STRATIGRAPHY
The stratigraphic profile used here is from the site of Namu. It should be noted that this profile was created through several depositional episodes. The author has chosen to outline the distinctive changes in stratigraphy for the purpose of teaching about stratigraphy
Stratification is the layers of cultural or natural debris visible in the side of any excavation unit. A profile showing a series of layers is a sequence that has accumulated through time. Stratigraphic deposits conform to the law of superposition, meaning that where one layer overlies another, the lower layer was deposited first. This is true only where no disturbance has occured. In circumstances where soil has been excavated and reinterred, the layers may no longer represent sequential deposits over time. Undisturbed stratification can be a useful tool in relative dating.
Analysis can be of colour and texture differences. These differences indicate differences in formation processes. Formation processes may be cultural (c- transforms) or natural (n-transforms). A c-transform is defined as the deliberate or accidental activities of humans. It is important, in analysis, to determine the possible formation process. This profile provides us with evidence of both n-transforms, such as the animal hole on the left of the image, as well as c-transforms, such as the floor features that run horizontally from the left.
Humus
Humus is a rich dark organic material that is created by decay of dead leaves and plants. It is therefore a natural formation process. The dark colour in stark contrast to the shelly midden it overlays alloe for fairly easy stratigraphical ananlysis. There is evidence of both faunalturbation (an animal hole) and cultural formation processes (a post hole) in this deposit and they have affected the shell layer beneath.
Shell Midden
A midden is an accumulation of debris and waste produced by humans and is therefore a cultural formation process. This layer is a deposit of shell midden. Middens are essentially archaeological waste heaps. Middens also provide a wealth of information concerning climate and diet. Shell middens also decrease the acidity in the soil providing increased preservation of organic artifacts. Decreased acidity allows for the preservation of bone and wood artifacts that would not preserve otherwise. There are a couple animal burrow holes that intrude into this layer in the top left hand corner (click on them for more information). This layer has a few distinctive layers of large barnacles and whole clam shells. The stratigraphy in this layer is not clearly defined but is definitely the result multiple depositional sequences.
Dark Midden
This layer is distinguished from the dense shell layer because of its darker color and the lower density of shell present. There is a posthole that intrudes into this layer in the top right hand corner (click on it for more information). Stratigraphic layers are not always easily distinguished. Factors to take into consideration include: colour, texture, matrix, and presence and absence of materials, such as shell. This layer does not overlay the more dense shell layer, it is beside it, but it definitely represents a different depositional layer. The layers may have been deposited at different times or could simply indicate different types of deposits in a similar time, showing spatial differentiation.
Ash
This layer is dark in colour because of the large amount of ash present in the soil. The deposition is attributed to cultural formation processes rather than natural due to the presence of a hearth feature on the left hand side of the profile (click on it for more information). This is distinguished by its darker colour and the presence of fire cracked rock in the vicinity. This layer illustrates the uneven nature of stratigraphic deposits. The various layers are not always perfectly horizontal, nor are they always easily distinguishable from each other. Shell occurs in limited amounts in this layer. The presence of shell reduces the acidity of the soil and increases preservation of organic artifacts.
Basal Deposits
The bottom component of the profile is light brown in colour and is composed of fine, sand sized particles. This layer is cuturally sterile, meaning that it was deposited prior to human occupation and therefore the result of natural formation processes. This layer was deposited during, or shortly after, glaciation.
FEATURES
Features are the result of both cultural and natural transformation processes. Features include hearths, floors, middens, postholes, animal holes, and any other structures that leave their imprint in the archaeological record. The stratigraphic profile above has a heath feature as well as two floor features. There are other interesting things to discover in the profile: there is a birdbone as well as some giant barnacles.
Bioturbation
Bioturbation is the term for features created by the actions of animals and other creatures disturbing depositional layers. There are two very clear examples in this stratigraphic section. They are two burrow holes created by fairly small animals originating in the humus layer and intruding into the shelly layer beneath. Their visibilty is increased because of the crossing between two very distinctive layers. In many cases, features are more difficult to distinguish because they occur within or between fairly homogenous depositional layers.
| Bioturbation is the term for features created by the actions of animals and other creatures disturbing depositional layers. There are two very clear examples in this stratigraphic section. They are two burrow holes created by fairly small animals originating in the humus layer and intruding into the shelly layer beneath. Their visibilty is increased because of the crossing between two very distinctive layers. In many cases, features are more difficult to distinguish because they occur within or between fairly homogenous depositional layers. |
| Bioturbation is the term for features created by the actions of animals and other creatures disturbing depositional layers. There are two very clear examples in this stratigraphic section. They are two burrow holes created by fairly small animals originating in the humus layer and intruding into the shelly layer beneath. Their visibilty is increased because of the crossing between two very distinctive layers. In many cases, features are more difficult to distinguish because they occur within or between fairly homogenous depositional layers. |
Post hole
Posts, especially prehistorically, tend to be made from organic material that does not preserve in the archaeological record. Threfore, the only indication of structural features, such as posts, left to archaeologists are the impressions that these posts made on the stratigraphy of a site. This posthole feature is a perfect example of intrusion through several depositional layers. The humus layer is thrust through the dense shelly layer into the less dense shelly layer beneath. because it was pushed through the dense shell first, there is a layer of dense shell that lines the post hole. It is common for post holes to have large rocks associated with them, these rocks would have help to support the post.
Hearth
Hearth features are usually distinguished by high concentrations of charred material and fire cracked rock. Because of the large amounts of charcoal, hearths are ideal features to date. They are perfect indicators of human occupation and charred material is ideal for radio-carbon dating. Often times the charring of materials serves to increase preservation and hearths are ideal locations to uncover charred organic materials that can help to determine diet.
Floor Features
These narrow, darker layers are stratigraphic evidence of structure floors. They cut horizontally through the shelly layer. The upper feature was deposited later than the one below. Spatial analysis of artifacts associated with the floor deposits can provide clues as to spatial organisations within households.
Photos and original web page by Edwin Lee. Adapted for AEM by Melissa Rollit, 2016.