LABORATORY TESTING OF THE INFLUENCE OF SUBSTRATE ON DECAY INHIBITION AND EXCEPTIONAL PRESERVATION

In general, exceptional fossilization requires the inhibition of organic decay, the promotion of authigenic mineralization, or both. Substrate permeability and chemistry, which have long been hypothesized as important controls on such processes, were experimentally modeled in order to test their effects on organic preservation. Standardized masses of muscle tissue (cod: Gadus morhua) were buried in five different substrates ­– glass beads of three sizes, illite, or kaolinite. The experiments were regularly monitored for one month with infrared gas analysis (IRGA), which quantified the carbon dioxide emitted by each sample and provided a proxy for decay rate. The resultant data revealed a strong positive correlation between substrate permeability and decay: samples buried in large beads emitted more carbon dioxide and reached a maximum earlier than samples buried in fine beads. Samples buried in clay evidenced intermediate decay rates: kaolinite replicates emitted more carbon dioxide than their illite counterparts but reached a maximum simultaneously with them. These results support the hypothesis that preservation potential is maximized by low permeability conditions that restrict oxidant diffusion and that decay rate is sensitive to different chemical environments. CT scanning of selected samples revealed mineral precipitation (though not soft tissue replication) in both finer glass beads and illite.