Burial environment, changes

In addition to contact with the burial environment, the trophy head samples had been burned, presumably during ritual activities in the structures in which they were found (/, 21, 22). Although experimental data has shown that postmortem burning can change the 5I3C values in bone collagen, this is not the case for strontium isotope ratios (78). 

The processes of livor, rigor, and algor mortis can be useful indicators of a recently deceased person, but the processes may have expired by the time a body is placed in a shallow or deep grave site. Once these changes have passed, soft-tissue decomposition proceeds through the processes of autolysis and putrefaction (Fiedler and Craw 2003). In a burial environment, it is these processes that are likely to result in the disintegration of soft tissue and skeletonization. 

To summarize, the analytical information of archaeological or ancient wood shows variability in chemical changes and losses that may result from the burial environment, the wood species, sapwood or heartwood, outer or inner wood, anomalies in growth, and certainly the methods of analysis. The stability of wood biopolymers has been found to be (in decreasing order) lignin, pectin, cellulose, and hemicellulose. As a rule, increase in moisture content indicates increase in degradation. 

Changes in archaeological wood result from specific interactions between the wood and the burial or discard environment. Thus it is important that the parameters of the burial environment be recorded. 

Sediment, as a seawater nutrient buffer, can continuously receive and release biogenic elements to balance the water chemically or physically. The nitrogen in sediments includes two kinds one is released into water to take part in the cycling, and the other is buried in sediments. In addition, the burial part can also release when environment changed sharply. So the burial part is a potential source of nitrogen for water. 

Once in the burial environment, biodeterioration may promote further alterations in the structure of the higher terpenoids. Whilst the particular chemical character of the burial environment will dictate specific changes, once again, alterations likely to be encountered will include oxidation, hydrogenation, etc. Looking then at the composition of freshly exuded and aged resins, whilst the more stable terpenoids may be present in both, the older material is likely to exhibit a higher proportion of oxidised terpenoids. 

Conversely, perturbations in the burial rate of BSi have the potential to alter the marine silica cycle. For example, changes in sea level affect the expanse of continental shelf Since BSi burial is more efficient in shelf sediments (because of better preservation), a topographic change that alters the spatial extent of this depositional environment has the potential to alter the size of the DSi reservoir. 

Meade (1966) shows that claystones have a porosity decreasing to 0% at 1 Km depths and sandstones, 20% porosity at the same depth. Manheim (1970) shows that ionic diffusion rates in sediments are 1/2 to 1/20 that of free solutions when the sediments have porosities between 100 - 20%. It is evident that the burial of sediments creates a very different physical environment than that of sedimentation. As a result of reduced ionic mobility in the solutions, a different set of silicate-solution equilibria will most certainly come into effect with the onset of burial. The activity of ions in solution will become more dependent upon the chemistry of the silicates as porosity decreases and the system will change from one of perfectly mobile components in the open sea to one approaching a "closed" type where ionic activity in solution is entirely dictated by the mass of the material present in the sediment-fluid system. Although this description is probably not entirely valid even in rocks with measured zero porosity, for practical purposes, the pelitic or clayey sediments must certainly rapidly approach the situation of a closed system upon burial. 

Figure 8.16. A hypothetical trend of changes in the stable isotope composition of carbonate cements in different diagenetic environments. A- marine realm B-meteoric realm C- mixing zone D- successively deeper burial for calcite spar E-successively deeper burial for saddle dolomite. B through E are precipitated in progressively hotter waters. (After Choquette and James, 1987.)...

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