| Abstract: |
Wessex Archaeology (WA) was commissioned by Mackley Construction to undertake a program of geoarchaeological works in support of the Lydd Ranges Sea Defence Scheme. In order to offset the impact of coastal defence improvement works on deposits of geoarchaeological interest in the Dungeness, Romney Marsh and Rye Bay SSSI, a programme of geoarchaeological works was required on the foreshore, Green Wall and within marshland landward of the current Green Wall. The works target three areas of marsh (Zones, C, E and G) located between gravel ridges of the Dungeness Foreland. Work within the marshland landward of the Green Wall involved 30 hand-held window samples, 10 within each zone. This was accompanied by three rotary and sonic cores on the Green Wall to maximum depths of 15m to sample and record the full sequence of Holocene sediments to the surface of the basal sands. Exposures of silty clay were monitored on the foreshore in 14 test pits (scrapes), recording the elevation and retrieving samples where appropriate. The geoarchaeological works identified a consistent sequence of deposits across Zones C, E and G comprising a basal sand, in turn overlain by sands and gravels, gravels and a sequence of clays and silts with localised organic units. The deposits correspond broadly to the existing preliminary ground model for the scheme, although displaying lateral variation in the presence, composition, thickness and elevation of deposits. Basal sands, representing shoreface and intertidal deposits were recorded in sonic cores at elevations of -6.26 (Zone C), -6.58 (Zone E) and -6.35 m aOD (Zone G). The deposit will not be impacted by design elements of the scheme and drilling ceased when it was clear this deposit had been encountered. The overlying sands and gravels are interpreted as evidence for the development of a spit and barrier complex. The total thickness of sands and gravels was recorded in zone E where they reached 2.89 mOD. Poor recovery of this deposit made it difficult to determine the interface between the sands and gravels and overlying gravels. The overlying gravels represent contemporary storm beach gravels extending up to 6.7m thick. This barrier developed through the longshore movement of offshore derived gravels and form a series of defined ridges and intervening lows. Within the inter-ridge lows, the gravels have an elevation of -0.94 m aOD (Zone C), 1.23 m aOD (Zone E) and -0.15 m aOD (Zone G). The intervening inter-ridge depressions within the gravel barrier variously contain sequences of fine-grained sediment along with sands, clayey-gravels and localised peats deposited within former tidal inlets. The formation of these marshland sediments reflects a period of significant coastal dynamisms under the influence of the eastward progradation of the gravel barrier, together with rapid sedimentation of the intervening inter-gravel lows. The fine grained sediment comprised both structureless silty clays overlying laminated silty clays, with surface elevations between 2.05–1.52 m aOD (Zone C), 2.07–1.37 m aOD (Zone E) and 1.90–1.56 m aOD (Zone G). Exposures of silty clay on the foreshore only occur in relation to the corresponding inter-ridge depressions, varying in height from 2.22 m aOD (Zone C), 0.69– -0.85 m aOD (Zone E) and 0.37–0 m aOD (Zone G). A 0.38 m thick peat deposits was recorded in Zone G at -0.72– -0.94 m aOD, located landward of the seawall and stratified in silty-clay marsh deposits. Recommendations are made for a program of palaeoenvironmental assessment of samples to meet the aims and objectives outlined in the project scope. |
