EXPLORING MICROBIAL PRESERVATION IN IRON OXIDES WITH COMPUTED TOMOGRAPHY AND SCANNING ELECTRON MICROSCOPY

The porosity and permeability in rocks and the geochemistry of pore water influence the growth of endolithic microbes and their preservation with mineral coatings. In certain environments, iron minerals coat microbes, which preserve biosignatures as mm to μm -scaled filaments in rocks. Iron mineral precipitation is controlled by the acidity and chemistry of the water that flowed through the pores of the rock. Iron Mountain, CA, contains oxidizing sulfide bodies with porosity, permeability, and water geochemistry that promoted the preservation of biosignatures. In these rocks, biosignatures vary spatially, so we used various imaging techniques to characterize two samples. X-ray and neutron ray computed tomography (CT) scans record the porosity in 3D at mm to μm scales without destroying the sample. The scanned image stacks were used to visualize the interior of the rocks in the KeckCAVE 3D visualization environment. The porosity of the sample was calculated with NIH software Image J; Sample 1 (JS4) contained less porosity (1.1%) but most pores were interconnected, and Sample 2 (PS3) contained higher porosity (6.0%) but had poor interconnectivity of pores. Scanning electron microscopy (SEM) results show that the distribution and preservation style of biosignatures are spatially variable. Preliminary results suggest that both microbial growth and style of iron mineral precipitation was controlled by the local microenvironment. Future work will utilize nano CT and SEM to correlate pore interconnectivity and locality with filamentous biosignature preservation.