Geochemical indicators of preservation status and site deterioration at Star Carr

Abstract

This paper presents the results of a project aimed at investigating the deterioration of organic remains at the Mesolithic site of Star Carr. Analyses of pH, Electrical Conductivity and Redox Potential are reported from borehole transects across the unexcavated part of the site. A comparison of field and laboratory measurements is made, leading to the characterisation of different preservation zones and identification of ‘vulnerable’ sediments at the site. These data are augmented by geochemical analyses of contemporary borehole sequences and adjacent historic monoliths. Analysis of surface water and groundwater has also been undertaken to assist in the interpretation of the site hydrology and geochemistry. The relationship between ‘natural’ geology and preservation potential, and the evidence for a ‘halo’ preservation effect in virgin sediments adjacent to previous archaeology trenches is investigated. The results indicate a restricted ‘halo’ effect from adjacent backfilled archaeological excavations and the importance of the underlying glacial sediments in determining hydrology and preservation status. The disconnection of circum-neutral groundwater from the Mesolithic peats appears to be a crucial factor in their acidification. Most organic horizons appear to have suffered almost complete chemical oxidation of sulphide to sulphate. The hydrological isolation of Star Carr is shown by the large disparities in water chemistry in different local groundwater sources and strongly suggests an internal source for the elevated sulphur levels at the site.