Complementary Transformations of Buried Organic Residues and the Ambient Sediment: Results of Long-Term Taphonomic Experiments

Resumo

Long-term (18 month) experiments were conducted, burying soft bodied organisms (Artemia salina, Crustacea) in marine sediment. For the first time in experimental taphonomy, the mineralogical transformation of the sediment that accompanied the process of decomposition was correlated with the degree of preservation. To obtain different quantitative characteristics of preservation, we used four dilutions of marine water (marine water: to fresh water as 1: 0; 1: 1, 1: 4, 1: 9).It was shown that higher dilutions corresponded to lower degrees of preservation. The proportion of kaolinite decreased in the marine sediment and, accordingly, the amorphous phase increased; in the diluted variants, the opposite pattern was revealed: the crystalline kaolinite phase increased and the amorphous phase decreased. Since no differences in the chemical composition of the residues from different dilutions were identified, the effect of sea salt concentration on preservation was considered to be negligible. A plausible hypothesis suggested that dissolving of kaolinite slows of organic decomposition and the beginnings of mineralization. Due to the acidic hydrolysis of kaolinite, Al cations appear in the solution; subsequently proteins are converted into insoluble forms, and thus escape from bacterial degradation. These taphonomic experiments reveal some overlooked physicochemical aspects important for the mechanisms of exceptional preservation.