Condition of the archaeological deposits

Laboratory methods

Samples were stored under the best available conditions (in a cool, dark shed); it was not possible to store such a large volume of material in a temperature-controlled cold store, which would have been preferable. The tubs were opened and sediment descriptions made using a pro forma in October-December 1995, at which time 250g subsamples were processed to extract plant and invertebrate macrofossils for an assessment of their preservational condition. Blocks of coherent sediment were taken from three samples for the preparation of thin sections; it is hoped that information from these will be available in due course.

The field descriptions of the cores were supplemented in the laboratory when the samples were inspected and segments selected for processing and assessment of preservation. Subsamples for assessment of macrofossil preservation were processed using techniques described by Kenward et al. (1980), as modified by Kenward et al. (1986), but without the use of sodium carbonate (which might have further affected the condition of the already somewhat decayed remains).

Prior to this project, the preservation of 'waterlogged' plant remains was recorded only informally in the EAU. Preservation of insect remains had been recorded using two parameters: (a) 'erosion', i.e. supposed post-depositional chemical changes bringing about changes in appearance; and (b) 'fragmentation', i.e. an approximate measure of the degree of breakage of individual sclerites (skeletal plates). For both of these parameters, a scale of 1 (very good preservation) to 5 (very poor preservation) was employed.

More precise recording of preservation was clearly paramount for the present project, and considerable efforts were made to design methods which were objective, covered a wide range of characteristics, and were easy to implement. For the plant remains, this was surprisingly difficult: plant remains preserved by waterlogging do not consist of a single kind of material and represent a wide range of parts - fragments of woody and herbaceous organs, discrete items such as fruits and seeds, and whole or nearly whole organisms such as moss gametophytes ('shoots'). All of these have very different colours, textures and degrees of opacity, as well as different inherent rates of decay under any given preservational regime. In addition, plant remains will have undergone a very variable degree of pre-burial change, whether through natural decay or utilisation by people. For these reasons it was found impracticable to institute a detailed recording scheme for preservation such as that adopted for the insect remains, and a system of scoring as shown in Table 4 was used. The focus of recording was on a somewhat subjective three-point scale from excellent to very poor, with the use of two intermediate points, making a scale of five points in total. Scores were made for a variety of plant-derived components, and charred and mineralised material was recorded, as well as 'waterlogged'.

For the insects, the recording scheme could be somewhat more objective, and had the advantage that most insect remains have a fairly similar chemistry and degree of resistance to decay, as well as showing essentially similar responses to conditions in sediments. The scales previously used for erosion and fragmentation have been modified by adding intermediates and values above and below the former ones, giving a scale from 0.5 to 5.5. Degree of fragmentation of individual sclerite types (heads, elytra, etc.) is recorded where possible, and a record made of the proportions of each assemblage showing particular degrees of erosion and fragmentation where these are not consistent. Colour change is estimated in terms of direction ('towards brown', etc.) and degree. A series of other characteristics such as rolling, cracking, pitting and linear tracking, are recorded or estimated.

For the eggs of intestinal parasites the characteristics recorded are colour change, the loss of polar plugs and decay of the egg walls (for trichurids and capillarids) and, if appropriate, collapse.

The plant remains from the 250g subsamples were characterised by examination of a proportion of the residue, a record of the major components being made together with notes on interpretatively important remains. For the plants and insects, additional subsamples of 2kg from selected samples were processed in order to provide useful numbers of remains, which were semi-quantitatively scan-recorded (sensu Kenward 1992 for the insects).

Microfossils (diatoms, pollen and spores, phytoliths, and eggs of parasitic nematodes) were examined by means of 'squashes' (sensu Dainton 1992) but quality of preservation could only be assessed practicably for Trichuris eggs. The preservation of phytoliths and diatoms, both siliceous, is unlikely to be visibly affected by the processes apparently at work in the present deposits, and the numbers of pollen grains and spores observable using squashes were generally small. Squashes which gave one or a few Trichuris eggs were replicated in an attempt to provide sufficient numbers to represent the population.

The water and organic content of the sampled material were estimated using oven drying at 40°C to constant weight followed by loss-on-ignition at 850°C for at least 2 hours. In addition, pH was measured for a ~20g subsample dispersed in ~100 ml of deionised water, using an electronic pH meter.

Chemical analysis of the white 'efflorescence' infilling voids was carried out by the Department of Chemistry, University of York, using infra-red spectroscopy.


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