6. Practicalities

Peter Marshall

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6.1 Project organisation and planning

Government guidance set out in the National Planning Policy Framework (NPPF) (Department for Communities and Local Government 2024) enshrines the principle of sustainable development in the planning process. Where archaeological projects are commissioned to inform the planning process the information sought should be proportionate to the significance of the heritage asset and to the potential impacts of the proposed development.

Assessments of heritage assets in advance of determinations of planning applications should therefore be sufficient to provide an understanding of the significance of heritage assets and their settings, affected either directly or indirectly by the development proposals (e.g. desk-based assessment or field evaluation where appropriate).

Specifications/briefs

These guidelines apply to all archaeological projects, but are aimed primarily at those undertaken as part of the planning process. To facilitate early identification of potential Pleistocene deposits, a comprehensive desk-based assessment is critical. This should include consultation with local planning archaeologists, the Historic England regional science advisor and Palaeolithic archaeologists/Quaternary scientists with knowledge of the area (see Historic England 2023, section 3.1.2). Regional/period research frameworks, Historic Environment Records (HER) and British Geological Survey (BGS) mapping can also aid in establishing the potential to encounter Pleistocene deposits (see Historic England 2023, section 2).

Historic England’s ‘Curating the Palaeolithic’ guidance (Historic England 2023, section 7) outlines the key Pleistocene deposits within which Palaeolithic remains can be found. Many of these deposits are suitable for scientific dating. The selection of appropriate techniques is key, given the available types of datable material, its taphonomic relationship to the archaeological objectives of the project, and the expected time-range of the site (Figure 9).

Identifying the potential for encountering such deposits early in project planning is critical to enable inclusion of realistic costings and programming for scientific dating in fieldwork specifications. This is particularly important for Pleistocene sites because many of the available scientific dating techniques require specialist on-site sampling.

Curators who need further advice on the potential for using scientific dating on specific Pleistocene sites can obtain independent non-commercial advice from Historic England (see Where to get advice). Where advice is obtained from a commercial contractor, it is the responsibility of the commissioning body to ensure that vested interests are openly declared, and that subsequent competition is fair (CIfA 2022).

Specifications and briefs should state that scientific dating on Pleistocene sites is to be carried out in accordance with these guidelines. Strategies for dating Pleistocene deposits should be included in Project Designs and in Written Schemes of Investigation.

Definitions of briefs, specifications and project designs can be found in the Association of County Archaeological Officers’ (1993) 'Model Briefs and Specifications for Archaeological Assessments and Field Evaluations' and in the CIfA’s Standard and Guidance series (CIfA 2020a–c; 2023a–f). Named specialists should be included in such documents and curators should, if necessary, ask for details of relevant experience (published papers, reports, etc.).

Chronology is the framework for understanding all archaeological sites, including sites with Pleistocene deposits. When planning archaeological projects, full use should be made of all available sources of information on scientific dating potential. Construction of reliable chronologies should form an integral part of the initial project specification. It should not be simply seen as a contingency or luxury.

Accurate prediction of the presence of Pleistocene deposits and their suitability for different scientific dating techniques can be difficult. Further potential may become apparent during site investigations or in post-excavation assessment. Therefore, the identification of ‘contingency funds’ within the overall budget would be prudent (Brunning and Watson 2010).

Desk-based assessment

Desk-based assessment is critical in establishing whether Pleistocene deposits are present at a site (Historic England 2023, section 3). This will identify at an early stage the likelihood that scientific dating will be required.

The purpose, definition and standard for desk-based assessment are given in CIfA (2020a). Specialists can contribute to desk-based assessments with information and evaluation of existing scientific dating evidence from previous investigations, and the potential for scientific dating to contribute to the aims and objectives of the project. Such information can be used to inform where to excavate and the scientific dating strategy.

Field evaluation

The purpose, definition and standard for evaluations are given in CIfA (2023a–b). Evaluation to inform planning decisions and mitigation strategies is crucial to understand the nature of the archaeological resource. In some situations, an evaluation might be the only intervention undertaken. Where the potential for encountering Pleistocene deposits is uncertain, preliminary studies such as a geoarchaeological borehole or trial trenching may be appropriate (Canti and Corcoran 2015; Historic England 2023, section 3.4).

As part of the evaluation, scientific dating can make an important contribution to identifying and understanding the potential significance of the Pleistocene archaeological resource.

Examples of the types of questions scientific dating might be used to answer as part of evaluations include:

  • Are the deposits suitable for scientific dating?
  • What is the age of unexpected discoveries?
  • What is the age of the deposits?
  • What is the date of the archaeological remains?

Archaeological monitoring and recording

The purpose, definition and standard for archaeological monitoring and recording is given in CIfA (2023c–d). Scientific dating undertaken on samples collected during archaeological monitoring would only be expected in exceptional circumstances (e.g. completely unexpected archaeological finds).

Excavation

Where pre-determination field evaluation (Historic England 2023, section 3.4.3) identifies archaeological and/or palaeoenvironmental deposits with high Palaeolithic potential, further works may be recommended to mitigate their loss (Historic England 2023, section 4.2). The purpose, definition, and standard for excavation is given in CIfA (2023e–f).

Excavation presents better opportunities for the recovery of samples (e.g. Campbell et al. 2011) for scientific dating, and for better understanding their archaeological context. For many dating techniques employed on Pleistocene deposits, specialist on-site sampling can be essential (e.g. Luminescence dating and Palaeomagnetism), and should be stipulated in the Written Scheme of Investigation. Where in situ specialist sampling is not required (e.g. Amino Acid Racemisation or Radiocarbon dating), specialist handling procedures, including packaging and storage, can still apply.

Post-fieldwork assessment

The purpose of post-excavation assessment is to determine the suitability of the available samples for scientific dating and then to design a cost-effective sampling strategy for full analysis.

Analysis of a small number of ‘range-finder’ samples may be used to establish:

  • the broad age of the deposits;
  • whether a technique can be used successfully on the site;
  • how best to employ a technique.

The selection of samples for range-finder dating will be determined by the nature of the deposits, sample taphonomy, previous successful and unsuccessful dating studies in the area, and the relative ordering of samples as determined through deposit modelling (Historic England 2020) or stratigraphy. On Pleistocene sites, replicate dating using different techniques should be used whenever possible.

For example, at Lynford Quarry, OSL of quartz was successful, radiocarbon dating was at or beyond the limit of detection, and AAR failed because of poor preservation of shells. If dating of this site had relied solely on one of the dating techniques, the site chronology may not have been established.

In some areas of England, previous studies have shown that successful luminescence dating may depend on the local geology (e.g. Bridgland and Long 2011). On some sites, incomplete bleaching or mixing may require single grain, rather than aliquot, analysis to provide a viable chronology (see Luminescence dating). Some sites may be at, or exceed, the maximum age limit of OSL, requiring an alternative trapped charge technique, such as ESR or pIR-IRSL to be used instead (e.g. Voinchet et al. 2015).

Radiocarbon dating of organic deposits may confirm their suspected Pleistocene age, although the potential for older samples to give finite radiocarbon ages — because they contain low-level recent contamination — should be noted (see Table 2). The compatibility, or otherwise, of replicate determinations on different bulk organic fractions will indicate whether an organic deposit can be robustly dated, and thus whether further work on the environmental remains is merited (Bayliss and Marshall 2022, section 3.2).

Once a pool of potential samples that are viable for scientific dating has been identified, a sampling strategy for analysis is needed. This strategy should address the aims and objectives of the project. It needs to combine effectively the results of the scientific dating with other information (such as relative dating provided by site / regional stratigraphy and mapping), to produce a robust and accurate chronology.

The following information is required by the specialist to devise an effective strategy for scientific dating:

  • brief account of the nature and history of the site;
  • aims and objectives of the project;
  • access to the (geo)archaeological results;
  • context types and stratigraphic relationships;
  • sample locations;
  • assessment reports from other relevant specialists, including range-finder dating.

A cost-effective sampling strategy should maximise the relative dating information among the analysed samples. Within this framework, the number of samples that should be dated can be assessed through simulation and Bayesian Chronological Modelling (see Bayliss and Marshall 2022, section 3.3.1).

The resultant assessment report should contain:

  • statement of potential — how scientific dating can contribute to site, specialist, and wider research questions;
  • a list of samples recommended for full analysis;
  • justification of the techniques used and number of measurements required;
  • details of dating specialists / facilities to be used;
  • tasks, time and costings (analysis and publication).

Given the technical complexity of using scientific dating on Pleistocene sites, and the potential expense of scientific dating programmes, a staged approach may be appropriate.

Post-excavation analysis

During post-excavation analysis, the work specified and agreed in the post-fieldwork assessment should be undertaken. Scientific dating specialists will need to work closely with other specialists throughout the analysis stage.

A full technical report should be produced for all the scientific dating undertaken on the site and, where appropriate, for the Bayesian chronological modelling. This report should include:

  • objectives of the study;
  • sampling strategy, (including discussion of the selection of scientific dating techniques employed, the available samples, the available prior information, the results of any simulation models, and the rationale by which these elements have been combined into a strategy;
  • statements on the methods for the scientific dating techniques employed;
  • details of scientific dating results, reported according to established standards for each technique (e.g. Bayliss and Marshall 2022, section 3.6.1);
  • chronological model definition and description, including references to relevant software and discussion of the scientific dates and prior information included in the model and their strengths and weaknesses;
  • sensitivity analyses, presenting the results of alternative chronological models, if undertaken;
  • how these results contribute to regional or period-specific research frameworks;
  • recommendations for further work, if appropriate.

Dissemination and archiving

Historic Environment Records (HER)

Current best practice is to report any archaeological intervention, even if only an evaluation. Any report should be deposited with the local HER as quickly as possible after the work is completed. It should also be added to the Online Access to the Index of Investigations (OASIS).

Chronological information may form a component of these reports and results from scientific dating methods should be recorded in HERs.

Publication

Where possible, full details of the methods used and the results generated from each scientific dating technique should be included in the publication. This information can be in the main body of the publication, in an electronic supplement, or deposited in an accessible open-access repository, signposted in the publication.

As Pleistocene deposits often require multidisciplinary analyses, the scientific dating results can also be published in dedicated archaeological, Quaternary science and other specialist journals.

Archiving

The scientific dating specialist reports should be included in the material deposited with the other project publications, in accordance with their standards. For guidelines on archive deposition see Brown (2011), Longworth and Wood (2000), Museum and Galleries Commission (1992), Walker (1990), Archaeology Data Service (2015) and Archaeology Data Service and Digital Antiquity (2011).

Physical samples are usually stored with the rest of the physical archive (e.g. bones, shells, etc.) and do not require specialist archiving. Package and store them in accordance with current best practice. Sediment samples usually do not form part of the physical archive, unless retention is specified by the curator. Where retention is required, these should be deposited in specialist long-term storage facilities.

6.2 Laboratories

An essential part of the successful application of any dating strategy is early discussion between the field project director and the specialist(s) undertaking the analysis. Note that not all laboratories undertake all forms of analysis, nor do they all provide commercial services.

Historic England regional science advisors can provide contact details for specialists and laboratories who may be able to provide scientific dating support.

Radiocarbon dating

All radiocarbon dating laboratories will be happy to advise on the technical aspects of radiocarbon dating that affect the selection of suitable samples, on suitable storage and packaging, and on the methods of sample preparation and dating used in their facility. Some will also be able to advise on the archaeological and statistical aspects of sample selection.

A full list of radiocarbon laboratories is maintained by the journal Radiocarbon.

Uranium-Thorium dating

U-Th dating facilities are common in universities with large geochemistry, oceanography or geology departments. Historic England regional science advisors can provide contact details if required.

Luminescence dating

There are a number of luminescence dating facilities in the UK, largely based in universities, which offer research and, in some cases, commercial services, including on-site sampling. Historic England regional science advisors can provide contact details if required.

Amino Acid Racemisation (AAR)

The main facility in the UK for AAR dating is NEaar (North East Amino Acid Racemization) based at the University of York.

Palaeomagnetism

Palaeomagnetism dating requires specialist laboratory facilities based within university departments. These might be able to undertake work on a commercial basis. Historic England regional science advisors can provide contact details if required.

Tephrochronology

The chemical analysis of tephra shards requires an Electron Probe Microanalyser (EPMA) for major elements and either Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICPMS) or Secondary Ion Mass Spectrometry (SIMS) for trace elements. These are hosted by earth science or geography departments in several UK universities, which might also be able to undertake tephra extraction on a commercial basis. Historic England regional science advisors can provide contact details if required.

Biostratigraphy and the ‘Vole Clock’

The identification and analysis of Pleistocene biological remains for biostratigraphic purposes, including the ‘Vole Clock’, requires a specialist. Historic England regional science advisors can provide contact details if required.