Archaeology in the Severn Estuary 17

Vol 17 2006 Title Pages

This paper presents the results of pollen, charcoal, macrobotanical and sedimentological analysis at the intertidal site of Hills Flats, south Gloucestershire. Here a sequence of interbedded peats and estuarine silts of mid-Holocene date are exposed along a c. 1.5 km stretch of the intertidal zone, from the surface of which a small collection of unstratified lithics of Neolithic and early Bronze Age date have previously been reported. Analysis suggests an environment of saltmarsh, punctuated by periods of peat formation characterised by reedswamp, fringed by carrwoodland, with Quercus-Ulmus-Tilia-Corylus woodland on the adjacent dry ground. Significant quantities of charcoal were recorded from the base of the upper peat, representing probable anthropogenic burning of reedswamp and sedgefen of late Mesolithic and early Neolithic date. The archaeological and palaeoenvironmental evidence may indicate a special activity site, peripheral to, and perhaps associated with evidence for extensive settlement activity recorded from the intertidal zone 3 km to the south at Oldbury Flats. The results of analysis from Hills Flats are set within the context of previous palaeoenvironmental and archaeological work on the Oldbury Levels, suggesting sustained occupation and exploitation of the intertidal marshes during prehistory.

Vol 17 2006 Jon Brett

An archaeological watching brief undertaken during waste cell excavations within a thick sequence of Holocene estuarine clays, has recorded several early-Neolithic accumulations of wood, including the remains of structural trackways and lines of vertical stakes, both within and crossing palaeochannels. Dispersed bones from an aurochs were also found scattered along one of the channels. Radiocarbon dates from structures recorded in 2005 and from aurochsbone provide calibrated dates between c. 4000 BC and 3000 BC. Lias bedrock, the lower, western slopes of a large, buried island or outcrop of the formation, was recorded along the east side of the excavation area in 2005, and a number of bog oak fragments were recorded in that area. In 2006, a trial, exploratory excavation was undertaken at the western end of the swface of the buried Lias island. A drainage or boundary ditch was recorded. Finds from within and below a buriedsoil layer that lies above the natural Lias clay and stone forming the island or outcrop, and that is sealed, in turn, below the overlying, alluvial clays that accumulated from the later-Roman period onwards, included prehistoric flint flakes, animal bone fragments and occasional pottery sherds ranging in date from the late Bronze Age through to the Roman period. Small palaeochannels were recorded cutting through the buried soil and the surface geology and were also recorded within the overlying, post-Roman, alluvial clay

The alluvium of the Oldbury Levels resembles similar Holocene alluvial sequences in adjacent areas. It consists of a sequence of alternating silty clay and organic deposits which represent deposition from estuarine waters and under periods of terrestrial peat growth during phases of marine regression against a background of gradually rising sea levels. Pollen evidence appears to reflect gradual change in the flora associated with changing tidal regimes, broader environmental change and the encroachment of human landuse which gradually diminished the forest cover. Foraminifera and very limited plant macroscopic remains supply evidence which support the conclusions drawn from the sedimentary evidence. Buried Roman archaeological sites, lying close to the dry-land margin, occur within estuarine alluvium which appears to have continued to be deposited, at least occasionally, while the sites were occupied. This suggests that the sites were sometimes flooded, and increasingly so towards the end of the occupation, perhaps indicating seasonal use of the floodplain edge. Darker bands of dispersed organic matter, known as stasis horizons, are considered to be depositional strata, and not in situ accumulations of A-horizon organic soil material. While some form surfaces from which cracks extend downwards, implying that they formed during periods of persistent drying, there is little associated mixing or other evidence for soil formation. Thus they probably represent only short periods of relative stasis within periods dominated by continuing alluvial silt deposition under tidal conditions.

Vol 17 2006 Publications List