Sediment Speaks: A Day at the Kaims – Part 2

This post is a continuation of “A Day at the Kaims – Part 1“, and focuses on both the technical and experiential aspects of environmental coring at the Bradford Kaims wetland site.

Archaeological coring: how and why?

Matt Ross teaching BRP students how to describe core samples

The following has been written by Matt Ross, a graduate student currently researching at the Bradford Kaims. He’s also generously been teaching those interested and willing to brave the knee-high muddy bog water how to core and describe sediment samples in the field.

Anne, Matt, and Eva following a day of coring

Throughout the season a team of sediment corers have been braving the wet and mud that is the Bradford Kaims, to record the sediment that lies beneath.

Using a 6m long auger, as demonstrated by Richard Tipping in our earlier blog post, it is possible to extract sediment samples and compile a vertical stratigraphy. Repeating this along a transect, a cross-profile of the landscape can be constructed. By examining changes in sediment type, colour, composition and organic content (i.e. wood fragments, plant stems and calcareous shells) both vertically and laterally throughout the profile we can then piece together the history of environmental change across the site.

Matt and Anne with 5 metres of auger

Such changes occur over time in response to natural and/or anthropogenic forcing: examples include climate change or forest clearance for agriculture. As sediments are composed of material (and organisms) within the catchment, they accumulate vertically and, unless disturbed, will remain in chronological order. The rate of change is also indicated in the sediment profile.

Measuring the depths of various sediment layers–the empty sections mark the areas where we’ve removed sections to feel and analyze

For example, a unit of coarse sand with a sharp upper boundary may mark a rapid flood erosion event, whereas the accumulation of several metres of peat reflects relative climate stability over thousands of years. Sediment coring can therefore provide a rapid assessment of palaeoenvironmental conditions over vast areas. But why does it matter?

Establishing the past climatic conditions and landscape history can provide important context to understand prehistoric settlement at the site. For instance, if we know there was an open body of water during the time of occupation, we can assume that it may have been exploited.

Site exploitation: our burnt mound. Evidence of occupation and long-term site use, the mound is the likely the discarded build-up of shattered stones used for heating water. Click the photo for more information.

Coring at the Bradford Kaims has focused on the low-lying Embleton’s bog, where we have identified two open bodies of water, either side of the promontory, on which Trench 42 is located. These lakes appear to originate in the lateglacial, or the early Holocene (10,000 years ago) and have experienced fluctuating water levels, as indicated by bands of Marl – a lacustrine deposit of calcium carbonate rich mudstone. The lakes were then quickly succeeded by wetland conditions as the climate ameliorated.

Pollen analysis, currently being carried out at Stirling University, will provide detailed reconstruction of vegetation cover at the time of settlement.

The Kaims wetlands regressing into a lake state

Learning to Core 

After first break, Anne (a fellow BRP-er) and I joined Matt for a day of coring.  Knee-high grass lined the foot-flattened path to the most recent transect line where we would be coring. After hearing stories of thigh-high muddy water and the need to bring a complete change of clothes, I was pleasantly surprised to discover that the bog water only rose halfway up my knee-high wellies (though it did get deeper as we moved further south).

Matt and Anne in a slightly damper area

Our first core of the day–Core 4–was marked with a bamboo shaft sticking a few inches above a mud and water filled hole in a circle of flattened grass. It was decided that, to start, I would help Matt with the auger while Anne recorded the sediment changes for each metre core, since she had cored previously. Because we were continuing with a core sample from a previous day’s work, albeit at a greater depth, we had to “clean out” the infill of sediment and water in the hole, by coring to the same depth reached before.

Matt and Anne with 5m of auger

Let me tell you, finding the right hole amongst a half-dozen similar holes filled with muddy water and grass, and trying to fit the auger into it without creating a bigger hole, is no mean feat. I think we gave up on the old hole and made a new one after 3o minutes of struggle. We also never managed to get past the 4 meter depth at that particular spot. While we struggled though, Matt did give me a very nice introduction to the coring process and the geography of the Kaims.

Later in the day, Anne and I switched off and I got an opportunity to record the data. Richard Tipping joined us later in the afternoon and showed us the benefit of years of coring experience–he was almost quicker at setting up and adjusting the auger by himself, than Anne, Matt, and I were together. His equally quick assessment of the core samples was also impressive. 

Using a knife to clear away excess sediment and expose the core

I was surprised to learn how similar the process of coring is to the environmental archaeology and flotation I do here at the castle. It was vindicating that my description of the soil matrices, colours, and inclusions of the BRP environmental samples have been semi-accurate and that I’ve developed a somewhat transferable skill. 

By the end of the work day, we had completed an additional 3 cores to a depth of 6m each. The cores themselves showed a variety of sediment layers including peats, peaty clays, sandy clays, sandy silts, silty sands, and marl. The marl was a creamy to light grey very soft clay. Never having heard of it or encountered it before, I looked it up. Apparently, marl is a “calcium carbonate or lime-rich mud containing large amounts of clays or silts”, and is formed under freshwater conditions.

An example of marl from Urswick Tarn, similar to what we found at the Bradford Kaims

It’s interesting, not only because it was the most markedly different in appearance, but because its presence indicates a period of fairly rapid climate or landscape change–warming or deforestation–and rise in water levels.

Other things we noted in the core samples included the presence and relative quantities–very rare, rare, common, abundant–of wiry and fleshy stems, wood fragments (incl. size), whole shells and shell fragments. I found it interesting that there was significantly more variation in the cores to the north, even at less depth, than there were to the south. For instance, between 3 and 4 metres at Core 4, we encountered maybe 6 or 7 distinct changes in matrices. At the same level in Core 6, the sample was almost entirely a mid-reddish brown silty peat.  Despite this, Matt suggested that all the core results were fairly consistent with what they expected (and hoped) to find.

Last, but not least, for your and my enjoyment:

       

I would love to see a final report of the results, to see how my work was used. I would also like to thank Matt for his wonderful demonstration of coring methods and techniques as well as an illuminating explanation of some of the recent environmental findings. 

— Megan Taylor

“I personally thought it was a great (if not slightly wet) and informative experience, and even though I will probably be sore for the next few days, I can definitely recommend splashing around in the wetlands for a day!”

–Anne Hartog

A Day at the Kaims – Part 1

The following is a report from my day at the Kaims… it’s taken me a while to get it posted.

Last week, I heard Matt Ross was looking for coring volunteers. I’d never done coring before and knew very little about the process or it’s archaeological potential. Keen to try my hand at something new and archaeologically relevant, I decided to take a day off Environmental and escape to the Kaims. After a week of rain, we had a day of sunshine and almost-blue skies. It was amazing. In the morning, they even let me have a go at trowelling in the west extension of Trench 42—it’s been so long since I’ve done actual archaeology. (I may have been a bit overzealous and taken out a few more stones than necessary… sorry, Graham).

Walking down to the trenches at the Kaims

To begin, I was extremely impressed with the archaeology at the Kaims. I, along with the other new students, got a site tour from Jackie, the Kaims Assistant Supervisor, first thing in the morning.

The last time I was at the Kaims, was in June 2011. Trench 6 had been opened and expanded to reveal a large burning area, possible hearth, and post-hole. Victorian era drainage pipes were being found and excavated. And the whole area didn’t look like a bog, though I admit to having to stand in a few inches of water to attempt a section drawing.

This is what it looked like when excavation of the Kaims began in 2010.

What a typical trench at the Kaims used to look like – a 1 m x 2 m rectangle.

First Kaims Supervisor Joanne Kirton teaching students how to test pit

What we once thought was interesting archaeology

This is the Kaims now. That’s progress.

Part of Trench 42, originally 20 m x 2 m. (It continues both to the north and west off the photo).

Community diggers excavating Trench 6 in the off-season

The archaeological features that have appeared this season are enough to satisfy the appetite of all you prehistoric archaeologists–a burnt mound reminiscent of others found across the UK and Ireland and what was originally hoped was a cist burial.

Kaims Supervisor and Director standing at the edge of T42 – note the sharp boundary at the south edge of the burnt mound.

Recent theories as to origins/purpose of the burnt mound and surrounding area: cist burial , beer production site, fish drying site, tanning site, sweat lodge, cooking area.

An extension was made to the east of trench 42 to allow for a pit to be dug to explore the theory that the large worked stone that was uncovered in T42 might be a stone slab/head stone of a Bronze Age cist burial.

West extension of T42 – edge of burnt mound not yet uncovered

The extention has revealed one edge of the burnt-stones area, but as of yet, there is no compelling evidence of a burial in that direction. Could it possibly be under the stones to the west?

Sarah attempting to find the edge and base of the test pit in T42

When I was up there on Friday, Sarah Aguirre was continuing the excavation of the long, thin sondage/test pit in the east quadrant of T42—next to the stone slab. The work revealed a series of stones, but no burial as originally hoped.

Meanwhile, Eva Rankmore was excavating a pit feature in the northern part of the trench. As of yet, it’s unclear whether the pit is natural or man made, though the most recent (and mostly likely) theory is that it’s a tree throw.

Eva in her possible pit feature (the north part of T42)

Nearby, in the area to the SE of T42, students new to the Kaims were taught how to set up and excavate test pits in the hopes of uncovering the cluster of possible burials. As of today (Thurs. July 19), 10 new test pits have been put in, and nothing particularly archaeologically exciting had been uncovered. However, two of the test pits did reveal a continuation of the modern (Victorian era) drainage feature, evident—although the terracotta pipes had been removed at some point—in the south end of T42.

Opening test pits and new trenches at the Kaims

Other than excavating what I feel is some very promising/intriguing archaeological features, a number of interesting finds have also been found this season – A piece of prehistoric (Bronze Age?) ceramic. A beautiful little flint point (likely an arrowhead). A lot of what is believed to be un-worked jet.

BK12 (4209) <92> Prehistoric pottery (Bronze Age?)

Same piece of pottery in profile

BK12 (4202) <054> Flint blade

Same blade in profile

BK12 (4202) <048> Flint arrowhead

Same point in profie

BK12 (6020) <019> Raw jet?

That was somewhat my morning at the Kaims. I hope you enjoyed it. Tomorrow’s blog post will continue my insider’s view of a day at the Kaims, accompanied by a more technical explanation of the coring process provided by Matt Ross. A more detailed summary of this season’s work at the Kaims will also be forthcoming.

If any of you readers have any questions for the Kaim-anites about any of the archaeology or finds coming out, feel free to post to the blog or our facebook page. We’re more than happy to answer your questions to the best of our abilities.

Coming up – Part 2: Coring at the Kaims, with Matt Ross