ADDITIONAL ROLES FOR MICROBES: DO MICROBES INCRUST INVERTEBRATES (BRYOZOA), ALTER EXOSKELETAL MINERALOGY AND POSSIBLY AFFECT THE SEDIMENTARY RECORD?

Microbes, which are ubiquitous in the terrestrial environment, are the most ancient forms of life on Earth. With the development of a diverse invertebrate fauna, new substrates became available for microbial colonization, thus affecting the complexity of the communities. The complex microbial-invertebrate communities can form distinctive signatures that are different from the earlier geological record. It is this distinctive record that is the focus of our recent work.

A high resolution scanning electron microscope, an energy dispersive x-ray spectroscopy (EDS), and x-ray diffraction (XRD) system were used to determine qualitative elemental and mineralogical compositions. We have identified a diverse biota of microbial fossilized remains covering extensive areas of calcium carbonate bryozoan exoskeletons. These microbes include cyanobacteria, coccoliths, diatoms, probable fungal remains, and various rod and ovoid shaped morphologies. The morphologies appear to represent various stages of fossilization that include precipitation of metallic cations. The cations include calcium, magnesium, iron and aluminum. In some instances the microbial remains appear to be incorporated into the exoskeleton to the extent that the original microbial morphologies are unidentifiable. The colonies are all heavily incrusted with microbes and there does not appear to be any preferential location on the exoskeleton for either calcite or aragonite.

Our studies indicate that a search for microbial signatures should not be restricted on the basis of our present level of information. We will need to look for less obvious evidence of the potential role of microbes in nontraditional environments.