Monday, 28 April 2014

Animal dung and the beginnings of sheep domestication in the Near East?

There's an exciting paper out today in PNAS on Aşıklı Höyük, an early sedentary pre-pottery Neolithic site in central Anatolia, occupied a millennia earlier than that site oft discussed on this blog, Çatalhöyük. This paper by Stiner et al. is a great example of research that brings together work from different archaeological specialists to produce a coherent story, supported by multiple lines of evidence. The argument is based around the zooarchaeological analysis of animal remains, which demonstrates a shift over the occupation of the site from a broad spectrum of wild species, to a dominance of sheep by 8200 cal BC. However it is the geoarchaeological analysis that arguably provides direct evidence of deliberate animal management, and as a micromorphologist with a special interest in all things coprolite and dung related, I am very happy to see that this technique is one of the highlights of the paper! (Phytoliths also get a mention!).

The researchers identify accumulations of animal dung deposits within enclosed spaces using micromorphology, and suggest that animals were held captive in these areas. Just to play devil's advocate (and because I promised I'd do more critiques) let's have a look at those deposits in a bit more detail. On closer examination it is unclear whether they are really 'stabling' or just the sporadic presence of dung.  I suspect the use of this noun may be overstating things a bit. The researchers identify what are described as primary dung accumulations between the structures, on the basis that they are micro-laminated and inter-bedded (this means that they formed thin horizontal layers with other material in between the dung layers).

On reading the micromorphology descriptions we see that these areas between the structures are midden (according to the caption in Figure S3, image F) and an open area (Space 1, 7 and 13 according to Table S.8), and there is also dung identified in a post mold. The earlier dung deposits of level 4 appear to be sporadic and thin. It is not until the transition of level 4/3 (4/3C?) that we see the multiple thick layers with a significant lateral extent that could suggest 'stabling'. This makes sense. It would not be until animals were kept in larger numbers that we would expect to see 'stabling'. But then the latest deposits (3E/3D) go back to being a bit ambiguous. A burnt dung layer from the later level 3E/3D is suggested as being evidence that a midden area was being used to keep livestock. This clarifies the problem with 'midden' as a space/deposit category! And it is also quite possible that this simply represents an accumulation of dung on the midden surface that was used as fuel for some sort of in situ burning activity, as is seen frequently at Çatalhöyük (e.g. Shillito et al. 2011).

Interestingly the deposits described from level 3E/3D (can't find the specific date for this level) sound incredibly similar to those seen at Çatalhöyük, where we also have trampled dung and occasional in situ burning of dung in place, albeit at a later date, in an area that was once 'midden' but then shifted to being a 'street like' deposit with frequent fire spots (Shillito and Ryan 2013). Alas it is difficult to assess whether these areas are truly similar without seeing the area in detail, and the only photos in the paper are not a high enough resolution. Also, check out the depth of that trench (Fig S3, A)!!

EDIT - paper preview image removed 19 April 2016 as it was doing weird things to the blog layout

Wednesday, 23 April 2014

Geoarchaeological surveying in Powell Butte, OR

Deschutes National Forest
April is not usually this busy but I've been away for almost 2 weeks visiting family in Oregon, hence the lack of updates. Prior to that I had a mad week of coursework marking, and now upon returning there's a stack of exam marking in my near future. Do not despair however, exciting micrographs are ready to be posted for May, and to make up for the lack of posting in April, here are some lovely images from hiking in central Oregon.

Sorted sediments on meander beach
Although it was technically a holiday, I can never resist having a bit of a dig, and spent a lovely afternoon test pitting around the in-laws property in Powell Butte (Crook County). It's hard to break the habit of staring at the ground looking for finds whilst taking a stroll, and last year we found a single fragment of worked obsidian, so this year we decided to start a survey. Nothing archaeological in the test pits alas, but we hope to extend the survey gradually every time that we go back! Being the geo geek that I am, I got a little obsessed with the soil profile, and found this amazing soil resource for the US: 

It's an interactive GIS that lets you view soil (and other data) for anywhere in the US! So I managed to find our survey area and check my field descriptions against the official records. We are located on what is called the Ayresbutte-Ayres complex, which is an alluvial fan with a parent material of ash and alluvium from volcanic rock with a duripan. A duripan is a term used in US soil classification to describe a soil horizon cemented by illuvial silica. The silica has been displaced through the profile by rainwater, forming a very hard B horizon not too far below the surface.

The typical profile consists of a sandy loam that becomes increasingly gravelly and cobbly before turning into cemented material. Which brings us on to the point of this post - I am developing some new practical classes on soil and sediment analysis, and I need samples of different types and textures for lab testing. I have a few different examples but it would be great to have a wider variety, especially different types of clays. So, do you live near any exciting sediment types? Would you be willing to send me a sample bag of it? If so, send me an email!

Map showing soils in the Powell Butte area 

Tuesday, 1 April 2014

Micrograph of the Month: Foram with a Calcite Hypocoating

This month we have some micrographs from floor deposits in the refectory at Margat Castle, Syria. Here we have a fragment of lime, within which is embedded a lovely little foraminifera. Forams are tiny little marine creatures which have calcium carbonate shells, and when they die they form part of the fine sediment which is deposited on the sea floor. This in turn becomes sedimentary rock, and that's the origin of this tiny fragment of limestone.
In XPL we can see that the void space inside the foram has a coating of highly birefringent (sparkly) material. These are tiny little calcite crystals. Calcite hypocoatings can result from several processes, but in this case it is likely the result of carbonate rich water percolating through pores in the sediment. Similar coatings can be seen in other voids in this layer. When the water evaporates the carbonate precipitates on the walls of the voids. A bit like the layers of lime-scale that form on taps and kettles if you live somewhere with 'hard' (i.e. calcium rich) water.