ISSUES WITH ARCHAEOLOGICAL REMAINS
WITHIN PLOUGH ZONES: UNDERSTANDING
SURFACE AND SUB-SURFACE MATERIAL
CULTURE
JASMYNE PENDRAGON
ACKNOWLEDGEMENTS
I would like to thank my son for being such a good boy for me by trying his hardest to keep
quiet while I wrote this article. I would also like to thank my loving husband for his
encouragement and support.
CONTENTS
ACKNOWLEDGEMENTS………………………………………………...................1
CONTENTS…………………………………………………………………………....2
SYNOPSIS……………………………………………………………………………..3
INTRODUCTION…………...………………………………………………………..4
TO IGNORE OR NOT TO IGNORE..........................................................................4
EXPERIMENTS IN PLOUGH ZONES......................................................................5
COWEN AND ODELL’S RESULTS...........................................................................9
SUB-SURFACE ARTIFACTS.....................................................................................10
CONCLUSION..............................................................................................................12
REFERENCES...............................................................................................................14
SYNOPSIS
In this article, I have attempted to explain some of the difficulties that are associated with
interpreting material culture in plough zones. I have mainly focused my analysis on the
issues involved in interpreting surface materials in plough zones on the North American
continent and the experimental work, which was done by Odell and Cowen. However, I used
a report on subsurface conditions in plough zones in Britain to explain effects on subsurface
material culture. I have tried to illustrate how material culture is displaced, and or damaged
in a ploughed field. I have done this in the hope that interpreting these plough zones will be
more easily understood by archaeological researchers in the future.
To reiterate I have essentially described the processes and effect of tilling in archaeological
sites on material remains so that one will be able to understand how surface materials are
associated with subsurface materials. Lastly, I have attempted to illustrate what happens to
material culture when it is affected by plowing, for example, I have illustrated how artifacts
are moved and how they can be damaged by repeated ploughing.
ISSUES WITH ARCHAEOLOGICAL REMAINS WITHIN PLOUGH ZONES:
INTERPRETING SURFACE AND SUB-SURFACE MATERIAL CULTURE
INTRODUCTION
Within the totality of the archaeological record, a large percent of artifacts have been affected
by agricultural processes such as ploughing (Dunnell & Simek 1995: 305). Ploughing causes
damage to artifacts and redistributes them from their original abandonment site. As such the
ploughing process has often been seen as both a blessing and a hindrance (Shott 1995: 477).
For example, the blessing is recognized by the fact that artifacts that would otherwise be
unseen are brought to the surface of ploughed fields, which gives archaeologists an
opportunity to analyze and research them. On the other hand, the hindrance is recognized by
the fact that the material remains are disturbed and redistributed, which results in the artifacts
becoming difficult to date and the size and shape of the artifacts no longer resemble what
they originally looked like. It therefore, becomes difficult to interpret the technology used to
make them (Dunnell & Simek 1995: 305). Hence, interpreting artifacts after they have
succumbed to the ploughing process is very difficult (Roskams 2001: 46).
In addition to difficulties in interpreting ploughed zones, night hawkers, particularly in
Britain, take advantage of these sites by means of using metal detectors to locate treasure, for
example gold, which leads to the removal of the artifacts. However, this article is not about
the problems associated with treasure hunters so that is all that will be said on the issue
herein.
TO IGNORE OR NOT TO IGNORE
Until recent decades, most archaeologists generally ignored plough zones. However, there
were a few exceptions to the rule such as Ford, Griffin and Phillips in 1951, Hayden in 1965
and Ruppe and Wauchope in 1966. The reason for archaeologists ignoring ploughed zones,
which contained artifacts, was the artifacts inside ploughed zones were generally believed to
have lost their context. Therefore, it was assumed that no real information regarding human
behavior could be gained from ploughed sites. However, throughout the last few decades
archaeologists have found a growing need to understand plough zone formation processes
because of the vast number of finds, which have been discovered in them.
EXPERIMENTS IN PLOUGH ZONES
Dunnell and Simek conducted a series of experiments, which pertain to artifact distribution in
plough zones that yielded some surprising, yet enlightening results (Dunnell and Simek 1995:
305-319). Their experiments were designed to test how archaeological artifacts become
displaced during ploughing and their aim was to understand how much a ploughed site could
be disturbed during and after ploughing. In addition, they wanted to know how far artifacts
were likely to be displaced from their original abandonment location and what direction the
artifacts would move in during ploughing processes (Dunnell and Simek 1995: 305-319).
According to Dunnell and Simek, because ploughing moves particles of sediment, plough
zones are depositional units. Consequently, deposition and re-deposition occurs after short
distances in a continuous fashion, which provides the plough zone with a contemporary
stratigraphic age (Dunnell and Simek 1995: 306). However, they argue that plough zone
spatial distribution similarities are not justifications for the interpretation of sub-surface
plough zone structures. For example, they argue that only when an archeological structure or
feature has been bisected by ploughing, and only when that structure or feature does not
contain complicated material remains would it necessitate and imply correspondence to the
distribution and composition of the archaeological record within a deeper stratigraphic unit
(Dunnell and Simek 1995: 306).
If one works under the assumption that the size of artifacts are deposited heterogeneously in
a ploughed zone, and, if one then assumes that their mean size is bigger than their stable size.
One can suggest that the more a field is ploughed, the more the assemblage will contain an
assemblage that will illustrate that the size of the materials signify a certain amount of
generalized balanced values. For example, equilibrium can often be found in the distribution
size of pottery, glass, bone and metals (Dunnell and Simek 1995: 309 and Cowen and Odell
1987: 456-482).
Odell and Cowan initiated some experimental tests in a plough zone. These tests sought to
answer questions such as; if a site is located in a plough zone, how far will the artifacts be
displaced from their original location. What percentage of artifacts can be expected to be
found while field walking?
What direction will the artifacts be scattered during the
ploughing process, and does ploughing completely destroy a sites integrity? All of the latter
questions were unquestionably in dire need of answering otherwise archaeologists will have
little hope of truly understanding the archaeological record in plough zones
According to Odell and Cowen, prehistoric sites in west central Illinois in North America
generally consist of flaked stone artifacts of varying sizes, stages of manufacture and various
shapes (Odell and Cowen 1987: 457). Using the latter artifact distinctions Odell and Cowen
gathered one thousand stone tool items such as bifaces, flakes, broken tools and other chipped
stone tools from a pile that had been accumulated by Cowen whilst he practiced stone
knapping techniques (Cowen and Odell 1987: 457). This pile of one thousand artifacts was
used to conduct their experiment, which they titled the Blue Flake Experiment (Cowen and
Odell 1987: 457).
Each of the one thousand stone artifacts was weighed as close to a gram as possible and the
length, width and diameter of each piece was recorded meticulously. Odell and Cowen then
marked each of the pieces with bright colonial blue paint. Hence the reason for the name of
the Blue Flake Experiment (Cowen and Odell 1987: 457). There were three reasons for the
aberrations on the stone artifacts. Firstly, the bright blue paint would help to reduce any bias
in the artifact recovery process by the collectors and it would ensure that none of the artifacts
would be missed during the recovery process. Secondly, the paint helped to aid in the
analysis and identification of damage to the stone material artifacts after the ploughing stage
of the experiment had been accomplished. Lastly, the bright blue colonial paint was used to
ensure that if any archaeologists in the distant future excavated the site they would realize
that the stones artifacts were not prehistoric cultural remains (Cowen and Odell 1987: 457).
All of the artifacts that Odell and Cowen planted were placed at a depth of 10-15 cm in to the
soil and laid out in a grid system at 50 cm intervals. The size of the site grid for the
experiment was 15 by 15.5 meters. They ploughed the site and bisected it to break up
potential dirt clods and then they waited for it to rain before they returned to the site and
recorded the artifacts that had become visible on the surface. All of the artifacts were flagged
with pins and the location of each artifact was carefully recorded. The procedure was
repeated twelve times from October 1981 to November 1983 so that the experiment
replicated a generalized typical process found in most plough zones (Odell and Cowen 1987:
459).
Odell and Cowen were systematic in the technique that they used to plough the site. For
example, they started ploughing the site from the outside edge and ploughed in an outward
and forward motion. Then they moved to the center of the experimental site and ploughed it
by continuously moving in an outward direction while making sure to always push the newly
tilled soil towards the center of the site. Both of the techniques maintained an east-west
direction of movement at all times (Odell and Cowen 1987: 459). They maintained this
uniform technique because there have been suggestions that whilst farmers do change
direction whilst ploughing occasionally, farmers generally maintain the same pattern and
direction once they have established their technique (Odell and Cowen 1987: 459 and
Hoffman and Roper 1976: 373 and Knooerl and Versaggi 1984: 78). However, there can be
exceptions to the latter rule on the odd occasion.
COWEN AND ODELL’S RESULTS
The results of Cowen and Odell’s Blue Flake Experiment showed that less than 10% or
artifacts are recovered in a plough zone (Cowen and Odell 1987: 460). This result is
supported by an accurate prediction that was made by Lewarch in 1979, which suggested that
only 1 in 20 artifacts would be recovered in a plough zone (Lewarch 1979: 144). Cowen and
Odell’s experiment showed that whilst the rate of recovery in a plough zone can fluctuate by
5-6 %, there are factors that influence the recovery rate of artifacts (Cowen and Odell 1987:
461). For example, artifact recovery rate is controlled by the mean length and width of an
artifact. Furthermore, the size or weight of an artifact tends to be affected by repeated
ploughing. The length and width of an artifact seems to be more of factor in appearing on the
surface of a plough zone rather than weight and thickness (Cowen and Odell 1987: 461).
This result has been supported by Frink’s study of plough zones in 1984 (Frink 1984: 359).
SUB-SURFACE ARTIFACTS
So far this article has focused on surface artifacts in plough zones in North America. Yet,
what can be suggested of sub-surface artifacts? What happens to them during the tilling
process? Do they escape damage and does the sub-surface assemblage resemble its original
abandonment process?
Considering that the act of ploughing is a taphonomic agent that displaces artifacts from the
sub-surface and relocates them to the surface, one can confidently argue that the sub-surface
artifactual site will not be the same as it was after ploughing has occurred. The size of a subsurface site will decrease accordingly with the distribution of artifacts to the surface of a
plough zone. If a plough displaces 10 % of the sub-surface artifacts to the surface then it is
likely that 10 % or more of the sub-surface archaeology will have been decreased in size as
well. However, the magnitude of sub-surface site shrinkage will be dependent on the depth
in which, a plough is struck in to the field (Spandl et al 2009:5).
In addition to the reduction in size of a sub-surface archaeological site in a plough zone,
damage occurs to the sub-surface artifacts when ploughing occurs (Spandl et al 2009:5).
Other factors that influence the magnitude of destruction to a sub-surface plough zone are the
applied force of ploughing, the load of the plough, the depth of the buried artifacts, the
strength of the soil and the amount of moisture that is trapped beneath the surface (Spandl et
al 2009:5).
Spandl et al conducted experiments on replica ceramic pots, which they had buried
horizontally in soil at a depth of 0.25 m below the surface. The lowest reading of the
breakage points of 1.3 bars was recorded for shell-tempered pots (Spandl et al 2009:5).
These shell-tempered pots were designed to replicate some of the later historic period wheel
thrown vessels. The rims of all of the pots that were buried happened to brake at slightly
lower pressures than the bodies of the pots. This provides a reference for pot breakage that is
indicative of the worst case scenario for the most fragile pots that are found in a plough zone.
The other pots broke at higher subsurface pressures, which ranged from a low of 1.6 bar to
and maximum of 3.6 bar (Spandl et al 2009:5).
The results showed that the fragments of the imitation vessels suggest that fabric composition
is less important than factors such as the extent of firing in determining the capacity of the
vessel to withstand force. However, superior fired pots will often be more resistant to
pressure (Spandl et al 2009: 6). Yet, once the pot is broken their component fragments will
still have been more robust than low-fired pots. Moreover, high-fired pot- sherds such as
modern terracotta pots can often be delicate and may continue to fragment under pressure.
Whilst some pots that were made in softer clay materials may be distorted after initially
cracking instead of being broken further during persistent pressure (Spandl et al 2009: 6).
This may explain why a few of the handmade prehistoric styled pots were cracked but not
shattered, although, this might have been due to the shape of the vessel (Spandl et al 2009: 6).
Analysis of aged non-collagenous medieval human radius bones indicated that when buried
upright the bones mainly broke under pressure. The direction the bones were buried was a
significant factor regarding whether or not they broke. None of bones that were placed
horizontally were broken. Yet most of the vertically orientated bones did.
CONCLUSION
In order for archaeologists to understand artifact spatial distribution within a plough zone and
the spatial correlation of artifacts that have been buried underneath the distributed artifacts,
lots of statistical analysis is required.
This is because without statistical analysis
archaeologists will struggle to interpret the age, use and the abandonment processes of
material cultural artifacts within a ploughed site. Odell and Cowan have concluded after
conducting experiments in a plough zone that these tests were greatly needed to shed light on
the effects of tilling in North America (Odell and Cowan 1987: 456-484).
The interaction between plough zone characteristics and artifact size can sometimes be used
as a means of analyzing how tillage can effect and signify a plough zone history of
agricultural processes and disturbances. It can all so aid in the recognition and identification
of the processes for which the remains were distributed on the surface of a ploughed field
(Dunnell and Simek 1995: 309). Broken artifacts can be a valuable tool for analysis because
they can aid in interpreting surface materials that have been located in a ploughed field
(Dunnell and Simek 1995: 309).
It is common knowledge amongst professional archaeologists that all archaeological
excavation is destructive and agricultural processes destroy archaeological sites. However, it
is the extent of destruction to the ploughed sites and the artifacts in them, which is of
importance and needs to be understood before archaeologists can accurately interpret tilled
landforms (Burke and Smith 2004: 78, Odell and Cowen 1987:457). Due to humankind
ploughing more and more of the earth’s landmass, archaeologists will be required to
understand and interpret disturbed artifacts more regularly, particularly in countries such as
the United Kingdom and North America, for example. However, hopefully experiments such
as described in this essay will aid in the analysis of plough zones.
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WEB SOURCES
Spandl, K. et al
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Appendix 5 Conclusions and Recommendations. In Oxford
Archaeology. Issue (1): 5-12. Trials to Identify Soil Cultivation
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