Castles and Coprolites

Close-ups of decaying waterlogged wood. Upper left showing 1. latewood with secondary cell wall intact 2. earlywood with loss of secondary cell wall. Upper right showing loss of birefringence in areas subject to decay Another fab example of the sorts of things that go on in medieval waterlogged deposits. I posted some pictures of this waterlogged wood a couple of months ago, as well as a nice example of the formation of vivianite in the same deposits . Here we have another example of waterlogged wood, but I've added some close-ups in cross polarised light (XPL). For the non geoarchaeologists in the audience, this is a technique in microscopy where you change the type of light you use to look at a sample, by inserting polarisers on the microscope. Polarised light vibrates only in one direction. On the geological microscope, the lower polariser causes the light to vibrate in an E-W direction, whilst the upper polariser/analyser filters light that is not vibrating in the N-S d...

This month we have a lovely image of a particularly colourful mineral feature called vivianite. Vivianite is an amorphous hydrated ferrous (iron) phosphate, which is blue when oxidised. It has been linked to the decomposition of bone and/or human and animal waste in wet sediments, which fits with what we know about this context. Yes, we are still looking at those waterlogged deposits from medieval Riga ! This is just one example of the many occurrences of vivianite in this layer. The small fragment of wood is also interesting. Unlike the waterlogged wood we looked at a couple of months ago , this fragment has been completely mineralised due to the presence of phosphate in the waterlogged sediment - at first glance I thought it was a bit of bone! You can also see that the pores spaces within the wood have been completely filled with fine sediments, which also indicates waterlogged conditions - the infilling of the voids occurs as fine sediments suspended in water are deposited within...

Here are two examples of waterlogged wood, in deposits from Medieval Riga, currently being analysed as part of the Ecology of Crusading project. It's been almost a year since I started on these slides, which were prepared in December last year - there are so many of them it is taking me quite a while to get through. It's a fascinating set of samples, such a mix of materials with some interesting post-depostional processes going on. In the upper image you can see a fragment of wood preserved entirely through waterlogging, within a mixed deposit containing charred material. This little fragment of wood has been stained orange, which is typical of waterlogging and mineralisation. In the lower image you can see a fragment of wood which has been preserved through a mix of partial burning (as seen by the black colour in the lower part of the wood), whilst the non-charred part has been preserved through waterlogging. Waterlogged deposits are relatively rare - most plant material ...