Series: ARCA unpublished report series

In August 2017, ARCA carried out a geoarchaeological borehole survey at 13 - 21 Baldwin Street, Bristol, BS1 1SE, at the request of Bristol and West Archaeology Ltd to investigate the Late Pleistocene and Holocene strata. Two boreholes were drilled by Geotechnical Engineering and the results were combined with that of earlier work at the site. The stratigraphic units identified were: Modern made ground, archaeological deposits, Wentlooge Formation Alluvium (Holocene, fluvial/estuarine fine grained alluvium), weathered sands of the Redcliffe Sandstone Member, and the Redcliffe Sandstone Member bedrock (Triassic, local bedrock). The Redcliffe Sandstone Member sub-cropped against the Wentlooge Formation at +0.30m OD in ARCA BH1 and -0.30m OD in ARCA BH2. The top surface of the fine grained alluvium of the Wentlooge Formation was found between +7.00m OD in GTS WS2 and +6.10m OD in ARCA BH2. The thickness of the unit was c. 5.5m. The site is therefore located on the line of pinch out of these sediments where they on-lap against the Redcliffe Sandstone Member. No dateable peat units were recovered. Archaeological deposits truncate the upper, oxidised fraction of the alluvium. No dateable artefacts were recovered. Modern made ground associated with the present day building on the site truncated the archaeological deposits and capped the sedimentary sequence.

Borehole survey In June 2016, ARCA monitored the drilling of three geoarchaeological boreholes at 33 – 35 Monier Road, Bow, London. In conjunction with five borehole logs from ground investigation work by Jomas Associates Ltd, the Lea Valley Gravel Member was determined to sub crop at between -1.1m OD and -0.27m OD. Overlying this Member was a suite of paludal and fine grained alluvial deposits that were truncated by deep Made Ground strata at between +1.2m OD and +3m OD. Evidence was recorded in BH2 for a possible loessic palaeosol overlain by organic mud at +0.41m OD. Peaty strata were recorded at a similar elevation in BH3. These deposits were subsequently buried by fine grained alluvium that, on occasion, showed evidence of minor channel formation probably draining the higher terraces to the west. Diatom evidence was preserved only in the upper strata and points towards estuarine conditions at 1640 – 1935 cal AD succeeded by more freshwater conditions. Pollen was preserved throughout the paludal and fine grained alluvium and indicates pine wood dated to the Late Mesolithic 5315 – 5209 cal BC and broadly contemporary with the possible palaeosol, succeeded by a mixed deciduous woodland. At this date, sedge fen and reed swamp dominated the floodplain. Low values for Alder, however, imply that this woodland type was rare. A clear anthropogenic signal was recorded in the upper alluvial strata with high values of herbaceous pollen including cereal and open/disturbed ground species. Minor values for tree pollen suggests clearance.

In August 2019 ARCA examined six 0.5m monolith tins of sediment from three trenches excavated by Cotswold Archaeology Ltd at the Former Kwiksave, Black Dog Way, Gloucester. The three sequences were comparable and represented a soil profile that had developed in the top of Roman building debris. The debris is suggested to be in part cob and as such provided a clay-rich substrate for subsequent pedogenesis. No evidence was found for middening, however the black, humic deposits conform to a category of archaeological sediments known as 'dark earth'.

In March 2017 at the request of Cotswold Archaeology, ARCA visited the Farndon Fields site to inspect the geoarchaeology revealed in a series of test pits. Holm Pierrepont Sand And Gravel Member is represented by Units 3 and 4. The top of the Member (Unit 3) has possibly been truncated because finer strata recorded elsewhere at Farndon Fields are absent. LUP artefacts must lie above the superface of Unit 3. They might be expected above the gravel surfaces that are lower in elevation where the overlying stratigraphy may be thicker and more complete. However in situ occupation surfaces/sediments are not apparent on the site. Coversands (Unit 2) are thin and heavily bioturbated. There is no evidence of later channelling.

A watching brief carried out during the installation of a new septic tank at the site revealed a layer of brick rubble thought to relate to a demolished wing of the house. [Au(adp)]

Borehole survey The document reports geoarchaeological works at Pan Lane, Newport, Isle of Wight carried out in advance of ASDA Stores Ltd's construction of a new supermarket on the site. Previous works on the north and east side by Oxford Archaeology and Archaeology South-East had suggested the presence of fluvial terraces within the site. Therefore the aim of the present work was to characterise the Pleistocene fluvial deposits and assess their potential for preserving Palaeolithic archaeological materials. Geoarchaeological works were carried out between November 2015 and February 2016 and comprised the excavation of 21 test pits, the drilling of 3 boreholes and associated laboratory description of the sampled sediments, assessment for biostratigraphic palaeoenvironment proxies and optically stimulated luminescence (OSL) dating. The test pits demonstrated that a single Pleistocene fluvial terrace – a former course of the River Medina - runs down the western part of the site and reaches a maximum thickness of 2.1m within the site boundary. The terrace is equated with 'Terrace 2' of Oxford Archaeology's (2005) previous study and comprises clast-supported flint gravels, with occasional thin and lenticular beds of coarse-medium sand. Terrace deposits are not present on the central and eastern part of the site, but rather matrix-supported gravels in these locations are Pleistocene Head. The Terrace 2 fluvial gravels were sampled in three boreholes drilled with a Pioneer rig. OSL dating of sand strata within the gravels suggest that the terrace dates to the 120-69,000 BP interval, i.e. Marine Isotope Stages (MIS) 5d-4. Archaeological materials were not found in any test pit and there was no faunal (i.e. Mollusca or Mammalia) or pollen preservation in any of the sampled deposits. Terrace 2 is assessed as having a low archaeological potential on account of both its high energy mode of deposition and because humans were absent from /present only occasionally in Britain in the MIS 5d-4 interval. The Head deposits are also assessed as having low archaeological potential as they likely formed at the height of the MIS 2 Late Glacial Maximum when people were also absent from Britain.

In June 2014 ARCA monitored the drilling of six geotechnical boreholes at the site of Avon Fire Station, Temple Back, Bristol. Two boreholes, ARCA AFS BH1 and ARCA AFS BH2 were drilled through the Quaternary sedimentary sequence into the bedrock (maximum depth 20-25m), whilst the four other boreholes were drilled to maximum depths of 4-5m below ground level (BGL). MMG bedrock was encountered in the base of the two deep boreholes and was overlain by Pleistocene fluvial gravels of the Avon Formation. The Avon Fm was in turn overlain by strata of the Holocene Wentlooge Formation: first by a series of laminated fine sands (most likely deposited on a point bar in the inner bend of a meander of the Avon), and then by fine-grained alluvial/intertidal sediments. Deposits of possible archaeological interest, up to 9.60m thick, which may represent the remains of one or more phase of structural masonry were encountered between +1.19 and +8.09m OD in BH2. Proto-urban deposits were encountered between +6.70 and +7.12m OD in BH8.

Logging and assessing lithology of borehole cores. In January 2020, ARCA logged cores from borehole BH07a recovered from the Bridgewater Tidal Barrier Project on the River Parrett, Bridgwater, Somerset. This was an Environment Agency project undertaken by Jacobs Engineering Group. Ground investigation included a further 30 boreholes, the logs of which were also examined. Lithological data from these records were transferred to a RockWorks 15 database for interpretation and analysis of lithostratigraphic cross sections. The Triassic bedrock, Mercia Mudstone Group, is found between -2.10m OD (9.2m below ground level (bgl)) and -16.99m OD (25.0m bgl) in BH07 and BH11, respectively. The latter records a deep palaeochannel located on the northeast of the site. The bedrock on the majority of the site lies at c. -3.4m OD and forms a relatively high elevation bench. The basement is unconformably overlain by Devensian sandy gravels in one borehole only, BH01, and is found at -1.52m OD (9.9m bgl). Intertidal aggradation has laid down fine grained deposits with sands accounting for up to 8.8m of deposit (88%) in BH06, for example. Interbedded silt and clay laminae are common and record intertidal mudflats. No peat deposits were found and there was only very rare evidence of any organic clay. Thick deposits of Made Ground top the stratigraphic sequence particularly in the south (WS13 to WS07) where there is possibly a landscaped landfill site.

Borehole survey In December 2018, ARCA was commissioned by Wardell Armstrong to review the geoarchaeology of six boreholes drilled on the Plot 4 Site, The Bridge, Dartford. Nine geotechnical boreholes and Trial Pits were also reviewed. The lithostratigraphy of the site comprised four units: White Chalk Subgroup, Taplow Gravel Member (river terrace), fine grained deposits and Made Ground. The Chalk lies at -5.16m OD (8m bgl) in BH4-03. It is overlain by the flint gravel and sand terrace that lies at a maximum elevation of +0.17m OD and dates to the Middle Pleistocene. This terrace has been truncated by thick and ubiquitous deposits of Made Ground that reach a maximum thickness of 7m. Two boreholes sampled humic fine grained deposits at -0.69m OD (3.44m bgl) in WS5 and +0.29m OD (2.52m bgl) in WS6. They attain a maximum thickness of 1.3m in WS6. These deposits are believed to represent flooding and drainage of the terrace that has laid down silty clays in a reducing environment, and exist as isolated pockets by truncating Made Ground. The date of the deposits is unclear but a fragment of waterlogged leather was recovered from WS5.

Assessment of dating, lithology and palaeobotany of borehole cores. A geoarchaeological borehole study was undertaken of land west of Cutbush Lane East, Shinfield, Reading in October 2021, while subsequent laboratory examination took place from October 2021 to February 2022. The purpose of the work was to test the Palaeolithic archaeological potential of deposits on the site that had been revealed by a previous archaeological evaluation. Six geoarchaeological boreholes were drilled, four with an Atlas Cobra TT hammer driving gouge auger heads and core samplers, and two with a Pioneer 2 rig collecting 115mm diameter core samples. Strata in the gouge auger heads were described in the field, while cores were described and sub-sampled in the laboratory for optically stimulated luminescence (OSL) and 14C dating, and palynological and plant macrofossil assessment. Between 4 and 5m of Quaternary (the last 2.6 million years) deposits were found overlying London Clay (Eocene) bedrock. The basal Quaternary deposits are 1.1–1.5m thick fluvial gravel strata that probably formed in the bed of the Loddon river, a south bank tributary of the Thames. Two OSL dates from sand layers within the gravels suggest deposition in Marine Isotope Stage (MIS) 3 (29–57,000 years ago) and possibly MIS 4 (71,000–82,000 years ago). Overlying the gravel in one part of the site is a c 0.4m-thick organic mud, which is also thought to be of MIS 3 age. This latter deposit contains moderate to well preserved pollen, which was mostly of aquatic and herbaceous taxa, but also included possible evidence for trees. Plant macrofossils were not, however, found in the stratum meaning that it could not be chronometrically dated by 14C measurement. Lying above the gravels and organic mud, and likely separated from them by a hiatus are 3–4m of Brickearth and Head deposits. The brickearths formed first, but later interdigitate and are therefore contemporary with the Head. While both are likely to be of MIS 2 age (11.7–29.0 thousand years ago). The organic muds are assessed as being of moderate to high Palaeolithic archaeological potential on account of their age, gentle mode of deposition, the presence of a former land surface in one record and the moderate–good pollen preservation. The remaining deposits are assessed as either low to moderate (fluvial gravels) on account of their high energy deposition or low potential (Brickearth and Head) because of their chronology and the absence of humans for the majority of MIS 2.