| Abstract: |
Overall, data from 36 geotechnical samples were included in the deposit models.These comprised a combination of test pit, window sample and cable percussionborehole data. The distribution of the boreholes is illustrated in Figures 2 and 3 and
the locations listed in Table 1. The maximum depth achieved was 12.5m below current ground level (BGL). For comparison, data from 7 geoarchaeological borehole samples
from Plot 5000 has been included to assess the continuity of the Wentlooge Formation and these locations are presented in Table 2.
A pdf of the graphical borehole logs, along with AGS compatible digital database was
provided by the client as an Excel workbook. The digital data was imported into
geological modelling software (Rockworks 2022) for correlation of lithological data
into stratigraphic units. Correlation was carried out in tandem with analysis of a series
of data layers in GIS software (QGIS). The layers included Environment Agency (EA)
LiDAR data (Figure 3), and BGS 1:50,000 Superficial Geology. The litho-stratigraphic
borehole profiles were arranged into four transects, Transect A, Transect B, Transect C
and Transect D, which dissected the site broadly E-W, NE-SW and N-S respectively.
These were then exported and illustrated in Figures 5-8. 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. |
