Monday, 10 June 2013

Micrograph of the Month: Different views of dung ash

I seem to post quite a lot about ash. As an archaeological ecofact, it is often overlooked, but can provide a wealth of information on fuel use, both through the shape and form of the ash crystals, and the microscopic materials contained within it. This month's set of micrographs shows different views of another ashy deposit from Catalhoyuk (from a midden in the 4040 Area), this time we have a pseudomorph of an animal dung pellet that has been transformed into ash from burning. In photo C you can see the pellet (labelled 1) overlying another mixed dark brown ashy deposit (labelled 2). Photo A shows a magnified area of the pellet, with the arrows pointing to phytolith inclusions embedded within the pellet. Photo B shows the same photo under cross polarised light, where you can see the calcaerous spherulites that are distinctive of certain animal dung deposits. In photo D you can see a well preserved conjoined phytolith that was extracted from the dung pellet. This series of photos demonstrates a number of things - firstly, we can see that this activity involves a mix of dung and non-dung ash (i.e. mixed fuel type), secondly we can see that some phytoliths are contained within animal dung (i.e. they were ingested by the animal) whereas others are contained within the ash matrix, thirdly we can see that phytoliths in thin section can be difficult to identify as they can be obscured by the surrounding matrix. This is a good example of why it is important to combine thin section micromorphology with analysis of extracted phytoliths. Without the micromorphology it would be impossible to distinguish between phytoliths from the animal dung pellet and those which are coming from the surrounding deposit, and without conducting analysis of extracted phytoliths it would be very difficult to identify the plant types or to conduct quantitative analysis of the different proportions of plant types.

A: Dung ash showing embedded phytoliths B: Same view as A in XPL, showing calcaerous sperhulites C: Dung ash at lower magnification showing shape of pellet (1) and relationship with underlying layer (2) (note phytoliths in lower layer also) D: Stem phytolith extracted from the dung pellet showing well preserved hair cells