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- Stratigraphy | geology | ibohyhozeq.tk
- Chronology and dating methods
The concept derives from the geological use of the idea that sedimentation takes place according to uniform principles.
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When archaeological finds are below the surface of the ground as is most commonly the case , the identification of the context of each find is vital in enabling the archaeologist to draw conclusions about the site and about the nature and date of its occupation. It is the archaeologist's role to attempt to discover what contexts exist and how they came to be created. Archaeological stratification or sequence is the dynamic superimposition of single units of stratigraphy, or contexts.
Contexts are single events or actions that leave discrete, detectable traces in the archaeological sequence or stratigraphy. They can be deposits such as the back-fill of a ditch , structures such as walls , or "zero thickness surfaciques", better known as " cuts ". Cuts represent actions that remove other solid contexts such as fills, deposits, and walls.
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An example would be a ditch "cut" through earlier deposits. Stratigraphic relationships are the relationships created between contexts in time, representing the chronological order in which they were created. One example would be a ditch and the back-fill of said ditch. The temporal relationship of "the fill" context to the ditch "cut" context is such that "the fill" occurred later in the sequence; you have to dig a ditch before you can back-fill it. A relationship that is later in the sequence is sometimes referred to as "higher" in the sequence, and a relationship that is earlier, "lower", though this does not refer necessarily to the physical location of the context.
It is more useful to think of "higher" as it relates to the context's position in a Harris matrix , a two-dimensional representation of a site's formation in space and time. Archaeological stratigraphy is based on a series of axiomatic principles or "laws". They are derived from the principles of stratigraphy in geology but have been adapted to reflect the different nature of archaeological deposits.
Harris notes two principles that were widely recognised by archaeologists by the s: He also proposed three additional principles: Understanding a site in modern archaeology is a process of grouping single contexts together in ever larger groups by virtue of their relationships.
Dating Techniques In Archaeology
The terminology of these larger clusters varies depending on the practitioner, but the terms interface, sub-group, and group are common. An example of a sub-group could be the three contexts that make up a burial; the grave cut, the body, and the back-filled earth on top of the body. Sub-groups can then be clustered together with other sub-groups by virtue of their stratigraphic relationship to form groups, which in turn form "phases.
Phase implies a nearly contemporaneous Archaeological horizon , representing "what you would see if you went back to time X". The production of phase interpretations is the first goal of stratigraphic interpretation and excavation. Archaeologists investigating a site may wish to date the activity rather than artifacts on site by dating the individual contexts which represents events.
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Some degree of dating objects by their position in the sequence can be made with known datable elements of the archaeological record or other assumed datable contexts deduced by a regressive form of relative dating which in turn can fix events represented by contexts to some range in time. For example, the date of formation of a context which is totally sealed between two datable layers will fall between the dates of the two layers sealing it. However the date of contexts often fall in a range of possibilities so using them to date others is not a straightforward process.
Take the hypothetical section fig A. Here we can see 12 contexts, each numbered with a unique context number and whose sequence is represented in the Harris matrix in fig B.
If we know the date of context 1 and context 9 we can deduce that context 7, the backfilling of pit 8, occurred sometime after the date for 9 but before the date for 1, and if we recover an assemblage of artifacts from context 7 that occur nowhere else in the sequence, we have isolated them with a reasonable degree of certainty to a discrete range of time. Following the failed attempts during the last half of the 19th century of the International Geological Congress IGC; founded to standardize a stratigraphic scale, the International Union of Geological Sciences IUGS; founded established a Commission on Stratigraphy to work toward that end.
Traditional stratigraphic schemes rely on two scales: These schemes, when used in conjunction with other dating methods—such as radiometric dating the measurement of radioactive decay , paleoclimatic dating, and paleomagnetic determinations—that, in general, were developed within the last half of the 20th century, have led to somewhat less confusion of nomenclature and to ever more reliable information on which to base conclusions about Earth history.
Because oil and natural gas almost always occur in stratified sedimentary rocks, the process of locating petroleum reservoir traps has been facilitated significantly by the use of stratigraphic concepts and data. An important principle in the application of stratigraphy to archaeology is the law of superposition—the principle that in any undisturbed deposit the oldest layers are normally located at the lowest level. Accordingly, it is presumed that the remains of each succeeding generation are left on the debris of the last.
Stratigraphy | geology | ibohyhozeq.tk
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Chronology and dating methods
Learn More in these related Britannica articles: This is termed the law of superposition and is one of the great general…. In dating the past, the primary value of fossils lies within the principle of faunal succession: Stratigraphy covers all aspects of sedimentary rocks, particularly from the perspective of their age and regional relationships as well as the correlation of sedimentary rocks in one region with sedimentary rock sequences elsewhere. For further information about these fields, see geologic sciences.
Such time determinations are made and the record of past geologic events is deciphered by studying the distribution and succession of rock strata, as well as the character of the fossil organisms preserved within the strata. More About Stratigraphy 16 references found in Britannica articles Assorted References field of study In sedimentary rock major references In Earth sciences: Paleontology and stratigraphy In geology: Establishing Tertiary boundaries In Tertiary Period: