Former Avlon Works, Avonmouth, South Gloucestershire Geoarchaeological Deposit Model Report

Oxford Archaeology (OA) was commissioned by BSA Heritage on behalf of
Avonmouth Industrial Estates (UK) Ltd to prepare a geoarchaeological deposit
model to inform archaeological mitigation for the redevelopment of the former
Avlon Works site.
The site is located within an area of significant historic environmental and
archaeological interest, comprising the historic Avon Levels and the Severn Estuary.
Although no designated heritage assets were identified in the archaeology and
heritage statement (BSA Heritage, 2021), several historic medieval or post-medieval
farmstead sites are recorded by the South Gloucestershire Historic Environment
Record (HER) both within the site and the vicinity. In addition, several archaeological
and geoarchaeological investigations have been undertaken in the vicinity, identifying
the presence of Romano-British settlement and a complex series of Holocene
sediments attributed to the Wentlooge Formation with significant
palaeoenvironmental potential.
The purpose of the deposit modelling was to provide additional base-line data with
which to inform the design and implementation of any post-determination mitigation.
The sub-surface litho-stratigraphy was analysed using sediments recorded from
geotechnical (GI) investigations combined with previous geoarchaeological data from
the surrounding area. The work utilised data from 94 ground investigation records that
were obtained from a mixture of cable percussion boreholes, window samples and
test pits.
Four stratigraphic units were identified overlying the Mercia Mudstone bedrock and
were correlated to the Wentlooge Formation. The earliest deposits form the Lower
Wentlooge Formation and comprise sandy and gravelly deposits deposited through
marine and outer estuarine processes during the early to mid-Holocene. Overlying
these are a sequence of intercalated alluvial deposits and organic peat horizons
belonging to the Middle Wentlooge Formation. These accumulated during the early
Neolithic to Late Bronze Age periods and represent alternating periods of wetland
expansion and salt marsh development associated with fluctuations in sea-level rise.
The Upper Wentlooge alluvium began to accumulate during the Iron Age and contains
a Romano-British archaeological horizon associated with settlement activity identified
in neighbouring plots. Made ground deposits truncate the Upper Wentlooge deposits
throughout the central and western areas of the site, although these deposits remain
relatively undisturbed in the eastern and northern parts of the development area.
The presence of Upper Wentlooge sediments throughout site suggests any
archaeological remains occurring may remain undisturbed, although more likely in
areas where there is less modern truncation and made ground. The site lies
immediately west of Plot 5000, and it would therefore seem reasonable to assume
there is potential for the continuation of archaeological activity within the eastern and
northern areas of the site, albeit diminishing in intensity, as it moves away from the
main settlement areas. The surrounding plots to the north and northwest of the site also have not produced any remains, so the presence of archaeology across the area
is therefore not certain.
The Roman land surface was identified at c 5.45m OD in Plot 5000 and if present, it
should be preserved within the eastern and northernmost parts of site. The central
and western areas appear to have been widely truncated by modern development
with made ground deposits present within the upper 1-2m, up to 4m BGL in some
places.
The Middle and Lower Wentlooge sediments survive throughout site, which indicates
any prehistoric activity is also likely to remain undisturbed. There is significant
palaeoenvironmental information preserved within the organic peat deposits.
However, this has been extensively assessed in adjacent plots, creating a detailed
picture of landscape evolution throughout the Holocene. These deposits will not be
significantly impacted by the development and appear to correlate well with the
sedimentary sequence studied in the previous areas.