PILOT STUDY: IDENTIFICATION AND INTERPRETATION OF ORGANIC COMPOUND DISTRIBUTIONS IN SERPENTINITES AND RELATED TRAVERTINES USING MICROFTIR

The preservation of organic compounds in secondary minerals in ultramafic rocks may allow study of the habitability of past microenvironments fueled by serpentinization. Serpentinization, the alteration of peridotites to serpentine mineral assemblages in the presence of water, co-occurs with the production of hydrogen, methane, and diverse organic compounds (McCollom and Seewald, 2013), evolving water appropriate for carbonate precipitation, including in ophiolite groundwater flow systems and travertine-producing seeps/cold springs. Serpentinization is regarded as a geologic process important to the sustainability of the deep biosphere (Schrenk et al., 2013) and the origin of life (Sleep et al., 2011; Schulte et al., 2006). Using serpentinite and travertine samples obtained in the McLaughlin Natural Reserve (administered by the University of California-Davis, Lower Lake, CA) at the Coast Range Ophiolite Microbial Observatory (CROMO, Cardace et al., 2013, http://cromo.arc.nasa.gov), we manually polished 20-50 µm thin wafers of serpentinite and travertine (10 of each; Wysoczanski & Tani, 2006) for µFTIR analysis in reflection mode. We used a Thermo Nicolet iS50 FTIR bench spectrometer coupled with a Continuum IR microscope, equipped with 150 µm and 50 µm MCT-A detectors, to map and contrast selected organic matter inventories in serpentinite vein fillings and carbonate minerals in travertine. After identifying FTIR bands associated with mineral groups present in the samples, we consider the following frequencies as a proxy for preserved molecules common to microbial biomass (thus, biomarkers): 2955 cm^-1 [C–H antisymmetric stretching of –CH₃ in fatty acids], 2918 cm^-1 [C–H antisymmetric stretching of >CH₂ in fatty acids], 2850 cm^-1 [C–H symmetric stretching of >CH₂ in fatty acids], 1680– 1715 cm^-1 [>C=O in nucleic acids], 1200– 900 cm^-1 [C– O, C–C stretching, C–O–H, C–O–C deformation of carbohydrates] (cf. Maquelin et al., 2002). FTIR profile patterns in and out of (1) late stage veins in serpentinites and (2) mineralogically distinct bands in travertine were stacked and interpreted to highlight similarities and differences between samples and identify (if any) possible candidate biomarkers.