I am a geoarchaeologist and Marie Skłodowska-Curie Global Fellow at the University of York, UK, currently seconded to Macquarie University, Australia. I use geoarchaeological methods from the site to the landscape scale to reconstruct past environments and landscapes, particularly in the Palaeolithic of the Saharo-Arabian belt.

Coastal (Geo)Archaeology on my Mind

Human occupation and coastlines have a long, but not very well-understood history. Global sea level has fallen and subsequently risen by over 120m during the last glacial cycle (~132,000 years), driven by fluctuations of the masses of ice sheets. These changing coastal landscapes have produced, or take away, opportunities for humans to exploit the resources they offer. In early prehistory, the use of coastal resources has been argued to have facilitated the dispersal of hominins out of Africa and across the globe and/or aided the development of fully modern human brains and behaviours, as well as providing resources to support specialised, marine-focussed ways of life in later prehistory. Coastal archaeology is therefore at the forefront of some of archaeology’s ‘Big Questions’. Yet it’s not just about understanding the past – studies of past sea level change, and the location and survey of ‘benchmarks’ left by these sea levels, helps us to better predict how, in a world of rising seas, the hundreds of millions of people who live along coastlines will be impacted in the coming decades.

The Greek Islands. Someone has to work there… Photo: R. Inglis.

My month has been decidedly more coastal than usual in theme, and not just because I’m pining after my recent holiday in Western Australia. Working backwards from today, this week I have been analysing sediments from excavations at a Neanderthal cave site on one of the Ionian Islands, Greece. During periods of low sea level, the area around the island would have been very different, with lagoons and wetlands and all the marine resources they would have contained in the area now covered by sea. Investigations on land and underwater are being carried out in order to understand more about how the landscape changed over time, and how this affected the humans and Neanderthals who left archaeology within it.

After a week making thin sections of some of the sediments (#TBT my 2016 DoA post on how and why to make thin sections), I’ve been running particle size analysis on the sediments from the cave in order to learn more about how these sediments got to where they did, and how these site formation processes impacted the archaeology within them. Of course, things are never straightforward, and getting the stony clay samples sieved and prepared for analysis was about as pleasant as excavating through them had been, involving wet sieving, muck, and ovens – I may even have to change tack and restart the whole thing. So to be honest, I’m not in the mood to talk more about them just yet…thank goodness it’s Friday!

Sediments on their way to becoming the worst brownies ever baked – in the oven overnight at 110ºC. Photo: R. Inglis.

The Mastersizer in motion! The particle size distribution curve, showing the number of particles in each size class can be see on the graph on the screen. Photo: R. Inglis.

Also in the batch were more straightforward sandy samples (though obviously not THAT straightforward, this is applied science…) from southwest Saudi Arabia, the study area for my current project, SURFACE. With these sediments, taken from a fossil beach and dune complex that formed during a period of higher sea level (Dhahaban Quarry – learn more here), I was using Particle Size Analysis (PSA) to distinguish between shallow marine sediments and the windblown dune sediments – the transition from one to the other would mark the highest point of past sea level, thus providing a sea level ‘benchmark’. It worked after a fashion – the aeolian sediments appear to be ‘well-sorted’ e.g. all one size class, what you’d expect from a dune, and the muddy lagoonal sediments were, well, a muddy mix of all particle sizes. Still more work to be done, but it’s encouraging!

Shallow marine sediments at Dhahaban Quarry, now approximately 5m above sea level. The holes are for samples taken for optically stimulated luminescence (OSL) dating. Photo: R. Inglis.

Away from the lab, and the muck, and the clay (which actually maybe predominantly fine silt – who knew!), coasts still dominate my to-do list. I’m wrestling with reviewer revisions on a book chapter presenting the field survey of the coral and marine terraces that are along the coastline of the volcanic Harrat Al Birk, SW Saudi Arabia, including the Dhahaban Quarry site, which we undertook in December 2014. Through this detailed survey of the marine terraces, and future dating of the corals that are found within them, we will learn more about the position of the past coastline that created them. This has geological implications for understanding the opening of the Red Sea Rift, (which is pushing its western and eastern coastlines up and out), helps us to place the archaeology we find on land in its relationship to the sea and potential use of coastal resources, and is another data point to underpin future sea level predictions.

The final piece of coastal news this week is the publication, after a looong process, of a paper by the MEDFLOOD community, which takes a long-term view of sea level change and human occupation and use of coastal regions in the Mediterranean (the last 132,000 years). It’s chock-full of methodological data on measuring sea level, evidence for the use of coastal resources by Neanderthals and humans up to the historic period, and areas in which new research, both underwater and on land, needs to be undertaken. A superb effort to bring together this diverse group of researchers with different approaches.

MEDFLOOD meetings are always held in challenging locations, such as the Northern Adriatic, close to Venice. Photo: R. Inglis.

So there you have it. From very challenging lab work to writing to that sweet feeling of seeing a paper finally published, almost the full cycle of coastal research. I’ll wind up this post by wishing you a happy Day of Archaeology 2017, and leave you with this thought from Coastal Archaeologist extraordinaire Prof. Geoff Bailey (tweeted to the world by MEDFLOOD’s Dr Alessio Rovere):

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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.