Cambridge Rowing Lake Milton, Landbeach and Waterbeach Cambridgeshire Geoarchaeological Assessment and Deposit Model

In September 2004 Oxford Archaeology (OA) was commissioned by the Cambridge Rowing Trust to undertake a eoarchaeological assessment at the proposed site of the Cambridge Rowing Lake. The Research Design for the Archaeological Mitigation of the Cambridge Rowing Lake,
Revision 7 (OA 2003), identified the creation of a sub-surface deposit model for the site as an important step in the development of a mitigation strategy. This report presents the results of the deposit modelling and is
based upon data gathered during the various phases of evaluation at the site.
The model demonstrated that variable thicknesses of undisturbed alluvial and peat deposits exist, predominantly on the low-lying areas of the floodplain, sealed beneath a thin layer of ploughsoil. These deposits thin and disappear against the rise of the terrace in the north western sector
of the development where topsoil and a thin subsoil seal features dated to the late Iron Age and Roman period.
The greatest depths of fine-grained alluvium appear to date to the late Pleistocene to early Holocene period and consist of sands, sandy clays and silts, which directly overlie the Pleistocene gravels. Along the line of
the proposed Cut these deposits infill undulations in the surface of the gravels, which may represent relict Pleistocene or early Holocene channels. In areas at the edges or between the channels, sand bars, eyots
or elevated gravel ridges may have existed which persisted as ‘islands’ of drier ground during later periods before they were buried by later alluvial deposits. As such they may have acted as a foci for activity and
provided a platform from which the abundant resources of wetland environment could be exploited. Bronze Age features were identified in Trench OA18 (OA 2004) associated with a gravel high.
In the evaluation trenches to the south of Fen Road, at the southern extent of the development, a possible weathered horizon or remnant buried soil was identified at the upper surface of the sands and silts. A number of prehistoric worked flints have been recovered during the various
evaluation phases from this horizon. However, the presence of Romano-British features cut into the top of this deposit suggests it represents a surface that may have been extant over a considerable timespan. On the floodplain, to the north of Fen Road, a localised sequence of peat/organic
mud was identified in two trenches overlying the basal gravels. This was in turn overlain by a more extensive complex of intercalated minerogenic sediments and grey, carbonate rich deposits. Initial impressions indicate
that a permanent shallow water body, perhaps a poorly drained backswamp, probably existed in this location. A broad prehistoric date can be inferred for this sequence of deposits although sedimentation may not have occurred contemporaneously across this area. Sedimentation
however appears to have ceased by the early Roman period as evidenced by features of this date cut into the surface of this unit.

Both the weathered horizon and calcareous deposits are overlain by an extensive layer of peat/organic silt clay, which sealed and infilled features dated to the early Roman period and indicates a subsequent expansion of
fen environments. This layer was, in turn, overlain by an intermittent minerogenic silt-clay indicative of subsequent seasonal overbank flooding and alluviation from adjacent river channels. Detailed examination of the sediment sequences revealed significant local variations representative of a range of depositional environments existing at any one time. In some areas these variations are clearly associated with topographic features that were subsequently buried by later alluviation and are no longer visible. The range of the depositional environments represented at the site has varying potential for the
preservation of archaeological and palaeoenvironmental remains.
Previous investigations in floodplain environments have shown that evidence of human activity has been found in association with the margins of channels and at the wetland/dryland interface. As such these locations
are considered to represent significant areas of archaeological potential.