Introduction
We were invited to evaluate the geoarchaeology of a site at College Square, Bristol, to help the excavating archaeologists, both in understanding the origins of the deposits and in assessing the archaeological potential of the site.
Background
The bedrock of the area is known to be Triassic sandstone which lies against the quartzitic Brandon Hill grits and is overlain by estuarine alluvium, we found the soils on the site would have been similar to nearby pelo-calcareous alluvial gley soils, which are deep stoneless, mainly calcareous clayey soils which have formed from marine alluvium on flat land at risk from flooding. The site at College Square lies within an area of low-lying land in the western part of Bristol city centre.
We examined deposits exposed during the excavation of the site and took samples for later analysis.
Findings
The analysis of the samples provided a detailed understanding of the origins of key parts of the site, in the southern part they were found to represent naturally deposited estuarine alluvium which had been disturbed by later soil formation. Where as immediately to the north similar alluvium was found to have been redeposited in large masses. Deposits in a deeper section in the middle of the site have been laid down in wet conditions which in most cases was not standing water. The upper part of this section contained organic matter, magnetic susceptibility readings were taken on the mineral parts of the section and analysis of the phosphate content was carried out on the organic parts.
Conclusions
From our investigations we were able to tell the excavating archaeologists that the high magnetic susceptibility of the deposits measured was due to their being mixed with material of higher magnetic susceptibility before they were redeposited, and the organic matter may well be animal bedding waste.