IDENTIFICATION AND PRESERVATION OVER GEOLOGIC TIME OF BIOSIGNATURES IN COLD SPRING CARBONATES

Unambiguous recognition of biosignatures is a crucial research area. Differences between biotic and abiotic minerals are difficult to interpret as a direct sign of biological activity and diagenetic alteration further obfuscates identification. This preliminary study documents precisely what features are preserved during diagenetic alteration in order to better recognize biosignatures in both terrestrial and extraterrestrial environments, particularly on Mars. Defining the relationship between indicators of initial microbial influence and subsequent preservation and alteration of these biogenic fingerprints provides crucial insight into interpreting microbial impacts on early terrestrial and martian carbonates and associated iron (oxyhydr)oxides and clays.

Ten Mile Graben in southern Utah, USA hosts a modern cold spring that is actively precipitating tufas. This spring system also comprises a preserved series of progressively older tufas extending back to ~400ka. Additionally, a Jurassic spring-fed carbonate is exposed in the same area present in the upper part of the Brushy Basin Member of the Morrison Formation. This study area provides a unique opportunity to document precisely how morphological, chemical and textural biosignatures are formed and altered throughout geologic time.

Morphological biosignatures preserved in iron (oxyhydr)oxides exhibit degradation and recrystallization on millennial times scales but are still clearly recognizable. LA-ICP-MS and principal component analysis of trace element configurations associated with morphological biosignatures suggest that chemical biosignatures are being preserved on geologic time scales (100Ma). Unusual metastable and unstable mineral phases are present in ancient deposits (i.e., aragonite and 6-line ferrihydrite) suggesting that these phases may function as biomarkers as well even in rocks that have undergone burial diagenesis. Characterization of the biogeochemical evolution of microbial mats furthers our understanding of depositional and diagenetic alteration processes and aids in recognition - via remote sensing and in situ applications - of these systems and their associated biosignatures on any Earth, Mars or any rocky planet that potentially harbors fossil evidence of life.