Geoarchaeology

Zen and the Craft of Thin-Sectioning

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On a brief visit to the northern hemisphere, and after a pleasant few days in Tübingen discussing the Lower Palaeolithic of Arabia (more later), the morning of the Day of Archaeology 2016 found me once more in the Mary Cudworth Lab at the Department of Archaeology, University of York, sanding away at a resin block attached to a small glass slide in the name of ‘Science’.

The slides I was preparing are used for thin-section micromorphology, that is, the examination of sediments or soils at the microscopic scale. By looking at the arrangement of the sediment particles, inclusions and any coatings or areas of dissolution of material, micromorphological analysis can be used to tell how a sediment deposited, and how it has been altered after it was deposited, information that can be used to reconstruct past environments and the means by which archaeological deposits were formed and preserved.

My PhD used this technique to examine at the changing sedimentation in the Haua Fteah, a Libyan cave site, during the Middle to Later Stone Age, and what these changing processes meant for environments during this transition. implications of these. The slides I was working on today are from an exposure of shallow marine deposits in SW Saudi Arabia, at Dhahaban Quarry, as part of the SURFACE project. These marine deposits were covered by windblown sediments. Micromorphological analysis of samples from the sediments will allow confirmation of these field interpretations, and, in establishing the contact between the marine and aeolian deposits, mark a past sea level, information that is incredibly important to understanding past coastal change, and human activity within it.

But before analysis, the thin sections have to be made, and it is this time-consuming, and at times frustrating, thin section-making process which is about as far away from Indian Jones as you can get…

Manufacture of the thin sections is technically straightforward:

  • Remove an intact block of the deposit to be studied, transport it to the lab and dry it out.
  •  Soak it in crystallitic polymer resin, and place it for a day or so in a vacuum, to make sure the resin fully impregnates the sample before it hardens.
  •  Wait a few months for the resin to harden fully.
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Ready for the fun to start! A resin-impregnated sample ready for thin-sectioning. Photo: R. Inglis.

 

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Cut resin blocks – time to choose the face to be mounted. Photo: R. Inglis.

  • Cut a slice off the resin block and trim it down to the size of a slide.
  • Grind one face of this slice so it is flat and even.
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Grinding the blocks on the Logitech. Photo: R. Inglis.

  • Clean the face and glue it to a 2mm-thick glass slide using epoxy resin.
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On the press – not too hard, not too light…Photo: R. Inglis.

  • Remove all but 1-2mm of the slice by cutting off the excess sediment/resin.
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Cut the sample as thin as you can stomach to avoid long grinding times. Photo: R. Inglis.

  • Grind off all but 30µm (0.003mm – about the thickness of clingfilm) of the sample using a grinding machine, such as a Logitech as we have at York.
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Diagnosis: human error. I set the jigs up wrong on the left-hand samples, causing loss of large areas of the samples. Time to start over! Photo: R. Inglis.

  • Check for thickness using a microscope (quartz grains under cross-polarized light should look grey or white).
  • Polish the surface of the slide, and there you have one lovely thin section, ready for analysis and interpretation!
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Not perfect, but a finished slide ready for analysis. Photo: R. Inglis.

The whole process should, after the resin has hardened, take only a few days to complete. It varies a little based on the equipment used – at Cambridge, the Brots we used produced ‘mammoth’ thin sections (13x7cm, or 7x5cm – see Julie Boreham’s excellent Facebook site ‘Hidden Worlds: Off the Bench’ –  whereas the Logitechs produce 11x7cm slides and grind the samples in a slightly different way, using water rather than oil as lubricant. It’s therefore been a learning curve adapting my skills to the Logitech equipment after spending my PhD on the Brots.

Thin section manufacture is more a craft than a rigid science. At every step, these slides can be tricky: the chemical composition of the sediment or what it’s packed in may react with the resin, preventing it from hardening; too thick resin may not be drawn to the centre of the sample, meaning you have to impregnate it again. And that is just the resin. Cutting the blocks to the right size, and mounting them on the presses under a pressure firm enough to press the sample to the glass, but not so firm it cracks the glass, is the next hurdle. Further challenges include: cutting enough of the excess off so the grinding doesn’t take a whole day to remove the rest, but avoiding tearing the entire sample off the slide; making sure you’ve set the machine up properly (I am very much still learning about the Logitech’s finer points!); and whilst grinding, making sure the sample remains fully attached to the slide to avoid losing your sample at the last stages. And of course, the machines have their own foibles…

It’s this latter challenge which has me this morning gently sanding away microns of sample to get to that magic 30µm thickness – after it seized up on my last visit, our resident Logitech whisperer, Dr Carol Lang has been hard at work fixing it alongside her own research (on East African agriculture and Scottish hillforts), and we are on the road to perfect function once more. Yet whilst we are on that road, the monitoring continues and my slides come off a little thick, just in case, hence the sanding or ‘hand-finishing’. But slowly and surely, the beautiful structures and the sought-after grey/white quartz grains begin to appear, another thin section will be in the box, and I’ll be one step closer to unravelling the mysteries of the Dhahaban Quarry sediments.

And to the title of this blog. Sometimes thin sectioning goes perfectly, other times everything that can go wrong will, leaving you weeping over an amusing (to everyone else) set of six slides that have each broken at different stages. But it is also satisfying to work through a problem sample, coaxing it along and working out ways to adapt the process to the awkward reality of each sediment whilst finding out multiple new uses around the lab for the ultimate multi-tool, the large screwdriver. And then, sometimes, you just have to accept that a sample is lost and start again – and that this is OK.

My Day of Archaeology in photos

I work archaeology, study archaeology, volunteer archaeology.  Each day my archaeology is everything from reminders of the First World War to traces of Stone Age life.  Here is a little collage of some of the things I was thinking about on 29 July 2016.


Its not all mud and artefacts

I thought it would be fun to write for the Day of Archaeology as I believed I’d be in the lab elbow deep in soil thin sections from exotic and far flung places, finishing off micromorphological slides before heading off later on in the month for 2016’s field work season.

A day in the life of a geoarchaeologist though never seems to run smoothly and as my blog post for DoA loomed I was faced with the stark reality that I was going to have a tidy up and get ‘stuff’ finished day before I went on a week’s holiday (Holiday: a week of prep’ing for teaching).

 

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Holiday reading

 

But being as everyone seems to leave before I could press that magic on holiday button I was charged with several tasks the first of those being attending a meeting to discuss the progress of publications on the project I was part of for my Ph.D. The meeting went well and everyone seemed to leave with a much needed spring in their step, progress on who was writing what was achieved.

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The AAREA office where it all happens

I managed to get back to the office, quite a pleasant space, shared by myself and colleagues on the project I am currently working on. As you can see from the pictures, particularly of the white board, we spend lot of time discussing ideas. We, at the AAREA Project are rather proud of our white board and believe that if the archaeology doesn’t pan out we may have jobs as code writers and secret agents.

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The white board of mystery and mayhem

The big ideas on the board are based around sustainability, resilience and the adaptive cycle with a biscuit-meter in the bottom right hand corner. So in essence, I returned to the office, noted the biscuit-meter was reading full steam ahead on the chocolate digestives and refuelled prior to finishing off a paper that’s been hanging around waiting for geochemical analysis results.  A few hours later I managed to tick the submit box, the air of satisfaction that flows over you is amazing that after all the sampling, soil shuffling, chemical juggling theory testing and microscope monitoring you can sum up two year’s work in 7500 words.

On a wave of euphoria my last job on this DoA was to head into the lab for a bit of polycarbon resin impregnation. I have some lovely vitrified stone samples collected from another project I’m involved in where we are looking at vitrified Iron Age forts with the SIAVH Project in Scotland. That completed I successfully pressed the out of office button.

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Last job of the day: setting vitrified stone in resin

However, when I reflect on my day, it’s not all, as the title says ‘mud and artefacts’. When you typically think of an archaeologist you imagine them visible from the waste up, in a field covered in dirt and uncovering the mysteries of  the historic world but, in reality archaeology is a multidisciplinary subject that can provide you with a wide range of skills and eclectic days where you just have to get ‘stuff’ done.

Death, dating and dirt

This year despite doing the same job in same location as I have done for the previous 3 Days of Archaeology the name of organisation I work for is different. This is due to the recent split of the old English Heritage into Historic England (who I work for) and the English Heritage Trust. Historic England is the public body that looks after England’s historic environment by championing historic places, helping people understand value and care for them.  English Heritage cares for over 400 historic buildings, monuments and sites.

My day started with reading some new guidelines from APABE – the Advisory Panel on the archaeology of Burials in England which had been written by my Historic England colleagues Jane Sidell and Simon Mays. More and more projects are taking place on land which includes some very large burial ground so this guidance is particularly welcome.

Next I read and responded to a number of WSI (written schemes of investigation) for commercial projects in London. These are basically method statements and have to be approved before work can commence. My colleagues in GLAAS Greater London Archaeological Advisory Service provide advice to the planner in many of the London boroughs (the City of London and Southwark have their own in house archaeological advisers). The archaeology advisers will contact me on projects which include aspects of archaeological science such as Geoarchaeological borehole surveys. Random interesting fact 1 – when writing about the East and North East London wetlands the term Lea is used for the natural river valley and its deposits whilst Lee denotes the manmade channel of the Lee Navigation.

The highlight of my morning was a site visit to see the Crossrail site of Bedlam near Liverpool Street which is being excavated by archaeologists and osteologists from MOLA. All staff on site must to wear full PPE (personal protection equipment). Random interesting fact 2 – because this is a rail project the colour of that clothing is orange rather than the more familiar yellow. So for the purposes of my visit I donned the full orange.

The skeletons were being carefully recorded before being excavated. The site is covered by a large tent in order to shield the public from accidental views of human remains but is also makes the process of excavation a lot easier for the archaeologists especially on rainy days. In addition to evidence relating to the use of the graveyard, a large quantity of bone working waste had been found this week, which comprises mostly sawn through fragments of cattle metapodials (cannon bones) including a fine example of a pinners bone. These were used to hold the metal blanks during the process of filing them down to fine points. Examples of these artefacts are online.

After lunch I joined my colleagues in GLAAS for some training in Radiocarbon dating from Alex Bayliss. Establishing the chronology of a site is key to understanding and interpreting the archaeological features and finds present. Helping to arrange and provide training both inside the organisation and for the wider sector is a big part of the work of the Science Advisors.

Alex’s presentation on radiocarbon dating

Alex’s presentation on radiocarbon dating

On returning to my desk I checked my email and was pleased to discover that the results of a project looking at what we currently know about London’s burial grounds was now available online. This project was carried out by Allen Archaeology and funded by Historic England.

Sylvia Warman, Science Advisor Historic England

Using archaeology to promote the study of STEM subjects

My Day of Archaeology is a bit different to previous years. Back in 2012 and 2013 I was doing lab work (for Feeding Stonehenge and Paisley Caves respectively) and in 2014 I was doing teaching preparation and looking at microscope slides. This year I am technically not doing archaeology at all, though I have been using archaeology. Let me explain – I am a geoarchaeologist, which means I use methods and approaches from geoscience to address questions about the human past. In my current job, which I just started this month, a large part of my role is trying to increase the numbers of students (and women in particular) studying Civil Engineering and Geosciences at Newcastle University. Like archaeology with the popular image of adventure and Indiana Jones, civil engineering has it’s own public image (bridges, buildings! machinery!) and if you say geoscience, the first thing most people think of is rocks. Compared to the image of archaeology which has a broad appeal, it can be much harder to convince people that civil engineering is something they would enjoy. Likewise, there is much more to geoscience than rocks (though personally I am quite a fan of rocks…). This is where the archaeology comes in.

For my Day of Archaeology, I have been putting together outreach events for schools and families, to try and broaden the appeal of geosciences, and to convey the diversity and breadth of the subject. One of the talks I am doing is on Geoscience and Archaeology, using case studies from archaeology to show how we can apply geoscience methods in ways people might not have thought about. I am also working with the Great North Museum: Hancock, to develop geoscience inspired activities for Earth Science Week in October. In a similar vein, I have been writing a blog post (not yet published), on the links between civil engineering and heritage. Back to the bridges stereotype, many famous bridges (or civil engineering structures in general), have become part of the cultural heritage of a place, and it could be argued that their symbolic function is equally as important as their practical one. The Golden Gate, Millau Viaduct, London’s Tower Bridge – all have become iconic symbols of a region or city. In Scotland, the Forth Bridge was recently awarded UNESCO World Heritage status. And of course anyone with an interest in Roman archaeology knows the importance of bridges as material culture. Newcastle itself was known as Pons Aelius (Hadrian’s Bridge) to the Romans! Archaeology is everywhere, even where you may least expect it.

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Bridges: iconic landmarks and heritage symbols (images from Wikipedia)


The many researchers of the GeoSatReSeArch Lab: high tech archaeology!

For the last year (and for the next three weeks), I have been working with a team of archaeologists and scientists from related disciplines at the Laboratory of Geophysical – Satellite Remote Sensing and Archaeo-environment (GeoSatReSeArch Lab), at the Institute for Mediterranean Studies, in Rethymno on Crete. The lab and the IMS are part of the Greek research foundation, FORTH. The IMS is the only FORTH centre which deals with the humanities and social sciences. The other Institutes based at Heraklion, Patras and Ioannina, cover the fields of computer science and the natural and biomedical sciences. The specific purpose of IMS is to support and invigorate research in the field of the human and social sciences, as well as to promote the application of advanced technologies in the field.

In that respect, the Lab conducts its own research,  but also participates in collaborations with the Ephorate (the Greek State Archaeology service), Universities, Foreign Schools and many others. A key aspect of our work is showcasing the potential of high-tech methodologies in archaeology, and we do a lot of teaching and outreach work alongside the frontline scientific research.

After a year working here, I thought it would be interesting to make my ‘Day of Archaeology’ post about the whole lab, not just me, to give you all an idea of the diversity of the work we do and the projects we are involved in.

Conducting Archaeological Geophysics:

Kelsey Lowe- PostDoc Researcher

Kelsey and her data

Kelsey and her data

“While fieldwork generally beckons most of us this time of year, or at least myself, I find that today I am sitting comfortably at my desk processing geophysical data from a Middle Bronze Age site in Cyprus. As part of my current position at IMS, having the chance to work along other Mediterranean experts has provided a very unique experience, especially in regards to archaeological and geophysical interpretation of Bronze Age landscapes. Oh look, what do we have here?!? Architecture! Happy Processing!”

Abir Jrad- PostDoc Researcher

Abir surveying, coring, and processing

Abir surveying, coring, and processing

“Hello, I am Abir, I am not an archaeologist, but a geophysicist who has the pleasure to work with archaeologists  searching for buried archaeological features using geophysical methods. Today I will continue the processing of the data acquired in the last field work on the archaeological site of Kenchreai, in Greece! We combined several geophysical methods to prospect the studied area. As usual the main method was the gradiometry with the Sensys instrument. The gradiometry and also the electromagnetic acquisition show an anomaly with high magnetic gradient intensity and also a high magnetic susceptibility. In the location of this potential archaeological anomaly, we did a hand coring, to collect samples on a vertical profile. The samples collected were analyzed using the Bartington susceptibility meter in the Lab, which allowed us to measure the magnetic susceptibility at different frequencies. The correlation between the field geophysical data and the laboratory analysis will allow me to realize a constraint modelling for the suspected anomaly!

Carmen Cuenca-Garcia – PostDoc Researcher

Figure 1: Carmen and her data!

Figure 1: Carmen and her data!

“Hi there, this is Carmen reporting from her desk on Day A (see photo). Figure 1 above encapsulates today’s work, which is… more reporting. In this case, I am writing up the results of analyses of soil samples collected at several Neolithic tell-sites (or magoulas as they are called here in Greece). Before the soil sampling sampling, we surveyed the magoulas using a range of geophysical techniques during several fieldwork campaigns and got fantastic results. We analysed the soil samples using magnetic susceptibility and phosphate analysis, then we correlated the results with those from the geophysical surveys. This type of integrated analysis is extremely interesting and informative for archaeological prospection but it also involves lots of intense work: dealing with many and diverse types of datasets, stats, cross referencing many graphs, tables… which may be a wee bit tough to deal with when you are in a celebratory mood like today ☺ Such analysis also require lots of collaborative work and I particularly enjoy the enthusiastic chats I have with my colleague Abir Jrad, who is working with me on the correlations. Part A in Figure 1 shows a view of how you would find me if you pop into my office right now and part B is where I would rather like to be… outside, fieldworking and enjoying the anticipation of tasting the delicious and well-deserved Thessalian food after a days work on the top of a magoula!”

Teaching and Training Activities:

Kayt Armstrong (me!) – PostDoc researcher

Interns Valanto and Aggeliki testing their RTK GPS skills on the IMS roof terrace

Interns Valanto and Aggeliki testing their RTK GPS skills on the IMS roof terrace

“My day-to-day job at the lab is as the GIS officer for a project looking at the dynamics of settlement on Crete in the Early Byzantine period (roughly the 4th-9th centuries AD). Part of the goals of that project are to further the use of GIS, aerial prospection and other high-tech methodologies in Greece. As a result, I have two interns working with me at the moment, from the Archaeology programme at the University of Crete. They are making important contributions to the project, and in exchange learning database skills, GIS methods and how to survey using the latest RTK GPS equipment. Today they are testing some user manuals I have made for the team, so that the amazing high tech kit can continue to be used after I have left in August. My job isn’t just to bring in these skills to the project, but to train local archaeologists, students and researchers in them, so that they are taken up more widely in the profession. Pay it forward!”

Developing Prospection Methods and Equipment:

Apostolos Sarris- lab Director, Ian Moffat – Post Doc Researcher and Beatrice Giuzio- engineering student intern

Drift testing the EM kit (on the beach!)

Drift testing the EM kit (on the beach!)

“We  spent the day testing electromagnetic induction (EMI) instruments on the beach near Episkopi on the north coast of Crete.  EMI is a geophysical technique that is frequently used in archaeology to measure the conductivity and magnetic susceptibility of the soil to find archaeological sites and map the geology that contains them.  Despite the usefulness of this method, recent research has shown that EMI instruments are prone to drifting, that is that their data values change during the course of a day even when sitting in the same location.  To determine if this drift exists for the EMI instruments used at IMS we set them up near the beach and collected data continuously in the same location for 7 hours while monitoring changes in temperature.  This experiment showed two clear findings: 1) that the adjacent taverna has excellent seafood dishes, and 2) that the EMI instruments drift in ways that are not correlated to temperature change.  These findings suggest that much more research to understand drift is required, particularly when using EMI to map archaeological sites that are difficult to map with this method, such as those without extensive metal in the subsurface.”

Aerial Prospection and Photogrammetry:

Gianluca Cantoro- PostDoc Researcher

Gianluca processing images from a flight earlier in the day

Gianluca processing images from a flight earlier in the day

“My name is Gianluca and I am an aerial archaeologist and photo-interpreter. My job consists in looking into photographic archives in search for aerial images where archaeological traces can be identified. In combination with historical photographs study, I also undertake aerial survey myself with Remotely Piloted Aerial Systems (RPAS or simply drones) or ultralight high-wing aircraft (usually something like a Cessna 172) over specific areas.

In the photo, I’m just back from one of these archaeological aerial surveys and I am sorting the pictures I took during the flight. You can see a map with notes I had in the plane, my ideal flight path and areas of interests, my pilot-flight kneeboards and my camera.

Once images have been synchronized with the GPS logger (so that each photograph holds the GPS location in the EXIF tags), they are entered in a digital database and then photogrammetrically processed, to obtain orthophotos and 3D models of the photographed areas (or potential “unknown” archaeological sites). A part of my work at the IMS I have developed software to make these tasks easier, which is free to use and downloadable here. ”

Augmented and Virtual Reality for Cultural Heritage:

Lemonia Argyriou- software engineer

Testing the Augmented Reality application

Testing the Augmented Reality application

“Working in Rethymno, Crete during summer … it’s  burning hot outside (34 degrees) and I’m finalising an Augmented Reality android educational app for Cultural Heritage.

At least things have become easier the last years after the release of the Unity3D, an extremely powerful and easy to use game platform. By the use also of AR APIs (such as Vuforia or Meteo), text, images and also small objects can be tracked and allow the triggering and presentation of 3D models along with 3D text and voice-over explanations. This leads to a more informative and immersive experience that could easily enhance the level of quality and edutainment in cultural heritage education.

The application I’m working on at the moment is accompanied by a printed map of Crete, displaying aerial photos of the most attractive ancient monuments on the island. By using an android mobile device and hovering over the location of a monument on the map, the relevant 3D model of the monument appears on the screen and can be observed from any side simply by moving closer or tilting the device. There is also a UI that allows the user to listen to the historical information of the specific monument in their preferred language (Greek or English), learning about their story of preservation and their role in the past.

That’s all by now…the beach is calling me 🙂 Day Of(f) Archaeology!”

Nikos Papadopoulos Jr – software engineer

Screenshot from the kinect navigation of the model of Koule Castle

Screenshot from the kinect navigation of the model of Koule Castle

“Hello there,  and many greetings from Rethymno, Crete. Although the day is suitable for going to the beach, I’m working in the lab developing a cultural heritage virtual navigation application for Koule Castle (Iraklion, Crete) based on natural human interaction. The specific application can capture simple user gestures, like steady walking or torso rotation and lean, with the use of a Microsoft Kinect sensor. The gestures are used for navigating in the virtual space of Koules castle offering the user a more immersive cultural experience. All of this this happens thanks to the Unity3D game platform and of course lots of coffee (sorry…programming). Time for some raki now :-)”

And lots more besides:

Quite a few of the scientists at the lab didn’t have time to write something today, or were off elsewhere doing fieldwork or attending meetings and workshops. Other ongoing activities at the lab include using near-surface geophysics to monitor pollution, complex systems and agent based models for historical and archaeological research, GIS classifications of landscapes in terms of geomorphology, risk-mapping, shallow marine geophysics, processing algorithms for GPR data…. I could go on!

I’ve had an amazing year here in Rethymno. I have learned so much, and hopefully I have given something back and passed on some skills to colleagues and students here. I’ll be keeping in touch with the lab team via their facebook page, and I hope to come back to use the huge archive of geophysical data they hold here for a project I am cooking up with my old Dutch colleagues 🙂

As it starts to cool down (a bit), I am going to shut down my computer and head for home, where I will spend what is left of the evening pouring over the other Day of Archaeology posts from around the world, and being very thankful I get to work in such an amazing community.

Happy Day of Archaeology!

Kayt x

Core blimey! Jason Stewart and the Sediment Core Samples

The best thing about working as a geoarchaeologist at MOLA is the variety; one day I could be watching a machine ripping through the odorous remains of a 19th century gas works, the next day could find me wrestling with the implications of a newly returned set of radiocarbon dates.

Today however finds me in the lab examining sediment cores retrieved from an evaluation. The site is in Dartford within the Thames estuary and has early prehistoric peat forming on top of the cold climate landsurface with various phases of being mudflat, marshland or flooded.

The cores are carefully laid out with the top of the borehole at one end of the lab and the base at the other. As there is 16m of sequence and the cores are 1.5m long and filled with heavy sediment this can take longer than you would think.  The cores are then methodically cleaned and the colour texture, inclusions and nature of the boundaries are recorded.  This detailed cleaning and logging allows me to think about the depositional environment of the site and the nature and rate of the changes that occur.

The next task is to select the locations from which to take samples, we take samples for radiocarbon dating, this enables us to places the changes in environment in some kind of chronological framework allowing us to compare the developments onsite with other work we have done in the surrounding area.  We also sample for things which will tell us about the environment in the past (usually pollen, diatoms, ostracods and plant remains).  These are carefully sliced from the core and sealed in labelled bags to be sent off to the various specialists.  The cores are then re-wrapped and returned to their climate controlled environment, the lab surfaces cleaned and the results typed up.

Jason Stewart

New Island Day Trip

20140709_151151Post by Dr Martin Bates. Geoarchaeologist. Ice Age Island Project.

My day saw geoarchaeological work on Jersey extended off-shore to Maître Île on Les Minquiers as well as continuing work at Les Varines where the excavation of a Late Pleistocene archaeological site is on-going. The visit to Maître Île was made thanks to the Fisheries department on Jersey and we travelled across on their patrol boat. Landfall was made through transfer to a RIB and a fast journey across the sound.

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IMG_1545I was accompanied by a botanist and entomologist and all three of us were grateful to be back on terra firma as the journey across was not perhaps the most pleasant with a large swell running throughout the 1hr transit.
Once on Maître Île we were able to examine the island and a large patch of eroding Neolithic organic soil was recorded and sampled.

A number of flint flakes were found and a piece of pottery (probably of Iron Age date) was also recovered. Augering at three locations confirmed the stratigraphy reported by previous excavators and the chance was taken to recover the first samples from the island for pollen analysis. We returned to Jersey rather more rapidly than we went out satisfied with a good days work.
The remaining work has focused on augering at Les Varines where we are attempting to understand the geology of the slopes where archaeological material has been under excavation for the last 4 years. Our geophysical data gathered in previous years and in May of this year is now making more sense and auger holes are allowing us to begin to understand the distribution of the main sediment bodies. We can now think the possible origin of the flintwork and where we might locate our excavations next year.

Paisley Caves – a view from the microscope

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Working on the microscope

So this is my second year taking part in the Day of Archaeology. It’s great to look back at my post from last year, when I was working as a research associate on the Feeding Stonehenge project – lots of new things have happened since then, including a new position for me as a research fellow at the University of Edinburgh. Since joining Edinburgh I’ve been working on a lot of new and exciting projects, which you can read more about in my blog, Castles and Coprolites. This week I’ve mostly been sat in front of a microscope, analysing thin section samples from the site of Paisley Caves, Oregon USA, directed by Dr Dennis Jenkins. Paisley provides evidence for the earliest dated human occupation in North America, famously in the form of ancient human DNA recovered from coprolites, aka fossilised faeces. The samples I am working on are known as thin section micromorphology samples – perhaps not as well known as animal bones and charred plant remains, thin section samples investigate the actual sediments in which archaeological materials are found.

The way in which sediments are deposited can actually tell us a great deal about the environment and human activity in the past, and are also useful in helping interpret the artefacts that are found within the sediment. For example looking at soils and sediments under the microscope, we can tell whether they were deposited by wind or water action, or whether they were trampled by humans or animals. With the Paisley samples we are looking at the formation processes in the cave environment, to see whether this can help understand the activities that were occuring in the cave.

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Thin section slide of sediments from Paisley caves. Photo by Julie Boreham, Earthslides.com

Thin section micromorphology is quite a specialised technique, and requires laboratory processing. We cut out blocks of sediment from profiles during excavation, wrap them very carefully to avoid any disturbance, then take them to the lab where they are set in resin and cut into slides for viewing under the microscope. I have been working with Earthslides to process the Paisley samples, and we will be presenting a poster exhibiton of the thin sections at the European Association of Archaeologists conference this September.

Virgil Yendell: Geoarchaeologist and his lovely sediments

Here are some shots of a trial pit under a former pub in Victoria. The lovely sediments from the base show c. 10,000 yr old fluvial gravels over lain by sandy deposits of a substantial tributary of the Thames, possibly the Tyburn, running through Victoria. During the prehistoric this river appears to have silted up and a waterlogged woodland is evident from the brown peaty deposits, which later developed into possible clayey water meadows that would have been used for pasture during the historic period.