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Author Topic: Three Excavation Types  (Read 863 times)
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« on: August 21, 2006, 08:24:02 PM »

 Methods of excavation are extremely precise and time consuming. Archaeologists do not just dig holes of random sizes until something is found. The dimensions of each hole is determined before excavation begins and is sectioned off with rope, usually in one by one meter units. Once the excavation starts the hole is dug down evenly in levels. At the Lamoka Lake site each level had a maximum thickness of no more than ten centimeters and was ended at any change in soil color or texture, but this is not the case for every archaeological site. It is imperative when digging the unit to keep all walls smooth and straight and to excavate soils of different colors within a level separately. These areas of different soil composition are designated as features and are caused by rodents, fire, organic material that has decayed and human activities. All soil removed is then placed in a sieve, which is a screen that lets soil pass through and traps artifacts that would go otherwise unnoticed like small flaked stones and fish and rodent bones. All artifacts and bones found insitu (in there original resting place) are mapped and excavated using a mason?s trowel paint brushes and even chop sticks to avoid any damage. All charcoal found, which is used for radio-carbon dating is placed in tinfoil and never touched by hand to avoid contamination. While the excavation is taking place, the more tedious aspect of archaeology, recording ones findings is also occurring.

 Recording and mapping all findings during excavation, while time consuming, is the most important task an archaeologist has. Each level of a unit is described in various ways, including, start and stop depths, soil color and texture, and a list of what was bagged and removed from the hole, for example charcoal, soil samples, artifacts and bones. Every artifact and bone is placed in a bag designated to a unit and level, which intern receives a catalog number. When features or artifact and bone concentrations occur a plan map of the level is drawn to show there specific location and when a unit is complete or not producing any further finds a profile map of the walls is drawn to show soil changes through the unit. Photographs of features and completed units are also taken to further document the excavation. . Once a unit has been excavated there in no way to go back and check for overlooked information, which makes it imperative to continuously record all findings to maximize the knowledge we can obtain from any given excavation.

There are three types of modern archaeological excavation:

   1. Research excavation - when time and resources are available to excavate the site fully and at a leisurely pace. These are now almost exclusively the preserve of academics or private societies who can muster enough volunteer labour and funds. The size of the excavation can also be decided by the director as it goes on.

   2. Development-led excavation - undertaken by professional archaeologists when the site is threatened by building development. Normally funded by the developer meaning that time is more of a factor as well as it being focused only on areas to be affected by building. The workforce is generally more skilled however and pre-development excavations also provide a comprehensive record of the areas investigated.

   3. Rescue excavation - when the site has already been damaged, eg. by erosion, time is extremely limited and the excavation becomes a damage limitation exercise. Usually funded by the state and undertaken by commercial archaeologists.
« Reply #1 on: August 28, 2006, 12:29:09 PM »

Very good I can say I have been a part of all three forms...
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« Reply #2 on: August 28, 2006, 11:18:26 PM »

I also can echo 99*.


« Reply #3 on: February 09, 2007, 06:24:29 PM »

Concepts in excavation

In archaeology, especially in the course of excavation, stratification is a paramount and base concept. It is largely based on the Law of Superposition. 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 to enable the archaeologist to draw conclusions about the site and 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. In archaeology, the context (physical location) of a discovery can be of major significance. More precisely, an archaeological context is an event in time which has been preserved in the archaeological record. The cutting of a pit or ditch in the past is a context, whilst the material filling it will be another. Multiple fills, seen in archaeological section would mean multiple contexts. Structural features, natural deposits and inhumations are also contexts. By separating a site into these basic, discrete units, archaeologists are able to create a chronology for activity on a site and describe and interpret it. Stratigraphic relationships are the relationships created between contexts in time representing the chronological order they were created. An example would be a ditch and the back-fill of said ditch. The relationship of "the fill" context to the ditch "cut" context is "the fill" occurred later in the sequence, IE: you have to dig a ditch first before you can back-fill it. A relationship that is later in the sequence is sometimes refereed to as "higher" in the sequence and a relationship that is earlier "lower" though the term higher or lower does not itself imply a context needs to be physically higher or lower. It is more useful to think of this higher or lower term as it relates to the contexts position in a Harris matrix which is a two dimensional representation of a sites formation in space and time.

Combining stratigraphic contexts for interpretation
Understanding a site in modern archaeology is a process of grouping single contexts together in ever larger groups by virtue of their relationships. The terminology of these larger clusters varies depending on practitioner but the terms interface, sub-group, group and land use 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. In turn sub-groups can be clustered together with other sub groups by virtue of their stratigraphic relationship to form groups which in turn form "phases". A sub-group burial could cluster with other sub group burials to form a cemetery or burial group which in turn could be clustered with a building such as church to produce a "phase". A less rigorously defined combination of one or more contexts is sometimes called a feature.

Excavation in phase has reduced this site to the occupation level of a Romano Celtic temple.

The same Romano Celtic temple reduced in phase to the construction level immediately post the building of the inner wall and before the construction of the outer wall to the left of picture. Note reduction in phase has produced detailed information concerning the exact sequence of temple construction.

Phase and phasing
Phase is the most easily understood grouping for the layman as it implies a near contemporaneous Archaeological horizon representing "what you would see if you went back to a specific point in time". Often but not always a phase implies the identification of an occupation surface "old ground level" that existed at some earlier time. The production of phase interpretations is one of the first goals of stratigraphic interpretation and excavation. Digging "in phase" is not quite the same as phasing a site. Phasing a site represents reducing the site either in excavation or post excavation to contemporaneous horizons where as "digging in phase" is the process of stratigraphic removal of archaeological remains so as not to remove contexts that are earlier in time "lower in the sequence" before other contexts that have a latter physical stratigraphic relationship to them as defined by the law of superposition. The process of interpretation in practice will have a bearing on excavation strategies on site so "phasing" a site is actively pursued during excavation where at all possible and is considered good practice.
« Reply #4 on: February 09, 2007, 06:27:12 PM »

Stratigraphic excavation in practice

Best practice of stratigraphic excavation in its basic sense involves a cyclical process of cleaning or "troweling back" the surface of the site and isolating contexts and edges which are definable in their entirety or part as either

   1. Discreet discernible "edges" that form an enclosed area completely visible in plan and therefore stratigraphically later than the surrounding surface or

   2. Discrete, discernible "edges" that are formed by being completely separated from the surrounding surface as in 1 and have boundaries dictated by the limit of excavation.

Slumped top fill revealing edges of a late roman pit.

Following this preliminary process of defining the context, the context is then assessed in relation to the wider understanding of the site for considerations of reduction of the site in Phases and then removed and recorded by various methods. Often, owing to practical considerations or error, the process of defining the edges of contexts is not followed and contexts are removed out of sequence and un-stratigraphically. This is called "digging out of phase". It is not good practice. After removing a context or if practical a set of contexts such as the case would be for features, the "isolate and dig" procedure is repeated until no man made remains are left on site and the site is reduced to natural.
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