Introduction
We were invited to evaluate the geoarchaeology of a site at Keynsham, North Somerset, 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 was known to be Lower Jurassic Lower Lias and we found the soils to be alluvial soils recharged from groundwater below. The site lies on the edge of a river terrace overlooking the River Frome and near the base of a hill. At the time of our visit the site was undergoing re-development and had been the site of some 16th Century houses.
A number of trenches had been dug across the site and it was in these trenches that we examined deposits visible in the sides and took samples for later analysis.
Findings
In the sample we took, we could see a fine-grained light brown deposit covering a cobbled surface and the excavating archaeologists had discovered no finds in either. The site was near the base of a hill and the deposit looked like colluvium washed down from the nearby hillside. When we examined the coarser grains from the fine-grained deposit we found them to be rounded rather than angular, which told us that they had been deposited by a river rather than washed down from a nearby hillside.
Conclusions
From our investigations, we were able to tell the excavating archaeologists that the rounded grains meant that the deposit was alluvium, deposited by floodwaters of the nearby River Frome, at a time in the past when the river ran high due to wetter conditions. The fine-grained structure also allowed us to tell them that this alluvial deposit had built up slowly over time and that a considerable period of time had probably passed since the laying down of the cobbled surface.