| Abstract: |
The excavation of 7 boreholes was monitored across the three main site areas by a geoarchaeologist. The boreholes were drilled using a shell and auger cable percussion rig up to depths of 6-15m from both river edge locations and from several floating platforms located in the river. Bulk and disturbed samples were retrieved at intervals for geotechnical purposes as well as a smaller number of in-situ piston samples. The sediments were described according to Jones et al 1999 The Description and Analysis of Quaternary Stratigraphic Field Sections, Technical Guide No 7, Quaternary Research Association 1999, to include information about depth, texture, composition, colour, clast orientation, structure (bedding, ped characteristics etc.) and contacts between deposits. Notes were also made on the presence/absence of visible ecofactual, or artefactual inclusions. The lithological data from each sample location was in-putted into geological modelling software for analysis and correlation of deposits into key stratigraphical units. These units have been used to demonstrate and describe the nature of sediment accumulation patterns across the sites. In October 2011 Oxford Archaeology undertook a Watching Brief on geotechnical boreholes associated with the creation of series of new floating landing stages adjacent to seven locks across Cambridgeshire and Norfolk. The scheme aimed to provide new or replace existing landing stages for users of the waterways to safely moor whilst using the locks. The drilling of 7 boreholes were monitored across three main sites: Water Newton, Downham Market, and Earith. The purpose of the Watching Brief was to provide base-line data regarding the character, extent and archaeological potential of the alluvial and peat stratigraphy that may be effected by the Scheme. The borehole samples were examined for signs of archaeological indicators and were subsampled for further sedimentary analysis and radiocarbon dating. Despite the sites being located near to areas which have previously produced significant prehistoric, Roman and Medieval archaeology, no archaeological deposits were identified within the boreholes sequences. A series of boreholes were taken through the base of the modern river beds revealing that the Fenland sequence has been significantly truncated or removed in these locations. Prehistoric Fen peat deposits was only found to be preserved along the river banks at the Earith and Downham Market sites. These sequences have the potential to preserve import early prehistoric remains and contain a sequence of environmental and hydrological change that spans the Holocene. The surface of these peats are preserved at depths of 5.25m bg (-1.25m OD) at Salter Lodge, 4.65m bgl (+0.15m OD) at Denver Lock, 3.6m bgl (-0.9m OD) at the Old Bedford Sluice and 4.45m bgl (+1.95m OD) at Hermitage Lock. The peat sequences accumulated from the early Bronze Age into the late Roman period. Two of the sequences provided indirect evidence of archaeological potential, in the form of buried soils at Water Newton (BH01) and Downham Market (BH04). In the former, an early Mesolithic landsurface was found sealed underneath a lower peat overlain by channel deposits. A later buried alluvial soil containing charcoal was also identified within OABH4 underlying post-medieval made-ground deposits, possibly associated with the digging of the Old and New Bedford rivers. The main impact of the proposed Scheme will be predominantly from piled structures in the base of the modern riverbeds. Only at Salter's Lode, Old Bedford Sluice and Hermitage Lock will adjustments be made to the river banks to aid site access. The bank-side modifications are to be confined to a depth of 1m and will leave the identified buried surfaces and Nordelph peat sequence unaffected by these works. |
