Ploughzone Sampling in Denmark: Isolating and Interpreting Site Signatures from Disturbed Contexts

Article excerpt

In 1990, the Thy Archaeological Project (TAP) began an experiment to 'excavate' the ploughzone. In the years that followed we refined a methodology of recovering flakes and stone tools by mechanically screening large, discrete samples of ploughzone soil. We quantified prehistoric lithic activity using the distribution of the artefact frequencies in these samples. Our results confirm that ploughing neither completely destroys nor homogenizes sites into background noise. What is left after ploughing is not the 'site' familiar to archaeologists but rather a distinctive 'site signature' (Schofield 1991b). Site signatures enlighten us about the amount and type of lithic production that took place at each location. The striking result of an overview of site signatures in Thy, northern Denmark [ILLUSTRATION FOR FIGURE 1 OMITTED] is that most lithic production took place at a relatively few locations.

Ploughzone paradoxes

In Thy, over 75% of the area is under cultivation, typical for the fertile soils of lowland Europe (Haselgrove 1985; Lawson 1980). Cultivation, primarily ploughing, destroys the top 30 cm of archaeological sites (the ploughzone) by mixing, turning, and spreading out artefacts and strata (cf. Dunnell & Simek 1995; Hoffman 1985). The ploughing turns up and exposes the artefacts and features that make identification of prehistoric activity areas routine (Ammerman 1981; Haselgrove et al. 1985b; Mills 1985). Finding sites in ploughed fields is easy, but the artefacts in the ploughzone are 'out of context' and nothing - it is thought - can be done with them (Asch 1975:187 cf. Dunnell & Simek 1995; Shott 1995). This is the ploughzone paradox.

Accordingly, the current practice in Danish contract archaeology is to remove the disturbed ploughzone (and most of the artefacts) to discover the truncated post-holes, pits and graves that outline prehistoric activity in undisturbed lower levels (e.g. Ethelberg 1991; Kristensen 1989; cf. Holm 1991). Shallow and ephemeral sites (Wood & Johnson 1978) with little post-occupational soil deposition and no sub-surface features are found easily on ploughed agricultural land, but are not investigated further than their surface finds. Systematically excavated sites, preserved because they are in poor agricultural land or sealed by some chance processes, are the unusual ones; the shallow and ploughed sites need not be of the same character. We need to be able to 'excavate' shallow sites in good agricultural land in order to bridge the information gap between excavation and survey: we need to circumvent the ploughzone paradox.

Surface survey and the ploughzone

Surface surveys in ploughed fields are biased, so that even very intense, accurate surveys will not circumvent the ploughzone paradox. Surface survey is so coarse that those who conduct surveys have shied away from the concept of a site, either in terms of habitation (Schofield 1991b) or as any useful entity at all. Although many researchers think of site as a useful concept (e.g. Binford 1982; Cherry 1984; Dancey 1981; Ford 1987; Haselgrove 1985; Schiffer et al. 1978; Warren 1982), others involved in surface survey wish to view the archaeological record as a continuous but variable distribution of artefacts (e.g. Clark 1977; Dunnell & Dancey 1983; Ebert 1992; Foley 1981a; 1981b; Gaffney et al. 1985; Plog et al. 1978; contributions to Rossignol & Wandsnider 1992, especially Dunnell 1992; Thomas 1975). Surface survey is an excellent indicator of the presence or absence of archaeological remains. When present, the content and meaning of these remains is difficult to determine with surface survey data alone. Surface survey usually defines a landscape on the basis of artefact density, but survey can give a misguided impression of what is in the ploughzone (Richards 1985). Surface collection is not a methodology that allows us to circumvent the ploughzone paradox.

The sample size generated by surface survey can be too small to overcome the ploughzone paradox. …