Archaeological contractors

Geoarchaeological assessment is recommended as a standard component of development-led archaeological investigation within Lincolnshire, particularly where proposed works may affect alluvial, colluvial, coastal, or other sedimentary deposits. Such deposits often preserve important paleoenvironmental sequences that inform on past landscapes, land use and human activity and may help with understanding site formation, potential and deposit modelling.

Geological and geoarchaeological context: The Fenlands, The Wash and River Valleys

Lincolnshire contains extensive superficial deposits of alluvial silts, marine clays, blown sands and peat sequences. These are particularly developed in the Fenland basin and coastal margins, where long-term marine, fluvial and aeolian processes have created thick, complex sedimentary sequences. Archaeological remains can often be found within or buried beneath these deposits, sometimes at considerable depths, and the ability to recognise these requires appropriate geoarchaeological techniques. Depending on the scale of development and complexity of the geological context it may be necessary for a geoarchaeologist to provide input.

The Fenlands and The Wash are characterised by a distinctive Holocene sequence of clays, silts, peats and paleochannels. Subtle elevation changes created localised “islands” or roddon crests that were attractive for past human settlement, while extensive tidal silts and marine alluvium often mask underlying archaeology.

• The Terrington Beds (tidal-flat deposits) dominate the northern Fens.
• Earlier deposits of Upper and Lower Peat and Fen Clay remain buried at depth, preserving paleoenvironmental archives of high research potential.
• Roddon crests (silted paleochannels) are a recurrent geomorphological feature; they can be detected by aerial photography, LiDAR or geophysics and may contain both archaeological material and paleoenvironmental remains sealed within former channel fills. Understanding this sequence is fundamental to evaluating archaeological potential and to developing proportionate mitigation strategies in fenland and coastal settings. Where LiDAR, geophysics, aerial pictures or terrain models identify roddon crests, it is important to assess their depth and internal composition. Former channel fills may contain well-preserved paleoenvironmental remains and waterlogged deposits within later freshwater channels of archaeological significance.

Why it matters

Understanding landscape context

Many archaeological sites in Lincolnshire are preserved within or beneath superficial deposits (for example, river valleys, fenland, estuarine margins). Geoarchaeological assessment provides evidence of past topography, hydrology and landscape change.

Particular relevance in The Fens

This landscape is characterised by complex sedimentary processes and subtle elevation changes. Archaeological remains are often located on slightly raised ground or “islands,” but can also be sealed beneath marine silts, alluvium or blown sands. Without geoarchaeological assessment, this masked archaeology may be overlooked.

Dating and phasing

Sediment cores and stratigraphic analysis allow correlation with regional sequences and provide opportunities for absolute dating (for example, radiocarbon, OSL). This contextualises archaeology within a reliable chronological framework.

Assessing preservation potential

Paleoenvironmental remains such as pollen, molluscs, diatoms and macrofossils are often preserved in waterlogged contexts. Targeted geoarchaeological investigations can facilitate the systematic recovery of such material, enabling structured evaluation of their survival and preservation.

Informing evaluation

Early engagement with geoarchaeological approaches can help shape subsequent evaluation strategies. For example, a desk-based geoarchaeological assessment may identify ground conditions that limit the effectiveness of certain geophysical survey techniques.

Informing mitigation

Results guide decisions on appropriate mitigation strategies (preservation in situ, sampling, targeted excavation), ensuring proportionate responses aligned with planning requirements and research frameworks.

When to recommend

Geoarchaeological assessment should be considered whenever it will substantively inform the pre-determination evaluation process:

• development affects:
  • floodplains
  • valley bottoms
  • former wetlands
  • peat deposits
  • complex and, or deep deposits in urban contexts
  • estuarine and foreshore environments
• there is potential for deeply stratified sequences containing or masking archaeology
• previous investigations indicate paleoenvironmental survival or significant sediment accumulation

For large-scale or complex schemes, geoarchaeological assessment should be considered as part of the evaluation strategy, particularly where it can inform deposit modelling and landscape reconstruction. It can complement standard techniques by improving understanding of stratigraphy, site formation processes, and preservation conditions. This is especially important where deeper deposits may be present that standard approaches, such as magnetometry surveys, are less effective at characterising.

Methodological expectations

We currently accept several approaches and strategies for geoarchaeological assessment. Any chosen method should be tailored to the development proposal impacts and ideally be informed by the results of the geophysical survey and developed in consultation with a suitably experienced geoarchaeologist and the LPA planning archaeologist.

Method selection relative to likely impact

Approaches should be proportionate to the anticipated depth of impact, the complexity of the sequence, and the level of uncertainty.

The following case studies provide examples of how different methodological considerations were applied in two different impact scenarios.

Accepted strategies include:

Geoarchaeological desk-based assessment (GDBA)

The use of existing geotechnical data, including historic borehole or geotechnical records, any developer-commissioned ground investigations, and data from adjacent areas to model site conditions without further intrusive work. Depending on the nature and scale of the project this may be presented as a section of a standard desk-based assessment, or a standalone document.

Boreholes and drilling transects

Commercial rig, power auger or hand auger. Undertaken when the deposits of interest are too deep for shallower methods, or when large areas need to be covered. Core extraction geoarchaeological borehole records are required to enhance understanding of site stratigraphy and to assess paleoenvironmental potential. Boreholes are used to clarify the nature and depth of subsurface deposits, to locate and date former land surfaces, roddons, alluvial and peat layers, and to evaluate their archaeological potential. The method also allows the identification of natural and anthropogenic changes to the landscape, both wetland and dryland, including activity associated with valley use or historic crossing points.

Geoarchaeological test pits (rapid sondages)

On sites where the sequence of interest is shallow it can be more effective to use test pits. Depending on the nature of the research question, geoarchaeological test pits (rapid sondages) may be excavated with an appropriate, fit-for-purpose mechanical excavator. In such a scenario the work proceeds in controlled spits of approximately 50mm to the safe reach of the machine arm, with depth reduced where groundwater, flooding or instability occur. Sedimentary units are recorded in sequence, noting grain-size, consolidation, colour, structures and materials.

Drawing can be done from a distance or sketched and there is no need to enter a deep rapid test pit. The drawing should be sufficient to understand the stratigraphic sequence and depths of deposits. The method is designed primarily to investigate and model Fenland deposits while also assessing the potential for deeply buried archaeology. Where archaeological features are identified in overlying deposits, these may be recorded (in agreement with the LPA planning archaeologist and client) or the sondage relocated to avoid disturbance, and modern intrusions truncating the deposits may be removed where practicable.

Combined approaches

In most cases a staged, iterative approach should be adopted, starting with a GDBA, deposit modelling, and targeted field investigation (for example, test pits or boreholes) where necessary. Techniques should be selected and applied in a proportionate, question-led manner to refine understanding of deposit sequence, extent, and preservation. The phasing of work will be determined by the nature of the project Early-stage fieldwork may be required in some cases, for example to inform the selection of geophysical techniques or to be carried out in parallel with geotechnical site investigations. Alternatively, test pits, sondages and/or boreholes may be undertaken simultaneously with archaeological evaluation, within or adjacent to trenches, depending on project design. Geoarchaeological engagement with the project may need to continue through mitigation phases.

Specialist advice and site attendance

Samples

Following the outline strategy presented in the Written Scheme of Investigation and in consultation with a geoarchaeologist, samples will be collected for:

• scientific dating
• analysis of chemistry
• magnetic susceptibility
• particle size
• micromorphology
• other techniques as appropriate

Special consideration should be given to any evidence for recent changes in preservation conditions that may have been caused by alterations in the site environment.

Geoarchaeology studies should follow the guidance provided by Historic England (2015, 2020). Consultation with an environmental archaeologist or the Historic England Regional Science Advisor may be required. This incudes site visits to refine sampling strategies and advise on palaeosos or deposits of high environmental potential.

In some cases, the presence of a geoarchaeologist on site during evaluation or sampling will be required to provide real-time advice.

Health and safety and ecological constrains

Particularly in the case of geoarchaeological test pits and rapid sondages, it is paramount to abide by all relevant and current health and safety requirements. Risk assessment and compliance with site-specific health and safety procedures must be built into the project design and fieldwork strategy. Other considerations and potential risks from open deep excavations on local wildlife should be considered.

Historic England guidance and further reading

Please contact us by email at Archaeology@lincolnshire.gov.uk for details on the above.

Version history

This guidance was authored by Ruben Lopez Catalan, Historic Environment Officer at Lincolnshire County Council with input from:

• Matt Nicholas, Science Advisor for the East Midlands
• Matt Canti, Senior Geoarchaeologist based at Fort Cumberland
• Hayley McParland, Science Advisor for the South West
• Nick Carter, Inspector of Ancient Monuments covering Derbyshire and Staffordshire, Historic England

June 2026