Raman spectroscopy of biosignature in methane-related microbialites

Tim Leefmann, Martin Blumenberg, Burkhard C. Schmidt, Volker Thiel
A major challenge in geobiological studies is the localization of organic compounds in a mineral matrix. Raman spectroscopy is here potentially powerful as it can be employed directly on rock surfaces and is capable of the characterization of organic and inorganic compounds in one analyzing step. In this study we tested Raman spectroscopy to approach the organic matter information locked in the complex mineral phase association of methane-related carbonate chemoherms of different age (Hydrate
more » ... dge, Lincoln Creek, Münder Formation, Black Sea). Our data show that Raman spectroscopy allows detecting differences in the amount of organic material in geobiological samples on a micrometer scale. Particularly for the microbialites from Hydrate Ridge and the Lincoln Creek Formation, these studies were able to distinguish on a mm-scale fossilized biofilms of methanotrophic consortia from precipitates that were not directly mediated by microorganisms. However, Raman spectroscopy did not allow for a compound-class specific characterization of the organic material within the microbialite samples. A laser excitation wavelength of 244 nm was determined as most promising for the analysis of organic matter contents of carbonates, as it largely avoids autofluorescence. Comparisons with published extract-based studies (GC-MS) of the same samples demonstrate that the different techniques cannot replace each other, but should rather be used in conjunction in geobiological studies.
doi:10.3249/webdoc-3922 fatcat:ym73opfdubewbkibbll4f53bme