| Abstract: |
Wessex Archaeology was commissioned by Boskalis Westminster Limited, on behalf of the Defence Infrastructure Organisation, to undertake a Stage 2 investigation involving detailed recording and deposit modelling of geoarchaeological boreholes recovered during geotechnical investigations within the Portsmouth Harbour area and the approach channel. This assessment was undertaken in support of ongoing investigations related to a proposed scheme of dredging and development to be undertaken prior to the planned arrival of a Queen Elizabeth Class Aircraft Carrier at Portsmouth Harbour in 2016. The Stage 2 geoarchaeological description of vibrocores and deposit modelling has recognised a complex sequence of sediments in the study area initially described during the Stage 1 geoarchaeological review of geotechnical logs. The Stage 1 geoarchaeological review divided these sediments into three units, conformed to in this report, comprising the underlying Eocene bedrock (Unit 1), a sequence of Pleistocene to early Holocene sands, gravels, clays and silts associated with the Palaeo-Wallington and Palaeo-Solent (Unit 2), and a sequence of intertidal clays and peats deposited during the Holocene under conditions of rising sea-levels following the end of the last (Devensian) ice age, sealed by modern sands and gravels (Unit 3). These units were divided into a series of sub-units in order to more clearly identify the specific geoarchaeological potential. The study area has been divided into four separate areas defined by broad similarities in the dominant shallow geology and modern environment (Areas A – D).
Detailed geoarchaeological recording of sediments was undertaken on 19 vibrocore sequences acquired from Coastline Surveys, five each from Areas A, B and D and four from Area C. The cores do not contain any Bedrock (Unit 1) and predominantly contain Units 2 and 3, but particularly the latter unit, largely estuarine alluvium, marine sands, palaeobeach deposits and localised deposits of peat interbedded in alluvium.
Recommendations are made for Stage 3 geoarchaeological assessment, focusing on the palaeoenvironmental analysis of peat and over- and underlying alluvial deposits in three cores (DT- 10, 026 and 029) from Area D. The remaining cores from Area D and those from Areas A-C largely comprise marine sands and alluvium and thus have limited or no potential for further geoarchaeological assessment. |
