THE IMPORTANCE OF MICROBIAL MATS IN THE PRESERVATION OF SOFT-BODIED ORGANISMS IN EDIACARAN COARSE-GRAINED SILICICLASTIC ENVIRONMENTS

Soft bodied organisms were frequently preserved on the bedding soles of coarse-grained siliciclastic sediments of the terminal Proterozoic. Microbial mats were more widespread during this time, when grazing and bioturbating organisms were absent, and were hypothesized to have contributed to the preservation of soft tissues. Cyanobacterial mats themselves can be preserved in sand and silt due to the biological precipitation and trapping of clay minerals. Here, we experimentally test whether microbially mediated processes can facilitate the preservation of soft tissues. To do this, we buried scallop and shrimp tissues within cyanobacterial mats growing on siliciclastic sand in the presence of 0.4 mM dissolved silica. Control experiments replicated these conditions, but without microbial mats. Energy Dispersive X-Ray Spectroscopy (SEM-EDS) revealed the presence of calcium on the surfaces of soft tissues in our experiments with microbial mats (after 3 months of incubation) but after 6 months, iron was the predominant element. X-Ray Absorption Near Edge Structure (XANES) revealed an abundance of iron (III) oxyhydroxides after 6 months of incubation. Soft tissues in the absence of microbial mats were not preserved, and fell apart before analysis. These findings suggest that microbial mats may have been critical to the development of mineral molds around soft tissues, facilitating their preservation in Ediacaran sandstones. Further work should assess the specific mechanisms of microbe-mineral interactions associated with the preservation of soft-bodies organisms.