Soil-based analysis methods to aid the detection of cropmarks over buried features

Without contention, aerial surveying has been one of the most fundamental and effective tools in archaeological research. The mapping of cropmarks using aerial surveys, which appear over buries features, has revealed tens of thousands of new archaeological sites in Britain in the last few years. Cropmarks have most commonly been found when the weather is dry and in areas where soils drain quickly, causing crops to come under stress due to a lack of water. This knowledge informs archaeologists in the planning of surveys. However, targeting these areas in dry conditions introduces bias into the dataset and the rate of new discoveries is slowing. This research assesses the underlying geotechnical characteristics of soils within and adjacent to buried ditches at four field trial sites, to increase the understanding of why these cropmarks form and the conditions in which they appear. Analysis methods using existing archaeological and geotechnical data have been proposed to increase the knowledge of the conditions in which cropmarks form. The methods have been tested and the results showed that cropmarks formed in areas of clay-dominated soils in wet conditions, and cropmarks were recorded across a much wider range of soil-water conditions than was expected from current knowledge