THE CO-EVOLUTION OF FE-,TI-OXIDES AND MICROBIAL FOSSILIZATION DURING EARLY DIAGENESIS IN SANDY SEDIMENTS: ESTABLISHING POTENTIAL MINERAL BIOSIGNATURES

One of the biggest issues faced by geoscientists studying early life is absolutely proving the biogenicity of microstructures in early Archean sedimentary rocks. The “fossil” microstructures in these rocks often resemble modern microbial structures, but rarely contain original cellular material. Instead, many fossils are composed of interesting mineral assemblages such as clays and Fe-,Ti- oxides. Unfortunately, the mineral composition of such features we see today in these ancient rocks differs from what was originally formed in the sediments billions of years ago as a result of long, complicated histories and atmospheric influences. The contribution of microbes is not typically considered, and the complex microbe-mineral relationships under different chemical and geologic conditions are still not well constrained. Here the goal is to understand the co-evolutionary path of microbes and minerals in sandy non-hydrothermal environments with laboratory experiments that simulate diagenesis. The precipitation of minerals on microbial cells and extra polymeric substances and the phase changes in natural ilmenites (FeTiO₃) were documented to determine if microbes passively influence mineral phase pathways. The precipitates, ilmenite grains, and fossilized cells were analyzed using high-resolution imaging and geochemical techniques: scanning electron microscopy (SEM), X-ray diffraction (XRD), and micro Raman spectroscopy. Preliminary results of this study indicate that microbial fossilization and mineral phase changes occur under early diagenetic conditions in non-hydrothermal sandy environments. The results also show that minerals precipitated in the presence of microbes differ from those without microbes. This provides the geobiological community with much needed information to aid in the understanding of the intricate relationship between microbes and minerals and helps establish geochemical biosignatures in ancient sedimentary rocks both on Earth and on other planets.