The Potential of Environmental Archaeology and Geoarchaeology at the site of the Staffordshire Hoard

Benjamin Gearey (Birmingham Archaeo-Environmental, Institute of Archaeology and Antiquity, University of Birmingham)

This paper will briefly consider the potential of environmental archaeology (i.e. the analysis of the sub-fossil remains of material including pollen, plant and insect remains) and geoarchaeology (i.e. the analysis of the formation processes of the soils and sediments associated with the archaeology) to provide information regarding the find-spot as well as the wider landscape of the Staffordshire Hoard.

These studies are currently in progress and hence the discussion is restricted here to some general thoughts as to how such data may help us understand how the site might have changed over time. More specifically: what can a consideration of the character of geomorphological processes at the site itself tell us about the context of the hoard? What light may environmental archaeology shed on the site itself? What is the potential for further on-site and off-site work, investigating the development of the wider landscape during and since the Anglo-Saxon period? How may these lines of evidence help us to further understand why the hoard was deposited where it was?

The potential of environmental archaeology to provide information regarding any site is dependent on the character of the soils and sediments at the study location. The topsoil (‘A’ horizon) across much of the hoard site is a ploughsoil derived from the Wildmoor sandstone which forms the solid geology of this part of Staffordshire. It is immediately apparent (Fig. 1) that there is an erosive contact between this ploughsoil and the underlying subsoil (the ‘B’ horizon).

Fig. 2: test pit showing 0.6m deep topsoil at the hoard findspotOf course, today’s topsoil was yesterday’s subsoil, due to this process of erosion and re-working of the upper layers of soil through ploughing, with other variables such as the prevailing climate also affecting soils over time. The rate of these processes of erosion via agriculture, and also the re-deposition of soil material through colluviation (the movement of sediment downslope via gravity) means that the current depth and character of the soils across the site are likely to be somewhat different to those prevailing when the hoard was originally deposited.

The test pits excavated at the site on the top and downslope of the site suggest some variation in the depth of the upper soil horizon (Fig. 2) with top and subsoil depths of c. 0.30m recorded in test pits at the top of the ridge increasing to over 0.60m downslope (Fig. 2).

Fig. 3: trenches at the hoard findspot, with the M6 toll road in the background

The rate and extent of erosion of the topsoil of course has significance for the possible original depth of sediment overlying the hoard find-spot towards the top of the ridge. Although it would appear that the location was not ploughed prior to the 19th century, assessing the subsequent rates of the loss of soil across the site through human and natural processes of environmental change is very difficult. There are a number of methodological and practical issues with exploring this further. For example, the close proximity of two large roads (the A5 and M6 toll) (fig. 3) to the north and west of the site makes it difficult to investigate the depth of colluviation at the base of the slopes.

There is evidence for variation in the superficial deposits across the site which is most probably associated with Late Quaternary environmental processes, rather than more recent land-use. Sands derived from the sandstone bedrock predominate over much of the investigated area, but there are coarser, gravel-rich deposits and also a pronounced band of pinky-grey clay apparent in Trench 2 (Fig. 4). Fig. 4: Trench 2, showing band of pinky-grey clay  If the results of the geophysics are draped over the topography of the site (Fig. 5) there is indication of a curvilinear feature which appears to correspond to this band of clay, near to the top of the ridge where the hoard was found.

Fig. 5: geophysical results (resistance) draped over topography (vertical scale exaggerated) (image courtesy of Eamonn Baldwin)

A closer examination of this clay deposit (Fig. 6) indicates that it is a maximum of some 0.40m thick and has an erosive contact with the underlying sands. The clay is very fine-grained, dense and generally stone-free. This sediment was probably deposited in a cold climate, in a pro-glacial or a glacial environment. The topsoil that is derived from this feature are clay-rich (Fig. 7) and hence somewhat different in texture to the sandy soils across the rest of the site (e.g. Fig. 1) and it would appear (Bob Burrows pers. comm.) that although the hoard was found over a relatively large area (c. 20x20m), there was quite a close association of the material with the clay soils rather than the sandy soils.

Fig. 6: close-up of the clay deposit in Trench 2   Fig. 7: clay-rich topsoil associated with the hoard find-spot (contrasting with sandy soils in Fig. 1)

The geomorphic context of the site therefore consists of the pre-Holocene sands, the clay deposits, and the gravels over the Sherwood sandstones (Wildmoor formation). This is a weathered pre-Holocene surface, relating to pro-glacial or glacial processes during the Devensian glaciation of this part of Staffordshire. The area was probably ice-free by about 13,500 years before the present, hence the clay and coarser gravel deposits almost certainly pre-date the hoard’s deposition by some thousands of years, but scientific dating using methods such as Optically Stimulated Luminescence would be required to demonstrate this conclusively. However, as we will consider further below, the character of the deposits may have had some significance in terms of the later formation processes and possible vegetation across on the site.

Initially, it was hoped that a range of scientific techniques might help to provide shed further light on the soils and sediments at Hoard site and any archaeological features subsequently excavated. Such palaeoenvironmental analyses might typically include micro-fossils including pollen, which is generally preserved in waterlogged, acidic environments and macrofossils such as plant remains, which can be preserved by charring or by waterlogging. The analysis of archaeological deposits using these techniques can provide information concerning the past vegetation of the site and associated landscape but tend to be most useful where waterlogged, organic sediments are present and preserve relatively intact and continuous records of changes in pollen and other proxies.

Fig. 8: Trench 5, showing section of possible palisade trench

However, the largely free-draining character of the soils means that any such organic material has not been preserved very well. In any case, the Hoard itself was recovered from the ploughsoil and hence scientific analyses of these overlying sediments is not likely to provide any information on the original context of the archaeology, as the processes of ploughing have disturbed and re-worked the original archaeological context. The identification of archaeological features during the second phase of excavation at the site, such as the possible palisade trench in Trench 5 (Fig. 8), have provided deposits for further palaeoenvironmental analyses which are currently on-going. However, there is currently no clear archaeological relationship between these features and the Hoard itself. Analyses of fills of the ditches have the potential to indicate the nature of the environment on the site during the period of the accumulation of these deposits. However, successful results in the on-going analyses from the site may not necessarily provide direct information about the hoard per se ,given its discovery in the ploughzone. 

Summary

Deep ploughing of the find-spot has apparently resulted in the re-working of the hoard into the upper layers of soil and in the process has also effectively destroyed the location as one of a sealed, in situ archaeological site. The current working hypothesis is that any feature such as a pit that the items were deposited in no longer survives as a context definable or identifiable as anything other than ‘ploughsoil’. However, the extent of the truncation by ploughing and indeed other natural and/or human factors is unclear. This means it is very difficult to make any firm statements regarding the original depth or nature of the deposition of the hoard. In addition, this also begs several questions concerning, for example, how far the material has been spread by ploughing, and whether the hoard was buried in a single discrete location, or several in close proximity. It may be regarded as unlikely that the hoard was originally buried especially deeply, or some evidence of a context might have been apparent. However, in the absence of firm data regarding the denudation of soil from the site, or indeed the precise date of the burial of the hoard, it would be unwise to speculate further on this.

However, the presence of other archaeological features at the site may have some implications in this respect. Establishing the date of these features is thus critical, although negative features such as ditch or pit fills might be expected to have survived ploughing and any other disturbances better than, for example, an upstanding feature such as a mound. Likewise, the possibility that the hoard was buried in a relatively shallow cut cannot currently be ruled out and for that matter, in the absence of a securely sealed archaeological context, determining precisely when this happened (other than the Anglo-Saxon period or later) has by no means been clearly established.

On a more positive note, it seems almost certain that the clay deposits revealed in Trench 2 and apparently corresponding to the curvilinear feature identified in the geophysics (Figs. 9 and 10; see also Alex Jones’s paper), was formed long before the hoard was deposited.

Fig. 9: Resistance plot showing curvilinear feature (pale)  Fig. 10: Magnetometry plot showing curvilinear feature (dark) in relation to the hoard findspot

The apparent association of the hoard with this clay band may be significant, given that the soils that developed on this clay band are different to the soils elsewhere on the site; clay-rich soils probably would have drained less well than those formed on the sand. This may have had some significance in the past in terms of the character of the vegetation across the site, although what the precise differences would have been on a local scale and whether this might have had some significance with respect to the location of the hoard is again a matter of some conjecture. It is of course possible that the association is purely coincidental.

In terms of further work, studies of the later Holocene development of the wider landscape would provide information regarding the character of the environment during the Anglo-Saxon period and later, and would help to clarify Hooke’s contention (see Della Hooke’s paper) that the area was ‘waste’ at this time. There are currently very few palaeoenvironmental studies available for the immediate vicinity, partly because of the lack of sites such as peat bogs, where deep organic sequences which provide the source material for palaeoenvironmental analyses can be preserved. Possible targets for further investigation do exist, such as the valley of the Crane Brook to the north of the site. The analysis of any floodplain peats in this area might assist in understanding of specific aspects of the pattern and processes of environmental changes in this area. However, the original context of the deposition of the hoard therefore remains, for the time being, frustratingly elusive.