran 1998 pp. 45-48).

Geochemical prospecting

This is another significant method that has been used for analyzing several archeological sites. It focuses on the chemical properties of samples, especially soil samples. It was used to investigate agricultural practices in the Isle of Lewis in Hebrides. It was used in measuring the impact of human activity on the site. The history of the site was established through the chemical analysis of soil samples. They were collected from more than 300 points along lines of transects. The chemical properties that were analyzed include; pH, Phosphorous, Magnesium, Calcium and Losson-ignition as well as the depth of the top soil (Palaeo R. 2005 pp. 51-53). These properties assisted in the determination of the land use practices that took place on the site many years ago. For example, Potassium and Calcium indicated that there was settlement. The presence of Calcium indicated the presence of lime in the soil, while Potassium was an indication of the use of fertilizers that are rich in Potassium signifying farming activities. Phosphorous is an indicator of the presence of animals since it mainly originates from their droppings (Reddi G. and P.N. Nayak. 2005 pp.87-91).

Archeological research in the MSA archeological Porc Epic site in Ethiopia has been surveyed through the use of the Obsidian geochemical analysis. In the hydration study, archeological specimens obtained from excavations were used in the early 19th century. The study of the soil samples produced various characteristics which were attributed to particular artifacts such as Mojjo. (J. A. entwistle1, R. A. Dodgshon and P. W. Abrahams 2000 pp. 121-122).

Geophysical and geochemical surveys produce undesirable results at certain times. Calibration of instruments is usually important and can affect the quality of results. Wrong calibration yields substandard results. Environmental factors are also significant in determining the outcome. At times, lack of existing data to make a comparison with the data from survey is usually a problem (Leet L.D. 2001 p. 81). If the wrong surveying design is used, the results will most likely be defective. In case many materials are detected with the use of a single sensor, the results may also be faulty. Control experiments should be set up before the actual survey. These will enable the determination of possible faults that may arise in the process of surveying.

The two techniques require trained personnel and therefore there is need to hire experienced personnel. It is therefore not cost effective if the people involved in the survey are not adequately trained. More over, the geophysical and geochemical techniques are usually limited by the site that needs to be surveyed. They might therefore be inappropriate for surveying some sites (William G. 2004 p. 36). They depend on the land use patterns, the type of soil as well as the geology of the particular site. All these factors determine the effectiveness of these archeological prospecting techniques. Another limitation in the use of the two methods is that the location of the potential site that needs to be surveyed should be known. This is because the techniques are time consuming and therefore require much time for planning.

Conclusion

Archeological prospecting has been made easier and more effective through the use of geochemical and geophysical techniques. The two methods are comparatively recent and are still being developed. They have eliminated the use of excavation and many other tedious and ineffective ways. Currently, equipments are available in the market and more are being produced depending on the need. It seems that in future, archeological prospecting will be much more effective with improvement in the instruments. Due to the advancement in archeological prospecting, it is necessary for archeologists and survey personnel to acquire more skills in order for them to be effective in their work. They need to be equipped with techniques that can assist them to use the two techniques and equipment in order to produce the most accurate data. The techniques are significant in increasing the probability of identifying sites that are of low visibility.

 

 

Bibliography

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