Condition of the archaeological deposits

Water content, pH and loss-on-ignition

Data for water content, pH and loss-on-ignition are presented in Table 10. The water content clearly increased with depth, although values were widely scattered. If the succession is divided at its midpoint (approx. 13.0m OD), the values for deposits above and below are as shown in Table 11. The values for pH were very scattered and the values in the upper and lower halves of the succession scattered to about the same extent about an identical mean (Table 12). Those for organic content were fairly scattered, but with a moderately close fit to the regression line (R2 = 0.38); values for the upper and lower halves of the succession are given in Table 13. Not surprisingly, the correlation between organic content and water content was very good, with an R2 value of 0.82.

It is obviously difficult to be sure whether the increasing water content with depth is primarily an effect of depth, or a result of the increasing organic content and consequent water retention, or, indeed, whether the increasing organic content results from better preservation brought about by a higher water content. Since there is no significant trend in quality of preservation of invertebrate or plant fossils, however, we suspect that the former may apply. It might be argued that the trend could result more from essentially random differences in the feature types (which will affect preservation); this is not the case, since the estimates of mean organic content for deposits broadly classified as 'dumps' and 'pit fills' are effectively identical (22%, SD 7.2 and 23%, SD 6.5, respectively). It is worth noting that the correlation between height and organic content for the 'pit fills' is much better than that for the 'dumps' (R2 = 0.71 and R2 = 0.25 respectively).

There was no correlation between pH and context type. When pH measurements were being made, it was noted that some samples gave an inky black suspension, and that these samples tended to have a high pH within the rather narrow range observed. It is possible that in these cases ash was present and that this was a source of basic ions. However, there was in fact no correlation between the coarse (>300 µm) charcoal component of the samples (as measured via the 250g subsamples) and pH; this is perhaps not surprising since charcoal is robust and may have entered deposits secondarily or be residual from leached ash, whereas the presence of very fine carbon particles suggests primary ash deposits which might be expected to be more strongly alkaline. It may be that pH measurements will add to the range of techniques available for identifying ash dispersed amongst other materials in archaeological deposits; this is something open to further research. No correlation between organic content and pH could be established.


© Author(s). Content published prior to 2013 is not covered by CC-BY licence and requests for reproduction should usually go to the copyright holder (in most cases, the author(s)). For citation / fair-dealing purposes, please attribute the author(s), the title of the work, the Internet Archaeology journal and the relevant URL/DOI.

University of York legal statements

Last updated: Wed Mar 6 2002