زمین شناسی باستانی-Geoarcheology
Geoarcheology
Geoarcheology entails the use of geologic
concepts, methods, and knowledge for solving archeological problems. Geology and
archeology are historical sciences based largely on the study of a complex
stratigraphy that contains mineral, fossil, and cultural remains in a spatial
and implicitly chronological context, and that is used to reconstruct the
succession of events that produced the sedimentary record. Of all the natural
sciences now incorporated into archeology, geology has the longest association
with it. A union of the young science of geology with the even younger
discipline of archeology occurred in the midnineteenth century, growing out of
the same intellectual ferment that gave birth to evolutionary biology and much
of modern geology. The importance of geology in the solution of archeological
problems is now well understood by archeologists. Colin Renfrew, a leading
British archeologist, wrote in 1976 that “since archaeology, or a least
prehistoric archaeology, recovers almost all of its basic data by excavation,
every archaeological problem starts as a problem in geoarchaeology.” The term
“archeological geology” is essentially synonymous with geoarcheology.
In the last half of the twentieth century,
geoarcheology became a recognized discipline with its own journals, scientific
organizations, and graduate programs. Although geoarcheology is not
theory-driven—it adopts theories as needed from both geological sciences and
archeology—its progress often depends on new instrumental techniques that have
been borrowed or adapted from physics and chemistry. Examples are
ground-penetrating radar and instrumental neutron activation analysis.
Prospecting
techniques
Locating buried archeological sites presents
special problems for geoarcheologists. Many prospecting techniques are
available, including geophysical, geochemical, core drilling, and aerial
satellite remote sensing. Geophysical methods such as ground-penetrating radar
can detail the location, extent, and character of modified terrain. Surface
geophysical surveys can be combined with soil magnetic analysis and geochemical
prospecting to give a fair picture of the extent of anthropogenic remains of a
buried site or feature.
The first known geophysical survey for an
archeological application in
Core drilling can provide an accurate
picture not only of the sedimentary record but also of ancient landscapes. For
at least 2000 years, scholars have debated the location of
Fig. 1 Paleogeomorphic reconstruction of the
Trojan landscape at the time of the Iliad, based on core drilling at numerous
sites, shows that Homer was accurate in his
descriptions.
Provenance and age
analysis
The provenance of an artifact material is
its origin or source area (for example, locality, site, or mine). In
geoarcheological terms, this means the geographic/geological source of the raw
material from which the artifact was made, that is, a specific geological
deposit—normally a quarry, mine, geological formation, outcrop, or other
geological feature. A large number of chemical, physical, and geological
techniques have been used to source artifactual materials, including
trace-element concentrations, isotopic composition, diagnostic minerals or
assemblages, microfossils, and geophysical parameters. Throughout the Neolithic
of the Old World and the prehistoric of the
Chemical fingerprinting of rocks as a guide
to raw material sources now extends far beyond obsidian. J. Greenough and
coworkers used major- and trace-element concentrations of Egyptian basalts to
source Egyptian basalt artifacts. The chemical data showed that First Dynasty
basalt vessels (Abydos), Fourth Dynasty basalt paving stones (Khufu's funery
temple, Giza), and Fifth Dynasty paving stones (Sahure's complex, Abu Sir) came
from the Haddadin lava flow in northern Egypt. Other geoarcheologists are using
isotope ratios, electron spin resonance, and petrography (using a polarizing
microscope) to source the marble used in ancient monuments throughout the
In North America north of the
Fig. 2 A piece of native copper flattened (but
not made into a tool) by Native Americans over 3000 years ago. The small hole
was drilled for INAA analysis; also shown are the two pieces drilled
out.
Geoarcheologists also use a number of
physical methods in the absolute dating of archeological materials (that is, in
estimating their actual age in years). These methods include fission-track
dating of the damage in a mineral caused by fission of uranium-238;
archeomagnetic dating based on the fact that the Earth's magnetic poles migrate
and reverse polarity over time; and electron spin resonance and
thermoluminescence dating, both based on the accumulation of trapped electrons
in minerals. Fission-track dating was used to resolve the date of the earliest
example of the genus Homo outside
Sediment and soil
analysis
Most archeological data, as well as
environmental and climatic data, are recovered from sedimentary deposits or
associated soils. Consequently, much of geoarcheology is involved with detailed
field and laboratory studies of site or regional sediments and soils. The term
“archeological sediment” is used to distinguish deposits in the sedimentary
record that result directly from past human activities. A major interpretational
problem for geoarcheologists can be determining whether artifacts were part of
the initial deposit or were introduced later by human activities or by natural
mixing processes.
An understanding of soils is vital to
archeology. Both sediments and soils are horizontally layered but have very
different origins. Unfortunately, semantic confusion has been common in
archeology because the word “soil” is used for two very different things. “Soil”
has been used incorrectly, and loosely, for surface and near-surface sediments
of many descriptions. More correctly, soil is that portion of the Earth's
surface materials that supports plant life and is altered by continuous chemical
and biotic activity and weathering. It may be useful to think of sediments as
biologically dead. In contrast, soils develop from the weathering of a variety
of rock material at the surface of the Earth and are very much chemically and
biologically alive. Because they indicate the presence of stabilized landscape
surfaces, soils can contain evidence of possible human occupation and artifact
accumulation.
Geoarcheologists are turning more and more
to a broad range of chemical analyses of archeological sediments and soils to
recover indications of ancient lifeways. The amount and chemical nature of the
phosphorus can distinguish burial grounds and agricultural and habitation areas,
as well as indicate a variety of industrial remains. Organic carbon is perhaps
the most important element for animal and plant life. When found in soils and
sediments, it retains many characteristics of the role it played in ancient
human landscapes. For example, many of the carbon compounds in oil, wine, meat,
and plants are different and recognizable if not degraded.
Most chemical nutrients required for all
life on land are supplied from the soil. The chemical elements nitrogen (N),
phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), and sulfur (S) are
macronutrients. Because all plants use these elements, the removal of vegetation
by human activities depletes their concentration in soils and underlying
sediments. Eight chemical elements are considered important micronutrients
(required in much smaller amounts than the macronutrients): iron (Fe), manganese
(Mn), zinc (Zn), copper (Cu), boron (B), molybdenum (Mo), cobalt (Co), and
chlorine (Cl). One of the ways human activities alter the soil environment is by
addition or subtraction of these elements, depleting some nutrients to the point
of deficiency and augmenting others to the point of toxicity. Toxicities are
often recorded in human paleopathologies. Examples can be seen in the raw
material processing and use of lead and arsenic. Most of these chemical
activities leave clear records in archeological sediments, as trace elements
released from anthropogenic sources become part of normal biogeochemical
processes.
See also: Archeological chemistry;
Archeological chronology; Archeology; Geochemical prospecting; Geology;
Prospecting; Provenance (geology); Soil; Soil chemistry; Stratigraphy
George (Rip) Rapp
Bibliography
R. E. Chavez et al., Site characterization
by geophysical methods in the archaeological zone of
J. Greenough, M. Gorton, and L.
Mallory-Greenough, The major- and trace-element whole-rock fingerprints of
Egyptian basalts and the provenance of Egyptian artefacts, Geoarchaeol. Int. J.,
16:763–784, 2001
J. C. Kraft et al., Harbor areas at ancient
G. Rapp et al., Determining Geologic Sources
of Artifact Copper: Source Characterization Using Trace Element Patterns,
University Press of
Alifazeli=egeology.blogfa.com
Additional
L. B. Conyers and D. Goodman,
Ground-Penetrating Radar: An Introduction for Archaeologists, AltaMira Press,
R. D. Mandel (ed.), Geoarchaeology in the
Great Plains,
G. Rapp and C. Hill, Geoarchaeology,
M. S. Shackley (ed.), Archaeological
Obsidian Studies: Method and Theory, Plenum Press,
J. K. Stein and W. R. Farrand (eds.),
Sediments in Archaeological Context, University of Utah Press, Salt Lake City,
2001
Archaeological Geology Division of the
Geological Society of
American Quaternary
Association
Society for Archaeological
Sciences
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