Types of Museums and Ownership

Section 2.6.4 introduced coring as a sampling method for archaeological geochemistry. This section outlines the common method, with site specific methods detailed under site specific sub-headings below.

Locations were selected either in reference to GPR data, or were selected as the area was marked for excavation. This was dependent upon the purpose of the core. Once the location was selected, a point was marked and its 3D coordinates recorded, and therefore the core was geo-referenced and numbered within the site based system. If the core failed as it hit a stone and had to be moved slightly and restarted, the new point was surveyed to reflect this. If the core was taken from topsoil, the excess vegetation was removed. This could remove the upmost 1-2 cm of topsoil. It was discovered that grass/vegetation putrefied within the core liner upon storage, thus the excess was best removed in advance. Each core was manually hammered into the soil and removed via vertical lifting by one or two people. Extension rods were added to the core as the depth increased. As each core was taken, major stratigraphic boundaries were recorded in a notebook, including Munsell colour, thickness, interface details and texture where possible.

The distortion of the stratigraphy and compaction to the cored soil is minimal in most conditions, although topsoil can be slightly compressed due to the higher organic content and porous

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structure. The author has also observed compression in waterlogged clays and histic (peaty) horizons; however, these factors were minimal at Avaldsnes and the other case studies. The maximum depth achieved was 2.35 m, although the majority of cores were less than 1 m in depth. At a depth of 2.35m, raising the core was challenging, and always required two people.

Cores became stuck, especially in stonier conditions, and had to be lifted using either many people, levers, or digging it out with a shovel. As the soil at all sites was fairly stone free, despite the few setbacks experienced, the method was effective. The resulting core sample proved robust and stable when the plastic liner was wrapped in plastic film and tape to maintain the moisture content.

The verticality of the cores was also an occasional issue. If the core was begun at a slight angle, the whole core continued with this tilt. Practice did help reduce this, but it cannot be assumed all cores were perfectly vertical. Although the error is usually slight, this can have an effect on depth recordings, especially in the deeper cores. The recording of depth was generally done with a foldable measuring stick, and the depth recorded to the top of the topsoil or surface. As the cores were in set section lengths, in the rare instances where measurements were not done due to human forgetfulness, they were calculated based upon the core section lengths.

4.2.3 Avaldsnes

Background, geophysics and excavation

This multi-period site is detailed further in chapter 5. The site was investigated over two field seasons using excavation and prospection techniques. The excavation by the Royal Manor Project (RMP hereafter) was led by project leader Prof. Dagfinn Skre and excavation leaders Mari Arentz Østmo and Egil Lindhart Bauer, all from the Museum of Cultural History, University of Oslo. A major issue that arose during this fieldwork was that the archaeological excavation was often limited by more modern features, such as access roads, parking areas, upstanding buildings and vegetation. Figure 4.1 shows the areas of the site excavated by the RMP over 2011 and 2012.

Initial geoarchaeological research on the site was to assess coring as a prospection method in combination with geophysics and excavation. This was undertaken by the author, however, it was not directly connected to this thesis and research. In areas marked for trenching and excavation, cores were taken prior to excavation, and in reference to GPR data provided by a survey conducted by the Vienna Institute for Archaeological Science (VIAS) (Stamnes and Bauer, in press). Therefore a substantial coring campaign was undertaken in 2011 and 2012 on the site, which provided collaborative information on soil and site formation processes and background samples. The coring proved to be minimally disruptive and damaging to archaeology. Upon

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examining the cores, the only archaeological finds beyond charcoal were two very small slag fragments and tiny amounts of burnt bone, from a total of 364 cores. Previously, and also unconnected to this research, many surface samples had been taken for fractionated P and magnetic susceptibility analysis elsewhere. This accumulative experience from previous fieldwork on the site raised concerns over contextual security in light of the complex and disturbed archaeology. For this research, samples were selected and taken in an area that posed questions over the divisions and use of space in the later Iron Age, and offered sufficient contextual security to allow data comparison.

Coring for geochemical analysis

As the first case study, Avaldsnes was a testing ground for the use of pXRF and potential for three dimensional (thus temporal) geochemical data via cores, therefore some trial and error was anticipated. In the area selected for geochemical sampling, Area 6, the three dimensional aspect was investigated via limited coring, although the bulk of the samples analysed were surface samples.

Cores from without Area 6 confirmed the depth of the archaeological deposits and provided valuable site formation, environmental details, and material for later subsampling, and two of these cores served as background samples for geochemistry. However, within Area 6, only four such cores were used directly for geochemical analysis. These cores were taken in maintained sections as examples of the stratigraphy in Area 6.

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Figure 4. 1. Map showing the excavation areas at Avaldsnes as referred to in the text. The dotted lines denote the extent of each labelled area. These extents were used for geophysical prospection and excavation planning (Bauer

& Østmø, 2013). Map source: Author/Ingvild Tinglum Bøckman, MCH/Norwegian Mapping Authority, 2016.

Horizontal sampling for geochemistry

The area of interest for horizontal sampling was selected on the basis of preservation, archaeological interest connected to the research aims and objectives, and suitability to the methods.

Area 6 is located in undulating terrain, with bedrock intrusions close to the surface in parts, including within the excavated areas. Naturally, this alters the soil’s vertical profile, and the properties of the soil with changing depth. Samples near bedrock rises were excluded wherever possible. This, however, limited the size of the sampling grid and partly defined the sampled area. The sample area was also limited by a large kerbed Bronze Age burial mound (Kjellerhaugen) to the north, a maintained section over a modern pipe to the west, and a bedrock rise and modern intrusions to the south. The area was multi-period: dating from the site confirmed the main period of activity for Area 6 was late Iron Age, particularly the Viking Age. This reduces the measured duration of the main occupation, but it must be stressed this does not equate to single phase occupation.

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During sampling, each sample point was scrutinised for the purposes of sampling consistency and quality. As detailed further in chapter 5, the site was affected, severely in places, by modern disturbances and contextual contamination. Samples deemed too close to such intrusions were discarded. In addition, sample points that were located within an identified archaeological feature were also excluded, as the purpose was to understand the spatial distribution and nature of the occupation within the selected area, and therefore sampling a specific feature would hinder this analysis. There was one exception; an oven was specifically sampled to test the use of the feature, obtain comparative data, and to see if this sampling approach could be used in future work.

Figure 4. 2. Sampling at Avaldsnes. Left: horizontal sampling, Area 6, with Mari A. Østmo surveying sample points and Jessica L. McGraw checking sample labelling. Right: Coring in Area 2, with the author and Magnar M. Gran.

Photos: Royal Manor Project, MCH, UiO.

Geochemical samples were taken from an archaeologically defined layer over a predefined 1 x 1 m grid system. Each sample was taken with single use plastic spoons and placed in clean, marked bags. Samples were taken at the end of the excavation season to minimise disruption to the excavation of archaeological features. Where present, samples were taken from the base of archaeologically defined layer 25600, others from the immediate subsoil. These layers are pedologically very similar; a cambric, silty loam upper B horizon that undulates with the bedrock formation. Archaeologically defined layers do not always relate to soil horizon processes;

samples can be from different soil horizons, and thus potentially have different processes and subsequent compositions. These factors can influence the chemical and physical composition of samples, hence the retention capacity of the sample for anthropogenically-sourced inputs. The samples taken from the grid represent a combination of potentially selective leaching and accumulation in the soil without temporarily. Obviously this has inherent problems for interpretation, which is discussed in chapters 5 and 8.

61 Challenges specific to Avaldsnes fieldwork

Two challenges dominated fieldwork at Avaldsnes. The first was all pervasive, to this research and the fieldwork, and was in the form of disturbance from modern construction activity. Cable trenches cut through areas and even the Bronze Age burial mound, Kjellerhaugen. Within area 1, the building of the car park some few decades previously had left deep tracks from a toothed digger bucket in the hearth and postholes of a Roman Iron Age house. Previous trenches dug in Area 6 for archaeological investigation also disrupted stratigraphy, and because digging in narrow trenches is always challenging, the archaeology was not recorded in corresponding detail to the RMP’s observations. This was due to the accrued experience the RMP gained from working on larger scales and over an extended time frame. Areas 1, 5 and 6 were the most damaged by modern activity, however, in Area 6 it was far easier to delimit and thus manage compared to Area 1, hence the selection of Area 6 for this research The truncation of the archaeology had undoubtedly removed archaeological features and objects, a phenomenon familiar to archaeologists, and one which always complicates the interpretation process.

Investments were made in sampling and analysis such as micromorphology, macrofossil, osteoarchaeological and metallurgical analysis, magnetic susceptibility and fractionated P analysis to optimise the information gleaned from the present evidence (see Chapter 5).

The second challenge was that the site was not a level field. The coring evidence strongly indicated that in the Bronze Age, the site consisted of undulating waves of thinly covered, low bedrock peaks and scarps over corresponding depressions. The shallow regnosols in the depressions formed histic, peaty layers because of impeded drainage. Land use changes; the gradual conversion of the land to agriculture began the incremental levelling of the terrain, which covered Iron Age cooking pits and earlier structures as ard-induced colluvium filled in the hollows. Upon excavation, the re-cutting of these hollows and depressions through the deep colluvium meant that one archaeological horizon would be composed of C horizon material against the weathering bedrock, and cambric, iron enriched B horizon material. Sampling on this plane would result in samples being compared that had contrasting material properties in grain size, organic content, chemical composition and thus retention mechanisms. This is difficult to compensate for without measuring these properties and including them as factors in the statistical analysis, as research has clearly shown these to be a major factor in elemental retention (Crowther, 1997, Oonk et al., 2009b, Cannell, 2011).

These issues were mitigated as far as possible by careful selection of the sample locations, choosing samples that appeared visually and texturally to be comparable, as measuring every parameter would have resulted in more laboratory work than could feasibly be contained with

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this research. The subject of measuring additional parameters with geochemical analysis is returned to in the discussion (chapter 8).