Probing the role of clay minerals in the preservation of organics and soft tissues

Abstract

Interactions between organics and various types of minerals have been well documented and studied both experimentally and in nature. Clays, which are aluminum silicate minerals, have been shown to be exceptional at the adsorption and/or incorporation of organics. These minerals have also been the focus of understanding how exceptionally preserved fossils are formed, particularly in the Ediacaran and Cambrian; however, it is debated if these clays are original to the sediments preserving these organisms. Sedimentary rocks containing Fe-rich clay and amorphous phases will be sampled for return by the Mars Sample Return Campaign to search for preserved organics; however, the ability of these clay and amorphous phases to preserve organic carbon has yet to be tested. In this thesis, I seek to create a more thorough understanding of how clay minerals present within these two systems can aid in organic preservation.

I begin this thesis by examining two morphotypes of erniettomorph fossils (soft-bodied Ediacaran organism with unknown phylogenetic placement) preserved in a clay-rich siliciclastic deposit from the Woods Canyon Formation in Nevada. From the data collected to characterize both morphotypes, we concluded that the clay minerals present were likely important in the preservation of the organics and better three-dimensional preservation was due to the abundance of large-grained quartz within the organism pre-burial. For the remaining chapters of my thesis, I examined organic preservation in a simulated Martian lacustrine system. I begin by incubating basaltic sediments and a 5% pCO2 headspace with solutions containing a range of organic molecules which have plausible abiotic sources. I subsequently expand on these experiments by amending the solutions with Fe2+. Finally, I use the same solution conditions (with and without added Fe2+) and incubate microbial EPS with the sediments. The results from these experiments allow us to create a model for organo-mineral associations that would occur on early Mars, and the types of organo-mineral associations and textures that would be association with abiotically vs biologically produced organic carbon.