Condition of the archaeological deposits

Insect preservation

Insect remains (mainly beetles and fly puparia) were present in small to modest quantities in most of the samples, providing sufficient data for any trends and correlations to be established (Table 17). For the material from Trench 1, the degree of erosion of the remains was not generally extreme, most of the values ranging from 3 to 4, with a mean of 3.5. The fossils were thus not much worse preserved than in typical material from a wide range of sites with anoxic preservation (3 on the scale of erosion used here being, by coincidence rather than design, about the normal state of preservation for such material). The mean for the distribution of erosion scores for Anglo-Scandinavian material from 16-22 Coppergate, was 2.8 (i.e. appreciably better preserved). What sets the Parliament Street material aside from that from the great majority of other sites is the coloration of the insect fossils, most of which show a distinct change towards 'brown'. No systematic record of the kind used here has been made previously, but subjectively it may be stated that at most other sites poor preservation (in terms of chemical erosion) is reflected by a trend towards 'orange' or 'pale'. At the present site, it was (again, subjectively) thought likely that in many cases fossils recorded as 'pale' represented a stage beyond 'brown'.

There was no significant trend in the degree of chemical erosion or fragmentation of the insect remains with depth within Trench 1, although colour change (one component of erosion) appeared to be slightly greater in the upper layers. However, including the data for Borehole 8 (which effectively extended the sequence below the floor of Trench 1) produced a rather different picture, with distinct trends of increasing degradation upwards. This may suggest that the peculiar preservational change seen in Trench 1 had penetrated throughout the uppermost 2m of stratigraphy, but that the effect was falling off below this, giving an indication of the depth which accelerated decay has reached.

The regressions for insect erosion versus water content and organic content were effectively flat. There was no correlation between colour change of the insect remains and pH, but there was a weak positive correlation between chemical erosion and pH.


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Last updated: Wed Mar 6 2002