Reburial and Analyses of Archaeological Remains in the Marine Environment — Investigations into the Effects on Metals

Abstract

The treatment and long-term storage of recovered cultural material from underwater heritage sites is becoming less cost effective, and reburial of archaeological sites and the associated artefacts in the marine environment is becoming increasingly common practice in managing the submerged cultural resource. Following recent large-scale underwater archaeological excavations in Marstrand harbour, Sweden, the majority of recovered finds were reburied in defined trenches in the harbour sediment. Subsequently, the Studio of the Western Sweden Conservators in conjunction with the Bohus County Museum initiated a fifty-year research project to evaluate reburial as an appropriate method of preserving waterlogged archaeological artefacts in the long term. The research project, entitled ‘Reburial and Analyses of Archaeological Remains’, was launched in 2002 and consists of six sub-projects. The main aims of these sub-projects are to analyse the extent of deterioration of the most common material types found on underwater archaeological sites, assess the stability of packing and marking materials used in archaeological documentation, and monitor the reburial environment.

The aim of the metals sub-project is to investigate the short- to long-term corrosion behaviour of metals buried in the marine environment by examining the deterioration of reburied and exposed modern metal coupons and eventually compare these results to the analysis of actual shipwreck artefacts. The environmental monitoring sub-project is designed to complement the other sub-projects by assessing the physico-chemical changes occurring in the reburial environment over time and the effect on the deterioration of the different reburied material types. In comparing the results obtained over the past seven years from both the metals and monitoring sub-projects, it should be possible to more accurately evaluate the effectiveness of reburial as a long-term in situ preservation strategy for metallic archaeological remains.     

Chaco Canyon reburial programme

Abstract

Chaco Culture National Historical Park in northwestern New Mexico contains a wealth of archaeological resources, including 150 large earth and masonry structures under active management and preservation. In response to loss of original fabric from exposure over the last 100 years and more, as well as from continuous cycles of maintenance and repair, an extensive and long-term reburial programme was embarked upon in the late 1980s. The overall context of the site and the decision to undertake reburial as a principal conservation strategy is described in Part I of this paper. Part II provides a summary of the results of partial reburial at Chetro Ked, one of the ‘great houses’ of the canyon, in which protection of original timber was the main objective. Most of the wood at Chetro Ked could be covered only by a shallow overburden of soil, necessitating a specialized reburial design and materials to exclude moisture. Recent evaluation of the efficacy of the wood reburial was undertaken. Problems and shortcomings that were identified have led to re-design of part of the reburial and more careful attention to quality control during the intervention, as well as to selection of more appropriate geosynthetic materials. Additional monitoring techniques have been developed to allow direct withdrawal of samples of wood for assessment of deterioration.     

The reburial of mosaics: an overview of materials and practice

Abstract

A significant proportion of the literature on the reburial of archaeological sites concerns mosaics. These publications reveal that a variety of materials have been used for mosaic reburial, including specialized fill and separation layers, from the early 1980s onwards. Although reburial practice often demonstrates an ad hoc and indiscriminate use of fill and separation materials, or the following of trends and anecdotal information favouring certain materials, knowledge of their characteristics is very important in developing an appropriate technical design for reburial of mosaics. The materials most commonly employed in mosaic reburial practice, including geotextiles, are reviewed and an assessment of their positive and negative characteristics within a reburial design is provided. Recent but limited laboratory and field testing, monitoring and evaluation of reburial interventions have begun to provide preliminary evidence about the behaviour of these materials, indicating which ones are most appropriate and how they should be utilized to best advantage. However, their selection and use remains uneven, and positive results continue to be as much a function of adequate maintenance as proper design and execution.     

Reburial and protective covering of ancient mosaic pavements: The experience of the conservation department of the Israel Antiquities Authority

Abstract

Four case studies are presented illustrating different attempts to protect excavated ancient mosaics by reburial or protective covering, with varying degrees of success, at three archaeological sites in Israel: Tel Itztaba, a site excavated between 1991 and 1994 where planning for reburial at the outset of the excavation could have prevented considerable losses; Khirbet Minya (Horvat Minim), a site excavated in the 1930s, reassessed after four years of reburial; the Promontory Palace at Caesarea Maritima, a site excavated in 1978, partially destroyed by the sea, reburied and regularly monitored since 1994; and an experimental test site at Caesarea Maritima. These examples demonstrate the importance of planning, monitoring and maintenance for successful reburial, and allow an assessment of which materials and methods performed better than others.     

The Suakin Dilemma: Conservation and Heritage Management in Eastern Sudan

Abstract

A four-step process for the stabilization of fragile, exposed historic adobe structures has been developed. The structures are first stabilized by consolidation with an alkoxysilane. Protection for the tops of walls is provided by capping with mud made with an acrylic polymer emulsion instead of water. A similar modified mud is then sprayed over the entire structure to provide a veneer that does not significantly change the appearance of the wall surface. Finally, when dry, this is covered with a polysiloxane water repellent. Small test sections of walls of the adobe ruins at Fort Selden, New Mexico, USA, were subjected to various treatment combinations. After two winters, it was found that the four-step procedure gave the best results.     

Relevance of soil biology and fertility research to archaeological preservation by reburial

Abstract

This paper discusses how soil biological information can help to improve understanding of, and possibly inform decisions about, preservation of organic archaeological remains by reburial. A brief summary of the properties of the soil biological community is followed by an outline of results from recent biological investigations following the recovery of archaeologically relevant materials that had been buried for thirty-three years in one of the experimental earthworks in England UK. Examples from the soil biology and fertility literature are discussed to illustrate the effects of fluctuations in soil wetness and aeration, and of nitrogen availability on decomposition. Finally, the impact of soil handling and physical disruption on biological processes in soil are discussed, as they influence whether soil functions can be restored at a reburial site once the archaeological resources have been ‘protected’ beneath.     

The RAAR Project — Heritage Management Aspects on Reburial After Ten Years of Work

Abstract

The general purpose of the international reburial project, Reburial and Analyses of Archaeological Remains (RAAR), is to evaluate reburial as a method for the long-term storage and preservation of waterlogged archaeological remains. Since 2001 material samples have been buried, retrieved, analysed systematically, and the results reported.

RAAR has mainly focused on the degradation of materials commonly encountered on archaeological sites, and on environmental monitoring techniques in order to determine what type of material can be reburied and for how long. The project has concluded that a heritage institution could provide short- or long-term curation for its archaeological archive by using reburial depots provided they are set up according to guidelines and restrictions stipulated by the RAAR project.

However, there are management and legal aspects that need to be discussed and resolved before each reburial project. Actual reburials that have been carried out so far are often a solution to emergency situations and lack collection and management policies. The questions ‘what’, ‘why’, and ‘for how long’ have been forgotten and need to be addressed. The legal protection of a reburial site is also important. This paper discusses these aspects and their consequences and highlights possible differences in approaches between the countries involved in the RAAR project.     

The use of geosynthetics for archaeological site reburial

Abstract

Applications of geosynthetic materials in reburial practice include geotextiles for separation, filtration and protection (cushioning); geomembranes and geosynthetic clay liners for infiltration control; geonets and geocomposites for sub-surface drainage; and geocells for erosion control. Mechanically stabilized earth reinforcement using geocells, geogrids and geotextiles can also provide substantial benefits for reburial projects by reducing lateral earth pressure against backfilled structures. Other aspects of modern geotechnology that may be useful for reburial projects include micro-piles and soil nailing for foundation and excavation support and evapotranspirative capping technology to establish the depth of soil cover required to isolate a structure or artefact from moisture and temperature fluctuations. Optimal application of these geotechnologies requires an understanding of the basic engineering principles associated with their implementation, as well as knowledge of the factors influencing archaeological site preservation.     

Establishment of conservation,design and construction criteria for protective shelters at Fort Selden State Monument,New Mexico

Abstract

Foit Selden State Monument, located in southern New Mexico, consists of the exposed adobe ruins of a military post that was occupied from 1865 to 1981. A management plan for the site is currently being developed in which an option being considered for preservation is the construction of a protective shelter.

The process of establishing conservation, design and construction criteria for a potential shelter at Fort Selden involves the assessment of technical issues and the evaluation of public support for the criteria and purpose of the monument. The conservation concerns are based upon accepted standards for conservation and construction criteria while the design and construction standards involve a higher degree of Public concern, particularly the public expectations exerted on a historic site in the United States.

The criteria for Fort Selden are currently being codified. This paper outlines the preliminary criteria as well as the process by which these criteria will be established and meshed with the public expectations of the site. The planning process is presented and the underlying philosophies of deciding to shelter, designing the shelter and constructing the shelter. Future evaluations of the shelter's success can be gauged against these original criteria and mindset.     

‘Site unseen’: the case for reburial of archaeological sites

Abstract

The decision-making process for managing and conserving archaeological sites is increasingly accepted as being driven by a thorough assessment of values, physical condition of the resource and the management context. Reconciling the results of these assessments, which may point in different directions, to arrive at a decision that is most appropriate for the resource can be a complex process. When reburial (also referred to as backfilling) is being considered as an option for the preservation of an excavated site (especially long-term reburial), there are particular opportunities and constraints and a host of considerations (stakeholder, technical and management) that need to be taken into account if the values of a place are not to be compromised and stakeholders alienated. For, however beneficial reburial may be from a conservation perspective, it is generally viewed with scepticism or disfavour by those with legal authority over a site, and by those stakeholders who want access to the site for study, education or money-making. This paper examines the rationales for reburial, as well as the objections to it, and puts forth a decision-making model for reburial interventions that takes into consideration stakeholder, technical and management needs.     

Some considerations for the reburial of painted lime stucco façdesin the Maya region

Abstract

The conservation of Maya stucco façadesin humid tropical conditions poses significant challenges. Professionals in the region consider that reburial is one of the most easily accomplished and cost-effective conservation options; and reburial of modelled and painted lime plaster façades, in conjunction with the construction of exposed replica façadesoverlying the reburied originals, has been or is being considered as a preservation strategy at a number of sites in the region. This is illustrated by two case studies from Belize and one from Guatemala. However, more research is needed to fully understand the benefits and risks of reburial, and to determine the optimal conditions and techniques specifically suitable for wet tropical climates. The range of issues that must be considered for reburial of stucco façadesin this region include their conservation needs in relation to the susceptibility of ancient materials to climatic conditions, management issues such as visitor and interpretation needs and the problem of looting in the region, the feasibility of solutions in relation to available resources, choice of methods and materials used in interventions, and the impact of reburial on the significance of a site, amongst others.     

Monitoring through replication: Design and evaluation of the monitoring reburial at the Laetoli trackway site

Abstract

How is it possible to monitor the condition of a site or artefact after it has been reburied? In the case of the reburial of the extremely fragile and remote site of Laetoli in Tanzania this problem was addressed by creating a replica reburial close to the site in 1995. The method and materials used to rebury the trackway are replicated in the monitoring trench, which thus provides a ‘window’ on the condition of the trackway. A series of samples and indicator objects of different materials placed in the trench are intended to provide an understanding of the burial environment over the long term. Additionally, triangular recesses with sharply defined edges were cut into the floor of the trench to allow determination of the mechanical stability of the tuff to deformation under the reburial overburden. The trench was lined with root-inhibiting Biobarrier® geotextile and then reburied in the same manner as the trackway; existing acacia trees at the edge of the trench were allowed to remain. In 1997 excavation of part of the trench was undertaken. Of particular interest was the fine detail of the topography of the floor of the trench and the effectiveness of the Biobarrier®. Geosynthetics showed no evidence of deterioration, but severe degradation of all wood samples without preservative chemical treatment and of indicator objects indicated a very aggressive environment. Many of the findings, such as survival or deterioration of the indicator objects, use of geosynthetics and the efficacy of Biobarrier®, have relevance to a broader understanding of buried environments.     

Archaeological Site or Natural Marine Community? Excavation of a Submerged Shell Mound in Ninigret Pond,Rhode Island

ABSTRACT

Submerged shell midden sites and natural shell deposits can have similar characteristics and can be difficult to distinguish archaeologically. We excavated two test units from a large (at least 35 m×70 m) submerged shell mound in Fort Neck Cove in southern Rhode Island to assess whether it was natural or cultural in origin. This mound had been recognized as a potential archaeological feature as early as the 1970s. Excavation, radiocarbon dating, and subsequent laboratory analysis of excavated materials suggest that the mound was a natural oyster reef rather than a submerged archaeological site. No artifacts were found; there was no clear evidence for human modification of any shells; small species that would not have been targeted as food were present; and δ¹³C values of oyster shells from the mound were consistent with freshwater input into their growth environment, suggesting that they grew in an estuarine environment that did not exist prior to the inundation of the ponds. The stratigraphically oldest radiocarbon date we could obtain (430–190 cal BP, 2σ range), from 70 cm below the pond floor, placed deposition of shells at least 3,000 years after the inundation of the pond. The excavation methods that we used and the process of testing, irrespective of whether the feature is cultural, are valuable contributions to the methodological literature on submerged site archaeology and help provide insight for other researchers working to discern natural from cultural shell midden sites.     

Towards a benign reburial context: the chemistry of the burial environment

Abstract

The successful reburial of exposed archaeological remains depends on the ability to recreate a benign preserving environment, especially for the desiccated and waterlogged environments that preserve organic and other valuable archaeological material. An introduction to the chemistry of soil and the burial environment is provided, covering the key variables: water, oxygen, cations and anions, pH, organic matter, clay and redox potential. The problems of monitoring these variables and their variation are highlighted. Recent work in monitoring the long-term effects of burial and the steps taken towards modelling actual burial environment chemistry are outlined. Factors to be considered when adding material for reburial are proposed. These include: the avoidance of soluble or potentially soluble minerals; the beneficial buffering effect of clays and organic matter; the minimization of changes in water level, redox potential and pH; and the desirability of retaining the porosity of the burial medium. This can often be achieved by re-using the soil in which the objects/structures were originally buried.     

Reburial in the context of development: Approaches to reburial in the English planning process

Abstract

Rescue archaeology in England is now firmly embedded in the planning process, following the introduction by the UK government of Planning Policy Guidance Note 16 in 1990 (PPG 16; Departmentof the Environment. Planning Policy Guidance Note 16 — Archaeology and Planning. HMSO, London (1990)). The basic premise of PPG 16 is a strong preference for in situ preservation of nationally important archaeological remains. This often includes reburial of archaeology prior to construction activity, once it has been exposed in test-pitting (‘evaluations’) or full excavation. Reburial strategies are often prepared by civil engineers and there appears to be an overemphasis on consideration of the potential physical impacts on the archaeology. These strategies usually include the use of geotextiles and sand, or other graded material, chosen for its particular particle size/shape characteristics. A greater awareness of the chemical and physical characteristics of a burial environment is now required to ensure that reburial is effective. Archaeologists and conservators are beginning to consider both the natural and, increasingly, the ‘man-made’ (industrial, domestic and agricultural) changes to the soil chemistry of an archaeological site. More use needs to be made of the potential information ‘locked up’ in the artefactual material retrieved from evaluations and excavation nearby. An assessment of the degree of preservation of material should be an integral component for the design of a reburial strategy.     

A programme for the conservation of architectural plasters in earthen ruins in the American Southwest: Fort Union National Monument,New Mexico,USA

Abstract

Plasters constitute an important component of many ruined architectural and archaeological sites. Methods for their in situ conservation have lagged far behind the field treatment of other materials due to their ephemeral nature and the lack of programmatic laboratory and field research. A preservation strategy involving documentation, stabilization, interpretation and maintenance offers a methodological approach adaptable to most contexts. A pilot conservation programme is described for the stabilization and interpretation of the lime plasters within the nineteenth-century adobe ruins of Fort Union National Monument in New Mexico. Methods of documentation, emergency stabilization, injection hydraulic lime grouting and mortar repairs are described.     

Temporary site protection for earthen walls and murals at Çata1höyük,Turkey

Abstract

The exposure of earthen architecture at archaeological sites presents tremendous difficulties both during and after excavation. While it is the intent of most reburial programmes to stabilize exposed structures against the long-term effects of loss of pressure and fluctuations in moisture, relative humidity and temperature, reburial does not easily afford practical protection against immediate damage caused during excavation. At the Neolithic site of Çata1höyük in Anatolia, Turkey, a phased programme to integrate the excavation and conservation of the site was developed. This included emergency stabilization and protection of the mud brick walls, plasters, mural paintings and relief sculpture, both during and between excavation seasons. One component of this programme included the development of a temporary perlite-vermiculite protection system.     

Do geotextiles affect soil biological activity in the ‘reburial’ environment?

Abstract

The effect of five different proprietary geotextiles on the activity of soil micro-organisms (respiration as measured by CO₂ production) has been investigated in model laboratory chambers. The aim was to determine whether geotextiles, used to ‘protect’ archaeological materials during conservation by reburial, influence microbial processes that may promote biodegradation of organic archaeological materials by altering the physical properties of the soil. Four of the geotextiles were composed of either polythene or polypropylene and did not provide substrates for microorganisms. These four geotextiles had no significant effect on microbial activity over a short-term (56 days) burial period. By contrast, one of the geotextiles had a core of wheat straw and coconut fibre bonded in a polypropylene mesh. This geotextile led to increased microbial activity as a result of biodegradation of the straw and fibre core. From a practical point of view, these data suggest that geotextiles that are not themselves readily biodegradable did not enhance biodegradation of other organic material in the short term in the burial environment. If the use of geotextiles offers other advantages, such as providing a marker in the soil or back-fill, or because they facilitate subsequent cleaning and preservation operations, then their use is warranted.     

Under the Boards: Archaeological Site Formation Processes at the Commissariat Store, Brisbane

The study of archaeological site formation processes, although routinely undertaken for prehistoric sites, is only carried out in historical archaeology in a limited way. Understanding the processes which formed the archaeological record of a site is an important first step towards developing justifiable inferences about past behavior and past societies regardless of the age of the site. This paper identifies and examines the cultural and non-cultural processes that formed the archaeological record at the Commissariat Store, Brisbane. The history of the site, from its construction in 1829 as part of the Moreton Bay penal settlement to the present, is examined and the expected impacts and processes on the archaeological record are identified. Archaeological evidence from the salvage excavation of the site undertaken in 1978 and 1979 is analyzed to identify the cultural and non-cultural site formation processes. This study identifies the presence of cultural formation processes including discard, loss, abandonment and re-use from an examination of the historical and archaeological evidence. Non-cultural formation processes at work in the site include faunalturbation, floralturbation, flooding, and aquaturbation.