Cereal Journey 1 – radiocarbon dating the grain samples from Structure Eight

Structure Eight from above in 2023, with Structures Seventeen and Eighteen clearly visible. (📷 Tom O'Brien)
Structure Eight from above in 2023, with Structures Seventeen and Eighteen clearly visible. (📷 Tom O’Brien)

Sarah-Jane Haston is looking at the charred plant remains from Structure Eight as part of her PhD with the UHI Archaeology Institute. Here she brings us her latest update.

Ness of Brodgar Trench P: Structure Eight.

Initial assessment of the archaeobotanical samples taken from Structure Eight at the Ness of Brodgar has revealed low but frequent concentrations of cereal grain across the sampled deposits.

Identification of these cereals builds a picture of the crops that were grown and/or utilised during the lifetime of this building and can help determine whether any change in cultivation practices took place through different phases of activity at the site.

The majority of charred cereal grains identified so far from the Structure Eight deposits are naked barley (Hordeum vulgare var nudum), which indicates that this was the dominant crop throughout the life of the building.

The cultivated species present at the Ness of Brodgar will add to the emerging picture of early arable activity across Orkney, which suggests that naked barley is the main cultivar across the islands in the Neolithic while naked barley has also been identified as one of the main cereals grown in Scotland during the Neolithic (Bishop et al., 2009).

Further analysis of the cereal grain, including radiocarbon dating and stable isotope analysis, will add further information on subsistence change and cultivation practices at the site and will help us to get a more nuanced picture about Neolithic agriculture and its importance to Neolithic communities.

Preservation of the cereal grain

Figure 1: Comparison photo of some poorly and well-preserved grain.
Figure 1: Comparison photo of some poorly and well-preserved grain.

Good grain preservation is necessary for success of both radiocarbon dating and stable isotope analysis and is important in the selection of samples for these analyses. During the assessment of the Structure Eight samples, the state of preservation of the cereal grain was identified and recorded. It is important to note the state of preservation of individual grains as it may provide information on any distortions that occurred during the carbonisation process or if any abrasions or fragmentation that may have occurred during the post-carbonisation deposition of the grain and the eventual burial on site (Hubbard and Azm, 1990).

The scale of preservation of the cereal grain ranges from Class 1, being of “excellent” preservation to Class 6, being “hollow or heavily pitted” Definition of the classes of preservation follows those outlined by Hubbard (1976), found in Hubbard and Azm (1990) and adapted by Boardman and Jones (1990) (See Table 1 below).

Table 1: Classes of Grain Preservation, after Hubbard (1977) and adaptation by Boardman and Jones (1990).

Individual grains often show multiple states of preservation. In this instance, Hubbard (1990) states that it is the worst state of preservation that should be recorded.

Radiocarbon dating cereal grains from the Ness of Brodgar

Radiocarbon dating is important for establishing a chronology for archaeological sites.

The dating of annual plant remains such as crops, which are limited to one growing season, produce a precise date range and combined with strict archaeological context data and artefactual evidence can provide detailed chronological models.   

The radiocarbon dating of the cereals from Structure Eight will help to clarify the stratigraphic relationships between the deposits and the different phases of activity identified. The construction of Structure Eight on top of, and incorporating, the earlier buildings, Structure Seventeen and Structure Eighteen may have led to subsidence of the walls and floors of the building. The earlier Structures Seventeen and Eighteen, can be seen clearly in an overview of Structure Eight, taken in the excavation season of 2023 (Figure 2).

The relationship between Structure Eight and its predecessors, Structures Seventeen and Eighteen.
Figure 2. The relationship between Structure Eight and its predecessors, Structures Seventeen and Eighteen.

The overview photo (figure 2) also shows the two main phases of use identified within Structure Eight.

In the initial phase, the central space is dominated by four large hearth settings, with two double hearths in either end of the building and two smaller hearths at the centre of the building.

In the second phase, it appears that different activities were being undertaken with the southern half of the building. The southern section of the building was no longer roofed, and Structure Ten appears to have been constructed overlying the building at this southern end (Card and Edmonds, 2020).

The addition of new radiocarbon dates will provide a better understanding of the timescale for these changes and enhance our knowledge of how the buildings at Ness were altered over time.

A more detailed chronology, combined with further analysis of the cereal grain assemblage, will allow for a more detailed picture of how agricultural activity changed over the lifetime of the building. This is important given the complexity of the occupation deposits present.

Selecting grains for radiocarbon dating

Ten samples of carbonised cereal grain were selected from samples that contained more than seven cereal grains.

Radiocarbon (C14) dating can be undertaken on a single well-preserved grain but, ideally, it is preferable to choose a sample with >5 grains to avoid dating grains that may be intrusive into the deposit/feature to be dated.  Dating a single entity will avoid errors caused by mixed samples and is now the standard procedure. The grain will be destroyed as part of the process, so the external morphological characteristics of the grain are assessed and described fully before being sent for C14 dating. 

It is important to select well-preserved carbonised cereal grains, as these are most likely to have the least distortion and greater density. The minimum weight for radiocarbon analysis is 3mg with a preferred weight of 10mg as a significant loss in weight can occur during the pre-treatment stages in the radiocarbon laboratory.

The selected grain is placed in a small glass tube with the site code, context id, sample id and sample type, for example carbonised cereal grain, as well as the species dated (in this case Hordeum vulgare var nudum), and the weight of the sample. Dating of the grain will be carried out by Scottish Universities Environmental Research Centre (SUERC) in East Kilbride.

Part two


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