3.5. Elemental composition of the carcasses.
In this analysis, we aimed to identify inorganic ions that enhance the preservation of SBO. Thus we focused on the correlation between the deposition of different elements on the carcasses and the degree of their preservation. We used SEM/EDX multiple point analysis to measure chemical elements (1) in the patches of tissues free of visible sediment particles and bacteria and (2) in the sediment particles that were adhered to tissues (Figure 5, Table 5).
In the three sediments with the highest degree of preservation (montmorillonite, kaolinite and silica, Table 3) the carcasses were enriched in aluminium and silicon. In the chamosite and clinochlore, where the preservation was poor, aluminium and silicon entered the tissues in minimal amounts (Table 5). Iron appeared in increased amounts in the well preserved carcasses from the montmorillonite and in the poorly preserved carcasses from the chamosite. The chamosite-hosted carcasses contained much more iron and less magnesium than the carcasses from the clinochlore, in concordance with the initial chemical composition of the two sediments (Tables 2 and 5, Figure 6 A).
Calcium was detected in the carcasses from all sediments and ASW, regardless of the initial elemental composition of the sediments and water. The results imply that calcium was effectively absorbed by the carcasses both from the sediment and from the water (Figure 6 B). Other elements from the dissolved sediments (Al, Si, Mg, Fe) apparently have entered the carcasses in a more passive way, and this is why the greater the amount of an element in the sediment, the higher is its content in the body tissues (Figure 6 B).
Different elements appeared in the solutions due to leaching of the corresponding sediments. This is in concordance with mineralogical transformations detected in the experimental sediments. The results of mineralogical analysis (STA, see Material and Methods) of the kaolinite and clinochlore were reported previously (Naimark et al., 2018 a, b). The results for the chamosite and montmorillonite are shown in Figure 7. They show that decaying organic matter promotes structural disintegration of the sediment and leaching of ions. In the montmorillonite, the strong alkaline environment accelerated the release of silicon species to a greater extent than in the artificial silica sediment with moderate alkalinity (Crundwell, 2014).