Chard Junction Quarry
Laura Basell1, Tony Brown2 and Phil Toms3
1Archaeology and Ancient History, University of Leicester
2Geography and Environmental Science, University of Southampton
3Environmental Sciences, University of Gloucestershire
Executive summary
Chard Junction Quarry: sustained monitoring of working quarry, utilising new and existing techniques, and grounded in very effective working relationships.
‘Monitoring and Modelling of the Palaeolithic Archaeological Resource at Chard Junction Quarry (CJQ) Hodge Ditch Phases I to III’ began as a project that aimed to contextualise and date new Palaeolithic finds from the Axe valley, but its focus widened to a project testing novel geoarchaeological recording and dating methodologies in the context of large-scale aggregate extraction.
The project was broadly concerned with Palaeolithic archaeology and Quaternary landscape change, but methodologically it employed, and trialled, a range of cutting-edge techniques. It addressed issues relating to four-dimensional sediment and landscape modelling, predictive modelling, and taphonomic implications for Palaeolithic sites in fluvial sedimentary sequences. While the Chard Junction work was not directly developer-funded, the methodological aspects are relevant to developer-funded scenarios.
Keywords
Where: Chard Junction Quarry (Hodge Ditch), Somerset
Region: South-West
Palaeolithic period(s): later Middle and Late Pleistocene (MIS 12–2)
Type of investigation:Fieldwork; Post-excavation analysis and publication
Methods: Terrestrial Laser Scanning; Grain Size Analysis; Gamma CPS; Cosmogenics; OSL; Geoarchaeology; Sedimentology; Deposit modelling
Type(s) of deposit: River Terrace Deposits (clay, silt, sand and gravel)
Features of interest: Recording by Terrestrial Laser Scanning; Novel use of borehole logs and digital granulometry; Working relationship with quarry operators
Project stages
Pre-application
- Desk based assessment
- Geotechnical/geoarchaeological survey
Pre-determination
- Test pitting/Borehole survey
Post-determination, Pre/during development
- Test pitting/boreholes
- Watching brief
Post-excavation/research dissemination/HER enhancement
- Post-excavation analysis (and reporting)
- Final Report
- Deposit with HER and museum (and Oasis) ?
- Publication (academic and/or public)
- 2005–2007: ‘The Palaeolithic Rivers of South West Britain’ project (PRoSWeB) established baseline data for south-west Britain. Chard Junction Quarry targeted as one of several sites across the South-West with good river terrace exposures. Aggregates Levy Sustainability Fund (ALSF)-funded via English Heritage. Authors became aware of planned new extraction area, Hodge Ditch, at CJQ.
- 2007–2009: Interim funding from the University of Southampton permitted Basell (PDRA on PRoSWeB) to continue monitoring Chard Junction Quarry and maintain a good working relationship with staff as extraction proceeded. 2008: bifaces discovered; Spring 2009: Hodge Ditch phase I extraction completed.
- 2009–2013: ‘Monitoring and Modelling of the Palaeolithic Archaeological Resource at Chard Junction Quarry Hodge Ditch: Stages 1 to 3’.
- March–May 2009: Stage 1; ALSF-funded via English Heritage; Hodge Ditch phase II extraction began.
- January 2010–March 2011: Stage 2; Historic Environment Enabling Fund (HEEP)-funded via English Heritage.
- August 2012–August 2013: Stage 3; Extension to Stage 2 to complete a range of outstanding tasks and archiving; HEEP-funded via English Heritage.
Development Context
As the only active large gravel pit in the Axe valley, Chard Junction Quarry was incorporated into the PRoSWeB project. Following extensive desk-based research and discussion with the Quarry managers the authors became aware that a new extraction area, Hodge Ditch, was due to be opened. Chard Junction Quarry lies at the Somerset/Dorset border with Hodge Ditch lying in Somerset. Although the setting is rural, the activity is industrial and relatively large-scale.
Frequent field trips were made to Chard Junction Quarry as part of PRoSWeB and when that project ended, visits to the working quarry continued between 2007–2009 to examine sections and maintain the working relationship with quarry staff. During one of these visits in 2008, bifaces were discovered in situ which led to the conception of the Chard Junction Quarry projects, which occurred in three stages. Based on the results of Stage 1 and due to anticipated changes in the ALSF funding, the project Stages 2–3 were Historic Environment Enabling Programme (HEEP)-funded, which resulted in a shift in focus.
Since aggregate was in demand, extraction at Hodge Ditch during the project period was particularly rapid. We estimated that extraction would descend through the Palaeolithic levels at a rate of 20,000–30,000 years per month on average. By the end of Stage 1 it was known that bone preservation was unlikely (though not impossible), but that palaeosols and further bifaces were both possible and likely, and that Stage 2 would allow the examination of the entire sequence from the surface to bedrock.
Archaeological Context
The Axe valley has long been known as a rich source of Palaeolithic artefacts, predominantly from the site of Broom. The thick (>20m) gravel deposits in the Axe catchment had also been a subject of interest both for Quaternary research and for commercial aggregate extraction. Chard Junction Quarry, which has been operational since the 1950s, has produced occasional Palaeolithic artefacts, but these lacked precise contexts.
Methodology and Research Questions
Following desk-based assessment the methods were geoarchaeological, combining field-based survey and sampling, museum-based artefact analysis, geochronological and geospatial methodologies and outreach activities.
Geotechnical and borehole data were also made available which aided targeted fieldwork and modelling significantly, in conjunction with occasional test trenches to check the sequence and establish the base of gravels in areas lacking borehole data.
Field techniques were selected to maximise accurately georeferenced data acquisition, usually by one person on regular but intermittent visits (1–2 visits every 2 weeks), in the face of rapid extraction over a large area.
The application of the new methodologies and changes in the project design were primarily reactive. They aimed to address the pressures of only one or two people working in a dynamic and rapidly changing pit and responded to archaeological and palaeoenvironmental discoveries as they came up.
After 2007 there were no significant changes in the methodologies across the different stages of the project. Finally, quarry staff played a key role by alerting project staff to any unusual or interesting deposits or finds.
For Stage 1 the justification for the project was to establish the age of the artefacts, their archaeological, palaeoenvironmental and geomorphological contexts. The primary objectives and their associated methodologies were:
- Collate all archaeological and sedimentological data pertaining to the Chard Junction Quarry area;
- Provide a clear understanding of the stratigraphic sequence from which the bifaces were discovered;
- Purchase 5 optically stimulated luminescence (OSL) dates from the University of Gloucestershire and two duplicate/validation OSL dates from the Research Laboratory for Archaeology and the History of Art (RLAHA) Oxford;
- Produce a report on the finds, their sedimentological and environmental context, and archaeological importance.
Having confirmed the context and approximate age of the bifaces, Stage 2 aimed to improve understanding of the biface-bearing gravels, refine the dates and develop methodologies better suited to maximising data retrieval in such a dynamic working environment. The four principal aims were to:
- Apply a unique combination of new technologies to the deep sequence at Chard Junction Quarry to record the sequence and test their efficacy in the face of large-scale and rapid mechanised aggregate extraction practice. These included gamma log analysis, digital granulometry and terrestrial laser scanning (TLS);
- Apply further OSL dating and cosmogenic burial dating to try and validate the OSL chronology and provide an alternative method for dating such sites;
- Elaborate why Chard Junction Quarry is important in understanding the British Palaeolithic and how it is representative of a difficult site type (stacked sequence/compound terrace) for the monitoring and management of the archaeological resource;
- Review other disused quarries near Chard Junction to inform the National Planning Policy Framework 2012 and county archaeologists of their Palaeolithic potential in case of reactivation.
Stage 3 of the project was an extension which permitted:
- Analysis of a newly discovered organic horizon;
- Workshop to feedback to the industry.
Methods
Gamma CPS
Material/object the method is applied to: Borehole
CJQ Specific Application: Used to identify major stratigraphic boundaries and for predicting which deposits would be most likely to yield artefacts.
Geoarchaeological value: Differentiating between debris flow deposits, matrix supported gravels and fluvial gravels, particularly for a pre-excavation assessment of the stratigraphy of large gravel extraction sites.
Sampling Strategy: Gamma detector is lowered down a borehole and records gamma radiation at incremental depths.
Accessibility/Cost/ Experience: Standard procedure in the drilling industry and site investigations industry. Commonly supplied with or alongside drillers' log sheets supplied by drilling companies. Specialist expertise and equipment required, but data may be freely available depending on context.
Problems: Borehole data may be commercially sensitive and therefore not readily accessible at all sites/reliant on goodwill and trust between operator and researcher. The success of the method partially depends on the geology.
Relevant publication & figure:
Brown et al. 2015
Brown et al. 2011a
Guide sheet available from authors or via ADS.
Terrestrial Laser Scanning
Material/object the method is applied to: Any solid object
CJQ Specific Application: Rapid recording of faces to record sampling locations and to explore use of point cloud data in grain size identification and definitions of major stratigraphic boundaries.
Geoarchaeological value: Rapid 3D recording of large areas at high resolution to generate fully georeferenced point clouds/virtual models/cross sections etc. Can be used to record morphology of a pit, excavation, or structures but also to record particular faces/sections, objects and sample locations. Point clouds can be stitched together to produce a composite image, models, novel viewpoints and animations. Useful because it causes no/minimal disruption to quarrying activity and accurately records the geospatial position of quarry faces, can be used to distinguish stratigraphic features and spatial analysis of sampled point clouds can be used as a proxy for variations in sedimentology.
Sampling Strategy: Surface/area of excavation can be scanned and photographed at high resolution to create DTMs, sections etc. Area scanned is user-defined.
Accessibility/Cost/ Experience: Cost of equipment is comparatively high, though costs are reducing and equipment and operators can be hired. It is a common methodology in the Minerals and other industries to record e.g. the morphology of quarries prior to blasting. Specialist expertise, equipment and software required.
Problems: Water and glass, or highly shiny surfaces are not suitable for scanning. Rain interferes with scanning and although modern systems have filters for light drizzle, ideally conditions should be dry. Scanning on unstable surfaces (e.g. peat) can be problematic.
Relevant publication & figure:
Brown et al. 2015
Brown et al. 2011a
Historic England 2018
Figure 2
Digital Granulometry (aka grain size analysis)
Material/object the method is applied to: Sediment bodies through which a clean section has been cut.
CJQ Specific Application: Tested against traditional grain size analyses (bulk sample sieving) to check efficacy, and to characterise the different units in order to understand how they were deposited.
Geoarchaeological value: Measures grain size using digital photographs and software ‘Sedimetrics©’. Permits characterisation of sediment body to facilitate the interpretation of sediment deposition and taphonomy. Provides alternative to bulk sampling and sieving. Is a rapid and cost-effective proxy method for true grain size variations and useful in distinguishing between different sedimentary units.
Sampling Strategy: Four markers in the corner rectangle of known dimensions. The sampling area must be small enough so that the diameter of the smallest grain of interest is 23 pixels in the image.
Accessibility/Cost/ Experience: A high-quality digital camera (10+ mpx); computer; bespoke software (around £500) and a means of demarcating the area of interest (frame usually in shape ratio of 4:3). Low-tech equipment and minimal training required to gather the data. Some specialist expertise required in its interpretation.
Problems: Although digital granulometry is a rapid method and data can be gathered by unskilled workers, it remains a relative grain size proxy. It is particularly good at distinguishing bimodal (e.g. sand and gravel) units but more sophisticated methodologies will be required to improve accuracy and extract more information from data, such as the 3D arrangement of clasts.
Relevant publication & figure:
Brown et al. 2011a
Guide sheet available from authors or via ADS
Graham et al. 2005a & b
Figure 3
Traditional Grain Size Analysis
Material/object the method is applied to: Sediment: any type of organic or non-organic granular matter.
CJQ Specific Application: Used to compare with grain size samples recorded by digital granulometry.
Geoarchaeological value: Procedure which assesses particle size distribution by passing samples through a progressively smaller mesh size by shaking the sieves. The amount of material gathered in each sieve is then weighed and displayed as a fraction of the whole mass. Useful in characterising different stratigraphic units/sediment bodies in order to understand the conditions under which they were deposited. Fractions may also be used for macro/microfossils and cultural artefacts.
Accessibility/Cost/ Experience: A widely used and fairly standard methodology. Cost is in the time taken to collect the samples, sieve the material and analyse the results. Basic equipment (sieves) and software (Excel) are sufficient, but some specialist expertise is required to interpret the data.
Problems: Logistically it can be challenging gathering, transporting and processing bulk samples.
Relevant publication & figure:
Bridgland 1986
Brown et al. 2011a
Figure 3
Clast lithological analysis
Material/object the method is applied to: Sediment
CJQ Specific Application: Used to identify 6 sources of the transported gravels and potentially artefacts and disprove Lake Maw hypothesis.
Geoarchaeological value: Particularly useful when combined with grain size analysis and angularity assessments in determining sediment deposition and taphonomy.
Sampling Strategy: To achieve a statistically significant result, then a large sample size is required. At Chard, 143 tons were sampled.
Accessibility/Cost/ Experience: Cost is in the time taken to collect the samples, sieve the material and analyse the results.
Problems: Logistically it can be challenging gathering, transporting and processing bulk samples.
Relevant publication & figure:
Bridgland 1986
Brown et al. 2011a
Brown et al. 2015
Figure 3
Geomorphological mapping
Material/object the method is applied to: Landscape
CJQ Specific Application: To define the terrace and search for terrace fragments. Specifically, to assess the provenance of the upper diamicton unit in CJQ and to improve understanding of biface distributions.
Geoarchaeological value: Fundamental technique in geoarchaeology producing valuable graphical inventories of a landscape. They may depict landform surfaces as well as subsurface materials. Required to assess the full resource.
Sampling Strategy: Site-specific depending on the questions being asked, but usually landscape-scale using walk-over survey and use of apps.
Accessibility/Cost/ Experience: Field mapping takes time and experience to distinguish and record relevant landscape features. Many maps now incorporate geological, DTM and other data (as at CJQ) and are usually generated using a range of software which requires expertise. For CJQ these incorporated a range of ArcMap and Adobe products.
Problems: Requires geomorphological mapping skills.
Relevant publication & figure:
Basell et al. 2011
Brown et al. 2015
Otto & Smith 2013
Smith et al. 2011
Brown et al. 2011a
Figure 4
OSL dating
Material/object the method is applied to: Sediment
CJQ Specific Application: To provide an assessment of burial period through dating the last exposure to sunlight of quartz in the fine silt or fine sand fraction.
Geoarchaeological value: Focuses on datable material that is naturally ubiquitous and physically robust. Offers the opportunity to directly date sedimentary events from c. 10 to 500 ka in the UK.
Sampling Strategy: Targets homogenous, thick (>15 cm) units or lenses of sediment.
Accessibility/Cost/ Experience: Bulk sampling is possible, but the normal method is to force opaque plastic tubing 100 x 45 mm into each face, then wrap each sample in cling film and seal carefully with parcel tape to preserver moisture content and sample integrity until ready for lab preparation. Multiple samples from the same lens is a good idea if possible. In situ gamma reading should be taken if possible, but if not, an additional 100g sediment sample for lab-based assessment of radioactive disequilibria is sensible.
Problems: Partial resetting of the time-dependent signal through limited sunlight exposure time, spectrum and/or power in waterlain deposits.
Relevant publication & figure:
Duller 2008
Cosmogenic Isotope Dating
Material/object the method is applied to: Sediment - pebbles/cobbles in the gravels.
CJQ Specific Application: To augment OSL dating since no carbonate or biological methods were possible. To extend the time range of sediments that can be dated, and to trial a method that could be used to date gravel bodies lacking fine deposits suitable for OSL dating. Samples were taken and application is in progress.
Geoarchaeological value: Additional chronological data. Burial dating of sediments uses the fact that sediment was exposed to cosmic radiation prior to and in the early stage of burial. The upper limit is 5 mya. Method is particularly useful in areas where no carbonate or biological methods are possible, where fine-grained deposits for OSL are lacking or deposits are likely to be beyond the range of the OSL method.
Sampling Strategy: Site-specific depending on the questions being asked, but at CJQ this involved paired samples of a small cobble (64-256 mm) of angular chert with a very well-rounded quartzite cobble of a similar size being sampled from 10 levels between 71 and 62 m OD in the same faces sampled for OSL. Where quartzite cobbles could not be found, flint was selected as an alternative.
Accessibility/Cost/ Experience: Extremely high cost at c. £1000 per sample.
Problems: Was not completed due to cost and requirement to submit to SUERC. Intention is still to submit these, and discussions continue regarding this.
Relevant publication & figure:
Application under preparation to SUERC: see their webpages for specific details
Sedimentological Logging
Material/object the method is applied to: Ideally a vertical section/profile exposure but could be a core.
CJQ Specific Application: To describe and identify the sedimentological information at regular intervals across selected sections as excavation proceeded, to understand stratigraphy, trends and provide a representative summary of large exposures for comparison with other recording methods such as TLS, sedimetrics etc. and understand depositional processes and taphonomy.
Geoarchaeological value: Since the method records and describes grain size (e.g. sand, silt, and clay), their form, combinations, structures and relationships, the method is useful in determining the processes that result in the deposits (erosion and weathering), their transport, deposition and diagenesis.
Sampling Strategy: Dependent on the questions being asked, the homogeneity of the deposit, and time available. At CJQ sampling intervals across sections of 20 - 100m could be every 2 or 3m or every 10m for example.
Accessibility/Cost/ Experience: Low cost beyond the time. Sedimentologists apply their understanding of modern processes to interpret geologic history through observations of sedimentary sequences, so specialist skills require development and ability to interpret deposits increases.
Problems: Logging requires recording skills that can be acquired relatively quickly but interpretation of the logs requires experience. Can be very time-consuming and working out relationships between features also requires skill.
Relevant publication & figure:
Brown et al. 2011a
Basell et al. 2011
Brown et al. 2015
Figure 5
Dating: (OSL and Cosmogenic Isotopes). Interlab comparison and age-depth modelling
Material/object the method is applied to: Suitable sand lenses /gravels targeted and divergent dosimetry approach.
CJQ Specific Application: A double check on chronology - unusual with age-depth modelling which took into consideration OSL dates and 5e organics to build a robust chronology.
Geoarchaeological value: More reliability and confidence in the chronology. Greater chronological precision. Confidence in the antiquity of the lithics.
Sampling Strategy: Targeted same sediments in same units. Suitable sand lenses targeted and divergent dosimetry approach.
Accessibility/Cost/ Experience: High at £600 per sample plus field visit by geochronologist.
Problems: Some variation between labs and very difficult to assure exactly same protocols. Age-depth modelling can be unreliable at some sites but not at CJQ due to multiple recording methods and understanding of sequence.
Relevant publication & figure:
Brown et al. 2011a
Microscopy and ESEM/EDS Analysis
Material/object the method is applied to: Organic-rich lens
CJQ Specific Application: To understand how the organic lens formed by looking for insects, structures, features, and textures within the sediment. Included identification of e.g. carbonised rootlet channels, plant tissues, smooth skin fragments within massive silt textures, cubic crystals identified as magnetobacteria.
Geoarchaeological value: Improved understanding of sediment including depositional and taphonomic processes. Can provide additional palaeoenvironmental data (e.g. insect, clues to palaeotemperature, moisture etc).
Sampling Strategy: Lens or horizon-specific. Samples need to be taken with clean equipment into bag and prepared for analysis in the lab.
Accessibility/Cost/ Experience: Specialist equipment and skills needed for interpretation.
Problems: Cost.
Relevant publication & figure:
Brown et al. 2011a
Pollen analysis
Material/object the method is applied to: Organic-rich lens
CJQ Specific Application: To provide additional chronological and environmental information.
Geoarchaeological value: Improve chronology and provide vegetation data for one point in the past; in this case MIS 5e.
Sampling Strategy: Bulk sampling or exposure.
Accessibility/Cost/ Experience: Sampling low cost and pollen about £200 per sample.
Problems: Low pollen concentrations and some degradation.
Relevant publication & figure:
Brown et al. 2011a
Brown et al. 2015
GIS
Material/object the method is applied to: Any data set with a geospatial aspect.
CJQ Specific Application: To record, display and analyse multiple datasets in multiple dimensions including OS maps, lidar and IFSAR data for DTMs and DEMs, TLS data, HER data, map regression (to identify old quarries into terrace deposits), BGS mapping data, differential GPS and other sample data, geomorphological fieldmapping etc.
Geoarchaeological value: Valuable as a framework for gathering, managing and analysing geospatial data with multiple applications. Can incorporate remote sensing data from lidar to sub-surface capture methods including borehole or geophysical data. Excellent for generating maps, visualisations and models of diachronic change in multiple dimensions.
Sampling Strategy: N/A
Accessibility/Cost/ Experience: For CJQ we used ArcMap which requires a licence. Other freeware GIS packages are available (e.g. QGIS). Requires skills in software and data manipulation, and depending on questions being asked, some understanding of the algorithms behind the tools in order to ensure correct interpretation of the data.
Problems: Licensed packages can be expensive. Large dataset manipulation requires a high specification computer and cloud or external hard drive storage for backing up datasets. Compatibility between different GIS software varies so saving in multiple formats to maximise usability is sensible.
Relevant publication & figure:
Brown et al. 2011a
Figure 6
Lithic Analysis
Material/object the method is applied to: Lithics found in field and contextualised via HER analyses.
CJQ Specific Application: Lithics were looked for during every visit to CJQ and sometimes via controlled survey in areas where artefacts were previously found. HER analyses drew on PRoSWeB work but also targeted museum visits and examination of collections where relevant artefacts were recorded using basic morphometric descriptions and photographed.
Geoarchaeological value: Understanding hominin/human occupation of an area, palaeoenvironmental conditions and potentially (depending on site) information about sedimentary body.
Sampling Strategy: Site-dependent. Could be controlled archaeological excavation to occasional site visits. Sampling of HER was controlled by defining area of interest as the catchment boundary.
Accessibility/Cost/ Experience: Dependent on sampling strategy and likelihood of finds. Expertise in lithics required for artefact identification, recording and analysis.
Problems: Cataloguing and analysis depends on questions being asked. Particularly with historic collections, artefacts recovered over many years from a site/area can be lost, mislabelled or spread between multiple museums.
Relevant publication & figure:
Basell et al. 2011
Brown et al. 2015
Brown & Basell 2008
Lithic Analysis Photography and field notes
Material/object the method is applied to: Any material object or artefact.
CJQ Specific Application: During every trip photographs and notes were taken on work done, conditions, contacts made etc.
Geoarchaeological value: Detailed, thorough notes and good photographs with different colour and large scales are vital for recording the precise observations on the day things are first seen or recorded. Notes provide information which is not always obvious from the photographs and other methods of capture/analysis applied later. Basic descriptions of colour, texture, sketches of relationships, errors with equipment, back-up records/sketches of survey points are imperative.
Sampling Strategy: All objects/sections/ locations/sites studied daily.
Accessibility/Cost/ Experience: Low cost. Time-consuming and knowing what to record improves with experience/depends on principal objectives. Waterproof notebooks make a big difference.
Problems: Abbreviated or untidy note taking that cannot be deciphered by others/ back in the office/lab. Cataloguing and backing up of photos and notebooks takes time. Waterproof notebooks and paper are more costly than standard paper.
Relevant publication & figure:
Basell et al. 2011
Brown et al. 2015
Brown & Basell 2008
Results and Significance
The project generated a wide range of outputs, spanning talks, conferences, reports, and publications (e.g. Brown and Basell 2008; Brown et al. 2009, 2011a, 2011b, 2013a, 2013b, 2019), data deposition (with ADS), outreach and training activities involving the aggregates industry (e.g. Basell et al. 2011).
The primary academic research results of the project are summarised in Brown et al. 2015: the combination of conventional and novel methods at Hodge Ditch underpinned a new interpretation of the River Axe’s distinctive fluvial terrace sequence, which has yielded over 2000 Palaeolithic bifaces. The formation was dated to at least the last 300,000–400,000 years, making it one of the U.K.’s longest Quaternary palaeoenvironmental archives.
The key methodological contribution was the development of a suite of significant methodological advances in rapid recording, which have a wide applicability within Quaternary geoarchaeology for sites being destroyed by commercial activities.
Other key results were:
- Terrestrial Laser Scanning (TLS) and Digital Granulometry
This can be an extremely valuable tool for the rapid recording of the location of faces and the derivation of both proxy stratigraphy and proxy grain size data. When used in combination with sedimentological logging and/or traditional or digital granulometry a significant quantity of data can be captured very rapidly. Establishing a semi-permanent network of georeferenced control points for the TLS significantly reduced the time spent post-processing point cloud data and facilitated model creation. TLS was not recommended as a proposed standard methodology but one which could be used if warranted by the importance of a face, due to in situ artefact finds and time pressure such as face collapse or safety considerations. It is also useful when a site is effectively out of bounds. Digital granulometry was compared against traditional bulk sieving methods and demonstrated to be a far more rapid and effective alternative in a gravel quarry context. - Sediment Dating
The OSL programme suggested that for Late and Middle Pleistocene samples, it is important to repeat measurements of time-dependent signals resulting from both low and high dose absorption to evaluate the accuracy of the equivalent dose value, De (the dose absorbed by the sample from the cosmos and surrounding sediments that gives rise to the datable signal). Taking multiple samples from equivalent stratigraphic units but in positions where dose rate exposure was significantly different offered some intrinsic measure of reliability. The inter-laboratory comparison highlighted that the choice of thermal treatment may strongly affect the resulting age estimate. In 2012 cosmogenic dating was still comparatively new. Following discussion with SUERC, the cosmogenic dating comparison was put on hold pending technical developments, but the samples have been retained for analysis. - Deposit Modelling
Using the geotechnical and borehole data from the quarry, in combination with wider landscape approaches including geomorphological mapping, British Geological Survey borehole data and exposure recording, was essential to understanding the depositional sequence at the Chard Junction Quarry. Without this, it would have been impossible to develop the deposit model that explains the sequence at Chard Junction Quarry, and how the Axe Valley landscape has changed through time. In combination with the dating the model demonstrated that the artefacts as well as the gravels are in a time-series from lowest/oldest to highest/youngest. This model is important beyond Chard Junction Quarry, because it directly informs where Palaeolithic finds and old soil horizons (palaeosols) are most likely to be found within the valley.
Key Insights
The research was greatly facilitated by the excellent working relationship and level of trust built up between LB and the staff at Aggregate Industries over many years. Chard Junction Quarry ground staff were generous in sharing their knowledge of working practice and detailed knowledge of the Hodge Ditch deposits.
Understanding how the pit was worked made it possible to cause minimal disruption when working there. Taking a geoarchaeological approach focussed not only on the site but the wider region was essential.
References
Basell, L.S., Brown A.G. and Toms, P. (eds.) 2011. 'Quaternary of the Exe Valley and Adjoining Areas': Field Guide. Quaternary Research Association: London.
Bridgland, D.R. (ed.) 1986. 'Clast Lithological Analysis'. Quaternary Research Association (Technical Guide No. 3): Cambridge.
Brown, A.G. and Basell, L.S. 2008. 'New Lower Palaeolithic Finds from the Axe Valley, Dorset'. PAST 60: 1–3.
Brown, A.G., Basell, L.S. and Toms, P. 2009. 'Monitoring and Modelling of the Palaeolithic Archaeological Resource at Chard Junction Quarry, Hodge Ditch, Phases II and III, Assessment Stage (Project No. 5695). Project Report Stage 1'. English Heritage Research Department Report Series.
Brown, A.G., Basell, L.S. and Toms, P. 2011a. 'Monitoring and Modelling of the Palaeolithic Archaeological Resource at Chard Junction Quarry, Hodge Ditch, Phases II and III, Assessment Stage (Project No. 5695). Project Report Stage 2'. English Heritage Research Department Report Series.
Brown, A.G., Basell, L.S. and Butzer, K.W. (eds) 2011b. 'Geoarchaeology, Climate Change and Sustainability'. Geological Society of America: Boulder.
Brown, A.G., Basell, L.S. and Toms, P. 2013a. 'Monitoring and Modelling of the Palaeolithic Archaeological Resource at Chard Junction Quarry, Hodge Ditch, Phases II and III, Assessment Stage (Project No. 5695). Final Report Stage 3'. English Heritage Research Department Report Series.
Brown, A.G., Basell, L.S., Robinson, S. and Burge, G. 2013b. 'Palaeolithic Site Distribution in Britain and North West Europe: A Nutritional Niche Reconstruction Approach'. PLOS One 8(12): e81476.
Brown, A.G., Basell, L.S. and Toms, P. 2015. 'A stacked Late Quaternary fluvio-periglacial sequence from the Axe valley, southern England with implications for landscape evolution and Palaeolithic archaeology'. Quaternary Science Reviews 116: 106–121.
Brown, A.G., Basell, L.S. and Toms, P.S. 2019. 'The Quaternary Rivers of the Jurassic Coast Region: from the Neogene to the Anthropocene'. Proceedings of the Geologists' Association 130(3–4): 451–462.
Duller, G. 2008. 'Luminescence dating: Guidelines on using luminescence dating in archaeology'. English Heritage: Swindon.
Graham, D.J., Reid, I. and Rice, S.P. 2005a. 'Automated sizing of coarse-grained sediments: Image-processing procedures'. Mathematical Geology 37: 1–28.
Graham, D.J., Rice, S.P. and Reid, I. 2005b. 'A transferable method for the automated grain sizing of river gravels'. Water Resources Research 41: W07020.
Historic England. 2018. '3D Laser Scanning for Heritage: Advice and guidance on the use of laser scanning in archaeology and architecture (3rd edition)'. Historic England: Swindon.
Otto, J.-C. and Smith, M.J. 2013. 'Section 2.6: Geomorphological mapping'. In S.J. Cook, L.E. Clarke and J.M. Nield (eds.) Geomorphological Techniques (Online Edition). British Society for Geomorphology: London.
Smith, M.J., Griffiths, J. and Paron, P. (eds.) 2011. 'Geomorphological mapping: Methods and applications'. Elsevier (Developments in Earth Surface Processes 15): London.
