INSIGHT INTO MINERAL FABRICS, BIOFABRICS, AND CHANNEL ARCHITECTURE TO COMPREHENSIVELY CHARACTERIZE MICROBIALITE TEXTURE

Microbialites–macroscopic organosedimentary structures (rocks) formed by the interaction between microbial communities and detrital or chemical sediments–represent some of the oldest evidence of life on Earth and remain a target for extraterrestrial investigation on Mars. Microbialites are recognizable as macroscopic manifestations of microbial activity because of their texture, which consists of visible remnants of primary mineralogy and cemented void spaces. Despite the importance of texture, little is known about the origin of texture, its evolution, and its dependence on local biofabrics and microbial processes. Here, we investigate incipient CaCO₃ microbialites from Little Hot Creek (LHC), a hot spring system in eastern California, where actively-lithifying microbial mats have a dendrolitic (shrub-like) texture strikingly similar to certain ancient microbialites, providing a unique opportunity to examine modern mat lithification in-situ with relevance to ancient structures. We use fluorescently labelled embedded coring to preserve internal textures in life position. Of these textures, mineral and biofabrics were analyzed in two dimensions using epifluorescence and petrographic microscopy. Micro Computed X-ray Tomography (microCT scanning) was used to render the samples in three dimensions, and Dragonfly software was used for three dimensional reconstruction. Pore network modeling software in Dragonfly was used to map channel architecture and characterize them based on porosity, amount of branching, tortuosity (curvilinear nature), and diameter. By combining these two- and three- dimensional approaches, we characterize the relationships between minerals, microbes, and fluid-filled channels with the highest possible detail. We find not only an unprecedented level of lateral textural heterogeneity within incipient microbialites, but also present mechanisms for how textures preserved in ancient microbialites could have formed under biological influence. In particular, we suggest a mechanism by which micro-clotted micritic dendrolitic microbialites form as well as a hypothesis to explain the micritic nature of microbialites through their multi-billion year history.