Archaeomagnetic Studies at the Bradford Kaims

Archmag

Sam Harris, Doctoral Research Student – University of Bradford

Firstly, it is purely coincidental that I study in Bradford (West Yorkshire) and am coming to take samples at the Bradford Kaims. As an archaeomagnetist, and we are pretty few and far between, it is always amazing the variety of sites that you get to see and work on. Having parachuted into the Bradford Kaims trenches for the second time, this site is no exception in its wonder. Placed at the edge of a fen, the variety of soil and sediment types on site is impressive! This offers the perfect opportunity for archaeomagnetic studies.

For those that aren’t quite sure what this odd science (magic) is, you are welcome to peruse my website, which is listed at the end of this blog post, for some answers. Simply put, the Earth has a magnetic field which varies over space and time. A record of the past geomagnetic field can be found in the in situ remains of hearths, furnaces, or other anthropogenically fired features that we as archaeologist excavate on a regular basis. Archaeomagnetic studies seek to improve our knowledge of past geomagnetic field changes through the analysis of this material. Why though, I hear you ask…

This is because we can use the knowledge of geomagnetic fluctuations over time to conduct archaeomagnetic dating and gain an idea of the last time that some fired archaeological features were heated. Having a dating method which directly relates to an anthropogenic activity, rather than to the end of an organism’s carbon absorption for example, is a powerful tool for the archaeologist.

Archaeomagnetic dating was first attempted at the Bradford Kaims in 2011. While the study was successful and the date recovered for a fired hearth feature in Trench 6 (c.4350 cal.BC) was considered accurate given other artefactual dating evidence for the site, newly acquired radiocarbon dating evidence suggests that the calibration methods used for the archaeomagnetic dates produced erroneous results. This was due to the use of an experimental and alternative calibration model from outside the UK, as the current UK calibration model does not stretch back into the Bronze Age or before. This previous study, and others since, have identified the need for further work to be undertaken. This is where me and my PhD come in! My main aim is to improve our understanding of geomagnetic field change during prehistoric periods, but particularly the Neolithic.

At the Bradford Kaims this season, I sampled two features associated with the Bronze Age burnt mounds, both of them interpreted as fire pits containing fired stones, burnt sediments, ash, and charcoal. These features will provide good radiocarbon dating records, alongside the archaeomagnetic signatures for the fired subsoils within and below them.

Thanks to the Bamburgh Research Project’s excellent radiocarbon dating programme at the Bradford Kaims, the fired archaeological features that I can archaeomagnetically study will have independent dates associated with them. By building up a number of well-dated features in this way, a new calibration curve for the UK can be created, with the Bradford Kaims being a central case study in this process. Through the combined use of radiocarbon dating and archaeomagnetic dating on prehistoric sites like the Bradford Kaims, we can gain a more nuanced understanding of their chronologies.

Sam’s website can be viewed at; www.neolithicarchaeomagnetism.weebly.com

Sam’s Twitter can be viewed at; @Archaeomagnetic

Field Work Update for the Bradford Kaims

Project Director, Graeme Young, gives us an update on the recent work undertaken at our Mesolithic/Neolithic site out at Hoppen Hall, near the Bradford Kaims.

In our last few visits to the site at Hoppen Hall near the Bradford Kaims, we have continued the work that has been ongoing for the last couple of years around the ‘hearth’ feature. We are hoping to increase our understanding of this enigmatic feature dated to 4000 to 4500 BC by archaeomagnetic dating. Just what it represents, and how it fits into the wider landscape still alludes us. I hope that through widening the area of excavation and sheer persistence  that this will work wonders. Click here to read an overview of past work at the site

The Aerial photography undertaken by  Horizon has been particularly useful. We always thought that this birds eye perspective would provide us with some great shots for publication, but it is surprising how much this change of perspective helps in seeing the bigger picture and how the individual components fit into a wider story. We know that the site lay close to the edge of a narrow channel, but it is apparent now that even to the south where the channel opens out we have a complicated picture including two separate bays. It must surely in the distant past, when there was still substantial open water, have been a prime area for attracting animals and perhaps for fishing too. Easier to see, therefore, why we have such clear indication of human activity. Albeit activity we are struggling to understand. Click here to see the results of Horizon AP’s most recent work for the project.

Initially we have been cleaning and planning, with the intention of better understanding the stratigraphy (the sequence of layers and features that tell the story of the order of events) so that we can hopefully understand the role that the site played when it was in use. Why for instance is there so much charcoal and burnt material here? Is this material waste material from a process that involved fires set on our burnt stone surface that they overlie. Or is there a substantial distance in time between them, if not a distance in space? We have also uncovered the presence of at least one substantial pit and are perhaps seeing traces of others too. If this is the case we can also ask if we are looking at a structure or further waste disposal.

The extension of the site to the south, cleaned up to show the extent of the burnt material in this direction.

Cleaning back towards the stone feature (seen behind the trowellers) has revealed at least one substantial pit. Planning of the trench extension is under way in the background.

Over the next few weeks we will be pursuing these inquiries and also opening a new trench down into the peat layers, that lie only metres to the west of the burnt stone surface. Hopefully finding evidence of material disposed of in the lake will add to our understanding of the site’s use.

Watch this space for updates.

If you are interested in getting involved with the project Click here for more information

Carved Stone and Archaeomagnetic Dating

An update from BRP Director Graeme Young:

The stone slab that was thought could very well be sculpted was taken to Durham for conservation and examination at the end of the season. Sadly once it was cleaned and properly examined by the experts, it was found to be almost certainly of natural origin, representing a type of fossil common in sedimentary rock on the northern part of the east coast of Britain. We held off publishing immediately as we were not sure if it would make it into the final edit for the Time Team episode that featured the BRP and was broadcast in late April in the UK. We didn’t want to spoil the moment of discovery as filmed! Although sad in a way it is an important part of research. Any theory is only as good as the evidence and new or better information often forces us to revise our thoughts I am sure there is every chance of finding the genuine article in the future and we will certainly be keeping our eyes peeled.

We also mentioned the archaeomagnetic dating samples that were taken on the stone surface uncovered at the Kaims site last season. We have the dates back and they are really exciting as it seems that the strange stone ‘platform’ dates back to 4000-4500 BC! We will certainly be expanding the trench to put this feature into a wider context during he summer season that is nearly upon us.

Our first days back on site at the castle will be the weekend of the 28th and 29th of May. The plan being to start to get our offices back into operation and start the process of cleaning the site up ready for work.

I hope may of you caught the Time Team episode on Bamburgh. As ever with TV its a bit of a snapshot of a much larger subject, but I thought they did a good job and some of the shots were pretty spectacular! I should add if anyone has any questions about the programme then do add a comment and we will do our best to answer them!

Archaeomagnetic Dating Project

Recently, BRP archaeologists have been working with the Paxton Before the House Community Research Project, which has been lucky enough to be included in an archaeomagnetic dating project undertaken by Lancaster University.
Archaeomagnetic dating is a method of dating archaeological material using changes in the Earth’s magnetic field. The direction of magnetic north on Earth changes over time. Some materials such as fired clay or burned stone ‘record’ the direction of magnetic north at the time of their burning. By comparing their unique record to a master curve showing the location of the North Pole through time, materials and events can be roughly dated. The technique is particularly useful at prehistoric sites such as the Bradford Kaimes.

The University of Lancaster team took samples from a site in the Kaimes wetland area that is currently being excavated by the Paxton Before the House Community Research Project team.

The samples were taken from a burnt clay surface adjacent to a stone feature identified at the site. The feature is unusual: it is a much localised spread of irregularly shaped sandstone slabs, the function of which is unknown. Current theories about their use are varied and range from the stones forming the base of a sweat lodge, to being part of a cist burial.

Team members taking samples from the area adjacent to the feature.

 

Much further investigation is needed before we can begin to refine our theories. A date for the feature will be key to its interpretation, so the work of the University of Lancaster team is much appreciated, and the results of the project eagerly anticipated.

The BRP and Paxton project team will be working on this puzzle throughout the winter – we’ll keep you posted as our results come in! If you’re particularly interested in the Paxton Before the House Project, visit their working blog to see how they’re getting on, and find out what they’ll be up to in the coming weeks.