Monday, 30 November 2015

Microfossil of the Month: Discus diatoms

Almost forgot to post a microfossil for November! That would be sad as I've managed to do the monthly micrograph then microfossil posts every month for almost two years now. I've just been so busy with teaching, and the lack of microscope camera makes taking pictures a bit more of an effort than it used to be. Good news is that we do have a new set of microscopes and cameras for the archaeology lab here at Newcastle, hurray! The lab however is located in a different building to my office, so photograph acquisition still requires a bit more planning than it used to. As it is almost the end of 2015 (yikes), I am thinking of a new monthly blog feature, perhaps a thin section of the month, where I show you exciting pictures of whole thin section slides!

But for now, here is something very pretty. Like the sponge spicules I posted earlier in the year, these little creatures are not my specific area of expertise, but they occasionally show up in my phytolith slides. They are little unicellular organisms that produce beautiful silica cell walls (or 'frustules') in all shapes and sizes. They are used in palaeoecological studies to look at things like changing water acidity, as they are very sensitive to local changes in the environment, and work well alongside other techniques such as pollen analysis. There have been very limited applications of diatom analysis in archaeology. The only purely archaeological case study I could find was in Antiquity journal - a study to determine the cause of death of a Neolithic child discovered in a well in Sweden. The diatoms recovered from the well and skeleton enabled the archaeologists to reconstruct the water conditions, and also to determine that the child was alive when they entered the water, as diatoms were recovered from inside the bone marrow. The study screamed 'taphonomy' at me, as it is unclear how the diatoms enter the bone marrow. But apparently the method is used in modern forensic cases, and diatoms in bone marrow are an 'accepted' sign of drowning - diatoms enter the lungs in water during drowning and are deposited around the body from blood circulation. My very brief review of the literature indicates that it is not entirely accepted in the forensic community, and that diatoms are also found in non-drowned cases. Pesky taphonomy.

Anyways, this image is from my diatom test plate - a set of 25 reference specimens. The close up is of Arachnoidiscus ehranbergi (left) and Coscinodiscus oculus iridis (right). What wonderful names, presumably from the Greek for spider and sieve respectively, and Latin discus, and both named by Christian Gottfried Ehrenberg in the 1800s. I chose these two to zoom in on as they remind me a bit of Xmas baubles, and I'm feeling a bit festive.


Tuesday, 17 November 2015

Call for Papers: European Geosciences Union General Assembly 2016, Geoarchaeology session

I am pleased to announce a session I am co-organizing at the EGU 2016, Geoarchaeology: Human adaptation to landscape changes, landscape resilience to human impact, and integrating palaeoenvironmental and archaeological records (GM6.2/SSS3.10), supported by the International Working Group on Geoarchaeology. If you are an archaeologist who has never been to a EGU I would highly recommend it - it gives you an important insight into work going on in the geoscience community, much of which is relevant to themes archaeologists are interested in. I first attended in 2010 (being lucky enough to be awarded an early career grant - see below), and I remember being very impressed my projects integrating historic documentary sources with climate data for example, in looking at human responses to environmental change, and if you are into isotopes, you are very likely to find the latest in cutting edge methods coming from the geoscience community. Likewise environmental archaeologists, come and learn about the new proxy methods that people are using for lake core analysis!

Our session is broadly geoarchaeology, with a focus on multidisciplinary approaches, integrating multiple datasets, and promoting a greater degree of interaction between archaeology and geosciences. So basically everything that I go on about in my blog all the time. Our keynote speaker is Professor Jamie Woodward, editor of Geoarchaeology journal and author of the popular The Ice Age: A Very Short Introduction. We are now accepting abstracts, which are open until January 13th 2016. However if you are an early career researcher (undergrad, postgrad or postdoc) and want to apply for financial support, you need to get your abstract in by December 1st. Any questions get in touch!

Sunday, 8 November 2015

AEA conference 2015 - some thoughts on taphonomy, equifinality, and multi-proxy approaches

This weekend I went to my first AEA conference. As a student, then as a fixed term post-doc, it is difficult to fund conference attendance, and also to find the time when there are so many conferences to choose from. Having done a few years of the big conferences (SAA and EAA) to maximise audience and networking opportunities, I’ve decided to spend some time at the smaller ones, where I can focus on my specific interests. Overall it has been an enjoyable weekend, and it was great to be back in York and catch up with old friends and colleagues, including Matthew Collins, who I can’t thank enough for writing me many references over these past few years (I bet he’s relieved that I finally got a job so he can stop writing them!).

There are three ‘themes’ that stood out for me at the conference. The first was the study of taphonomy, and how wildly different this is between different techniques in environmental archaeology. The second was the recognition of the advantages of integrating methods, approaches, lines of evidence, whether this be through the use of multiple environmental proxies, or using archaeological alongside historical evidence. The third was the social media side of things – a relatively highly tweeted conference, there was some discussion over the etiquette of live tweeting. My thoughts on the first two feature here, the latter I will write about in a different post.

A little bit of background for the unfamiliar, taphonomy is the word we use to describe the processes that have had an impact on the archaeological record. What has caused the patterns that we see? It is not a straightforward process of counting bones or plants, we have to consider things like preservation – how much has been eroded away? Have some materials preserved better than others? Has material been physically altered in some way? All of these things ‘blur’ the human activity signal that we are trying to ‘read’ from the archaeological record.

I was happy to see the glamorous world of dung analysis featuring on several occasions, the first of which was a paper by Don O Meara, in which he conducted his very own taphonomic experiments on the impacts of the human digestive system on the preservation of various botanical remains. I will spare you the methodological details (it’s exactly what you think). The results were very interesting. He showed that the survival of seeds within the digestive system is incredibly variable, with some species not surviving at all, whilst others preserved differently depending on the extent to which they are chewed etc. The most notable result was the lack of standardisation with such processes, the lack of consistency in the patterns, making it difficult to apply these experiments to archaeology in general. This contrasts heavily with zooarchaeology, where these sorts of experiments can produce repeatable results and patterns which can then be identified in archaeological material.
Unsurprisingly this got me thinking about phytolith taphonomy. Taphonomic studies seem to be taken much more seriously in other specialist areas, perhaps because it is possible to do repeatable studies and get meaningful consistent data? O Meara made the distinction between biostratinomy and diagenesis i.e. some material never even enters the archaeological record, whilst other material is modified after it enters the record. Both aspects of taphonomy influence the archaeological assemblage in different ways. With phytoliths we have the added problem that, unlike seeds, we really don’t have a clear idea of the variability in production between different plants, and the wide range of environmental and other factors that influence this. If a seed were studied as phytloliths, one seed would equal thousands of phytoliths – how then do we say anything meaningful with a sample set that could represent a fraction of a single plant? On a more positive note, O Meara also suggested that taphonomy is not simply destructive, but we can think of it as adding a layer of information.

The second ‘dung’ themed paper was by Eline van Asperen, who studies dung fungal spores as a proxy for past herbivore abundance. The potential of dung spores as a proxy is as an indicator of openness in the landscape. This is something that is difficult to achieve with pollen studies, which can give you an idea of vegetation composition, but not the ‘pattern’ of that vegetation within a landscape. Again the question of taphonomy was raised, and I was very impressed by van Asperen’s systematic experimental work, and the willingness to admit that interpretation of fossil data can be very problematic. As one example, spore abundance is assumed to correlate with herbivore abundance, but her studies showed that spores can actually show up, in large numbers, in areas that animals have not had access to. This is despite the fact that spores only travel c. 50cm. Something else which is directly relevant to phytolith studies was the impact of processing methods on the spore asssemblage. Spores have often been extracted alongside pollen, but she showed that this can alter the morphology of the spores to the extent that thy cannot be identified, whilst some types do not survive the process at all. Of great concern when you are looking at ratios of different fossil types, and when you are using (often subtle) morphological features to identify the genus or species. I look forward to reading more about her experiments, which are looking at the depositional pathways of the spores. Something else that really needs to be done for phytoliths.

Another paper I liked on Saturday was by Emily Johnson. It was a zooarchaeology paper looking at different types of bone fractures, but reminded me of the work we did on the Feeding Stonehenge project. There were a number of points I thought were interesting, and were lessons for the wider subject beyond animal bones. The first was to do with the way that we measure and present data, and the influence this can have on the interpretations we make. For me it also highlighted how essential it is for other studies, such as pottery lipid analysis, to integrate evidence to get a better picture of what was going on in the past. With the Stonehenge data, we know about the volume of animals and butchery through the zooarchaeology, whilst pottery lipids tell us more about how the animals were used and processed for a specific activity. Likewise with Johnson’s study, I wondered about the lipid signal for grease processing in pots, could this be distinguished from other types of fat from the same animal? Also the question of spatial distribution – often in pottery residue studies, a sample of pots is taken from a site, and considered as a single category. Both the Stonehenge study and Johnson show that specific context is hugely important - different activities are occurring, and associated waste is being deposited, in different locations. If we don’t consider the spatial dimension, we are only seeing a fraction (of a fraction) of the overall picture.
Another paper I really enjoyed was by Suzi Richer. From an archaeobotanical perspective, she questioned the way that commercial archaeology often puts forward one interpretation as objective fact when producing an environmental report, when there may be multiple possible interpretations. I don’t think this is a problem just in the commercial world, we see it all the time in academic archaeology as well. Suzi asks what is constraining us? Are we afraid to admit we don’t have an objective, definite explanation for what we see? In the commercial sector, will other stakeholders (such as engineers) not take archaeology seriously if it doesn’t say something definitive? In academia, why are we worried that admitting there may be more than one way to interpret the data? Do we choose the interpretation we like the best, or that is more exciting? I agree hold heartedly with her final point, that by integrating multiple lines of evidence we can help reduce the problem of equifinality.
This leads on nicely to the geoarchaeology papers. I think geoarchaeology is inherently multi-proxy, as it covers such a wide range of methods, compared to archaeobotany and zooarchaeology. So does this help narrow down the interpretations? The geoarchaeology papers variously combined micromorphology, phytolith analysis, geochemistry (µXRF, pXRF, ICP-AES). The first, which was commendable in its attempt to integrate geoarchaeology data with spatial patterning of lithics, was Charlotte Rowley (et al)’s study of Flixton Island. However I did have some concerns. The approach reminded me of my own PhD, where I spent the best part of my first year doing a similar ‘look and see’ geochemistry on sediment samples. It turned out that the (mountains of) data didn’t show much of interest, and/or there were so many possible explanations for the data as to make it of little use. This is a real problem with spatial geochemistry studies, discussed recently in a review by Matthew Canti and Dirk Huisman.
Barbora Wouters presented a range of examples from towns in medieval northern Europe, highlighting how integrating multiple methods can provide a better explanation of processes. As this has been my own methodological approach I am very keen to see that there are others working on this area. Overcoming (some) of the problems of phytolith taphonomy, but at the same time showing the daunting complexity. The µXRF showed the huge variation that you can get in geochemical data over a small area. If this is what we are seeing when we focus on specific points, what are we missing when we measure bulk samples? An averaged signal from hundreds of activities, a chemical palimpsest?
Hayley McParland’s study on phytoliths and macrobotanics at Songo Mnara looked for activity areas in different parts of the site. It offered some tantalising hints of the variety of plant use, and it is great to see the whole range of plant remains being analysed simultaneously across a site. As with other phytolith studies, I feel we are still unsure of the complexities of depositional pathways and whether we are seeing a direct activity indicator or something else? The more phytoliths I see from different environments, the more I realise that preservation at Çatalhöyük is highly unusual. To me this is an example of where taphonomy can be seen to be adding information – if phytoliths are degraded and worn, what is that telling us about the processes? At Çatalhöyük we only ever see phytoliths like this where they have been deposited in exposed external areas and have become highly trampled and weathered. Is there a difference in degradation index between different areas – external versus internal space?
Lots to think about! Hence the tl;dr post - thanks if you made it this far :)

Friday, 6 November 2015

Pollen for Archaeologists

The past few weeks have been pollen themed. Teaching pollen for Environmental Archaeology, and a new paper out on pollen analysis (and geoarchaeology) at Radzyń Chełminski in Poland. The latter is from my time working on the Ecology of Crusading project, and is a nice case study in using multi-proxy approaches, including historical documentary sources, to investigate landscape change. Pollen analysis is not my area of research expertise, but I have spent a long time working with pollen data. As a geography undergraduate I had several pollen classes for modules in Quaternary Environments and Biogeography, and it also featured heavily in my MSc Geoarchaeology. Pollen analysis does what it says on the tin - we extract pollen grains from sequential layers in sediment cores, and count them to see how vegetation has changed over time. If we have a sediment layer dated to 1000 years ago that is full of oak pollen for example, we can reasonably assume that there was an oak woodland somewhere in the region 1000 years ago, even if the landscape today looks quite different. Of course interpretation is complicated by a variety of factors, including differential production and dispersal of pollen in different species. Pollen analysis is sometimes referred to as palynology, from the Greek paluno (sprinkle) and logy 'study', but technically this refers to more than just pollen, and includes a wide variety of palynomorphs such as spores, dinoflagellates and algae. Palynology  doesn't however include my own favorite microfossils, the phytoliths, which are biological 'casts' of plant tissues.

Pollen is one of those techniques that I feel is under appreciated - all archaeologists should be aware of how pollen analysis works, as it forms the basis of vast majority of environmental reconstructions, which are central to our understanding of questions such as the development of agriculture, patterns of migration, to anthropogenic landscape change. It is for these reasons that pollen analysis is one of the key 'practical' techniques that I focus on in my Environmental Archaeology teaching. In the past I have focused largely on working with reference material, being able to identify key genera/species, and how pollen keys work. However whilst designing a new module at Newcastle, specifically for students without a background in sciences, I wanted to go beyond this and focus on the experience of working with archaeological samples, which I think is a better way of demonstrating some of the problems and limitations of the technique. But what to do without a good set of 'easy' archaeological slides to work with? I came across a great solution developed by Prof Christopher Hill at Boise State University, Idaho - create your own 'virtual' pollen slides! It's a pretty simple idea - using pictures of pollen grains you can create an 'assemblage' on a PowerPoint slide, provide a reference key for expected species, and students can go through the process of counting, data interpretation and presentation. It worked really well, and can easily be scaled for larger class sizes. I'm hoping to develop a similar exercise for phytoliths!