UWLAS Archaeological Services

Pollen analysis

PA3 Pollen analysis is carried out under the direction of Professor Mike Walker, with the assistance of Miss Sarah Jones. Mike Walker has more than 30 years’ experience of pollen analytical work on a wide range of sites, and he has published extensively on pollen analysis and related aspects of Quaternary research. His work has focused in particular on vegetational history and climatic reconstructions (see case studies, below), as well as on historic and prehistoric interactions between people and landscape.

A section through Lateglacial and early Holocene lake sediments at Sluggan Bog, Northern Ireland. Photo: A section through Lateglacial and early Holocene lake sediments at Sluggan Bog, Northern Ireland. Pollen analysis, supported by radiocarbon dates show that the lower organic sediments accumulated during a warm period between c. 14,800 and 12,900 years ago (Lateglacial Interstadial); the light coloured silt-clay unit formed during a cooler episode between c. 12,900 and 11,500 years ago (Nahanagan/Younger Dryas Stadial) while the overlying organic unit dates from the early part of the present (Holocene) interglacial (photo: Mike Walker).

Service provided

  • A sediment core from the submerged peats exposed in the estuary of the River Clettwr, near Borth, West Wales. Estuarine silts and clays are overlain by terrestrial peats, the base of which date to c. 5800 years ago. The pollen record from the core shows the transition from a salt-marsh environment to alder carr (photo: Sue Hurst). Advice on sampling procedures including, where necessary, site visits
  • Preparation of pollen slides*
  • Pollen counts to assessment level (typically 100 grains per sample) for preliminary evaluations*
  • Full pollen counts (minimum of 300 grains per sample) for more detailed  investigations
  • Production of results in either tabulated or diagrammatic form
  • Rapid reporting of results, normally within four weeks of completion of the laboratory programme. The reports are produced to publication-standard and contain a detailed account and thorough evaluation of the results obtained
  • Advice on the dating of pollen-stratigraphic sequences – see Dating advisory service

* These are also offered as ‘stand-alone’ services (i.e. we can prepare slides for clients to count and interpret and can do assessments of slides supplied by clients) – contact Dr John Crowther about this service (tel: +44(0)1570 424739; e-mail: j.crowther@trinitysaintdavid.ac.uk)  

For further information/advice or quotation in relation to this service, please contact Professor Mike Walker (tel: +44(0)1570 424736; e-mail: m.walker@trinitysaintdavid.ac.uk)

Pollen analysis: Case studies

Fig. 2: Section of organic deposits, the base of which dates to c. 3200 years ago, exposed on a site at Milford Haven, South Wales. A pollen-analytical assessment is currently being undertaken on these sediments for a client (photo: Martin Bates). Fig. 1: A section through estuarine deposits on the North Avon Level near Avonmouth, Bristol. The horizontal monolith tin is sampling a gleyed horizon, believed to be a late prehistoric buried soil. A pollen analytical assessment was undertaken on this sequence prior to the construction of an enterprise park (client Glamorgan-Gwent Archaeological Trust Ltd) (photo: courtesy of GGAT) Contract-based pollen analytical work has been undertaken on a range of sites, in different archaeological and environmental contexts, and for a number of clients. Typical projects include assessments of the archaeological and environmental potential of deposits that may be threatened, and frequently destroyed, by economic activities such as roadworks or industrial developments (Figs 1 and 2). An archaeological/ environmental assessment (which often includes pollen analysis) is normally required for planning consent for such schemes. Other projects have been carried out for agencies such as Archaeological Trusts, English Heritage, Cadw and the Countryside Council for Wales, where palaeoecological information has been requested to provide background information for sites of environmental and/or archaeological interest (Fig. 3).

Fig. 3: A core of sediment spanning the early part of the present interglacial from Cors Carmel, Carmarthenshire, South Wales. This site is a SSSI and a pollen record was produced at the request of the Countryside Council for Wales (photo: Mike Walker). Two such case studies are described below (click on link for further details)

  • Vurlong Reen, Severn Estuary, South Wales: a sequence of intertidal peats that was investigated in advance of the construction of the Second Severn Crossing

  • Llyn Llech Owain, Carmarthenshire, South Wales: a lake in South Wales which is at the centre of a Country Park, and for which a pollen assessment has been undertaken as part of the upgrading of the displays at the Park Visitor Centre (client: Carmarthenshire County Council)

Fig. 4: The excavation at Vurlong Reen (photo: Mike Walker). Vurlong Reen, Severn Estuary Levels, South Wales

Trial excavations in advance of the construction of the new Second Severn Crossing revealed thick sequences of peat buried beneath estuarine muds at several locations on the Severn Estuary Levels.  One such site is Vurlong Reen, located 2.5 km west of Caldicot, where the sedimentary sequence was investigated using a combination of pollen analysis and radiocarbon dating.

Fig. 5: The peat sequence exposed at Vurlong Reen. The machine-cut trench has been 'stepped' for ease of access too the peats, and the monolith tins in which the peat samples were taken are in place (photo: Mike Walker). A machine-cut trench (Figs 4 and 5) revealed over 2 m of peat which was overlain and underlain by estuarine muds and silts. Samples were taken for pollen analysis and radiocarbon dating using monolith tins (Figs 5 and 6). Radiocarbon dating showed that the peats began to accumulate c. 5700 14C yrs ago (around 6500 calendar yrs ago) following a relative fall in sea level, and peat formation ceased c. 2450 14C yrs ago (around 2800 yrs ago) as sea level rose to inundate the site once again.

The pollen record (Fig. 7 - opens in new window) shows that initially the landscape was one of alder (Alnus) carr, but that this gave way, around 4500 yrs ago, to fen dominated by grasses (Poaceae) and sedges (Cyperaceae). The gradual decline of the woodland cover, as reflected in the pollen record, and the presence of charcoal in the peats dating to around 4300 yrs ago, suggests woodland clearance by Bronze Age people. The present ‘cultural landscape’ of this part of South Wales therefore dates from this time.

Fig. 6: The peat sequence at Vurlong Reen following removal of the monolith tin (photo: Mike Walker). The Vurlong Reen pollen-stratigraphic record is important in that it provides evidence of local and regional vegetational change from Neolithic to Iron Age times, it contains evidence for human impact on the landscape, and it provides a record of late Holocene sea-level change in the Severn Estuary.

Further details are presented in M.J.C. Walker et al. (1998): Proceedings of the Geologists’ Association, 109, 51-78.

 

Llyn Llech Owain, Carmarthenshire, South Wales

Fig. 8: The coring site on the western margin of Llyn Llech Owain. The lake can be seen in the upper right of the photograph (photo: Martin Bates). Llyn Llech Owain is a Country Park and SSSI.  A series of cores was taken from a site near the western margin of the lake for pollen analytical assessment (Fig. 8). Prior to this work, the length of the sedimentary record and age of the sequence was unknown.

The stratigraphy at the coring site comprised almost 6 m of Holocene (present interglacial) peats overlying c. 2 m of lake muds. At the base of the sequence, silts and clays are overlain, in turn, by organic lake muds (Fig. 9), a further silt/clay unit (Fig. 10), a second series of organic lake deposits and then peat.

Fig. 9: The basal core from Llyn Llech Owain showing the transition from the lowermost minerogenic sediments to the overlying organic deposits (photo: Mike Walker). Fig. 10: The uppermost minerogenic unit at Llyn Llech Owain (between the two hands). This unit, which has been dated to between 12,900 and 11,500 years ago at other sites in Britain, represents a short-lived cold episode (the Loch Lomond Stadial) and was the last time that glaciers were present in the uplands of the British Isles (photo: Martin Bates).

This stratigraphic record is comparable with that found at other lake sites in Britain and western Europe, where the basal tripartite sequence of minerogenic-organic-minerogenic sediments spans the period known as the Lateglacial, during which climate first ameliorated (minerogenic to more organic sediment; 14,500-12,900 years ago), then deteriorated (organic to more minerogenic sediment: 12,900-11,500 years ago), before ameliorating once again at the beginning of the present interglacial.

The preliminary pollen assessment (Fig. 11) shows evidence of birch woodland during the initial warm phase, open tundra during the subsequent cold period, and then the expansion of mixed woodland during the present interglacial. Woodland decline in the upper part of the record in associated with increasing human activity.